DeCarlo, P. F. and Dunlea, E. J. and Kimmel, J. R. and Aiken, A. C. and Sueper, D. and Crounse, J. and Wennberg, P. O. and Emmons, L. and Shinozuka, Y. and Clarke, A. and Zhou, J. and Tomlinson, J. and Collins, D. R. and Knapp, D. and Weinheimer, A. J. and Montzka, D. D. and Campos, T. and Jimenez, J. L. (2008) Fast airborne aerosol size and chemistry measurements above Mexico City and Central Mexico during the MILAGRO campaign. Atmospheric Chemistry and Physics, 8 (14). pp. 4027-4048. ISSN 1680-7316 http://resolver.caltech.edu/CaltechAUTHORS:20090504-131712264
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The concentration, size, and composition of non-refractory submicron aerosol (NR-PM1) 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 MILAGRO 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-PM1 mass. OA correlates strongly with CO and HCN indicating that pollution (mostly secondary 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 urban OA, consistent with Volkamer et al. (2006) and Kleinman et al. (2008). The stability of the OA/CO while O/C increases with photochemical age implies a net loss of carbon from the OA. BB OA is marked by signals at m/z 60 and 73, and also by a signal enhancement at large m/z indicative of larger molecules or more resistance to fragmentation. The main inorganic components show different spatial patterns and size distributions. Sulfate is regional in nature with clear volcanic and petrochemical/power plant sources, while the urban area is not a major regional source for this species. Nitrate is enhanced significantly in the urban area and immediate outflow, and is strongly correlated with CO indicating a strong urban source. The importance of nitrate decreases with distance from the city likely due to evaporation. BB does not appear to be a strong source of nitrate despite its high emissions of nitrogen oxides, presumably due to low ammonia emissions. NR-chloride often correlates with HCN indicating a fire source, although other sources likely contribute as well. This is the first aircraft study of the regional evolution of aerosol chemistry from a tropical megacity.
|Additional Information:||© Author(s) 2008. This work is distributed under the Creative Commons Attribution 3.0 License. Published by Copernicus Publications on behalf of the European Geosciences Union. Received: 22 November 2007 – Published in Atmos. Chem. Phys. Discuss.: 20 December 2007. Revised: 20 June 2008 – Accepted: 20 June 2008 – Published: 25 July 2008. We are grateful to the NCAR RAF and C-130 personnel for much help and guidance during integration and research flights, especially A. Schanot, P. Romashkin, and M. Lord. We thank R. Bahreini, C. Simmons, and A. Middlebrook of NOAA for help with integration and the PCI. We thank C. Brock of NOAA for providing Mie Scattering code in the Igor programming language. We are also grateful to the rest of the C-130 investigators and the Jimenez group for many helpful discussions. This study was supported by grants NSF ATM-0513116, ATM-0528634, and ATM-0449815, NASA NNG04GA67G and NNG06GB03G, UCAR/NSF S05-39607, and by EPA fellowship FP-91650801 (to PFD) and NASA fellowship NNG04GR06H (to ACA).|
|Official Citation:||DeCarlo, P. F., Dunlea, E. J., Kimmel, J. R., Aiken, A. C., Sueper, D., Crounse, J., Wennberg, P. O., Emmons, L., Shinozuka, Y., Clarke, A., Zhou, J., Tomlinson, J., Collins, D. R., Knapp, D., Weinheimer, A. J., Montzka, D. D., Campos, T., and Jimenez, J. L.: Fast airborne aerosol size and chemistry measurements above Mexico City and Central Mexico during the MILAGRO campaign, Atmos. Chem. Phys., 8, 4027-4048, 2008.|
|Usage Policy:||This work is distributed under the Creative Commons Attribution 3.0 License.|
|Deposited By:||Tony Diaz|
|Deposited On:||13 Aug 2009 21:16|
|Last Modified:||26 Dec 2012 10:59|
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