HR: 1330h
AN: A12B-0080    [PDF]
TI: Measurements of Natural Radioactivity in Submicron Aerosols in Mexico City.
AU: * Gaffney, J S
EM: gaffney@anl.gov
AF: Argonne National Laboratory, Bldg. 203/ER, Argonne, IL 60439 United States
AU: Marley, N A
EM: marley@anl.gov
AF: Argonne National Laboratory, Bldg. 203/ER, Argonne, IL 60439 United States
AU: Sterling, K
EM: ksterling@uic.edu
AF: Dept. of Earth and Environmental Sciences, The University of Illinois at Chicago, Chicago, IL 60607 United States
AU: Sturchio, N C
EM: sturchio@uic.edu
AF: Dept. of Earth and Environmental Sciences, The University of Illinois at Chicago, Chicago, IL 60607 United States
AB: Natural radionuclides can be useful in evaluating the transport of ozone and aerosols in the troposphere. Beryllium-7, which is produced by cosmic ray interactions in the upper troposphere and lower stratosphere and becomes adsorbed on fine aerosols, can be a useful indicator of upper air transport into a region. Lead-210 is produced by the decay of radon-222 out-gassed into the lower atmosphere from ground-based uranium deposits. Potassium-40, found in soils, can act as a measure of wind-blown dust and also comes from burning of wood and other biomass that is enriched in this natural radioisotope. Thus, both lead-210 and potassium-40 can aid in identification of aerosols sourced in the lower atmosphere. As part of our continuing interest in the lifetimes and sources of aerosols and their radiative effects, we report here measurements of fine aerosol radioactivity in Mexico City, one of the largest megacities in the world. Samples were collected on quartz fiber filters by using cascade impactors (Sierra type, Anderson Instruments) and high-volume air samplers from the rooftop of the main laboratory of El Centro Nacional de Investigaci¢n y Capacitaci¢n Ambiental (CENICA). By using stage 4 of the impactor and timers, we were able to collect integrated samples of sizes $> 1$ micrometer and $< 1$ micrometer over 12-hr time periods daily for approximately one month in April 2003. Samples were counted at the University of Illinois at Chicago by using state-of-the-art gamma counting (beryllium-7, 477.6 keV; potassium-40, 1460.8 keV; lead-210, 46.5 keV). The beryllium-7 data indicate one possible upper-air transport event during April 2003. As expected, the lead-210 data indicate very little soil contribution to the fine aerosol. The potassium-40 data showed an increase in fine aerosol potassium during Holy Week that might be attributed to local combustion of biomass fuels. The data will be presented and discussed in light of future data analysis and comparison with other measurements taken during the study. The authors wish to thank the researchers at CENICA. This work was supported by the U.S. Department of Energy, Atmospheric Science Program. We also wish to acknowledge Drs. Mario and Luisa Molina for their help in organizing and directing the Mexico City Metropolitan Area 2003 field study, during which these data were collected.
DE: 0305 Aerosols and particles (0345, 4801)
DE: 0345 Pollution--urban and regional (0305)
DE: 0365 Troposphere--composition and chemistry
SC: Atmospheric Sciences [A]
MN: 2003 Fall Meeting