2013 Progress Report: Organic aerosol formation in the humid, photochemically-active Southeastern US: SOAS experiments and simulationsEPA Grant Number: R835412
Title: Organic aerosol formation in the humid, photochemically-active Southeastern US: SOAS experiments and simulations
Investigators: Turpin, Barbara , Carlton, Annmarie
Institution: Rutgers, The State University of New Jersey
EPA Project Officer: Chung, Serena
Project Period: April 1, 2013 through March 31, 2015
Project Period Covered by this Report: April 1, 2013 through March 31,2014
Project Amount: $399,928
RFA: Anthropogenic Influences on Organic Aerosol Formation and Regional Climate Implications (2012) RFA Text | Recipients Lists
Research Category: Air Quality and Air Toxics , Global Climate Change , Climate Change , Air
In an environment where photochemistry and abundant liquid water coexist (e.g., the Southeastern United States), gas followed by aqueous chemistry could plausibly be the predominant source of fine organic particulate matter (also called aqueous secondary organic aerosol; aqueous SOA). The Southeastern Oxidant and Aerosol Study (SOAS) is an ideal opportunity to test and study this. Understanding the atmospheric chemistry that provides mechanistic linkages between pollution emissions and air quality is important to the development of effective air pollution management strategies.
The objectives of this project are to: (1) compare predicted (funded herein) and measured (funded separately) aerosol liquid water concentrations during the SOAS campaign; (2) conduct ambient aqueous photooxidation experiments using water-soluble gases scrubbed from the ambient air during the SOAS campaign, and use these results to identify key precursors and products of aqueous chemistry leading to SOA formation during SOAS and evaluate the degree to which this chemistry is captured by our current aqueous chemistry model; (3) use model predictions of water-soluble gases in conjunction with the aqueous photooxidation experiments and other SOAS measurements to provide insights into the formation of SOAaq; and (4) collaborate, provide intellectual leadership and share data to achieve the SOAS science goals.
We have now modeled concentrations of aerosol liquid water and water-soluble gases across the United States for a 10-day time period (June 6–June 15, 2013) during SOAS. Aerosol liquid water was also measured by the Carlton group through separate (NSF) funding at the Centerville, Alabama field site during the SOAS campaign. We have used the aerosol liquid water predictions together with predicted concentrations of water-soluble gases across the continental United States and their Henry’s law constants to identify locations and days with high potential for aqueous SOA formation following the approach of Carlton and Turpin (ACP 2013). This work suggests that isoprene epoxide shows a high potential to be present in atmospheric liquid water in the Southeastern US (higher than glyoxal and much higher than methylglyoxal).
Water-soluble gases were scrubbed from filtered ambient air at the Centerville ground site in Brent, AL during SOAS and collected in water. Samples were collected from June 1–July 14, 2013. Photooxidation experiments were conducted (and repeated; with control experiments) on two samples (collected June 15 and 30, 2013) by adding OH radicals to these samples. We expect that these experiments, conducted with ambient mixtures of water-soluble organic gases, will provide insights into key precursors and products of aqueous chemistry during the campaign. Pyruvate, oxalate and glycolate and/or acetate were formed during all experiments but not control experiments. Note pyruvate and oxalate are found primarily in the particle phase in the atmosphere (perhaps as salts). Thus, these experiments suggest that aqueous oxidation of ambient water-soluble mixtures at cloud/fog relevant concentrations will form material that remains in the particle phase after droplet evaporation (SOAAQ). Electrospray ionization (ESI) mass spectrometry (MS) showed positive mode ions with precursor-like trends, decreasing in signal within 40 min of exposure to OH. Aldehydes, ketones, alcohols, epoxides, and organic peroxides are found in the positive mode. MS-MS suggested that these precursors were hydrated carbonyls or polyols. Both sampling days showed similar trends and masses. In the control experiments, these masses remained constant. We expect precursors identified through this approach will be important in clouds, fogs and wet aerosols, whereas products are likely to be different in wet aerosols.
Professor Carlton was onsite throughout the field campaign, providing leadership and solving problems. Drs. Turpin and Carlton participated in the data workshop in Boulder and are continuing to work with others to maximize the scientific output from the campaign. ESI-MS data have been posted for community use.
During year 2, we will conduct experiments with additional samples, provide model predictions for the remaining days of the SOAS campaign, and compare measured and predicted aerosol liquid water concentrations for Centerville, Alabama during that period. We will use the CMAQ model, experiments, and other SOAS measurements to develop new insights about SOA formation through aqueous chemistry in the Southeastern US. We will submit manuscripts from this work for publication in peer-reviewed journals.
Journal Articles:No journal articles submitted with this report: View all 15 publications for this project
SOA, secondary organic aerosol, PM2.5, aqueous chemistry, isoprene, ambient air