Transactions on Ecology and the Environment vol 4, © 1994 WIT Press, www.witpress.com, ISSN 1743-3541 Emissions of air pollutants in the north west region of England J.W.S. Longhurst, S.J. Lindley, D.E. Conlan, A.F.R. Watson Atmospheric Research and Information Centre, Department of Environmental and Geographical Sciences, Manchester Metropolitan University, Chester Street, Manchester Ml 5GD, UK ABSTRACT An emissions estimate for SO,, NO,, CO, CO,, VOCs, black smoke and lead in the North West of England is presented for 1987 and 1991. Calculations are made on a pro-rcita basis and the value of this approach is discussed within the framework of alternative emission estimation methodologies. Estimates, their spatial characteristics and temporal trends are then presented for each species considered. Finally, the relative position of the North West is considered within the context of the United Kingdom as a whole. INTRODUCTION Most emission estimates are made at the national level. There is, however, a need for complimentary estimations at regional and local scales as a key component in the formulation of successful air quality management plans [1]. Studies concerning emissions of pollutants form an important pre-cursor to modelling and the understanding of ambient concentrations at the local scale as well as providing an input to local air quality management plans [2, 3]. This work updates a previous paper which estimates emissions of SO?, NO*, HC1 and NH, from the North West region of England for the year 1987 using a pro-rota approach [1]. The aim has been to expand upon the number of species considered, develop a more refined pro-rota methodology and to provide a temporal comparison between the initial base year of 1987 and a new base year of 1991. A comparison of the basic and refined methodologies was undertaken for 1987 using original data sources which are then updated for a new base year of 1991 for which all necessary statistical data could be accessed [4, 5]. In order to examine temporal trends a revised calculation of emissions in 1987 was made using the same data source as for the 1991 estimate. This was necessary as the methodology used to calculate national emissions is constantly revised as new information becomes available and estimates for each year re-calculated on this basis [6]. Estimates are made for a number of key pollutants; carbon monoxide (CO), carbon dioxide (CO,), volatile organic compounds (VOCs), black smoke and lead from transportation in addition to sulphur dioxide (SO?) and oxides of nitrogen (NO,). It was Transactions on Ecology and the Environment vol 4, © 1994 WIT Press, www.witpress.com, ISSN 1743-3541 100 Pollution Control and Monitoring not possible to include HC1 and NH, in this study due to the lack of suitable data for 1991. As new data becomes available these will be re-introduced into the emissions database. The North West region is considered due to it being the most densely populated region of the UK [7] and also as a supplement to current research into air quality in Greater Manchester [e.g. 3, 8, 9]. For continuity, the North West region used here is that defined in Lee and Longhurst [1] comprising Lancashire, Greater Manchester, Merseyside, Cheshire and the High Peak district of Derbyshire ^Figure 1). EMISSION ESTIMATION METHODOLOGIES Estimates of emission can be made by taking either a 'bottom-up' or 'top-down' approach. The 'bottom-up' approach provides estimates for a particular region by utilising local datasets with appropriate emission factors. Providing that a careful choice of these factors is made then this method can provide the best representation of emissions from a specified locality. It does, however, have the disadvantage of being relatively complicated and time consuming. Alternatively, the 'top-down' approach involves dissaggregating national emission estimations to a local level through the use of indicators of the proportion of a particular polluting activity occurring in the specified region. This method is the simplest to carry out and the least expensive of time and resources but can still provide a good indication of local emission magnitudes and characteristics [1]. Lee and Longhurst [1] estimate emissions on a per capita basis pro-rota with nationally derived emissions estimates for 1987 except for the source area of power stations [4]. This and the refined method used in this study are shown schematically in Fig. 2 with data and sources shown in Table 1. National emissions estimates from power station sources are spatially disaggregated according to the contribution of North West fossil fuelled plants to the total UK fossil fuelled electricity generation. Emissions from other sources are summed and apportioned according to the percentage of the UK's population resident in the region. A refined method was designed in an attempt to reduce some of the uncertainties associated with the per capita pro-rota approach. Whereas the power station contribution could be estimated with some certainty, other estimates