Characterization of pollution events in the East Baltic region affected by regional biomass fire emissions

High values of aerosol black carbon (BC) and chemical compounds were recorded at the background station in Preila (55°55′N, 21°00′E, 5 m a.s.l., Lithuania) during the 31 Mach-3 April, 2008 and 2-8 April, 2009 periods. Temporal and spatial evolution and transport of biomass burning (BB) aerosols observed within this period were explained by the air mass backward trajectory analysis in conjunction with the fire detections data produced by the MODIS Rapid Response System. The surface measurements and analysis for chemical characterization of aerosol, stable carbon isotope ratio δ13C as well as calculation of Ångström exponent of the absorption coefficient done separately for shorter and longer wavelengths (i.e., α = 370-520 nm and α = 660-950 nm) showed that high levels of aerosol BC and chemical compounds were related to the transport of air masses rich in BB products from Kaliningrad region, Ukraine and southwestern part of Russia caused by active grass burning during the period of our study. During this event the aerosol particle number concentration of 1-hour average reached 30 000 cm−3, BC - 11 000 ng m−3, while normally average concentration values are about 3100 cm−3 and 750 ng m−3, respectively. During the event in 2008 the highest mean values of Ångström exponent of the absorption coefficient α370-520 and α590-950 nm were observed (2.4 ± 0.1 and 1.5 ± 0.1, respectively), as well as during the event in 2009 the peak values were determined (2.3 ± 0.1 and 1.6 ± 0.1, respectively). The negative carbon isotopic mean value (−30.9 ± 0.2‰) during 31 March-2 April 2008 obviously indicates that a major part of carbon mass in aerosol particles transferred by the continental air masses is from wildfire location.