ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-10-51-2010 Comparison of in situ and columnar aerosol spectral measurements during TexAQS-GoMACCS 2006: testing parameterizations for estimating aerosol fine mode properties Atkinson D. B. 1 Massoli P. 2 3 8 O'Neill N. T. 4 Quinn P. K. 5 Brooks S. D. 6 Lefer B. 7 Chemistry Department, Portland State University, Portland, OR, 97207-0751, USA University of Colorado, Cooperative Institute for Research in Environmental Sciences, Boulder, CO, 80309, USA NOAA Earth System Research Laboratory, Chemical Science Division, Boulder, CO, 80305, USA CARTEL, Département de géomatique appliqueé, Université de Sherbrooke, Sherbrooke, Quebec, J1K 2R1, Canada NOAA Pacific Marine Environment Laboratory, 7600 Sand Point Way NE, Seattle, WA, 98115, USA Department of Atmospheric Sciences, Texas A & M University, College Station, TX, 77843, USA Earth and Atmospheric Sciences Department, University of Houston, Houston, TX, 77204-5007, USA now at: Aerodyne Research, Inc. Billerica, MA, 01821, USA 06 01 2010 10 1 51 61 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/10/51/2010/acp-10-51-2010.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/10/51/2010/acp-10-51-2010.pdf

During the 2006 Texas Air Quality Study and Gulf of Mexico Atmospheric Composition and Climate Study (TexAQS-GoMACCS 2006), the optical, chemical and microphysical properties of atmospheric aerosols were measured on multiple mobile platforms and at ground based stations. In situ measurements of the aerosol light extinction coefficient (&sigma;<sub>ep</sub>) were performed by two multi-wavelength cavity ring-down (CRD) instruments, one located on board the NOAA R/V <i>Ronald H. Brown</i> (RHB) and the other located at the University of Houston, Moody Tower (UHMT). An AERONET sunphotometer was also located at the UHMT to measure the columnar aerosol optical depth (AOD). The &sigma;<sub>ep</sub> data were used to extract the extinction Ångström exponent (&aring;<sub>ep</sub>), a measure of the wavelength dependence of &sigma;<sub>ep</sub>. There was general agreement between the &aring;<sub>ep</sub> (and to a lesser degree &sigma;<sub>ep</sub>) measurements by the two spatially separated CRD instruments during multi-day periods, suggesting a regional scale consistency of the sampled aerosols. Two spectral models are applied to the &sigma;<sub>ep</sub> and AOD data to extract the fine mode fraction of extinction (η) and the fine mode effective radius (<i>R</i><sub>eff,f</sub>). These two parameters are robust measures of the fine mode contribution to total extinction and the fine mode size distribution, respectively. The results of the analysis are compared to <i>R</i><sub>eff,f</sub> values extracted using AERONET V2 retrievals and calculated from in situ particle size measurements on the RHB and at UHMT. During a time period when fine mode aerosols dominated the extinction over a large area extending from Houston/Galveston Bay and out into the Gulf of Mexico, the various methods for obtaining <i>R</i><sub>eff,f</sub> agree qualitatively (showing the same temporal trend) and quantitatively (pooled standard deviation = 28 nm).

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