based on population as a surrogate were less certain. Therefore, in addition to isolating power stations as a source, use was also made of the other source breakdowns to provide a more sensitive representation of activities within the North West region. This was possible for air traffic, shipping, refineries and road transport which are all significant activities within the region. This is important in estimating pollutants such as CO, as its dominant source is road transport as opposed to the predominance of power station sources in the emission of species such as SO2. Again, the remaining source categories for which individual calculations could not be made were summed and apportioned according to population. The refined method allows a more reliable estimate of emissions to be made although there are still a number of uncertainties. Firstly, there is the issue of data availability. It may be difficult to find appropriate regional data eg. North west vehicle registrations are used to estimate road transport emissions when vehicle km travelled may be a better indicator Another problem arises when data is Transactions on Ecology and the Environment vol 4, © 1994 WIT Press, www.witpress.com, ISSN 1743-3541 Pollution Control and Monitoring 101 Major road KEY communications A Fossil fuelled power stations in operation in 1987 and 1991 . Fossil fuelled power stations in operation in 1987 but not 1991 *' Closed 1993 *2 Closed pre-1991 *3 Closed pre-1991 (R) Stanlow oil refinery (A) Manchester Airport 6%j Urban counties Figure 1: A Map to show the North West Region of England. Detailed National Statistical Indicators from the DoE, DoT,DTI etc. NATIONAL ATMOSPHERIC EMISSIONS ESTIMATES North West Component of Errissions Calculable I>y using Regional Statistical Indieators with a Pro-Rata / 11 Approachi 1'he Original Pro-Rata The Idefined Pro-Rata AMethod (Method 1)[1] Method (Method 2) 41 1 1 4 4 1 1 F'ower Power ~~! RO£;n Other Refinery Shipping Aircraft Other Station Station Sourc < TrafBe Sources Source Sources ss sources Sources Sources Sources GWh GWh Tonnes of Pass- electricity \ NW electricity Tonnes of enger Vehicle 1 NW : i oil frcmNW regiona 1 from NW i produced i cargo traffic : registr- regional • bssil popula- i fossil ftomNWi from i ations in : popula- : fromNW fueled . tion fueled refinenes I docks NW the IsfW tion F)lants plants airportS II II 1 1 1 1 T Original NW Refined NW Emissions Emissions Estimate Estimate Figure 2: A Schematic Representation of the Original and Refined Regional Emission Estimation Methodologies. Transactions on Ecology and the Environment vol 4, © 1994 WIT Press, www.witpress.com, ISSN 1743-3541 102 Pollution Control and Monitoring Table 1: Statistics and sources used in the calculation of North West emissions. National North West North West Data Source Level of Certainty Emission Statistical Share of UK Source Indicator Source Total Category (%) 1987 1991 Power GWh energy from 5.8 6.3 [11,111], [12], High Stations fossil fuelled plants. [13], [14] 1987- 12105 1991- 14467 Refineries Stanlow Oil 14.3 13.8 [13], [14] High Refinery. 1987- 13 Mt oil. 1991- 12 Mt oil. Aircraft Manchester Airport 11 11 [15] Lower, no data for passenger traffic smaller airports & general aviation traffic Shipping Liverpool Docks 5.5 7.6 [15] Lower, no data for cargo smaller docks 1987- 25.3 Mt, 1991- 37.4 Mt. Road Vehicle registrations 10.6 10.6 [15] Lower, no data for Transport 1991 - 2,348,000 vehicle use Others Population 11.5 11.7 [1], [16] High for population, 1987- 6,435,230 lower as surrogate 1991-6,540,600 for other activities no longer available in the public domain eg. the privatisation of the electricity supply industry has resulted in much information becoming confidential and only available at the discretion of individual power generating companies. Secondly, there is the problem of data quality. Statistical indicators chosen have a degree of uncertainty associated with them and this may vary between data sources. The same is also true of the original national emission calculations where the level of confidence ranges from + /- 25% to + /- 50% [5]. Statistics may also change their levels of uncertainty over time [4, 5, 6]. The best regional estimates can only have the level of confidence associated with the original national estimates and in practice are likely to be much less confident. EMISSION SOURCES AND STRENGTHS IN THE NORTH WEST. North West emissions estimated for each species in 1987 and 1991 are given in Table 3 and discussed below. A comparison is made of the results from the original method (1) used by Lee and Longhurst [1] and the refined method (2) used by this study for 1987 and 1991. Two estimates for each method were made for North West emissions in 1987, one using the original national emissions data source and the other Transactions on Ecology and the Environment vol 4, © 1994 WIT Press, www.witpress.com, ISSN 1743-3541 Pollution Control and Monitoring 103 using the same source used to estimate the 1991 regional emission [4, 5].