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Aug
30
Thu
Radiative absorption enhancements due to the mixing state of atmospheric black carbon
Aug 30 @ 6:00 pm

Ibraheem Nuaaman, Phd, candidate, is co-author on a science paper, published in Science, Aug, 31, 2012, Vol. 337, no. 6098 pp. 1078-1081 - DOI: 10.1126/science. 1223447.   F3_mediumAbstract:  Atmospheric black carbon (BC) warms Earth’s climate, and its reduction has been targeted for near-term climate change mitigation. Models that include forcing by BC assume internal mixing with non-BC aerosol components that enhance BC absorption, often by a factor of ~2; such model estimates have yet to be clearly validated through atmospheric observations. Here, direct in situ measurements of BC absorption enhancements (Eabs) and mixing state are reported for two California regions. The observed Eabs is small—6% on average at 532 nm—and increases weakly with photochemical aging. The Eabs is less than predicted from observationally constrained theoretical calculations, suggesting that many climate models may overestimate warming by BC. These ambient observations stand in contrast to laboratory measurements that show substantial Eabs for BC are possible.

Nov
5
Tue
Method for the determination of concentration and stable carbon isotope ratios of atmospheric phenols
Nov 5 – Nov 6 all-day

Marina Saccon, Ph.D candidate, is co-author of Method for the determination of concentration and stable carbon isotope ratios of atmospheric phenols published in the Atmospheric Measurement Techniques Journal, an interactive open access journal of the European Geosciences Union, released on November 5 2013.

Marina Saccon presents thesis

Marina Saccon presenting thesis

Authors: M. Saccon, R. Busca, C. Facca, L. Huang, S. Irei, A. Kornilova, D. Lane and J. Rudolph

Abstract:  A method for the determination of the stable carbon isotopic composition of atmospheric nitrophenols in the gas and particulate phases is presented. It has been proposed to use the combination of concentration and isotope ratio measurements of precursor and product to test the applicability of results of laboratory studies to the atmosphere. Nitrophenols are suspected to be secondary products formed specifically from the photooxidation of volatile organic compounds. XAD-4TM resin was used as an adsorbent on quartz filters to sample ambient phenols using conventional high volume air samplers at York University in Toronto, Canada. Filters were extracted in acetonitrile, with a HPLC (high-performance liquid chromatography) clean-up step and a solid phase extraction step prior to derivatization with BSTFA (bis(trimethylsilyl) trifluoroacetamide). Concentration measurements were done with gas chromatography– mass spectrometry and gas chromatography–isotope ratio mass spectrometry was used for isotope ratio analysis. The technique presented allows for atmospheric compound-specific isotopic composition measurements for five semi-volatile phenols with an estimated accuracy of 0.3–0.5‰ at atmospheric concentrations exceeding 0.1 ngm−3 while the detection limits for concentration measurements are in the pgm−3 range. Isotopic fractionation throughout the entire extraction procedure and analysis was proven to be below the precision of the isotope ratio measurements. The method was tested by conducting ambient measurements from September to December 2011.

 

Updated on December 6th, 2012.