Informal document n° 5

DRAFT DOCUMENT (August 2014) Prepared by AC Le Gall (ICP M&M),

To be reviewed by ICP M&M NFCs

II. GUIDANCE ON MAPPING CONCENTRATIONS LEVELS AND DEPOSITION LEVELS

Updated by Anne Christine Le Gall, Chairwoman of the Task Force on Modelling and Mapping, from initial text edited by D. Fowler and R. Smith, Mapping Manual 2004

Please refer to this document as: CLRTAP, 2014. Guidance on mapping concentrations levels and deposition levels, Chapter II of Manual on methodologies and criteria for modelling and mapping critical loads and levels and effects, risks and trends. UNECE Convention on Long-range Transboundary Air Pollution; accessed on [date of consultation] on Web at www.icpmapping.org .”

Chapter II – Guidance on mapping concentrations levels and deposition levels Page II - 3

TABLE OF CONTENT

II. GUIDANCE ON MAPPING CONCENTRATIONS LEVELS AND DEPOSITION LEVELS ...... 1 II.1 INTRODUCTION ...... 5 II.2 INFORMATION RELATIVE TO MODELLING AND MAPPING CONCENTRATION AND DEPOSITION ...... 5 II.2.1 General remarks and objectives ...... 5 II.2.2 UN-ECE EMEP model: A LRTAP chemistry-transport model ...... 6 II.2.3 Mapped items in long range chemistry-transport models relevant to critical loads 8 II.2.4 Processes relevant to airborne pollutant concentrations and deposition ...... 8 II.2.4.1 ...... 8 II.2.4.2 Emissions ...... 9 II.2.4.3 Sea salts ...... 10 II.2.4.4 Deposition of airborne substances ...... 10 II.2.4.4.1 Bulk deposition ...... 11 II.2.4.4.2 Dry deposition ...... 11 II.2.4.4.3 Wet deposition ...... 11 II.2.4.4.4 Total deposition ...... 13 II.2.4.5 Stomatal conductance ...... 14 II.2.4.6 Land use roughness and topography ...... 14 II.2.4.7 Temporal variability ...... 15 II.2.4.8 Geographical variability...... 15 II.2.5 Complementing methods to assess air pollution: Long range modelling, nested models and monitoring ...... 15 II.2.5.1 Long-range chemistry transport models ...... 16 II.2.5.2 UN-ECEMonitoring based methods ...... 16 II.2.6 Characteristics of substances maps in relation to exceedances calculations ...... 18

II.2.6.1 Mapping ozone (O 3) concentrations and deposition ...... 18

II.2.6.2 Mapping sulphur dioxide (SO 2) concentrations and oxidised sulphur (SO x) deposition18

II.2.6.3 Mapping nitrogen oxides (NO x) concentrations and deposition of oxidised nitrogen (NO y) ...... 19

II.2.6.4 Mapping ammonia (NH 3) concentration, reduced nitrogen (NH x) deposition and total nitrogen deposition ...... 19 II.2.6.5 Mapping total reactive nitrogen ...... 20 II.2.6.6 Mapping base cation and chloride deposition ...... 20 II.2.6.7 Mapping total potential acid deposition...... 21 II.2.7 Use of deposition and concentration maps ...... 21 II.2.7.1 Issues related to map scales ...... 21 II.2.7.2 Some preliminary remarks regarding the use of model results by parties ...... 22 Page II - 4 Chapter II – Guidance on mapping concentrations levels and deposition levels

II.2.7.3 Identifying ecosystems position for critical loads calculation and their exceedances . 23 II.2.7.4 Uncertainties of mapping methods ...... 23 II.2.8 Who do you ask for further advice? ...... 24 II.2.9 References ...... 25 Chapter II – Guidance on mapping concentrations levels and deposition levels Page II - 5

II.1 INTRODUCTION (This refers to Chapter 1. This title is useful here in order to have the benefice of Word automatic section numbering. It will be removed in the final layout.)

II.2 INFORMATION RELATIVE TO MODELLING AND MAPPING CONCENTRATION AND DEPOSITION

II.2.1 GENERAL REMARKS AND OBJECTIVES The purpose of this chapter is to provide and depositions which can be used for general information to the participating effects assessments in specific countries on the generation and use of ecosystems. Such data are needed with a concentration level and deposition maps for much better spatial and temporal a range of pollutants. These maps may be resolutions than required for integrated used for different purposes, such as assessment modelling. National Focal assessment of air quality for human health Centers should aim at a sufficient spatial and assessment of ecosystems via critical resolution for the assessment process, loads exceedances. Depositions are then making use of national models and compared with critical level/load maps. In measurement networks. Large scale this chapter, main principles of mapping transport chemistry models provide concentrations levels and deposition are background, long-range transported air described and discussed. A range of components which can be used as different techniques for the provision of boundary conditions for such national maps of concentration and deposition, models. depending on the resources and ambition The third aim is to gain information on of the country are described. Modelling deposition at site level. This is particularly procedures are outlined and the reader is important for “monitoring” ICPs such as referred to specialist publications for further ICP and ICP Integrated monitoring. measurement and modelling approaches. Then concentration measurements, Note that within the LRTAP Convention, coupled with wet, dry and throughfall modelling and mapping of pollutant deposition measurements are used for concentrations in air and their deposition is deriving process parametrisations (mainly EMEP mandate (see section II.2). The micrometeorological measurements) and reader is therefore referred to EMEP for independent model validation (mainly documents and website for further details. throughfall measurements; see Chapter There are three main objectives for II.3.1, II.3.2 and II.3.10). This chapter does mapping of concentrations and depositions not detail field and laboratory methods for over a territory within the LRTAP concentrations and deposition Convention. measurements. The interested reader is refered to specific ICPs´ Manuals and to The first aim is to construct exceedance the EMEP publications on monitoring maps relative to critical levels and loads. At methodology (ICP Integrated Monitoring 1; large scale (covering several countries), ICP Forests 2; ICP 3; ICP Materials 4; transfer coefficients may be calculated. EMEP/CCC 5). They allocate critical loads exceedances in each grid cell of a transport chemistry model to emissions in all European countries This approach is particularly well suited to assess policy scenarios in 1 http://www.syke.fi/en- integrated assessment modelling. It US/Research__Development/Ecosystem_services_and_bio provides thus scientific results for a) logical_diversity/Monitoring/Integrated_Monitoring/Manual_f implementation of, and compliance with, or_Integrated_Monitoring 2 http://icp-forests.net/page/icp-forests-manual existing LRTAP Convention protocols and 3 b) their review and extension. http://www.icp-waters.no/ 4http://www.corr-institute.se/ICP-Materials/web/page.aspx The second aim is to map concentrations 5 http://www.nilu.no/projects/ccc/ Page II - 6 Chapter II – Guidance on mapping concentrations levels and deposition levels

II.2.2 UN-ECE EMEP MODEL: A LRTAP CHEMISTRY-TRANSPORT MODEL The EMEP model is the reference carried out within the LRTAP Convention, chemistry-transport model for the LRTAP and in particular within the MSC West and Convention and European air pollution East Centres of the European Monitoring policy assessments. The model covers all and Evaluation Programme (EMEP of Europe. Its geographic resolution has programme, http://emep.int ). It is increased over the years (initially it was continuously evolving. A recent update of 150 x 150 km²). Since 1999, EMEP model the model characteristics has been given was run on a 50 x 50 km² grid (1.0° long x by Simpson et al., 2012. Initial work is 0.5° lat) although local air pollution described in proceedings from several UN- emission and chemistry may now be ECE Workshops dealing with this subject, simulated on a 7 x 7 km² grid (0.125° long x most notably the 1992 "Workshop on 0.0625° lat). Its vertical resolution extends Deposition" in Göteborg, Sweden (Lövblad from ground level to the tropopause (100 et al. 1993), the 1993 "Workshop on the hPa or arout 16 000 m). It is divided in 20 Accuracy of Measurements" with WMO layers, the lowest having a thickness of sponsored sessions on "Determining the about 90m. Representativeness of Measured Parameters in a Given Grid Square as The model has changed extensively over Compared to Model Calculations" in the last ten years: with flexible processing Passau, Germany (Berg and Schaug of chemical schemes, meteorological 1994), and in Erisman and Draaijers inputs (from European Centre for Medium- 6 (1995), Sutton et al. (1998), Slanina (1996), Range Weather Forecasts ) and with Fowler et al. (1995a, 2001a) and ICP nesting capability. The model is used to Forests Manual (UN-ECE 1999). The simulate photo-oxidants and both inorganic model characteristics and performances and organic aerosols. It takes into account have also been discussed within the task land use (source CCE/SEI for Europe, 7 Force on measurements and modelling (cf. Global Land Cover 2000 elsewhere, or the http://www.nilu.no/projects/ccc/tfmm/index. CCE harmonised land cover map), at a html ) and as part of European Research resolution of about 5 km. Programmes (such as EC4MACS, The EMEP model is now available as EURODELTA…). Supplementary public domain code, along with all required information can be found in other workshop input data for model runs for one year. It is proceedings and in scientific journals. extensively documented in EMEP status Many other national chemistry-transport reports, EMEP publications and in the models are also available. A large number scientific literature (EMEP, 2013; Simpson of inter-comparisons in recent years have et al., 2012 and see also discussed their strengths and http://emep.int/emep_publications.html ). weakenesses (Colette et al., 2011; Colette Since 2003, the methodology has been et al., 2012; Cuvelier et al., 2013; Cuvelier revised for the simulation of dry deposition et al., 2007; Fiore et al., 2009; Huijnen et for particles, the emissions of hydrocarbons al., 2010; Jonson et al., 2010; Langner et from vegetation, NO emissions from , al., 2012; van Loon et al., 2007). In terms co-deposition of SO2 and NH3, the of performance, the EMEP model has calculation of mixing heights, or the ranked well in these studies, with introduction of pH response during consistently good performances for sulphate formation. Smaller changes in the different pollutants (ozone, PM, etc.). In equations or parameters values have also terms of complexity, the EMEP model is been carried out. fairly similar to other regional-scale European chemistry-transport models, The EMEP model is the fruit of 30 years of such as MATCH (Robertson et al., 1999), discussions and intense scientific work CHIMERE (Bessagnet et al., 2004) or DEHM (Christensen, 1997; Frohn et al., 2001). All of these models have some 6 http://www.ecmwf.int/ flexibility with regard to chemical schemes 7 http://bioval.jrc.ec.europa.eu/products/glc2000/glc2000.php and have zooming-capabilities. Chapter II – Guidance on mapping concentrations levels and deposition levels Page II - 7

Within the LRTAP convention, the EMEP values are regarded as default data allowing the assessment process to be completed everywhere. In the following sections, when references to chemistry- transport models are references to the EMEP model. Further description of the EMEP grid is given in chapter VIII. EMEP model has been developed together with the EMEP monitoring network. This is managed by the Chemical Coordinating Centre 8 (CCC), responsible for collating contributing parties data, as well as developing monitoring methods and standards.

