Articles | Volume 9, issue 13
Atmos. Chem. Phys., 9, 4261–4278, 2009

Special issue: MILAGRO/INTEX-B 2006

Atmos. Chem. Phys., 9, 4261–4278, 2009

  03 Jul 2009

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 L. I. Kleinman et al.
  • 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.

Special issue
Final-revised paper