Assessment of Air Pollution in the Vicinity of Major Alpine Routes

Peter Suppan*, Klaus Schäfer*, Johannes Vergeiner**, Stefan Emeis*, Friedl Obleitner**, Esther Griesser**

*Institute for Meteorology and Climate Research (IMK-IFU), Forschungszentrum Karlsruhe - 82467 Garmisch-Partenkirchen, Germany, email: [email protected] **Institute of Meteorology and Geophysics, University of Innsbruck, 6020 Innsbruck, Austria

Abstract

The Alpine environment as a sensitive region is heavily influenced by major traffic routes. Within the project ALPNAP (Monitoring and Minimisation of Traffic-Induced Noise and Air Pollution along Major Alpine Transport Routes) the integration of advanced scientific methods of monitoring and simulating the air quality distribution and noise propagation is a key aspect for the impact analysis on human health. A methodology for measurement strategies and model simulations for air pollutants will be demonstrated for the Brenner traverse. First results of a field measurement campaign give detailed insights of the complexity of the atmospheric conditions and the distribution of air pollutants in the Inn valley.

Introduction

Road traffic emissions combined with unfavourable meteorological conditions like calm winds and low inversion layers have severe impacts on the natural environment as well as on the socio-economic development of regions in the vicinity of major Alpine traffic routes. Increasing amounts of heavy duty vehicles and passenger cars force the increase of traffic emissions, which continually violate the EU air quality thresholds of e.g. PM10 and/or NO2 not only in this region. ALPNAP is an ongoing European Union research project focussing on corresponding effects along several major transit routes across the European Alps. Assisting regional authorities with appropriate output, a unique cooperation of scientists within the Alpine region was set up to better assess and predict the spatial and temporal distribution of air pollution and noise propagation close to major Alpine traverses. In a first step a measurement campaign in the lower Inn-valley was designed to determine cross-valley air pollution and meteorological information as well as vertical profiles to determine flow regimes (valley, slope winds), mixing layer height, stability in the boundary layer and emission sources at specific locations. Covering the major part of the winter season, this data will be used for enhanced analysis as well as for the set-up and validation of corresponding models merging the wealth of different remote sensing and in-situ measurements. In a second step air quality simulations will be carried out, in order to receive detailed 3D information of the distribution of air quality parameters.

Methodology

Measurements In the frame work of ALPNAP, a field campaign in the Inn valley was performed between November 2005 and February 2006. The campaign was based on existing background information and was focussed on air pollution (AP) and noise strain in the lower Inn valley. The target area was centred on Schwaz / Vomp (47°20’ N / 11° 41 E / 540 m a.s.l.), where exceedances of NO2 and PM10 are frequently recorded.

From the viewpoint of air pollution induced by inner Alpine traffic, the most important goals for the field campaign are outlined below: - Study the spatial and temporal variation and distribution of air pollution concentrations within a cross- section of the valley induced by inner Alpine traffic.

1 - Determine the dependence of the observed air pollution patterns on meteorological parameters like wind, stability / mixing height etc. - Evaluate the spatial representativeness of routine air pollution networks in the area as a function of distance to the main sources and altitude. - Evaluate the best use of an existing slope temperature profile for mixing height and stability analyses. - Use the field data for the set-up and validation of analysis of dispersion models used in the area of investigation.

Based on the existing routine AP measurements, a two-way approach was introduced for the field phase. Permanent AP and meteorological instrumentation including a SODAR (vertical profiles of acoustic backscatter intensity and Doppler signal as well as derived wind and turbulence parameters and mixing layer heights), a ceilometer (vertical profiles of optical backscatter intensity and derived mixing layer heights), an open-path DOAS (Differential Optical Absorption Spectroscopy, a long-path AP information at different paths), three automated weather stations (AWS) and 10 passive samplers for NO2 provide consistent datasets of the temporal development of the meteorology and air pollutants throughout the winter. The location of the instruments as well as some images of the measurement devices are shown in Figure 1. During high air pollution episodes additional measurements were performed. These include measurements with a tethered balloon to determine the vertical structure of dust particles, temperature, humidity and wind. Mobile car traverses yielded PM10 and meteorological information and sampling of volatile organic compounds (VOCs) at selected spots. The operation periods of the different measurement instruments are given in Figure 2.