8 http://www.nilu.no/projects/ccc/index.html Page II - 8 Chapter II – Guidance on mapping concentrations levels and deposition levels

II.2.3 MAPPED ITEMS IN LONG RANGE CHEMISTRY-TRANSPORT MODELS RELEVANT TO CRITICAL LOADS

In order to fulfil their role, long range Heavy metal deposition: chemistry-transport models simulate • total deposition of mercury, lead reactions between a large number of and cadmium, natural and anthropogenic substances and • other priority heavy metals as data take into account many processes. Here, in become available and policy needs the context of the calculation of critical are expressed (such as copper, levels/loads and their exceedances, the nickel, zinc, arsenic, chromium and following items are mapped: selenium). For critical level exceedance maps: Black carbon is also included amongst the • ozone flux (PODy for vegetation, species for which concentrations and SOMO35 for human health) and deposition are calculated. Although its ozone concentration (AOT40 impact was initially mainly calculated for values), human health, this pollutant also intervene • sulphur dioxide concentration, in material soiling and to an extent that now • nitrogen dioxide concentration, remains to be defined in ecosystem • ammonia concentration. functioning. For critical load exceedance maps: As input into deposition and critical load • oxidized sulphur (SO ) deposition computations: x • (total and non-sea-salt), amount and other • oxidized nitrogen (NO ) deposition, meteorological parameters, x • • reduced nitrogen (NH ) deposition, wet, dry, cloudwater/fog and aerosol y deposition. • total nitrogen deposition, • In the context of biodiversity and • base cation and chloride deposition climate changes, meteorological (total and non-sea-salt), parameters such as temperature, • total potential acid deposition. light availability, wetness become relevant.

II.2.4 PROCESSES RELEVANT TO AIRBORNE POLLUTANT CONCENTRATIONS AND DEPOSITION The behaviour and the fate of each at the interface with the ecosystems. These chemical species depend on its physico- processes may be measured at monitoring chemical properties. They are also the stations and/or taken into account in the consequences of the processes the chemistry-transport models. They are substance undergoes in the atmosphere or shortly described in the following sections.

II.2.4.1 METEOROLOGY Meteorological parameters are required observations within Europe. There are inputs for most critical levels or critical other sources for some data such as the loads calculations, whether at site level or US National Center for Atmospheric 10 for modelling on wide geographical area. Research global precipitation database . The data requirements and data provision Precipitation amounts are needed for will vary from country to country. Data are critical load computations, for wet generally avaialable from national weather deposition mapping and for surface services. European data can be obtained wetness parametrisations. from European Centre for Medium-Range Weather Forecasts (ECMWF 9), who provides modelled data based on

10 https://climatedataguide.ucar.edu/climate- 9 http://www.ecmwf.int/ data/gpcc-global-precipitation-climatology-centre Chapter II – Guidance on mapping concentrations levels and deposition levels Page II - 9

Fog and cloud occurence are needed for meteorological data is often a constraint to cloudwater/fog deposition estimates. detailled local high resolution modelling. Therefore the success of models in Wind speed, temperature and radiation are improving deposition estimates to specific basic requirements for the inferential ecosystems may depend as much on the modelling of dry deposition. Additionally, availability of quality meteorological data as relative , soil deficit and on the quality of the local concentration atmospheric stability are often required. estimates or measurements. The availability of accurate local

II.2.4.2 EMISSIONS

The precise knowledge of quantities as well • Biogenic emissions: The vegetation as localisation of substances sources is and the soil are receptors for essential to model their fate in the substances but are also emitters. atmosphere. For less well known sources, They are dependant on surface emission factors may be used. Recent types and meteorology. Biogenic work has shown that the importance of biogenic emissions in the total budget of emissions are of particular substance exchanges between the importance for mapping ozone atmosphere and ecosystems (Fowler et al., because of VOC emissions and for 2009). mapping ammonia, which is emitted Within the LRTAP Convention, emissions as well as absorbed by vegetation. are compiled by the Task Force on Biogenic emissions are therefore Emission Inventories and Projection 11 . Data linked to the type of vegetation and reported following the “SNAP” soil present over the area modelled. 12 nomenclature from each party is Their quality is therefore linked to compiled, provided to EMEP and integrated that of the land use map. by assessment modelling teams. This Task Force also provides guidance on estimating emissions from both anthropogenic and natural emission sources, with default methods and emissions factors (TFEIP, 2013). Total emissions include: • Anthropic emissions are emissions issued from human acitivities: industry, transport, energy, urban activities… They are essential in pollution management since they are the sources that can most easily be reduced.

11 http://www.UN- ECE.org/env/lrtap/taskforce/tfeip/welcome.html 12 SNAP: “Selected Nomenclature for Air Pollutants” nomenclature, which consists of yearly masses per surfaces for various domains and resolutions. Page II - 10 Chapter II – Guidance on mapping concentrations levels and deposition levels

II.2.4.3 SEA SALTS Primary marine aerosols are composed of salts generation: bubble bursting during sea salt and organic material, including whitecap formation and through spume sulphur compounds such as dimethyl drops under the wave breaking (Simpson sulphate (DMS). They are an important et al., 2012). In the EMEP model, sea salts contributor to the global aerosol load calculations includes particles with (Barthel et al., 2014). In the framework of diameters up to 10 µm that originate mainly critical loads, marine aerosols are from the bubble mediated sea spray (Tsyro important as they include acid anions et al., 2011). (sulphate and chloride) as well as base Depositions of base cations, sulphur and cations. Consequently, the base cation and chloride (given in equivalents) are chloride deposition in the charge balance corrected by assuming that either all from which critical loads are derived have sodium or all chloride is derived from sea to be corrected for sea salt contributions, salts, and that the relations between ions since critical loads are compared with are the same as in sea water (after Lyman anthropogenic inputs only (thus excluding and Fleming 1940, cited in Sverdrup 1946). also dust from erosion, especially from Details on how to carry out this correction Sahara). is given in Chapter V. There are two main mechanisms for sea

II.2.4.4 DEPOSITION OF AIRBORNE SUBSTANCES Deposition is the various processes The ICP Forests Manual (chapter 14: 13 through which airborne substances are Sampling and analysis of deposition ) and transferred from the atmosphere to the the World Meteorological Office Manual vegetation, the soil or the water. These (WMO, 2008 - updated in 2010). The processes occur at different time and interested reader will find more detailed space scales. It is once that they are information in these references. For deposited that these substances may information related to the simulation of impact ecosystem functioning and human these parameters, see Simpson et al., health or damage materials. 2012 for the EMEP model, as well as for instance, Hertel et al., 2013; Hertel et al., Total deposition is the sum of all dry and 2006; Pacyna et al., 2008; Vet et al., 2013). wet deposition processes. Distinction between the different “depositions” type is as much a matter of physico-chemical characteristics of the deposition as a matter of measurement technique. Some of these are briefly described below. Information given below is largely inspired from two documents :

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II.2.4.4.1 BULK DEPOSITION Bulk deposition includes parts of particulate implementation easy. However, the method and gaseous deposition during dry periods is sensitive to dust from neighbouring as well as wet deposition. It is sampled areas. In regions with calcareous soils, bulk continuously in an open area with a plastic deposition gives incorrect information on funnel connected to a sample bottle. This the pH and chemistry of atmospheric cheap and simple method makes its deposition.

II.2.4.4.2 DRY DEPOSITION Dry deposition is the settling due to gravity importance close to the sources of (sedimentation), impaction (due to emissions. turbulence) and interception (via chemical These processes are simulated through a and biological processes) of aerosols and resistance analogy, including aerodynamic, gases on a surface during dry periods. surface and substance specific These processes are strongly influenced by resistances and stomatal conductance the type of surfaces (, needles, (Menut et al., 2013; Simpson et al., 2012). rocks, water. etc), the humidity of surfaces, Resistances are modelled using the macro- and micrometeorology (stomata observations of meteorological parameters closure) and the bio-physico-chemical and parametrisation of surface exchange characteristics of the substances. processes for different receptor surfaces Dry deposition is a slow but continuous flux and pollution climates as described in of contaminants to the soil, water or Erisman et al (1994a), Smith et al. (2000), biogenic surfaces. It involves pollutants Nemitz et al. (2001), Emberson et al. carried in the lowest part of the atmosphere (2000), Grünhage and Haenel (1997), and is thought to be of particular Gauger et al. (2003).

