Impact of urban pollution emitted in Warsaw on aerosol properties

This paper presents the analyses of the long-term observations of aerosol optical thickness (AOT) and concentrations of particulate matter with an aerodynamic diameter <10 μm (PM10) in the Warsaw extended area. The AOT was observed between 2005 and 2011 in Warsaw and in Belsk (about 45 km away from Warsaw) with hand-held Microtops (Warsaw) and CIMEL (Belsk) sun photometers. The PM10 concentrations were measured at three Warsaw stations as well as in Belsk. The ground-based observations, and the satellite data from the Moderate Resolution Imaging Spectroradiometer (MODIS) provided information about the influence of Warsaw emissions on the AOT. The estimated effect is about 0.02 (at 500 nm) based on the sun photometersʹ comparisons and 0.03 (at 550 nm) based on the MODIS results. Relatively small impact of Warsaw emissions on the AOT (about 10–15%) is consistent with the PM10 data. The mean PM10 differences, estimated during the same time as sun photometer measurements, for Warsaw Ursynow (a residential area) and Belsk was only 5.7 μg m−3 (13%), and for Warsaw Targowek (a mixed shopping and residential area) and Belsk was about 9.8 μg m−3 (20%). For the station located in the central Warsaw, near to the street with the heavy traffic, the difference in the long-term mean of the PM10 was significantly larger and reached 22.1 μg m−3 (36%). Finally, an extreme smoke event observed on 4 April 2009, when favorable weather conditions led to the differences in the AOT between Warsaw and Belsk in a range of 0.11–0.2 (at 500 nm) has been described.