Journal cover Journal topic
Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
Atmos. Chem. Phys., 9, 4261-4278, 2009
© Author(s) 2009. This work is distributed under
the Creative Commons Attribution 3.0 License.
03 Jul 2009
The time evolution of aerosol size distribution over the Mexico City plateau
L. I. Kleinman1, S. R. Springston1, J. Wang1, P. H. Daum1, Y.-N. Lee1, L. J. Nunnermacker1, G. I. Senum1, J. Weinstein-Lloyd2, M. L. Alexander3, J. Hubbe3, J. Ortega3, R. A. Zaveri3, M. R. Canagaratna4, and J. Jayne4 1Brookhaven National Laboratory, Upton, New York, USA
2SUNY, Old Westbury, NY, USA
3Pacific Northwest National Laboratory, Richland, WA, USA
4Aerodyne Research Inc., Billerica, MA, USA
Abstract. As part of the MILAGRO field campaign, the DOE G-1 aircraft was used to make measurements over and downwind of Mexico City with the objective of determining growth characteristics of aerosols from a megacity urban source. This study focuses on number concentration and size distributions. It is found that a 5-fold increase in aerosol volume is accompanied by about a 5-fold increase in accumulation mode number concentration. There is growth in aerosol volume because there are more accumulation mode particles, not because of an increase in the average size of accumulation particles. Condensation and volume growth laws were examined to see whether either is consistent with observations. Condensation calculations show that the growth of Aitken mode particles into the accumulation mode size range gives the required increase in number concentration. There are minimal changes in the accumulation mode size distribution with age, consistent with observations. Volume-growth in contrast yields a population of large particles, distinctly different from what is observed. Detailed model calculations are required to translate our observations into specific information on the volatility and properties of secondary organic aerosol.

Citation: Kleinman, L. I., Springston, S. R., Wang, J., Daum, P. H., Lee, Y.-N., Nunnermacker, L. J., Senum, G. I., Weinstein-Lloyd, J., Alexander, M. L., Hubbe, J., Ortega, J., Zaveri, R. A., Canagaratna, M. R., and Jayne, J.: The time evolution of aerosol size distribution over the Mexico City plateau, Atmos. Chem. Phys., 9, 4261-4278,, 2009.
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