Primary and secondary contributions to aerosol light scattering and absorption in Mexico City during the MILAGRO 2006 campaign G. Paredes-Miranda1, W. P. Arnott1, J. L. Jimenez2, A. C. Aiken2, J. S. Gaffney3, and N. A. Marley4 1Department of Physics, University of Nevada Reno, and the Desert Research Institute, Reno, NV, USA 2Deptartment of Chemistry and Biochemistry and CIRES University of Colorado, Boulder, CO, USA 3Department of Chemistry, University of Arkansas, Little Rock, AK, USA 4Graduate Institute of Technology, University of Arkansas, Little Rock, AK, USA
Abstract. A photoacoustic spectrometer, a nephelometer, an aethalometer, and an aerosol mass
spectrometer were used to measure at ground level real-time aerosol light absorption,
scattering, and chemistry at an urban site located in North East Mexico City (Instituto
Mexicano del Petroleo, Mexican Petroleum Institute, denoted by IMP), as part of the
Megacity Impact on Regional and Global Environments field experiment, MILAGRO,
in March 2006. Photoacoustic and reciprocal nephelometer measurements at 532 nm
accomplished with a single instrument compare favorably with conventional
measurements made with an aethalometer and a TSI nephelometer. The diurnally
averaged single scattering albedo at 532 nm was found to vary from 0.60 to 0.85
with the peak value at midday and the minimum value at 07:00 a.m. local time, indicating
that the Mexico City plume is likely to have a net warming effect on local climate.
The peak value is associated with strong photochemical generation of secondary
aerosol. It is estimated that the photochemical production of secondary aerosol
(inorganic and organic) is approximately 75% of the aerosol mass concentration
and light scattering in association with the peak single scattering albedo. A
strong correlation of aerosol scattering at 532 nm and total aerosol mass
concentration was found, and an average mass scattering efficiency factor of
3.8 m2/g was determined. Comparisons of photoacoustic and aethalometer light
absorption with oxygenated organic aerosol concentration (OOA) indicate a very
small systematic bias of the filter based measurement associated with OOA and
the peak aerosol single scattering albedo.
Citation: Paredes-Miranda, G., Arnott, W. P., Jimenez, J. L., Aiken, A. C., Gaffney, J. S., and Marley, N. A.: Primary and secondary contributions to aerosol light scattering and absorption in Mexico City during the MILAGRO 2006 campaign, Atmos. Chem. Phys., 9, 3721-3730, doi:10.5194/acp-9-3721-2009, 2009.