September 23, 2016

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Yu Jun Leong Published in Atmospheric Chemistry and Physics Journal

Yu Jun Leong (Texas) co-authored the article entitled "Phase state of ambient aerosol linked with water uptake and chemical aging in the southeastern US," which was published in the peer-reviewed Atmospheric Chemistry and Physics Journal, Volume 16, Pages 11163–11176, 9 September, 2016.

This article discusses the results from the analysis of ambient air samples collected at a subtropical forest site in Alabama, US. Atmospheric secondary organic aerosols (SOA) were found to be primarily liquid in nature in the southeastern US during summer. However, standard sampling practices involving drying of these ambient particles to below 50% relative humidity (to reduce sample losses) were found to convert these particles to a semi-solid state. As such, the authors caution that ambient sample pre-conditioning could have a significant impact on changes in the phase state of SOA particles prior to analysis and these changes must be accounted for in past/future SOA sampling efforts.

He was part of a collaborative research team involving multiple institutions from Texas, Colorado, and Finland to collect ambient air quality data used in this article from the site in Centreville, Alabama. This led to extensive data analysis and interpretation efforts while Dr. Leong was invited as a visiting research scholar in the University of Eastern Finland, Kuopio, Finland. Please see the publication link below for the full list of co-authors.

Abstract:

During the summer 2013 Southern Aerosol and Oxidant Study (SOAS) field campaign in a rural site in the southeastern United States, the effect of hygroscopicity and composition on the phase state of atmospheric aerosol particles dominated by the organic fraction was studied. The analysis is based on hygroscopicity measurements by a Hygroscopic Tandem Differential Mobility Analyzer (HTDMA), physical phase state investigations by an Aerosol Bounce Instrument (ABI) and composition measurements using a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS). To study the effect of atmospheric aging on these properties, an OH-radical oxidation flow reactor (OFR) was used to simulate longer atmospheric aging times of up to 3 weeks. Hygroscopicity and bounce behavior of the particles had a clear relationship showing higher bounce at elevated relative humidity (RH) values for less hygroscopic particles, which agrees well with earlier laboratory studies. Additional OH oxidation of the aerosol particles in the OFR increased the O : C and the hygroscopicity resulting in liquefying of the particles at lower RH values. At the highest OH exposures, the inorganic fraction starts to dominate the bounce process due to production of inorganics and concurrent loss of organics in the OFR. Our results indicate that at typical ambient RH and temperature, organic-dominated particles stay mostly liquid in the atmospheric conditions in the southeastern US, but they often turn semisolid when dried below ∼ 50 % RH in the sampling inlets. While the liquid phase state suggests solution behavior and equilibrium partitioning for the SOA particles in ambient air, the possible phase change in the drying process highlights the importance of thoroughly considered sampling techniques of SOA particles.

More Information

For more information regarding the event, visit: Atmospheric Chemistry and Physics Journal
For more information on ambient aerosol, contact Yu Jun Leong at This email address is being protected from spambots. You need JavaScript enabled to view it.