1Dept. of Atmospheric Sciences, Colorado State Univ., Fort Collins, CO, USA
2Goddard Earth Sciences and Technology Center, Univ. of Maryland Baltimore County, MD, USA
3Atmospheric Chemistry Division, National Center for Atmospheric Research, Boulder, CO, USA
4The USDA UV-B Monitoring and Research Program, Natural Resource Ecology Lab., Colorado State Univ., Fort Collins, CO, USA
5Biospheric Sciences Branch, NASA's Goddard Space Flight Center, Greenbelt, MD, USA
6Dept. 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
Abstract. 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.