AGE ESTIMATION OF ATMOSPHERIC BLACK CARBON OVER FINLAND FROM COMBINEDAEROSOL-SIZE DISTRIBUTION AND RADON PROGENY MEASUREMENTS

Data on aerosol particle size distributions between 0.01 and 10 mu m w ere combined with Rn-222 and Pb-210 particle activities to analyze bla ck carbon characteristics. The activity ratio Pb-210/Rn-222 was applie d to estimate the aerosol and black carbon age. Aerosol with high conc entration in the size range of 0.100-0.320 mu m was related to high bl ack carbon levels with an estimated 2.8 d residence time, and easterly continental winds. Aerosol in the nanometer size range, 0.010-0.032 m u m, was associated with low black carbon levels, polar winds and 2.0- 4.4 d residence time. Aerosol number concentrations varied between 200 0-25,000 cm(-3), Rn-222 activity concentrations between 0.3-13 Bq/m(3) , radon progeny Pb-210 between 110-315 mu Bq/m(3), and black carbon le vels between 50-700 ng/m(3). Observed mass ratio of black carbon to to tal aerosol mass in the size range 0.010-10 mu m was on average 0.64%, which is substantially smaller than at other remote sites. A near con stant ratio of black carbon to the 0.100-0.180 mu m aerosol fraction i s proposed to represent an equilibrium state in an aged aerosol. Copyr ight (C) 1996 Elsevier Science Ltd