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Ambient fine particulate matter (PM2.5) represents the world's greatest environmental health risk factor and most EU citizens are still exposed to PM2.5 levels above WHO guidelines. Shaping effective urban air quality plans requires the knowledge of pollutants origin in terms of different spatial scales, emission sectors and precursors involved in their formation. Here we present a comprehensive PM2.5 source allocation assessment carried out with the SHERPA model in 708 urban areas in Europe. Urban sources show a significant impact on local PM2.5 levels (an average of 22% of local concentrations). With regard to emission sectors, the residential sectors contribution is greater than 50% in most cities in Northern Italy and Eastern Europe while the average contribution across all cities is 27%. The average contribution from industry, agriculture and road transport is 18%, 17% and 14%, respectively. High contributions from shipping and natural sources (>50%) are found in some Mediterranean cities exposed to southerly winds. Urban areas can be clustered in three main categories: a) where emissions from the residential sector and primary PM2.5 precursors dominate (northern Italy and Eastern Europe); b) where shipping and natural emissions are the main source and dust and SOx are the main precursors (Southern Europe); and c) where secondary PM2.5 (>70%) dominates with comparable contribution from agriculture, industry, and transport and NOx and NH3 are the precursors (Central Europe and UK). Secondary pollution accounts for more than half of PM2.5 concentrations in almost all cities with large areas of Germany and Netherlands showing secondary contribution higher than 70%. In these areas NOx and NH3 as precursors and the agriculture and industry sectors are the most important sources of PM2.5. This source allocation assessment of PM2.5 emissions in all medium to large urban areas in Europe highlights how crucial it is to reduce the emissions of the residential sector in most EU cities.
Sajani et al. (Fri,) studied this question.