II.2.4.4.3 WET DEPOSITION Wet deposition occur when gaseous or short times in which precipitation events particulate contaminants are scavenged occur. from the atmosphere by , snow or cloud The simulation of wet deposition integrates and fog and subsequently deposited to both in cloud and below cloud scavenging surfaces with the rain drops, the snow of gases and particles (Simpson et al., flakes or the fog droplets. Due to the 2012). scavenging process involved, wet deposition is a good integrator of the There are different sampling methods chemical content of the atmosphere and is possible for wet deposition. They are not potentially influenced by long range exactly equivalent as they do not sample transport of chemicals. Also wet deposition exactly the same fraction of wet deposition. leads to rapid delivery of pollutants, highly concentrated in precipitation, during the

II.2.4.4.3.1 WET ONLY DEPOSITION Wet only deposition determines the fluxes during dry periods. These equipments of dissolved components from the require electrical power and maintenance. atmosphere in rain, snow and hail in the They may not work properly in case of open field. It gives valuable information on heavy snow. the chemistry of atmospheric deposition Wet deposition is a function of precipitation and on long range transport of air masses. rates. If wet deposition is assessed from It requires collectors that open field monitoring, it would be inferred from automatically at the onset of precipitation relatively dense meterological data and by the use of a sensor and close at the end less dense monitoring of concentrations in after rain/snow/hail has stopped. It thus rain, snow and hail. excludes particles and gases deposition Page II - 12 Chapter II – Guidance on mapping concentrations levels and deposition levels

Then measured solute concentrations may Europe uplands, due to wash out of then be interpolated and wet deposition topographic cloud by falling rain or snow. may be estimated from a function of the As networks do not generally measure at mapped solute concentration and the high elevation in complex terrain, these precipitation amount, the latter provided by effects are generally omitted from network the meteorological service for the country measurements. The underlying physical (cf. for instance in Kopacek et al., 2012). process is well documented and the effects may be modelled using the network data A very important increase of wet deposition (Dore et al. 1992, Fowler et al. 1995b, occurs over wind exposed hills and Kryza et al., 2011). mountains, particularly in the Northern

II.2.4.4.3.2 OCCULT DEPOSITION Cloud, fog, rime, mist droplets also 2001b), provide the means of obtaining scavenge the atmosphere from aeorols and deposition parameters for many more gases. When they come into contact of a representative terrestrial surfaces in surface (as the air mass meets a hill or Europe. passes through a ), droplets are The methods mentioned here only work if deposited, with their chemical charge. This stringent prerequisites concerning is occult deposition. Although amounts micrometeorological variables (e.g. surface deposited are relatively small, homogeneity) are fulfilled. They cannot be concentrations in occult deposition can be directly extrapolated but the process very high, which could lead to direct knowledge obtained from such impacts. measurements can be parametrized in This deposition can be estimated from inferential models and fluxes can be concentration measurements of airborne mapped using this information (see high substances by micrometeorological resolution modelling above). measurements at the process level (for The deposition velocities of cloudwater/fog SO 2: Fowler et al. 2001c; for NH 3: Flechard droplets can be similarly estimated by and Fowler 1998; for cloud: Beswick et al. modelling momentum transfer (Fowler et al. 1991). Micrometeorologically based long- 1993) and a similar technique has been term flux measurements (i.e . continuous used to estimate base cation deposition flux measurements over more than a year) (Draaijers et al. 1995). Parameters are possible for O 3, NO x and SO 2 (LIFE determining the deposition velocity include project, Erisman et al. 1998a) and for CO 2 atmospheric parameters (e.g. wind speed, and H 2O (Aubinet et al. 2000). Such temperature, radiation, relative humidity, measurements give information about the atmospheric stability, cloud and/or fog seasonal and interannual variability in the frequency) and surface conditions (e.g. fluxes. Low cost micrometeorological roughness, wetness, stomatal response, methods, such as the Time Averaged soil water). Gradient (TAG) system (Fowler et al.

II.2.4.4.3.3 THROUGHFALL AND STEMFLOW MEASUREMENTS Throughfall deposition gives an estimate of in an important contributor to the deposition the total deposition (bulk, leached through do the forest floor. the canopy, dry depositions) that reaches Throughfall + stemflow give an estimate of forest floor. the deposition to the forest floor. Stemflow is wet deposition sampled on Throughfall is sampled beneath the stems, usually at the trunk base. As water canopy, stemflow near the base of the flows along the tree stems, it washes off trunk. Both use via cheap, simple, low gases and aerosols previously deposited maintenance devices. by rain, snow or occult deposition. According to ICP Forests, the main Stemflow also includes leachates from the drawback of the throughfall method is the and leaves. In beech forest, stemflow interaction between the canopy and the Chapter II – Guidance on mapping concentrations levels and deposition levels Page II - 13

throughfall water for nitrogen, potassium, overview of the deposition situation in the calcium, magnesium, manganese and forest, not only for sulphur but also for protons. However, the results from nitrogen compounds. Recent Swedish throughfall monitoring can still be used as a experiences have highlighted the problems valuable indicator for the nitrogen and base with comparing throughfall measurements cation deposition to the forest. Throughfall with wet deposition when the dry deposition deposition can give information on the contribution to the total is very low lower limit of the true deposition of nitrogen (Westling pers. comm. ), as is now the case and the upper limit of true deposition of for sulphur in many areas of Europe. Large base cations other than sodium. For uncertainties in wet deposition at wind- sodium and sulphur the canopy uptake and exposed sites have been shown with field leaching is considered to be negligible and intercomparison studies (Draaijers et al. consequently the throughfall flux is used to 2001). Even if it is not possible to estimate estimate the total deposition. the total deposition of nitrogen with this method, a lower limit can be set. Sampling The data will provide knowledge on the considerations (e.g. location of collectors, seasonal variation and the trends of species composition, spatial variability) are deposition. In many cases throughfall very important for achieving good results monitoring is considered to be sufficient, and sampling requirements are described and stemflow is only measured for some in detail in the ICP Forests Manual (UN- tree species, for which it is known to be of ECE 1999) and in review articles such as importance (e.g. beech trees). Draaijers et al. (1996a) and Erisman et al. Throughfall measurements give a good (1994b).

II.2.4.4.4 TOTAL DEPOSITION Total deposition is the sum of wet only and internal cycling. This method can give large dry deposition. It excludes ion exchanges overestimates of the true deposition flux within the canopy. It may be inferred from (CEX>0), due to canopy leaching (for some the values of the depositions described base cations), or large underestimates of above. the true deposition flux (CEX<0), due to canopy uptake (e.g., for nitrogen The relation between total deposition and compounds and protons). The sum of throughfall can be expressed as: throughfall and stemflow is considered to (II.1) Total DEP = DRY + WET + Cl/Fog be equal to total deposition only for sodium = THF - CEX and sulphur. For orther substances, throughfall plus stemflow fluxes may be where: interpreted as upper bounds of total base THF = Flux in throughfall plus cation deposition and as lower bounds of stemflow total nitrogen and proton deposition.

DRY, WET, Cl/Fog = dry, wet, In some cases, the total deposition to cloudwater/fog deposition canopies can be deduced from throughfall and precipitation measurements in the CEX = canopy exchange; CEX > 0 open field using empirical canopy budget for leaching, CEX < 0 for uptake models (based on equation II.1, see When CEX=0, the dry deposition can be Adriaenssens et al., 2013; Draaijers and estimated as the difference between total Erisman, 1995) . There are different flux in throughfall and independent possible approaches, some being more measurements of wet and cloudwater/fog reliable than others. For instance, special deposition. If CEX differs from 0, dry care should be given to the choice of the deposition cannot be distinguished from main tracer. Page II - 14 Chapter II – Guidance on mapping concentrations levels and deposition levels

II.2.4.5 STOMATAL CONDUCTANCE Stomatal conductance is the process Stomatal conductance increases when through which gas and water may enter surface are wet (due to humidity in air leaf cells. It is dependant on the plant greater than 90%) and when soil humidity species, its phenology (including leaf is high. Then the flux is mostly determined nitrogen content) and environmental drivers by atmospheric resistances (Erisman et al. such as water, CO2 and light availability. 1994a).

II.2.4.6 LAND USE ROUGHNESS AND TOPOGRAPHY Deposition increases with the roughness of Topography influences the exposition of a the vegetation, as it filters airborne site to air masses. In valleys, air may be substances. As a consequence, forests stagnant. Coasts are submitted to high receive larger quantities of dry and wet winds. Rainfall is more abundant on the depositions than grasslands or bare soils. winward side than downwind of mountains. These effects will influence results from a At high altitude, the air mass might be monitoring station and may be assessed by “connected” to the substance (ozone in modelling, with the help of land use maps. particular) reservoir in the boundary layer… It is then essential that the land use map Those aspects are therefore to be taken used for modelling deposition is the same into account when setting up a monitoring as the one used for calculating critical site and inferring deposition from collected loads and exceedances. Within the LRTAP data. Convention, land used maps are issued from Corine Land Cover 14 in Europe, Global Land Cover 2000 15 elsewhere. The development of work on biodiversity has led to map vegetation types at a very fine scale (100 x 100 m²) over Europe. The “harmonised land cover map” now used under ICP M&M is available from the CCE and is further described in Chapter V.

14 http://www.eea.europa.eu/publications/COR0- landcover 15 http://bioval.jrc.ec.europa.eu/products/glc2000/ glc2000.php Chapter II – Guidance on mapping concentrations levels and deposition levels Page II - 15

II.2.4.7 TEMPORAL VARIABILITY Annual deposition rates are sufficient in conditions, a 3 year average deposition for order to determine critical load calculation of critical load exceedances exceedances, whereas for critical level may be used. exceedances, short-term information is For some substances (ozone for instance), sometimes needed. However, since there it is essential to monitor and simulate can be substantial variability from year to diurnal concentration variability. A time step year with deposition and climatic may then be a minima of one hour.

