Atmos. Chem. Phys. Discuss., 8, 4811-4829, 2008
www.atmos-chem-phys-discuss.net/8/4811/2008/
doi:10.5194/acpd-8-4811-2008
© Author(s) 2008. This work is distributed
under the Creative Commons Attribution 3.0 License.
Review Status
This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
On the volatility and production mechanisms of newly formed nitrate and water soluble organic aerosol in Mexico City
C. J. Hennigan1, A. P. Sullivan2,*, C. I. Fountoukis3, A. Nenes2,3, A. Hecobian2, O. Vargas2, A. T. Case Hanks2, L. G. Huey2, B. L. Lefer4, A. G. Russell1, and R. J. Weber2
1School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, GA, 30332-0340, USA
2School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA, 30332-0340, USA
3School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, GA, 30332-0340, USA
4Geosciences Department, University of Houston, Houston, TX, 77204-5007, USA
*now at: Colorado State University, Ft. Collins, CO, USA

Abstract. Measurements of atmospheric gases and fine particle chemistry were made in the Mexico City Metropolitan Area (MCMA) at a site ~30 km down wind of the city center. Ammonium nitrate (NH4NO3) dominated the inorganic aerosol fraction and showed a distinct diurnal signature characterized by rapid morning production and a rapid mid-day concentration decrease. The concentration increase was due to both secondary formation and entrainment from the free troposphere. A majority (approximately two-thirds) of the midday concentration decrease was caused by dilution from boundary layer expansion, however a significant fraction (approximately one-third) of the nitrate loss was due to particle evaporation. The water-soluble organic carbon fraction of fine particles (WSOC) and nitrate were highly correlated (R2=0.80) for the entire three-day analysis period, however the WSOC-nitrate correlation was highest (R2=0.88) between the hours of 08:00–12:45, indicating similar sources and processing during this period. The results show that WSOC also experienced evaporation losses and that a significant fraction of the MCMA secondary organic aerosol (SOA) measured at the surface was semi-volatile.

Citation: Hennigan, C. J., Sullivan, A. P., Fountoukis, C. I., Nenes, A., Hecobian, A., Vargas, O., Case Hanks, A. T., Huey, L. G., Lefer, B. L., Russell, A. G., and Weber, R. J.: On the volatility and production mechanisms of newly formed nitrate and water soluble organic aerosol in Mexico City, Atmos. Chem. Phys. Discuss., 8, 4811-4829, doi:10.5194/acpd-8-4811-2008, 2008.
 
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