Modelling Additional to air quality measurements also the simulation of the horizontal and vertical distribution of air pollutants on a high temporal and spatial resolution is a key aspect. In this study it should be demonstrated how to utilize advanced methods to simulate the concentrations of airborne pollutants such as NO, NO2, different VOCs, and PM as a function of the emissions within such a complex topography. Furthermore, the evaluation of the consequences of specific emission reduction measures (e.g. traffic ban on certain vehicles as a function of time of day and year, future development of traffic) will be considered. Therefore a model hierarchy from the micro- to mesoscale has to be set up to calculate traffic emissions, to simulate meteorological and air pollution parameters for supporting further studies on the health impact assessment in an Alpine environment. In Figure 3 the hierarchy of the models starting from the traffic emission model system NEMO/GRAL to the online coupled mesoscale Chemistry-Transport-Model MCCM with a spatial resolution of less than 100 m and up to 100 km, respectively, is shown. The temporal resolution varies between hours and more than 1 year for the calculation of annual mean thresholds. The model chain comprises models used as forecast tools within a region of couples of kilometres up to mesoscale models which will simulate annual means of NO2, O3 and PM10 according to the European air quality directives for the whole Brenner traverse from Rosenheim/Germany to Verona/Italy in a resolution of up to 2 km.

Results

Generally, the NO concentrations are clearly dominated by the traffic volume. Thus, the highest values are found at the highway (DOAS, 570 m a.s.l.) followed by the valley floor in 800 m distance to the highway (Schwaz, 540 m a.s.l.) and at the southern slope (Arzberg, 720 m a.s.l.). The exceedance at the valley floor as compared to the slope station is basically related to a stable layering of the valley atmosphere more or less during all the time. Outstanding high pollution episodes were found during: 20 – 24 December 2005, 09 – 22 January and 25 January – 02 February 2006, when the detailed structure of the valley atmosphere was captured by the additional intensive measurements periods. Moreover, the data indicate that the ratio of concentrations near the highway to the background is systematically higher for NO2 and NO by more than a factor of 2. On a local scale the data allow e.g. to demonstrate the impact of nearby construction work imposing on the CO, NO and NOx measurements. As a well known feature on the other hand, a dominant “new year” peak in PM10 concentration at midnight (31 December 2005/ 01 January 2006) was found. These features are exemplified for the ten-day period from 6 to 15 January 2006, which was characterized by stable conditions within the valley boundary layer. A very regular and undisturbed weather pattern is revealed by Figure 4. The almost undisturbed cycle of short wave radiation indicates the prevailing clear sky

2 conditions. Very cold (dense) air at the valley bottom leads to inversion conditions most of the time (temperature gradient is positive, warmer air at AWS Arzberg 180m AGL than at AWS Schwaz), except for almost isothermal conditions in the early afternoon. The according wind pattern shows a typical winter-time valley regime. Outflow from SW, usually stronger in the second half of the night (more cold air has formed in the upper Inn valley), except for some early afternoon periods with very weak valley inflow. The temporal variations of air pollution concentration (CO, PM10, NO2) at the valley ground are clearly dominated by the mentioned weather conditions and emissions. As for the NO2 and CO emissions, the main source is road traffic at the highway. The NO2 and CO maxima in the morning and in the evening correspond to the local traffic maxima. In the early afternoon mixing height rises (see thin lower line in Figure 6) and the concentrations decrease (Figure 5), whereas the ozone concentrations increase. During midnight the CO concentrations show a maximum and PM10- and NO2–concentrations show a minimum. As outlined in Table 1, the daily mean values of PM10 and NO2 are increasing within this ten days period. This effect is attributed to the accumulation of pollutants due to a stable and high pressure dominated Grosswetterlage with an inefficient air mass exchange. In Arzberg the NO2 concentrations are generally lower than at the valley bottom. Only in the beginning of the period during well mixed conditions in the early afternoon the concentrations are on the same level as at the valley ground. The typical evolution of the polluted boundary layer is shown for 13 January 2006. The acoustic remote sensing technique of the SODAR detects vertical stratification (Figure 7a) and vertical wind profiles. The optical backscatter from a ceilometer is an indication of the aerosol density (Figure 7b). An inversion in the lowest 100 m (purple and whitish colours) persists until midday, when solar radiation leads to a short break- up in the early afternoon before reforming after sun-set. The ceilometer reveals, that the polluted layer is restricted to about 80 m a.g.l. before noon, when the intensity decreases from the bottom while still present below the sharp inversion layer. A more detailed picture at a given time can be seen from the tethersonde ascents depicted in Figure 8. The left graph shows the vertical structure around 1030 CET. The beginning of the marked inversion around 90 m a.g.l. marks the top of the polluted layer, with PM10 values gradually decreasing with height from 70 µg/m3 to background values close to zero. Two hours later radiation has heated up the surface layer, leaving a more pronounced inversion layer at 140 m a.g.l. Consequently the dust particles where vertically redistributed leading to more uniform values of around 50 µg/m3. Hence the surface exposure is reduced due to a deeper and more uniformly distributed aerosol layer. The mobile measurements of the PM10 concentrations give detailed information of the distribution at the valley bottom and on both slopes up to 200 m AGL (Figure 9). In the morning PM10 levels at the valley bottom are close to 80 µg/m3 and at the slopes close to 10µg/m3. Towards noon, as already seen in the tethersonde graph, the concentration in the valley decreases due to lower emissions. Moreover, the lowest layers show a more evenly distribution, while in levels above the PM10 concentrations are nearly unchanged.