II.2.4.8 GEOGRAPHICAL VARIABILITY Geographical variability is really what critical loads and levels calculations as mapping describes. input data. Geographical variability is induced by the It is the result of the sources localisation as spatial variability of climate, soil conditions, well as climatic, geo-pedologic, topographic topography, land use and so on. These conditions. parameters are taken into account in

II.2.5 COMPLEMENTING METHODS TO ASSESS AIR POLLUTION: LONG RANGE MODELLING, NESTED MODELS AND MONITORING Several methods are available to estimate o Measuring directly boundary layer atmospheric concentrations concentrations and depositions and wet, dry, and cloud-water/fog on sites: Air pollution deposition on different scales of time and representation is independent space. In the context of long range air from inventories but pollution, one main characteristic is interpolated (by krigging) from whether the methods take emission inventories into account or are based on field measurements, when the site measurements and monitoring. Two monitoring network is dense groups of methods can be defined on these enough. characteristics: o Examples: Monitoring networks • Group A: Long range chemistry- of air concentration and wet transport modelling deposition including EMEP and o Objectives: (1) regional past, national networks and their present and future situation interpolation (for instance by analysis, (2) basis for scenario kriging). analysis, (3) contribution to field • Group C: High-resolution models processes understanding. o Objectives: (1) simulate air o Simulations are based on pollution at high spatial emission inventories. resolution (ca. 1 x 1 km² or o Examples: EMEP, national long higher), (2) analysis of local range transport models or impacts of emissions scenarios. hemispheric models. o Either based on increasing the • Group B: Monitoring based methods griding of LRT models or on o Objectives: (1) model extrapolating (kriging) data from evaluation and validation, (2) dense monitoring network. site-specific effects analysis at o Simulations are based on local a very fine scale (1 to 1000 ha), emission inventories and on (3) monitoring and analysing LRT models for boundary trends. conditions. Page II - 16 Chapter II – Guidance on mapping concentrations levels and deposition levels

o Exemples: most LRT models monitoring may be used to map have now the ability to run in concentrations and deposition. The nested mode, allowing zooming accuracy of the results will be strongly on specific areas, including the dependant on the model grid size for the EMEP Model (Simpson et al., model and on the density of points in the 2012). monitoring network. Nested models are Group A models, in Well structured monitoring networks are set which simulations cover a wide area on a up and provide a wealth of results within coarse scale and a smaller area (nest) at a the LRTAP Convention (EMEP, ICP finer scale. Thus, they use LRT models for Forests, ICP Waters, ICP Integrated their boundary conditions, while focusing Monitoring, ICP Materials). They provide their calculations on smaller areas. EMEP measurements that are necessary to test, has nowadays the ability to run in nested validate and improve steady state model mode with for instance, its 7 x 7 km² grid. It parameterisations. They also provide long allows zooming around urban areas term trends that are essential for (Cuvelier et al., 2013; Simpson et al., assessments of policy efficiency and 2012). sufficiency as well as dynamic modelling These three approaches are essential and test, validation and improvement. Parties complementary to provide information to who are developing existing or new policy makers. Modelling may not be robust monitoring network may improve their data without validation via monitoring, while robustness and completion by combining monitoring alone can not be used for their results to these existing networks. scenarios analysis. Modelling and II.2.5.1 LONG-RANGE CHEMISTRY TRANSPORT MODELS Long range chemistry transport models are long range chemistry transport models are most suitable for scenario analyses and given as one number per year per country to country budgets (‘blame component per grid square and deposition matrices’) used in emission reduction fluxes are provided either as average negotiations (if the model domain is more deposition to the grid square or as than one country). They calculate patterns ecosystem specific deposition estimates. of concentration and deposition across These model output can be provided for large regions of the world. Withing the shorter time periods, but with the overall Convention, the EMEP model is used for constraint that one of the major inputs, the the UN-ECE region. emission inventory, is often provided only Standard multiannual concentrations from as an annual total.

II.2.5.2 UN-ECEMONITORING BASED METHODS There are several techniques that may be In the framework of long range air pollution, used to carry out site sampling and monitoring stations are set at rural location, monitoring of pollutant concentrations and avoiding local sources, including farms (for deposition. It is beyond the scope of this NHy) and roads (for NOx and SOx). manual to describe them here. The However, in order to get a monitoring interested reader is referred to EMEP- network representative of the whole range CCC 16 , to ICP Forests 17 and ICP integrated of existing situations, stations may be monitoring relevant documentations as well located at various altitudes and/or at as specific litterature (setting up a network: various distances from the emitters of Anshelm and Gauger, 2001). We will give pollutant sources and precursors (Table here only some general aspects, essential II.1). Stations at urban locations are not in the framework of critical loads representative for extensive areas but they calculations. may be required for differentiating areas with rural and with urban pollution

conditions. They are also essential for 16 http://www.nilu.no/projects/ccc/manual/ 17 population and material exposure http://icp-forests.net/page/icp-forests-manual assessments.

Chapter II – Guidance on mapping concentrations levels and deposition levels Page II - 17

Table II.1: Minimum distance to emission and contamination sources as recommended by EMEP, 2001. All values are indicative as optimum distances also depends on sources intensities, meteorological and topographic site characteristics.

Type Minimum Comment distance Large pollution sources (towns, 50 km Depending on prevailing wind power , major motorways) directions Small scale domestic heating 100 m Only one emission source at minimum with coal, fuel oil or wood distance Minor roads 100 m Up to 50 vehicles/day Main roads 500 m Up to 500 vehicles/day Application of manure, stabling 2 km Depending on the number of animals of animals. and size of fertilized field or pastures Grazing by domestic animals on 500 m Depending on the number of animals fertilized pasture and size of fertilized field or pastures

The preferred sampling height is 3-5 m and that simple models are used to assist the the monitoring station requires an open interpolation, e.g. using altitude aspect without the presence of trees or dependences. It is preferable to interpolate other tall vegetation in the proximity of the concentrations in rain or in air and then sample intake. The elevation of a particular calculate the deposition at the receptor site location determines the extent to which it using local estimates of rainfall and land- experiences the influence of air from the use specific ground-level dry deposition free troposphere and from the boundary rates (see above). layer. Data assimilation, combining observed and Maps may be produced directly from point LRT modelled concentrations, is another measurements, but only if the network is method applied to provide improved dense enough to account for spatial (and pollutant concentration fields (Flemming, temporal) variations. This may be the case 2003, Rouil et al., 2009). for networks measuring air concentrations In areas with clearly delineated of compounds with little spatial variation or watersheds, the “calibrated watershed for measurements of wet deposition in method” integrates deposition fluxes over a areas of simple terrain. Network (point) scale compatible to critical load measurements should be interpolated computations, for example for lakes and using the kriging technique and it may be surface waters. Major fluxes to the helpful to include monitoring data from groundwater and soil exchange have then neighbouring countries for interpolation. to be accounted for. It is most useful for For some air concentrations, such as conservative elements (e.g., S, Na, Cl). ammonia or ozone, or for rain The data are useful to validate deposition concentrations in complex terrain, the estimates derived from modelling. required density of the measurement network could be too dense for practical Catchment mass balance is an alternative application. In these cases, it is approach, valid at at small (catchment) recomended that concentrations are scale. It combines information from obtained from less dense networks and monitoring to local modelling. Page II - 18 Chapter II – Guidance on mapping concentrations levels and deposition levels

II.2.6 CHARACTERISTICS OF SUBSTANCES MAPS IN RELATION TO EXCEEDANCES CALCULATIONS Specificities to mapping of substances Usually the relevant information is provided concentrations and deposition are given either from the EMEP model, from small below, in the context of the calculation of scale modelling or from monitoring critical loads and levels exceedances. network.

II.2.6.1 MAPPING OZONE (O 3) CONCENTRATIONS AND DEPOSITION 2 Data on ozone concentrations may be grid of 1 x 1 km cell-size is useful to available from photochemistry/transport provide a spatial resolution of the ozone modelling or from monitoring networks. exposure on a horizontal scale which reflects the variations in the orography. As The concentrations of ozone close to the critical levels are based on the terrestrial surfaces (e.g. within 1 m) show a concentration measured in the turbulent large spatial variability in both rural and layer near the receptor, ozone levels urban areas. For urban areas, this modelled or measured at higher distances variability is mainly caused by the rapid from the ground are not directly related to chemical consumption of ozone by NO, the observed effects. The supply of ozone which is locally emitted. For rural areas to vegetation is provided by atmospheric away from local sources, this variability is turbulence and hence wind speed and the largely caused by spatial and temporal thermal structure of air close to the ground changes in the degree to which individual are taken into account. The deposition of sites are vertically 'connected' to the main ozone on terrestrial surfaces and reservoir of ozone in the boundary layer. vegetation causes a vertical gradient of the Like in urban areas O 3 might be consumed ozone concentration, which is largely by the reaction with NO which can be determined by the sink activity of the soil- emitted from bacterial processes in the soil vegetation system. (PORG 1997). An ozone concentration field at, at least, a

II.2.6.2 MAPPING SULPHUR DIOXIDE (SO 2) CONCENTRATIONS AND OXIDISED SULPHUR (SO X) DEPOSITION

Data on SO 2 gas concentrations, sulphate For rural areas away from local sources, 2- 2- (SO 4 ) aerosol concentrations and SO 4 spatial variability is largely caused by concentrations in rain are available from spatial and temporal changes in the degree long-range transport modelling, possibly to which individual sites are vertically coupled to small-scale modelling. 'connected' to the main reservoir in the boundary layer. SO 2, in contrast to ozone or sulphate aerosol, is a primary pollutant. It is emitted As for ozone, the SO 2 levels measured 3-5 by both high (e.g. power plants) and low m above ground are not directly related to (e.g. households) sources. Therefore the the observed effects, since dry deposition spatial variability of concentrations tends to causes a systematic vertical concentration be higher than that of ozone and sulphate gradient towards the surface, while the aerosol but lower than that of ammonia. critical levels are based on the Close to urban areas, the concentrations of concentration measured close to the rural sulphur dioxide are elevated and this receptor. However, surface-type specific effect should be modelled explicitly where corrections are not generally applied and possible, for example by using urban measured/modelled values usually taken concentration measurements and areas of uncorrected. urbanisation to model the urban effect.

