Interpretation of variations in fine, coarse and black smoke particulate matter concentrations in a Northern European city
Heal, Mathew R
Agius, Raymond M
Beverland, Iain J
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The PM2.5, PMcoarse and black smoke (BS) particle metrics broadly reflect different source contributions to PM10. The aim of this study was to generate data for PM2.5 at an urban background site in the UK, and to use the daily collocated measurement of PM2.5, PM10 (and hence PMcoarse) and BS to yield insight into source influences on particulate matter for input to developing PM air quality policy. Mean daily PM10, PM2.5 and BS for a year of measurement in Edinburgh were 15.5, 8.5 and 6.6 μg m−3. The PM2.5 data were well-within possible future limit values proposed by the European Commission Clean Air For Europe programme. Daily PM2.5 and PM10 were significantly correlated (r2=0.75) with PM2.5 contributing 54%, on average, to PM10. The daily BS:PM10 and BS:PM2.5 ratios were more variable, and significantly lower in summer than in winter, reflecting the greater contribution of non-black photochemical secondary particles to PM10 in summer. Analysis with respect to wind showed a dominant influence of dispersion on BS and PM2.5 but both dispersion and a wind-driven suspension influence on PMcoarse. The latter was higher than in central England (averaging about one-third of the PMcoarse), and greater for on-shore wind direction, suggesting a sea-salt source for this component in addition to other particle resuspension contributions. Overall, the data showed that excursions in PM10 were driven more by variations in PM2.5 than by PMcoarse or BS. Both PM2.5 and its proportion to PM10 were significantly elevated for air-masses passing over continental Europe and the British Isles, whereas BS varied less with air-mass origin, supporting the conclusion that concentrations of particulate matter, particularly of finer PM, are strongly influenced by regional scale synoptic meteorology (presumed to be predominantly secondary PM), whereas BS is dominated more by local sources. Comparison of BS with a nearby rural site suggested that approximately three-quarters, on average, of the urban BS was local in origin.