Conclusions

A methodology for the assessment of the air quality within Alpine valleys was introduced. Both, measurements and simulations will be used to extend our knowledge about the distribution of air pollutants in the inhomogeneous valley terrain of a valley and the impact on human health. In a first review a brief description of the air quality situation within the cross section of the Inn-valley near Innsbruck was summarized. First results of the measurements show the influence of weather conditions and traffic emissions to the overall air quality situation within the valley. Their qualitative interpretation confirms that stable meteorological conditions without relevant vertical and horizontal exchange are the main reasons for the observed NO2 and PM10 threshold exceedances during winter 2006. However, the detailed evolution indicates a number of complex interactions linking e.g. small scale topography, diurnal variation of sources (traffic volume) and the relevant meteorological parameters (solar insolation, inversion strength, wind and synoptic conditions), respectively. However, even detailed measurements like these cannot reflect the full temporal and spatial variability of the complex flow regimes or the horizontal and vertical distribution of chemical parameters in alpine valleys. Future numerical simulations will contribute there and the corresponding validation process will greatly benefit from the available data. Thus setting up different models in a most sophisticated way will enable for process oriented studies, model inter-comparisons and impact studies. Further information about the ongoing work can be obtained at the ALPNAP web site http://www.alpnap.org/ 3 Acknowledgements

The project ALPNAP is implemented through financial assistance from funds of the European Community Initiative Programme “Interreg III B Alpine Space”. We like to thank Andreas Krismer, Herbert Hoffmann and Carsten Jahn for their contributions to this work.

This project has received European Regional Development Funding through the InterregIIIB community Initiative.

Table 1. Daily mean concentrations of NO2 in the valley (Schwaz), NO2 on the southern slope (Arzberg) and PM10 at Schwaz between 6 and 15 Jan 2006.

NO -Schwaz NO -Arzberg PM -Schwaz Date 2 2 10 (µg/m³) (µg/m³) (µg/m³)

06 Jan 24.9 8.8 43.8 07 Jan 27.1 11.6 42.7 08 Jan 28.2 10.3 42.2 09 Jan 30.7 10.4 44.8 10 Jan 48.7 11.7 52.3 11 Jan 63.9 12.9 51.7 12 Jan 54.1 15.8 65.8 13 Jan 61.7 16.6 52.3 14 Jan 61.1 20.5 57.4 15 Jan 65.7 28.3 80.2

Fig. 1. Target area Schwaz / Vomp and instrumentation. Note the river Inn and the A12 highway (closer to the northern slopes). Images of the measurement devices clockwise from bottom left: (1) AWS Vomperberg on power pylon, (2) DOAS receiver/emitter unit, (3) 10 m AWS Schwaz, (4) measurement van with PM10 device, (5) SODAR and (6) AWS Arzberg. At location 5 a ceilometer was set up additionally. Tiny circles denote NO2 passive sampler locations.

Fig. 2. Operation periods of the different measurement instruments. Cal denotes calibration phase. The red dotted lines represent additional measurements, where tethersonde profiles, car traverses and VOC sampling were performed.

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Fig. 3. Model chain and modelling tools used by the ALPNAP project partners and their possible spatial and temporal field of application.

Fig. 4. Weather conditions in the period 6 to 14 Jan 2006. 2 m temperature at AWS Schwaz in degC (top), Temperature gradient between AWS Schwaz and Arzberg in K/100m and short wave radiation at AWS Schwaz in W/m2 (middle) and wind speed in m/s and direction in deg at AWS Schwaz (bottom).

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Fig. 5. Time series of NO2, O3, PM10 and CO at the station Schwaz and NO2 at Arzberg (instrument TE42C-96) including threshold for NO2 (half hourly) and target value for O3 (floating eight hourly)

Fig. 6. Temporal variation of mixing layer height (thin lower line) determined from acoustic backscatter signals (intensity classified from G to O) measured by SODAR.

Fig. 7. Temporal development of vertical structures on 13 Jan 2006 0000 to 2400 CET as measured by a SODAR and Ceilometer at location 5 in Figure 1. (a) Acoustic backscatter intensity from SODAR indicating thermal structure (the purple color shows the most stable stratification). (b) Optical backscatter intensity from LD 40 ceilometer basically indicating aerosol concentration.

Fig. 8. Tethersonde ascents on 13 Jan 2006 at (a) 1007 – 1042 CET, (b) 1154 – 1234 CET The four panels shows 3 temperature in degC, relative humidity in %, wind vanes and PM10 in µg/m .

Fig. 9. PM10 concentration (µg/m3) on 13 Jan 2006 from car measurements between 1011 and 1123 CET (left) and between 1154 and 1256 CET (right) including GLOBE30 topography. Note the decrease in concentration on the valley bottom towards noon due to the better mixing conditions.