On the volatility and production mechanisms of newly formed nitrate and water soluble organic aerosol in Mexico City

C. J. Hennigan (1) , A. P. Sullivan (2) , C. I. Fountoukis (3) , A. Nenes (2, 3) , A. Hecobian (2) , O. Vargas (2) , A. T. Case Hanks (2) , L. G. Huey (2) , B. L. Lefer (4) , A. G. Russell (1) , R. J. Weber (2)

1 School of Civil and Environmental Engineering [Atlanta]
2 School of Earth and Atmospheric Sciences [Atlanta]
3 School of Chemical and Biomolecular Engineering
4 Geosciences Department

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.

Domaines: Océan, Atmosphère

C. J. Hennigan, A. P. Sullivan, C. I. Fountoukis, A. Nenes, A. Hecobian, et al.. On the volatility and production mechanisms of newly formed nitrate and water soluble organic aerosol in Mexico City. Atmospheric Chemistry and Physics Discussions, 2008, 8 (2), pp.4811-4829. ⟨hal-00304021⟩