Chapter II – Guidance on mapping concentrations levels and deposition levels Page II - 19

II.2.6.3 MAPPING NITROGEN OXIDES (NO X) CONCENTRATIONS AND DEPOSITION OF OXIDISED NITROGEN (NO Y) Data on nitrogen oxides are available from for example by using distance to major long-range transport modelling, possibly roads. coupled to small-scale modelling or from The reaction products of NO x in the monitoring networks. atmosphere are collectively called NO y. Like SO , nitrogen oxides (NO =NO+NO ) The main chemical species of NO y are 2 x 2 - - are emitted by both high (e.g. power plants) NO x, NO 3 , NO 2 , HONO and HNO 3. and low (e.g. traffic) sources, mostly as NO Species of secondary importance for deposition (but essential if atmospheric and, to a lesser extend as NO 2. The spatial chemistry is to be modelled) are organic variability of NO x concentrations is mainly oxidised compounds such as PAN (peroxy controlled by reactions of NO with O 3. It tends to be higher than that of ozone and acetyl nitrates) and its homologues (peroxy nitrate but lower than that of ammonia. In alkyl nitrates, alkyl nitrates), dinitrogen rural areas, emission of NO from soils (both peroxide N 2O5, the nitrate radical NO 3 agricultural and semi-natural) can likewise (Hertel et al., 2011; Seinfeld and Pandis, 1998)… contribute to local NO 2 levels. Many national modelling activities are able to Dry deposition modelling includes - provide estimates of surface concentrations principally NO x, NO 3 aerosol and HNO 3 (ideally also HONO). Reactions with ozone of NO 2 at a high resolution of at least 2 5 x 5 km and these can incorporate models will affect both NO 2 and NO concentrations to adjust concentrations for local emissions, fields.

II.2.6.4 MAPPING AMMONIA (NH 3) CONCENTRATION, REDUCED NITROGEN (NH X) DEPOSITION AND TOTAL NITROGEN DEPOSITION Ammonia is emitted primarily from concentrations by interpolation from agricultural sources that may be grouped measurements alone requires extremely as (Hertel et al., 2011): high measurement network density and the method is only feasible over small areas. • Point sources, i.e. animal houses and manure storages, A long-range transport model with, for 2 • Application of manure and mineral example a 50 x 50 km spatial resolution, fertilizers to the fields, will not resolve these large variations either for ammonia concentrations or for the dry • Grazing animals, deposition of ammonia which will be the • Other sources including plants. major fraction of total reduced nitrogen Emissions from these sources vary with deposition close to an ammonia source. So agricultural practices and meteorological assessments of the exceedances of critical loads will be biased when using such LRT conditions, as NH 3 emissions is a process that is highly temperature dependant. models. In the absence of very detailed emission data (on the level of the individual Gaseous NH 3 has a short atmospheric residence time (Erisman and Draaijers farm), measurements in a dense network 1995) and as a result its concentrations in are needed to obtain accurate exceedance air may show steep horizontal and vertical levels (Asman et al. 1988). gradients (Asman et al. 1988). Even in It is also important to note that ammonia areas not affected by strong local sources, may be emitted by as well as deposited the ambient concentrations of ammonia onto vegetation, and therefore surface– may vary by a factor of three to four on atmosphere exchange modelling must be scales less then a few kilometres. used to quantify the net exchange over the The very localised pattern of ammonia landscape. The background developments concentration, and also of ammonia dry to allow these processes to be simulated deposition, has consequences for mapping use a compensation point approach procedures. Mapping of ammonia (Schjorring et al. 1998; Sutton et al. 2000). Page II - 20 Chapter II – Guidance on mapping concentrations levels and deposition levels

II.2.6.5 MAPPING TOTAL REACTIVE NITROGEN framework. It is defined as the sum of total Total reactive nitrogen (N r) released in atmosphere consists in three main parts deposition of reduced (NH x) nitrogen [NH 3 + (NH , NO and N O). Organic compounds dry deposition, NH 4 aerosol deposition, x x 2 + + form a fourth, poorly quantified, fraction of NH 4 wet deposition, NH 4 cloudwater/fog deposition] and oxidised (NO ) nitrogen Nr. N 2O takes part of the atmospheric cycle y of nitrogen and is important as a green [NO 2 dry deposition, HNO 3 dry deposition, - - house gas but not for the critical loads and NO 3 aerosol deposition, NO 3 wet - levels calculations. Organic compounds deposition, NO 3 cloudwater/fog deposition]. The methodological and N 2O will not be discussed further here. considerations concerning NH x and NO y The deposition of total nitrogen is needed depositon mapping apply accordingly. for many applications in the critical load II.2.6.6 MAPPING BASE CATION AND CHLORIDE DEPOSITION The deposition of physiologically active linked to emissions of acidifying basic cations (Bc = Ca + Mg + K 18 , i.e. the compounds (for example from emissions of sum of calcium, magnesium and Sahara dust, large-scale wind erosion of potassium) counteracts impacts of acid basic topsoil particles, etc.) should in deposition and can improve the principle not be accounted for within the status of ecosystems with respect to critical loads framework. The non- eutrophication by nitrogen inputs. Sodium anthropogenic, non-sea-salt atmospheric (Na) fluxes are needed for estimating the input of base cations is defined as a sea-salt fraction of sulphur, chloride (Cl) property of the receptor ecosystem and and Bc inputs, and as a tracer for canopy indirectly enters the critical load equation and soil budget models. In addition, inputs for acidity (see Chapter V, section V.3). of Bc as well as sodium and chloride Base cation particle deposition can been determine the potential acidity of estimated from concentrations in wet deposition. deposition and empirical scavenging ratios Emissions of base cations are from (Eder and Dennis 1990, Draaijers et al. anthropogenic and natural processes (such 1995). Dry deposition velocities can be 2- as rock weathering, sea salts, biomass inferred as for SO 4 aerosol and the burning, volcanic dust, industrial emission, obtained dry deposition estimates added to vehicle emissions…). Base cations occur in measured and interpolated wet deposition the air in the particulate phase and are estimates (e.g. Gauger et al. 2003, RGAR deposited in dry and wet processes. In 1997, CLAG 1997). precipitation, they are largely dissolved and Deposition of base cations have been occur as ions. In Europe, depositions of estimated for Europe, and especially for the base cations are srongly influenced by Nordic countries based on monitoring data Saharan dust, especially in countries on concentrations of base cations in around the Mediteranean. Sea salt precipitation and air-borne particles depositions tend to be correlated with the (Draaijers et al., 1997; Hellsten et al., 2007; distance to the sea, with highest Van Leeuwen et al., 1996; Van Leeuwen et depositions at western European coastal al., 1995; Van Loon et al., 2005; Vet et al., sites (Torseth et al., 2012; Vet et al., 2013). 2013; Werner et al., 2011, Lövblad et al., As the aim of the Convention is to minimize 2004). acid deposition irrespective of other man- made emissions, base cation inputs not

18 Na is not taken up by plant (and therefore not « physiologically active »). It is not included in the Bc sum. However, it is a base cation and included in the critical loads calculations in Chapter V in the BC sum : BC = Ca + Mg + K + Na). Chapter II – Guidance on mapping concentrations levels and deposition levels Page II - 21

II.2.6.7 MAPPING TOTAL POTENTIAL ACID DEPOSITION * * Total Potential Acid Deposition is defined BC dep , Cl dep = non-sea-salt base cation / as the sum of total deposition of strong acid chloride deposition anions plus ammonium minus non-sea-salt In areas strongly affected by sea spray base cations. (high sea-salt Na, Cl, S inputs), the "total As stated in the preceding subchapter, potential acid" definition of eq. II.3 becomes most chloride inputs are assumed to be of problematic, since base cations have a sea-salt origin, and these are removed beneficial nutrifying effect irrespective of from the equation by removing all other their chemical form (e.g. CaCl vs. CaCO 3). sea-salt inputs (i.e. of sulphate and base At the Grange-over-Sands Workshop 1994 cations including Na) using a "sea-salt it was concluded that total Mg+Ca+K correction" with Na as a tracer. The implicit deposition rates should be used for the assumption is that sea-salt is neutral and determination of critical loads for acidity contains no carbonates. Surplus chloride (Sverdrup et al. 1995) (see Chapter 5.3.2). inputs (Cl * ) are assumed to be due to dep As stated in Chapter V.3.2, eq. II.3 anthropogenic HCl emissions. assumes that deposited NH x is completely The sum of critical load (for sulphur) and nitrified and exported from the system as - background (non-anthropogenic) base NO 3 , thereby acidifying the system. Thus, cation deposition has formerly been with respect to it is * defined as critical (sulphur) deposition, as assumed that 1 mol of SO x is forming 2 + * used for the negotiations for the Second moles of H , and 1 mol of NO y, NH x and Cl Sulphur Protocol (Oslo, 1994). For each 1 mol of H +. comparison to CL(S) + CL(N), as defined in It is important to be consistent when Chapter V.3.2 (eq. V.19), only deposition determining total acid inputs: If results are values of S and N are needed. However, if determined on a site and process level, the amount of total acid input is of interest and if H + deposition rates are determined (e.g. for comparison to CL(Ac ), as pot separately, NH + inputs (max. 2 eqivalents defined in Chapter V.3.2), non-sea-salt 4 H+ per mol) have to be distinguished from base cation and chloride deposition has to + NH 3 inputs (max. 1 eqivalent H per mol). be included into the input side of the + The same applies to SO 2 (2 eqivalents H potential acidity exceedance equation: 2- + per mol) vs. SO 4 (0 eqivalents H per * (II.3) Ac(pot) dep = SO x dep + NO y dep mol). On a larger scale, this may be * * neglected: Note that the emission and + NH x dep - BC dep + Cl dep subsequent deposition of 1 mol SO and 2 where: 2 mol NH 3 yields the same potential acid * SO x, dep = non-sea-salt sulphate deposition as the deposition of 1 mol of deposition their reaction product (NH 4)2SO 4, namely 4

