| Abstract: |
To determine the impacts of radiatively important aerosol species on regional and global-scale climate, the processes that control their atmospheric concentrations must be understood. This proposal is a continuation of measurements of naturally occurring radionuclides and stable isotopic signatures to determine the sources, transport and removal processes, and atmospheric lifetimes of fine carbonaceous aerosols. High volume impactors are used in field efforts to collect size-fractionated fine (submicron) aerosols. In addition, samples of both interstitial aerosols and precipitation are collected simultaneously during rain events. Aerosol samples collected during the Megacity Aerosol Experiment- Mexico City (MAX-Mex) are currently being characterized for their black carbon (BC) and organic carbon (OC) 14C contents to determine the relative amounts of fossil vs. biomass derived material. The tropospheric residence times of size-fractionated fine aerosols are being determined by examining the relative amounts of the attached natural radionuclide tracers 210Pb, 210Bi, and 210Po. The measurement of 7Be along with meteorology during precipitation events allows for the evaluation of upper air sources of aerosols as well as the estimation of their washout rates. Total 7Be and 210Pb contents can yield an estimate of the relative amounts of aerosols originating from upper-air transport and lower tropospheric sources. Stable 13C/12C, 15N/14N, and 40K measurements are being examined to aid in evaluating biomass burning contributions to the optically absorbing aerosols. We have also initiated laboratory studies with standard soot samples obtained from NIST to investigate the aqueous stability of the aerosol attachment of these radionuclide tracers as a function of pH. Results from this work will help to determine aerosol mean residence times as a function of size, washout efficiencies of BC and total aerosols, sources of BC, and compound-specific determinations of organic molecular tracers to evaluate their applicability for biogenic or energy-specific source determinations. MAX-Mex Lead Scientist activities have also been undertaken as part of this project and include coordination with other agencies and publication of result summaries from the MILAGRO study. We are proposing to complete the current work, and extend these measurements to future studies in ASP including collection of samples at the ARM Barrow site during ASP field projects in 2008, and preliminary measurements from China, and India for future possible ASP field efforts in 2010. |
