Radiocarbon measurements of carbonaceous aerosols from Mexico City in 2003

CHED 1124

Amanda C. MacMillan, future_scientist22@yahoo.com1, Karen L. Steelman, ksteel@uca.edu1, Nancy A. Marley, namarley@ualr.edu2, Jeffrey S. Gaffney, jsgaffney@ualr.edu3, and Thomas P Guilderson, guilderson1@popeye.llnl.gov4. (1) Department of Chemistry, University of Central Arkansas, 205 Laney Hall, 201 Donaghey Ave., Conway, AR 72035, (2) Graduate Research Institute, University of Arkansas at Little Rock, SCLB Rm. 456, 2801 S. University Ave., Little Rock, AR 72204, (3) Department of Chemistry, University of Arkansas at Little Rock, Little Rock, AR 72204, (4) Center for AMS, LLNL, 7000 East Avenue, Mail Code L-397, Livermore, CA 94551
Carbonaceous aerosol samples, collected at an urban site in Mexico City during April 2003, were analyzed for radiocarbon content to determine their biomass-to-fossil fuel ratios. Using high-volume samplers, collection of less than one-micron particulates on glass-fiber filters occurred for continuous twelve-hour intervals. Our laboratory converted organic material in the aerosol samples to carbon dioxide and water using a custom-built plasma oxidation apparatus, followed by accelerator mass spectrometry radiocarbon measurement. For twenty-three samples, values ranged from 0.5552 to 0.8613 indicating a substantial contribution from modern carbon. A fire in the Yucatan impacted the city during the last seven days of the month with AM and PM fraction modern averages of 0.69735 and 0.76996. A slight increase in the 14C content during the fire event is consistent with biomass burning impact. Data clearly indicate that biomass sourced carbonaceous aerosols are a major contributor to the aerosol in this important megacity.
 

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