Hersey, S. P. and Sorooshian, A. and Murphy, S. M. and Flagan, R. C. and Seinfeld, J. H. (2009) Aerosol hygroscopicity in the marine atmosphere: a closure study using high-time-resolution, multiple-RH DASH-SP and size-resolved C-ToF-AMS data. Atmospheric Chemistry and Physics, 9 (7). pp. 2543-2554. ISSN 1680-7316. http://resolver.caltech.edu/CaltechAUTHORS:20090714-080423619
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We have conducted the first airborne hygroscopic growth closure study to utilize data from an Aerodyne compact Time-of-Flight Aerosol Mass Spectrometer (C-ToF-AMS) coupled with size-resolved, multiple-RH, high-time-resolution hygroscopic growth factor (GF) measurements from the differential aerosol sizing and hygroscopicity spectrometer probe (DASH-SP). These data were collected off the coast of Central California during seven of the 16 flights carried out during the MASE-II field campaign in July 2007. Two of the seven flights were conducted in airmasses characterized by continental origin. These flights exhibited elevated organic volume fractions (VF_(organic)=0.56±0.19, as opposed to 0.39±0.20 for all other flights), corresponding to significantly suppressed GFs at high RH (1.61±0.14 at 92% RH, as compared with 1.91±0.07 for all other flights), more moderate GF suppression at intermediate RH (1.53±0.10 at 85%, compared with 1.58±0.08 for all other flights), and no measurable GF suppression at low RH (1.31±0.06 at 74%, compared with 1.31±0.07 for all other flights). Organic loadings were slightly elevated in above-cloud aerosols, as compared with below-cloud aerosols, and corresponded to a similar trend of significantly suppressed GF at high RH, but more moderate impacts at lower values of RH. A hygroscopic closure based on a volume-weighted mixing rule provided good agreement with DASH-SP measurements (R^2=0.78). Minimization of root mean square error between observations and predictions indicated mission-averaged organic GFs of 1.22, 1.45, and 1.48 at 74, 85, and 92% RH, respectively. These values agree with previously reported values for water-soluble organics such as dicarboxylic and multifunctional acids, and correspond to a highly oxidized, presumably water-soluble, organic fraction (mission-averaged O:C=0.92±0.33). Finally, a backward stepwise linear regression revealed that, other than RH, the most important predictor for GF is VF_(organic), indicating that a simple emperical model relating GF, RH, and the relative abundance of organic material can provide accurate predictions (R^2=0.77) of hygroscopic growth for the California coast.
|Additional Information:||© Author(s) 2009. Received: 14 July 2008 – Published in Atmos. Chem. Phys. Discuss.: 4 September 2008. Revised: 17 November 2008 – Accepted: 24 March 2009 – Published: 7 April 2009. This work was supported by the Office of Naval Research grant N00014-04-1-0118. We acknowledge the committed, meticulous work of the CIRPAS Twin Otter crew, especially pilot Mike Hubbell and copilot Chris McGuire. Edited by: A. Nenes.|
|Official Citation:||Hersey, S. P., Sorooshian, A., Murphy, S. M., Flagan, R. C., and Seinfeld, J. H.: Aerosol hygroscopicity in the marine atmosphere: a closure study using high-time-resolution, multiple-RH DASH-SP and size-resolved C-ToF-AMS data, Atmos. Chem. Phys., 9, 2543-2554, 2009.|
|Usage Policy:||© Author(s) 2009. This work is distributed under the Creative Commons Attribution 3.0 License.|
|Deposited By:||Tony Diaz|
|Deposited On:||11 Aug 2009 16:40|
|Last Modified:||26 Dec 2012 11:05|
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