Natural radionuclides in fine aerosols in the Pittsburgh area

摘要

Natural radionuclides have been proposed for use as tracers in assessing the transport of ozone and aerosols in the troposphere. Beryllium-7 is produced in the upper troposphere and lower stratosphere and after formation rapidly attaches itself to fine aerosol particles. Measurements of ~7Be at ground level can therefore be used as a tracer of stratospheric/tropospheric folding events, leading to injection of ozone and upper atmospheric aerosols into the lower atmosphere. Since its concentration varies little on regional scales it can also be used to detect and correct for sampling problems in particulate monitoring networks. Lead-210 and its progeny, ~(210)Bi, and ~(210)Po can also be used to determine the apparent tropospheric residence times for fine aerosols by looking at the ~(210)Bi/~(210)Pb and ~(210)Po/~(210)Pb activity ratios. Reported here are measurements of the natural radionuclides ~7Be and ~(210)Pb, taken at two sites near Pittsburgh, PA in the summer of 2001 and at a site near Centerton, New Jersey in 1999 during the NEOPS field campaign. Beryllium-7 results show no evidence of upper atmospheric input during the sampling period. Apparent residence times as calculated from ~(210)Po/~(210)Pb ratios are shorter for Pittsburgh than for Centerton, and shorter for both sites than those obtained previously in other areas, indicating a local aerosol source as well as a higher loading of water-soluble species such as sulfate and nitrate. A comparison of fine and course aerosol lifetimes shows no contribution of excess ~(210)Po from wind-blown soil or from coal-fired power plants.