Journal article

Fast airborne aerosol size and chemistry measurements above Mexico City and Central Mexico during the MILAGRO campaign

Decarlo P, Dunlea E, Kimmel J, Aiken A, Sueper D, Crounse J, Wennberg P, Emmons L, Shinozuka Y, Clarke A, Zhou J, Tomlinson J, Collins D, Knapp D, Weinheimer A, Montzka D, Campos T, Jimenez J ...see all

Atmos. Chem. Phys. Atmospheric Chemistry and Physics, vol. 8 (2008) pp. 4027-4048

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Abstract

The concentration, size, and composition of non-refractory submicron aerosol (NR-PM 1) was measured over Mexico City and central Mexico with a High-Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS) onboard the NSF/NCAR C-130 aircraft as part of the MILA-GRO field campaign. This was the first aircraft deployment of the HR-ToF-AMS. During the campaign the instrument performed very well, and provided 12 s data. The aerosol mass from the AMS correlates strongly with other aerosol measurements on board the aircraft. Organic aerosol (OA) species dominate the NR-PM 1 mass. OA correlates strongly with CO and HCN indicating that pollution (mostly sec-ondary OA, SOA) and biomass burning (BB) are the main OA sources. The OA to CO ratio indicates a typical value for aged air of around 80 µg m −3 (STP) ppm −1 . This is within the range observed in outflow from the Northeastern US, which could be due to a compensating effect between higher BB but lower biogenic VOC emissions during this study. The O/C atomic ratio for OA is calculated from the HR mass spectra and shows a clear increase with photochemical age, as SOA forms rapidly and quickly overwhelms primary ur-ban OA, consistent with Volkamer et al. (2006) and Klein-man et al. (2008). The stability of the OA/CO while O/C in-creases with photochemical age implies a net loss of carbon from the OA. BB OA is marked by signals at m/z 60 and

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Authors

  • P F Decarlo

  • E J Dunlea

  • J R Kimmel

  • A C Aiken

  • D Sueper

  • J Crounse

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