The time evolution of aerosol size distribution over the Mexico City plateau 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
Received: 31 Oct 2008 – Published in Atmos. Chem. Phys. Discuss.: 16 Jan 2009 – Published: 03 Jul 2009Abstract. 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, doi:10.5194/acp-9-4261-2009, 2009.