Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 9 1 2009 10.5194/acpd-9-4971-2009 http://www.atmos-chem-phys-discuss.net/9/4971/2009/ http://www.atmos-chem-phys-discuss.net/9/4971/2009/acpd-9-4971-2009.html http://www.atmos-chem-phys-discuss.net/9/4971/2009/acpd-9-4971-2009.pdf 4971 5008 2009-02-25 Retrieval of aerosol single scattering albedo at ultraviolet wavelengths at the T1 site during MILAGRO C. A. Corr ccorr@cisunix.unh.edu N. Krotkov S. Madronich J. R. Slusser B. Holben W. Gao J. Flynn B. Lefer S. M. Kreidenweis Dept. of Atmospheric Sciences, Colorado State Univ., Fort Collins, CO, USA Goddard Earth Sciences and Technology Center, Univ. of Maryland Baltimore County, MD, USA Atmospheric Chemistry Division, National Center for Atmospheric Research, Boulder, CO, USA The USDA UV-B Monitoring and Research Program, Natural Resource Ecology Lab., Colorado State Univ., Fort Collins, CO, USA Biospheric Sciences Branch, NASA's Goddard Space Flight Center, Greenbelt, MD, USA Dept. of Earth and Atmospheric Sciences, Univ. of Houston, Houston, TX, USA now at: Climate Change Research Center, Inst. for the Study of Earth, Oceans, and Space, Univ. of New Hampshire, Durham, NH, USA Surface measurements of direct and diffuse voltages at UV wavelengths were made at the T1 site during the MILAGRO (Megacity Initiative: Local and Global Research Observations) field campaign in March 2006, using a multifilter rotating shadowband radiometer (UV-MFRSR). We used the MFRSR data, together with measurements from a co-located CIMEL Sun photometer at the site operating as part of the AERONET network, to deduce aerosol single scattering albedo (ω) at 368 and 332 nm for four cloud-free days during the study. Our retrievals suggest that T1 aerosols with aerosol extinction optical depth τ₃₆₈>0.1 that are influenced by Mexico City emissions, blowing dust, and biomass burning, are characterized by low ω₃₆₈=0.73–0.85 and ω₃₃₂=0.70–0.86, with small or no spectral variation of ω between 368 and 332 nm. Our findings are consistent with other published estimates of ω for Mexico City aerosols, including those that suggest that the absorption attributable to these aerosols is enhanced at UV wavelengths relative to visible wavelengths. We also demonstrate, via sensitivity tests, the importance of accurate τ and surface albedo measurements in ω retrievals at UV wavelengths. Bais, A. F., Kazantzidis, A., Kazadzis, S., Balis, D. S., Zerefos, C. 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