Seasonal variations of aerosol residence time in the lower atmospheric boundary layer

During a one year period, from Jan. 2002 up to Dec. 2002, approximately 130 air samples were analyzed to determine the atmospheric air activity concentrations of short- and long-lived (Rn-222) decay products Pb-214 and Pb-210. The samples were taken by using a single-filter technique and gamma-spectrometry was applied to determine the activity concentrations. A seasonal fluctuation in the concentration of Pb-214 and Pb-210 in surface air was observed. The activity concentrations of both radionuclides were observed to be relatively higher during the winter/autumn season than in spring/summer season. The mean activity concentration of Pb-214 and Pb-210 within the whole year was found to be 1.4 +/- 0.27 Bq m(-3) and 1.2 +/- 0.15 mBq m(-3), respectively. Different Pb-210:Pb-214 activity ratios during the year varied between 1.78 x 10(-4) and 1.6 x 10(-3) with a mean value of 8.9 x 10(-4) +/- 7.6 x 10(-5). From the ratio between the activity concentrations of the radon decay products Pb-214 and Pb-210 a mean residence time (MRT) of aerosol particles in the atmosphere of about 10.5 +/- 0.91 d could be estimated. The seasonal variation pattern shows relatively higher values of MRT in spring/summer season than in winter/autumn season. The MRT data together with relative humidity (RH), air temperature (T) and wind speed (WS), were used for a comprehensive regression analysis of its seasonal variation in the atmospheric air. (C) 2004 Elsevier Ltd. All rights reserved.