Estimation of the Mass Absorption Cross Section of the Organic Carbon Component of Aerosols in the Mexico City Metropolitan Area

Journal Article · Wed Nov 19 04:00:00 EST 2008 · Atmospheric Chemistry and Physics

DOI:https://doi.org/10.5194/acp-8-6665-2008· OSTI ID:947030

Barnard, James C. ^[1]; Volkamer, Rainer M. ^[2]; Kassianov, Evgueni I. ^[1]

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1. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
2. Univ. of Colorado, Boulder, CO (United States)

Data taken from the MCMA-2003 and the 2006 MILAGRO field campaigns are used to examine the absorption of solar radiation by the organic component of aerosols. Using irradiance data from an Multi-Filter Rotating Shadowband Radiometer (MFRSR) and an actinic flux spectroradiometer, we find aerosol single scattering albedo, ω^-0,λ, as a function of wavelength, λ. We find that in near-UV spectral range (defined here as 250 nm to 400 nm) ω^-0,λ is much lower compared to ω^-0,λ at 500 nm suggesting enhanced absorption in the near-UV range. Absorption by elemental carbon, dust, or gas cannot account for this enhanced absorption leaving only the organic part of the aerosol to account for it. We use data from a surface deployed Aerodyne Aerosol Mass Spectrometer (AMS) along with the inferred ω^-0,λ to estimate the Mass Absorption Cross-section (MAC) for the organic carbon. We find that the MAC is about 10.5 m2/g at 300 nm and falls close to zero at about 500 nm; values that are roughly consistent with other estimates of organic carbon MAC. These MAC values can be considered as “radiatively correct” because when used in radiative transfer calculations the calculated irradiances match the measured irradiances at the wavelengths considered here. The uncertainties of individual estimates are quite large, ±30% at 300 nm for the random error, and even larger for a worst-case estimate of the systematic error, ±80%. The error represents the unusual circumstance where no error cancellation is permitted, and is unlikely ever to be realized.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 947030
• Report Number(s): PNNL-SA--58227; KP1205030
• Journal Information: Atmospheric Chemistry and Physics, Journal Name: Atmospheric Chemistry and Physics Journal Issue: 22 Vol. 8; ISSN 1680-7316
• Publisher: European Geosciences Union
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
ABSORPTION
AEROSOLS
MEXICO
ORGANIC COMPOUNDS
SOLAR RADIATION
SORPTIVE PROPERTIES
URBAN AREAS