Atmos. Chem. Phys. Discuss., 11, 15831-15873, 2011
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Analysis of exceedances in the daily PM10 mass concentration (50 μg m−3) at a roadside station in Leipzig, Germany
C. Engler, W. Birmili, G. Spindler, and A. Wiedensohler
Leibniz-Institute for Tropospheric Research, Leipzig, Germany

Abstract. Five years of PM10 and PM2.5 ambient air measurements at a roadside, an urban, and a regional background site in Leipzig (Germany) were analyzed for violations of the legal PM10 limit value (1999/30/EC, 1999). The annual mean PM10 concentrations at the three sites were well below the legal threshold of 40 μg m−3 (32.6, 22.0 and 21.7 μg m−3, respectively). However, at the roadside site, the daily maximum value of 50 μg m−3 was exceeded on 232 days (13 % of all days) in 2005–2009, which corresponds to 57 days more than warranted by the EC directive. We analysed the meteorological and local source factors that eventually led to these surplus exceedences. Not surprisingly, the highest pollutant concentrations and most exceedance days were observed in winter. Average concentrations for exceedance and non exceedance days of 64 and 28 μg m−3 at roadside and 40 and 19 μg m−3 in the regional background were observed, suggesting urban contributions of 24 and 8 μg m−3, respectively. Statistical and back trajectory cluster analysis yielded the essential result that PM10 concentrations were regionally enhanced during high pressure conditions, characterized by very low temperature, dry air masses, very low wind speeds, and stable stratification. The latter factor was instrumental in generating high PM10 concentrations at roadside as well as in the regional background through pollution trapping below the atmospheric inversion. During winter exceedance days, the highest organic and elemental carbon mass concentrations were measured. The fewest exceedance days were observed during fast moving air masses from the west, characterized by slightly unstable stratification and lower air pressure. During wintrily exceedance days, about half of PM10 at roadside was originating from regional transport and half from the urban-related sources. This result indicates that both are equally important in generating exceedance days in case of favourable meteorological conditions and cannot be separately considered. Our conclusion is that a combined effort of local, national and international reduction measures could most likely avoid systematic exceedances of the daily limit value in the future.

Citation: Engler, C., Birmili, W., Spindler, G., and Wiedensohler, A.: Analysis of exceedances in the daily PM10 mass concentration (50 μg m−3) at a roadside station in Leipzig, Germany, Atmos. Chem. Phys. Discuss., 11, 15831-15873, doi:10.5194/acpd-11-15831-2011, 2011.
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