NO y dep , NH x dep = total eqivalents. oxidized/reduced nitrogen deposition

II.2.7 USE OF DEPOSITION AND CONCENTRATION MAPS II.2.7.1 ISSUES RELATED TO MAP SCALES Deposition and concentration maps are resulting in an underestimation of the designed to be used in combination with critical load exceedance. These issues critical loads and critical levels maps to have been discussed above and improved show where and by how much critical loads deposition estimates, for example by using and critical levels are exceeded. The use of national models at a finer spatial resolution, deposition data with critical loads data very can improve the quality of the critical load often involves different scales of the exceedances. One important point re- different data sources and, in most cases, iterated here is that it is essential to note the critical loads data are provided at a any different scales in the legends to finer resolution than the deposition data figures and maps. Page II - 22 Chapter II – Guidance on mapping concentrations levels and deposition levels

The scale at which critical levels/loads and These effects are minimised by estimating concentration/deposition are mapped deposition to the smallest spatial scale greatly influences the magnitude of possible. They are therefore becoming less exceedance values (Spranger et al. 2001, acute with the use of finer scale in new Bak 2001, Lövblad 1996, Smith et al. chemical transport models (the latest 1995). For example, if the average value version of EMEP is now based on a 0.1° x from a 50 x 50 km 2 grid square is matched 0.1° grid). However, there is an underlying to critical loads on the 250 squares of relationship that the critical load 1 x 1 km 2 within the 50 x 50 km 2 grid exceedances will increase as the spatial square, there will be generally be less resolution of the deposition gets closer to critical load exceedance than if the that of the critical loads. Beyond the effects deposition were available at the 1 x 1 km 2 caused by a change in grid resolution, it scale. The only circumstance in which this has been shown that the constant underestimate would not occur would be if improvement in scientific knowledge can the high deposition locations matched the modify air pollution risk assessment results. high critical load locations. Over many When comparing assessments of areas of Europe, exactly the opposite environmental situation, it is therefore occurs. In many areas of complex terrain important to make sure that different the parts of the landscape receiving the assessments are carried out with similar largest deposition, such as the higher tools and based on similar hypotheses areas in the mountains of North-West (Hettelingh et al., 2013). Europe, are also the most sensitive to the The comparison of national maps and effects of deposition, for example model outputs with data from the EMEP acidification. The same holds true for model is a source of science and policy forested areas, which tend to correlate with relevant information. Identification of poor soils in large parts of Europe. This differences between model outputs may problem is worse for components with local lead to model, parameterization and sources (NH , NO ) because the within-grid 3 x methodology improvements. These may be distribution of sources is not reflected in the of particular significance at borders grid average estimation from a LRT model, between countries and may contribute to but does markedly increase the within-grid avoid “border effects”. National data may variability of deposition and hence also complete the information provided to potentially increases critical load policy makers through EMEP. Whether exceedances over local sensitive areas. national data confirm or infirm European As the current deposition estimates from integrated assessments, they are part of EMEP are provided at a scale which is the information national representative may much larger than the scale of this spatial use during protocol negotiations or their variability, depositions are averaged over implementation. Models and approaches large areas and “hot spot” are smoothed intercomparisons are commonly carried out down. The critical loads exceedances for within the LRTAP groups and subgroups. these areas tend to be underestimated.

II.2.7.2 SOME PRELIMINARY REMARKS REGARDING THE USE OF MODEL RESULTS BY PARTIES Within UN-ECE countries, the expertise desirable, as both are complementary. and facilities for measurement of Besides, the cooperation of all parties to air concentrations and fluxes of pollutants is pollution impact assessment process is very variable. The extent to which the necessary to develop satisfactory and methods presented in monitoring manuals efficient strategies for control of pollutant can be applied is therefore variable. In emissions. These require full participation each country, it is necessary to assess the in the underlying science as well as in the range of options available. It is important to political process. stress that involvement in measurement National Focal Centres are strongly alongside modelling activities is highly advised to ensure that the monitoring and Chapter II – Guidance on mapping concentrations levels and deposition levels Page II - 23

modelling methodologies described in the Mapping Programme as well as with publications listed above are documented monitoring methods employed within other in the development or validation of a deposition monitoring programmes under database for national concentration and the Convention (ICPs on Forests and on deposition (and critical level and load Integrated Monitoring; EMEP) is very exceedance) maps. Compatibility of these important. maps with other national maps within the

II.2.7.3 IDENTIFYING ECOSYSTEMS POSITION FOR CRITICAL LOADS CALCULATION AND THEIR EXCEEDANCES The land use maps used for deposition ecosystems, land use type/vegetation type, modelling should be identical to the stock- vegetation height and coverage are at-risk maps used for critical levels/loads mapped as well on a scale that allows for mapping. Land use maps based on Corine correct allocation of deposition to all Land Cover in Europe, Global Land Cover ecosystem types in the model domain. 2000 elsewhere are used within the LRTAP For all maps, the most recent available Convention (cf. Section II.2.4.6 and cf data should be used. Should data not be Chapter V, section V.6.3). Vegetation types available for a given year, data set filling are then identified using EUNIS should not go back in time further than five nomenclature. In addition to the years (unless, of course, the objective is to geographical position of sensitive prepare time series).

II.2.7.4 UNCERTAINTIES OF MAPPING METHODS Since the 2004 version of the Mapping non-linearities) Manual, modelling has significantly • Pollutant dispersion and vertical improved. The EMEP/MSC-W 50 x 50 km 2 resolution Eulerian LRT has been used, tested, • Deposition and its relation to compared to other chemistry transport interactions of pollutants with models, calibrated to a greater number of surfaces and vegetation and monitoring stations over longer periods. At aerosol size distributions the time of the update of this Manual, finer grid scales at around 28 x 28 km² (0.5° When evaluating model-measurement Long x 0.25° Lat), or finer, are being intercomparisons, it is important to recall implemented in the EMEP model. that There are, of course, a number of a) there are also uncertainties with the persistant issues in chemistry transport measurements, model uncertainties that lead to b) the model may be estimating uncertainties in critical load exceedances something rather different from calculations (there are of course also some what is being measured. uncertainties in critical load calculations. For instance, the NO concentration at a They are discussed in relevant chapters 2 single site in a (50 x 50 km 2) grid square is and sections). The following points are only an estimate from a sample of size one mentioned in recent literature, including of the 'average' NO concentration in the that related to the EMEP Model, as 2 square, which is the value the EMEP/MSC- potential sources of uncertainties (Cuvelier W model is attempting to match. An et al., 2013; Hertel et al., 2011; Simpson et evaluation of the overall uncertainty of the al., 2012): model requires that some further • Emission data information is available on the effects of the • Climate spatial distribution of measurement sites. • Atmospheric processes (and their

Page II - 24 Chapter II – Guidance on mapping concentrations levels and deposition levels

II.2.8 WHO DO YOU ASK FOR FURTHER ADVICE?

For questions on ...... , please contact : Evaluating total deposition maps with throughfall measurements: EMEP long-range transport models : Gun Lövblad, Swedish Environmental Erik Berge, The Norwegian Meteorological Research Institute, Box 47086, 40258 Institute, P.O. Box 43 - Blindern, N - 0313 Göteborg, Sweden; Tel. +46-31-725 6240, Oslo, Norway, Tel. +47 2296 - 3000; Fax. +46-31- 725 6290, [email protected] Fax. +47 2296 - 3050 Jan-Willem Erisman, RIVM-LLO, P.O. Box 1, 3720 BA Bilthoven, The Netherlands; High resolution modelling of dry and Tel +31-30-274-2824; Fax +31-30- cloud/fog deposition, combination with 2287531 maps of interpolated wet deposition: Jan-Willem Erisman, RIVM-LLO, P.O. Box Diffusive samplers for air pollution 1, 3720 BA Bilthoven, The Netherlands, monitoring : Tel. +31-30-274-2824; Fax. +31-30- Martin Fern, Swedish Environmental 2287531 Research Institute, Box 47086, 40258 David Fowler, Centre for Ecology and Göteborg, Sweden; Tel. +46-31-725 6224, , Bush Estate, Penicuik, Fax. +46-31-725 6290 [email protected] Midlothian, EH26 0QB, United Kingdom, Tel. +44-131-445-4343; Fax. +44-131-445- 3943 General information on mapping excercises can also be obtained by contacting the Coordination Center for Effects, CCE, Combination of high-resolution models with Netherlands: Jean-Paul Hettelingh, Tel. long-range transport models : +31-30-74 30 48; Fax. +31-30-74 29 71 Jan-Willem Erisman, RIVM-LLO, P.O. Box 1, 3720 BA Bilthoven, The Netherlands; Tel. +31-30-274-2824; Fax. +31-30- General information on modelling : 2287531 Ron Smith, Centre for Ecology and Erik Berge, The Norwegian Meteorological Hydrology, Bush Estate, Penicuik, Institute, P.O. Box 43 - Blindern, N - 0313 Midlothian EH26 0QB, Tel. +44 131 445 Oslo, Norway, Tel. +47 2296 3000; 4343; Fax. +44 131 445 3943 Fax. +47 2296 3050

