Atmospheric 210Pb, 210Po and 210Po/210Pb activity ratio in urban aerosols: temporal variability and impact of biomass burning emission

Atmospheric Pb-210, Po-210 and their activity ratio (Po-210/Pb-210) have been studied for two years (January 2007-April 2009) from an urban site (Kanpur: 26.5 degrees N and 80.3 degrees E) in the Indo-Gangetic Plain. The average activities of Pb-210 and Po-210 centre on 1.8mBq m(-3) (range: 0.5-4.8mBqm(-3) for n = 99) and 0.094mBq m(-3) (n = 21, range: 0.002-0.28 mBq m(-3)), respectively. The temporal variability in the activity of Pb-210 is significantly pronounced, with relatively high levels during October-November and December-February; a trend similar to that observed for the carbonaceous species. The high aerosol abundance coinciding with the biomass burning emissions (agricultural-waste burning) during October-November and stagnant boundary layer in the wintertime (December-February) is the dominant factor for the observed temporal trend. The preliminary data suggest that biomass burning emissions also contribute to the atmospheric Po-210 activity, as evident from the large variability in the Po-210/Pb-210 activity ratio (range: 0.02-0.23) at this urban site. These results have implications to the model-based activity levels of Pb-210 and Po-210 from in-situ decay of the parent nuclide (Rn-222) for given latitude.