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The absorption of short wave incoming solar radiation by the organic component of aerosols has been examined by using data from the MCMA-2003 and the 2006 MILAGRO field campaigns. Both field efforts took place in and around Mexico City. Single Scattering Albedo (SSA) was derived as a function of wavelength (300–870 nm) by combining irradiance measurements from a Multi-Filter Rotating Shadowband Radiometer (MFRSR) and spectrally resolved actinic flux measurements by spectroradiometry with a radiative transfer model (TUV). In addition, organic aerosol mass measured by a surface deployed aerodyne aerosol mass spectrometer was used to estimate the Mass Absorption Cross-section (MAC) of Organic Carbon (OC). It was found that the MAC for OC is about 10.5 m2/g at 300 nm and falls close to zero at about 500 nm; these values are roughly consistent with previous MAC estimates of OC, and present first in-situ observations of this quantity. [ABSTRACT FROM AUTHOR]