General information on NO x, NO 3: Measurement and interpolation methodology (Ambient air concentrations, Kim Pilegaard, Riso National Laboratory, wet and bulk deposition) : PO Box 49, DK-4000 Roskilde, Denmark Tel. +45 4677 4677, Fax. +45 4677 4160 EMEP CCC, NILU, Postbox 100, N-2007 Jan Duyzer, TNO-MEP, Postbus 342, 7300 Kjeller, Norway, Tel. +47-6389-8000; Fax. AH, Apeldoorn, The Netherlands, Tel. +31 +47-6389-8050 55 549 3944; Fax. +31 55 549 3252 Chapter II – Guidance on mapping concentrations levels and deposition levels Page II - 25

II.2.9 REFERENCES Adriaenssens, S., Staelens, J., Baeten, L., (1995): European transboundary Verstraeten, A., Boeckx, P., Samson, acidifying air pollution. EMEP/MSC-W R., and Verheyen, K. (2013). Influence Report 1/95. The Norwegian of canopy budget model approaches on Meteorological Institute, Oslo, Norway. atmospheric deposition estimates to Beier, C., P. Gundersen and Rasmussen L. forests. Biogeochemistry , 116, 1-3, 215- (1992): A new method for estimation of 229. dry deposition of particles based on Anshelm, F. and Th. Gauger (2001): throughfall measurements in a forest Mapping of ecosystem specific long- edge. Atmos. Environ. 26A, 1553-1559. term trends in deposition loads and Berg, T. and Schaug J. (eds.) (1994): concentrations of air pollutants in Proceedings of the EMEP Workshop on Germany and their comparison with the Accuracy of Measurements with Critical Loads and Critical Levels. Part WMO sponsored sessions on 2: Mapping Critical Levels exceedances. Determining the Representativeness of Final Report of Project 29942210. Inst. Measured Parameters in a Given Grid for Navigation, Stuttgart University and Square as Compared to Model Umweltbundesamt. Calculations, Passau, Germany, 22-26 Asman, W.A.H. and H.A. van Jaarsveld Nov. 1993. (1992): A variable-resolution transport Bessagnet, B., Hodzic, A., Vautard, R., model applied for NHx in Europe. Beekmann, M., Cheinet, S., Honoré, C., Atmos. Environ. Part A-General Topics, Liousse, C., and Rouïl, L. (2004). 26, 445-464. Aerosol modeling with CHIMERE- Asman, W.A.H., Drukker, B. and A.J. preliminary evaluation at the continental Janssen (1988): Modeled historical scale. Atmospheric Environment , 38, 18, concentrations and depositions of 2803-2817. ammonia and ammonium in Europe. Beswick, K.M., Hargreaves, K., Gallagher, Atmos. Environ., 22, 725-735. M.W., Choularton, T.W. & Fowler, D. Aubinet, M., Grelle, A., Ibrom, A., Rannik, 1991. Size resolved measurements of U., Moncrieff, J., Foken, T., Kowalski, cloud droplet deposition velocity to a A.S., Martin, P.H., Berbigier, P., forest using an eddy correlation Bernhofer, C., Clement, R., Elbers, J., technique. Q. J. Roy. Meteor. Soc., 117, Granier, A., Grunwald, T., Morgenstern, 623-645. K., Pilegaard, K., Rebmann, C., Bredemeier, M. (1988): forest canopy Snijders, W., Valentini, R. and Vesala, transformation of atmospheric T. (2000): Estimates of the annual net deposition. Water Air Soil Poll., 40, carbon and water exchange of forests: 121-138. The EUROFLUX methodology. Adv. Ecol. Res., 30: 113-175. Christensen, J. H. (1997). The Danish eulerian hemispheric model — a three- Bak, J. (2001): Uncertainties in large scale dimensional air pollution model used for assessments of critical loads the arctic. Atmospheric Environment , 31, exceedances. Water, Air, and Soil 24, 4169-4191. Pollution Focus, Vol. 1 Nos. 1-2, 265 - 280. CLAG (1997): Deposition fluxes in the United Kingdom: A compilation of the Barthel, S., Tegen, I., Wolke, R., and van current deposition maps and mapping Pinxteren, M. (2014). Model study on methods (1992-1994) used for Critical the dependence of primary marine Loads exceedance assessment in the aerosol emission on the sea surface United Kingdom. Critical Loads Advisory temperature. Atmospheric chemistry and Group Sub-group report on Depositon physics Discussions , 14, 377–434. Fluxes. 45 pp. Penicuik: Institute of Barrett, K., Seland, Ø., Foss, A., Mylona, S, Terrestrial Ecology. Sandnes, H., Styve, H. and Tarrasòn, L. Page II - 26 Chapter II – Guidance on mapping concentrations levels and deposition levels

Colette, A., Granier, C., Hodnebrog, Ã., impact of emission reductions in Jakobs, H., Maurizi, A., Nyiri, A., European cities in 2010. Atmospheric Bessagnet, B., D'Angiola, A., D'Isidoro, Environment , 41, 1, 189-207. M., Gauss, M., Meleux, F., Dore, A.J., T.W. Choularton and Fowler, D. Memmesheimer, M., Mieville, A., (1992): An improved wet deposition map Rouï l, L., Russo, F., Solberg, S., of the United Kingdom incorporating the Stordal, F., and Tampieri, F. (2011). Air topographic dependence of rainfall quality trends in Europe over the past concentrations. Atmos. Environ., 26A, decade: a first multi-model assessment. 1375-1381. Atmos. Chem. Phys. , 11, 22, 11657- 11678. Draaijers, G.P.J. and Erisman J.W. (1993): Atmospheric sulphur deposition to forest Colette, A., Granier, C., Hodnebrog, Ã., stands - throughfall estimates compared Jakobs, H., Maurizi, A., Nyiri, A., Rao, to estimates from inference. Atmos. S., Amann, M., Bessagnet, B., Environ., 27A, 43-55. D'Angiola, A., Gauss, M., Heyes, C., Klimont, Z., Meleux, F., Memmesheimer, Draaijers, G. P. J., and Erisman, J. W. M., Mieville, A., Rouïl, L., Russo, F., (1995). A canopy budget model to Schucht, S., Simpson, D., Stordal, F., assess atmospheric deposition from Tampieri, F., and Vrac, M. (2012). throughfall measurements. Water, Air, Future air quality in Europe: a multi- and Soil Pollution , 85, 4, 2253-2258. model assessment of projected Draaijers, G.P.J., van Leeuwen, E.P., exposure to ozone. Atmos. Chem. Potma, C., van Pul, W.A.J. and Erisman, Phys. , 12, 21, 10613-10630. J.W. (1995): Mapping base cation Coyle, M., Smith, R.I., Stedman, J.R., deposition in Europe on a 10x20 km Weston, K.J., and Fowler, D. (2002): grid. Water Air Soil Pollut., 85, 2389- Quantifying the spatial distribution of 2394. surface ozone concentration in the UK. Draaijers, G.P.J., Erisman, J.W., Spranger, Atmos. Environ., 36, 1013-1024. T. and Wyers, G.P. (1996a): The Cuvelier, C., Thunis, P., Karam, D., Shaap, application of throughfall measurements. M., Hendricks, C. M. A., Kranenbourg, Atmos. Environ., 30, 3349-3361. R., Fagerli, H., Nyiri, A., Simpson, D., Draaijers, G.P.J., Erisman, J.W., van Wind, P., Schulz, M., Bessagnet, B., Leeuwen, N.F.M., Römer, F.G., te Collette, A., Terrenoire, E., Rouïl, L., Winkel, B.H., Veltkamp, A.C., Stern, R., Graff, A., Baldasano, J. M., Vermeulen, A.T. and Wyers G.P. and Pay, M. T. (2013). ScaleDep: (1996b): The impact of canopy Performance of European chemistry- exchange on differences observed transport models as function of between atmospheric deposition and horizontal spatial resolution. Technical throughfall fluxes. Atmos. Environ., 31, report EMEP MSC-W Rep. No. 1/2013, 387-397. Technical report 1/2013, 62 p. Draaijers, G. P. J., Van Leeuwen, E. P., De Cuvelier, C., Thunis, P., Vautard, R., Jong, P. G. H., and Erisman, J. W. Amann, M., Bessagnet, B., Bedogni, M., (1997). Base cation deposition in Berkowicz, R., Brandt, J., Brocheton, F., europe-part I. Model description, results Builtjes, P., Carnavale, C., Coppalle, A., and uncertainties. Atmospheric Denby, B., Douros, J., Graf, A., Environment , 31, 24, 4139-4157. Hellmuth, O., Hodzic, A., Honoré, C., Jonson, J., Kerschbaumer, A., de Draaijers, G.P.J., Bleeker, A., van der Leeuw, F., Minguzzi, E., Moussiopoulos, Veen, D., Erisman, J.W, Möls, H., N., Pertot, C., Peuch, V. H., Pirovano, Fonteijn, P. and Geusenbrock, M. G., Rouil, L., Sauter, F., Schaap, M., (2001): Field intecomparison of Stern, R., Tarrason, L., Vignati, E., throughfall, stemflow and precipitation Volta, M., White, L., Wind, P., and measurements performed within the Zuber, A. (2007). CityDelta: A model framework of the Pan European intercomparison study to explore the Intensive Monitoring Programme of Chapter II – Guidance on mapping concentrations levels and deposition levels Page II - 27

