Evidence for Carbonaceous Aerosol Absorption Change in Mexico City 2003

Measurements of black carbon (BC) were taken in Mexico City during April 2003 as part of the Mexico City Metropolitan Area (MCMA) and Mexico City Megacity 2003 Collaborative study by using a seven-channel aethalometer. During the month long study, aerosol samples were also collected for total organic 14C determinations by use of accelerator based mass spectrometry. That data indicated that during the latter part of the study there was an impact from biomass sources at the collection site in Mexico City. An analysis of the seven channel wavelength data is presented that shows a significant change in the shorter wave absorption during the biomass aerosol event that impacted Mexico City from large fires that were burning in the Yucatan area during April of 2003. The results are presented and discussed in terms of the potential for "aged" carbonaceous aerosols having stronger absorption in this region and increased heating by short wave radiation.

This work was sponsored by the U.S. Department of Energy's Atmospheric Science Program. The authors wish to thank Mr. Rick Petty of the U.S. DOE for his continuing support and encouragement.