EU/ICP Forests TNO report R2001/140. Erisman, J.W., A. van Pul and Wyers P. (1994a): Parameterization of dry Dragosits, U., Theobald, M.R., Place, C.J., deposition mechanisms for the Lord, E., Webb, J., Hill, J., ApSimon, quantification of atmospheric input to H.M. and Sutton, M.A. (2002): Ammonia ecosystems. Atmos. Environ., 28, 2595- emission, deposition and impact 2607. assessment at the field scale: a case study of sub-grid spatial variablility. Erisman, J.W., Beier, C., Draaijers, G.P.J. Environ. Pollut., 117, 147-158. and Lindberg, S. (1994b): Review of deposition monitoring methods. Tellus, Duyzer, J.H., Deinum, G. and Baak, J. 46B, 79-93. (1995): The interpretation of measurements of surface exchange of Erisman, J.W., Draaijers, G., Duyzer, J., nitrogen oxides; corrections for chemical Hofschreuder, P., van Leeuwen, N., reactions. Philosophical Transactions of Römer, F., Ruijgrok, W. and Wyers, P. the Royal Society of London A 351, 1-18 (1995): Particle deposition to forests. Duyzer, J., Nijenhuis, B. and Weststrate, H. In: Heij, G.J. and Erisman J.W.(eds.): (2001): Monitoring and modelling of Proceedings of the conference "Acid rain research: do we have enough ammonia concentrations and deposition answers?", `s-Hertogenbosch, The in agricultural areas of the Netherlands. Netherlands, 10-12 Oct. 1994. Studies Water, Air and Soil Pollution Focus, Vol in Environmental Science 64, 115-126. 1 Nos. 5-6, 131-144. Erisman, J.W., Mennen, M.G., Fowler, D., ű EDC (Environmental Data Centre) (1993): Flechard, C.R., Spindler, G., Gr ner, A., Manual for Integrated Monitoring. Duyzer, J.H., Ruigrok, W. and Wyers, Programme Phase 1993-1996. National G.P. (1998a): Deposition Monitoring in Board of Waters and the Environment, Europe. Environ. Monit. Assess., 53, Helsinki. 279-295. Eder, B.K. and Dennis R.L. (1990): On the Erisman, J.W., Bleeker, A. and Van use of scavenging ratios for the Jaarsveld, H. (1998b): Atmospheric inference of surface level concentration. deposition of ammonia to semi-natural Water Air Soil Pollut., 52, 197-215. vegetation in the Netherlands-methods for mapping and evaluation. Atmos. Emberson, L.D., Ashmore, M.R., Environ., 32, 481-489. Cambridge, H.M., Simpson, D. and Tuovinen J.-P. (2000): Modelling Ferm M. (2001): Validation of a diffusive stomatal ozone flux across Europe. sampler for ozone in workplace Environ. Pollut., 109, 403-413. atmospheres according to EN838. Proceedings from International EMEP/CCC (1996): EMEP Manual for Conference Measuring Air Pollutants by Sampling and Analysis. EMEP/CCC Diffusive Sampling, Montpellier, France Report 1/95. 26-28 September 2001, 298-303. EMEP (2001). EMEP manual for sampling Ferm, M. and Svanberg P.-A. (1998): Cost- and chemical analysis. EMEP - efficient techniques for urban and Chemical coordinating centre (CCC) background measurements of SO2 and EMEP/CCC-Report 1/95, 95 p. NO2. Atmos. Environ., 32, 1377-1381. EMEP (2013). Transboundary Acidification, Fiore, A. M., Dentener, F. J., Wild, O., Eutrophication and Ground Level Ozone Cuvelier, C., Schultz, M. G., Hess, P., in Europe in 2011. Norwegian Textor, C., Schulz, M., Doherty, R. M., Meteorological Institute 205 p. Horowitz, L. W., MacKenzie, I. A., Erisman, J.W. and Draaijers G. (1995): Sanderson, M. G., Shindell, D. T., Atmospheric deposition in relation to Stevenson, D. S., Szopa, S., Van acidification and eutrophication. Studies Dingenen, R., Zeng, G., Atherton, C., in Environmental Science 63, Elsevier, Bergmann, D., Bey, I., Carmichael, G., Amsterdam. Collins, W. J., Duncan, B. N., Faluvegi, Page II - 28 Chapter II – Guidance on mapping concentrations levels and deposition levels

G., Folberth, G., Gauss, M., Gong, S., Fowler, D., Pitcairn, C.E.R. and Erisman, J- Hauglustaine, D., Holloway, T., Isaksen, W. eds. (2001a): Air-Surface Exchange I. S. A., Jacob, D. J., Jonson, J. E., of Gases and Priticles (2000). Kaminski, J. W., Keating, T. J., Lupu, A., Proceedings of the Sixth International Marmer, E., Montanaro, V., Park, R. J., Conference on Air-Surface Exchange of Pitari, G., Pringle, K. J., Pyle, J. A., Gases and Particles, Edinburgh 3-7 Schroeder, S., Vivanco, M. G., Wind, P., July, 2000. Water Air and Soil Pollution Wojcik, G., Wu, S., and Zuber, A. Focus, Vol. 1 Nos. 5-6, 1-464. (2009). Multimodel estimates of Fowler, D., Coyle, M., Flechard, C., intercontinental source-receptor Hargreaves, K., Storeton-West, R., relationships for ozone pollution. Journal Sutton, M. and Erisman, J.W. (2001b): of Geophysical Research: Atmospheres , Advances in micrometeorological 114, D4, D04301. methods for the measurement and Flechard, C.R. and Fowler, D. (1998): interpretation of gas and particles Atmospheric ammonia at a moorland nitrogen fluxes. Plant Soil, 228, 117-129. site. II: Long-term surface/atmosphere Fowler, D., Sutton, M.A., Flechard, C., micrometeorological flux measurements. Cape, J.N., Storeton-West, R., Coyle, M. Q. J. Roy. Meteor. Soc., 124, 733-757. and Smith, R.I. (2001c): The Flemming, J. (2003): Immissionsfelder aus Control of SO 2 dry deposition on to Beobachtung, Modellierung und deren natural surfaces and its effects on Kombination, PhD thesis, Free regional deposition. Water, Air, and Soil University Berlin, FB Pollution Focus, Vol. 1 Nos. 5-6, 39-48. Geowissenschaften (in German). Fowler, D., Pilegaard, K., Sutton, M. A., Fowler, D., Granat, L., Koble, R., Lovett, Ambus, P., Raivonen, M., Duyzer, J., G., Moldan, F., Simmons, C., Slanina, Simpson, D., Fagerli, H., Fuzzi, S., S.J. & Zapletal, M. (1993): Wet, cloud Schjoerring, J. K., Granier, C., Neftel, A., water and fog deposition. (Working Isaksen, I. S. A., Laj, P., Maione, M., Group report). In: Models and methods Monks, P. S., Burkhardt, J., Daemmgen, for the quantification of atmospheric U., Neirynck, J., Personne, E., Wichink- input to ecosystems, edited by Kruit, R., Butterbach-Bahl, K., Flechard, G.Lovblad, J.W. Erisman & Fowler, C., Tuovinen, J. P., Coyle, M., Gerosa, 9-12. Copenhagen: Nordic Council of G., Loubet, B., Altimir, N., Gruenhage, Ministers. L., Ammann, C., Cieslik, S., Paoletti, E., Mikkelsen, T. N., Ro-Poulsen, H., Fowler, D., Jenkinson, D.S., Monteith, J.L. Cellier, P., Cape, J. N., Horvath, L., and Unsworth, M.H. eds. (1995a): The Loreto, F., Niinemets, U., Palmer, P. I., exchange of trace gases between land Rinne, J., Misztal, P., Nemitz, E., and atmosphere. Proceedings of a Nilsson, D., Pryor, S., Gallagher, M. W., Royal Society discussion meeting. Vesala, T., Skiba, U., Brüggemann, N., Philos. T. Roy. Soc. A, 351 (1696), pp. Zechmeister-Boltenstern, S., Williams, 205-416. J., O'Dowd, C., Facchini, M. C., de Fowler, D., Leith, I.D., Binnie, J., Crossley, Leeuw, G., Flossman, A., Chaumerliac, A., Inglis, D.W.F., Choularton, T.W., N., and Erisman, J. W. (2009). Gay, M., Longhurst, J.W.S. and Atmospheric composition change: Conland, D.E. (1995b): Orographic Ecosystems - Atmosphere interactions. enhancement of wet deposition in the Atmospheric Environment , 43, 33, 5193- United Kingdom: continuouse 5267. monitoring. Water Air Soil Pollut., 85, Frohn, L. M., Christensen, J. H., Brandt, J., 2107-2112. and Hertel, O. (2001). Development of a Fowler, D., R.I. Smith and Weston K.J. high resolution integrated nested model (1995c): Quantifying the spatial for studying air pollution in Denmark. distribution of surface ozone exposure at Physics and Chemistry of the Earth, Part the 1kmx1km scale. In: Fuhrer and B: Hydrology, and Atmosphere , Achermann (eds.)(1995), 196-205. 26, 10, 769-774. Chapter II – Guidance on mapping concentrations levels and deposition levels Page II - 29

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