Grantee Research Project Results

2008 Progress Report: Improved Prediction of In-Cloud Biogenic SOA: Experiments and CMAQ Model Refinements

EPA Grant Number: R833751
Title: Improved Prediction of In-Cloud Biogenic SOA: Experiments and CMAQ Model Refinements
Investigators: Turpin, Barbara , Seitzinger, Sybil
Institution: Rutgers
EPA Project Officer: Chung, Serena
Project Period: November 1, 2007 through August 31, 2010 (Extended to October 31, 2011)
Project Period Covered by this Report: September 1, 2007 through August 31,2008
Project Amount: $598,544
RFA: Sources and Atmospheric Formation of Organic Particulate Matter (2007) RFA Text | Recipients Lists
Research Category: Air Quality and Air Toxics , Particulate Matter , Air

Objective:

1) Develop mechanistic/ kinetic data needed to simulate in-cloud formation of secondary organic aerosol (SOA) in the presence of HNO₃, 2) Identify conditions for which predicted in-cloud SOA formed from isoprene decreases with reductions in interstitial concentrations of ·OH and HNO₃ (atmospheric oxidants with anthropogenic precursors), and 3) Incorporate an in-cloud SOA formation pathway into the Community Multiscale Air Quality (CMAQ) model and explore the magnitude of in-cloud SOA formation through a limited set of model simulations.

Progress Summary:

Overview: Recent models, laboratory experiments (conducted through our previous EPA STAR grant) and ambient measurements suggest that aqueous photooxidation of glyoxal and methylglyoxal in clouds by hydroxyl radical (·OH) results in the formation of organic acids (including oxalic acid) that remain mostly in the particle phase after cloud droplet evaporation, forming secondary organic aerosol (SOA). Our laboratory experiments with methylglyoxal + ·OH suggest that oligomers form as well. SOA formation through aqueous photooxidation (e.g., cloud processing) was only recently recognized (Blando and Turpin, 2000), is the only identified process that can explain the atmospheric abundance/temporal dynamics of oxalic acid, and could be a substantial contributor to total SOA globally and regionally. We hypothesized that similar chemistry also occurs in aerosol water, and two recent papers now support this hypothesis (a smog chamber experiment, Volkamer et al., ACPD, 2008; and ambient measurements in Atlanta , Hennigan et al., GRL, 2008). Another recent paper supports the hypothesis that SOA formation through cloud processing is an important contributor to global SOA (Fu et al., JGR, 2008). Controlled laboratory experiments conducted in our laboratory through a previous EPA STAR grant were important to validating and refining the key aqueous photochemistry.

One limitation of our previous work is that experiments were conducted at concentrations about 100 times greater than those found in clouds (and 1000 times lower than concentrations in aerosol water). Our current STAR grant included support (50%) for the purchase of instrumentation that has allowed us to conduct experiments at cloud-relevant (and higher) concentrations. Also, in a logical extension of our past work, we are conducting experiments in the presence and absence of nitric acid (HNO₃). Finally, we are collaborating with EPA scientists to incorporate in-cloud SOA formation into the CMAQ model.

Objective 1: With support from this grant and Rutgers University , we purchased a Dionex Ion Chromatography System (ICS-3000), which has allowed us to conduct aqueous photooxidation experiments at lower concentrations than previously possible. We have now repeated our previous experiments with glyoxal + ·OH at 30 μm, 300 μm, and 3000 μm. The 30 μm experiments are representative of conditions in clouds. (Previous experiments were conducted only at 3000 μm.) Glyoxal concentrations in aerosol water are on the order of 1-10 M. As expected, glyoxal oxidized to glyoxylic acid and oxalic acid in all experiments conducted with ·OH present, but not in control experiments. Interestingly, C3 and C4 organic acids (malonic and succinic acids) were formed in the 3000 μm experiments. Oligomeric products also formed, and increased in complexity with increasing precursor concentration. We found that our explicit cloud chemistry model (Lim model) could successfully reproduce oxalic acid concentrations in the lowest concentration experiment but not in the highest concentration experiment. Molar oxalic acid yields were very high in the low concentration experiments and decreased with increasing precursor concentration. This suggests that, under cloud-relevant concentrations the current chemical model is adequate. At the concentrations expected in aerosol water, prediction of SOA formed from glyoxal is more complicated due to the formation of higher molecular weight compounds, including oligomers.

Methylglyoxal and glyoxal (+·OH) experiments and control experiments have now been conducted with and without HNO₃. We are analyzing the results. We hypothesize that organic nitrates form in the presence of HNO₃. Further, we expect to find organic nitrates in cloud water. We had the opportunity to analyze a few New Jersey rainwater samples. In these samples we found series of compounds whose elemental compositions were identical to those formed through oligomerization reactions in methylglyoxal+·OH experiments performed earlier in our laboratory. Interestingly, only a modest proportion of the organic nitrogen was comprised of organic nitrates.

Objective 2: We have now hired a postdoctoral fellow who is closely examining and refining our cloud chemistry model. He has begun to incorporate higher molecular weight products into the model. He is also beginning to consider ways in which HNO₃and its precursor NOx (with anthropogenic sources) affect formation of SOA from isoprene (a biogenic compound) through aqueous photochemistry. Dr. Barbara Ervens, in collaboration with our group, showed that cloud processing of isoprene at high NOx resulted in higher SOA yields than it did at low NOx. This suggests that more SOA will form from a biogenic hydrocarbon like isoprene in polluted conditions than in clean conditions when the SOA is formed through cloud chemistry.

Objective 3: In-cloud production of SOA from glyoxal and methylglyoxal has been added to the CMAQ model using a yield based approach similar to that used for other SOA formation processes. The model was used to predict organic carbon (OC) concentrations measured on an airplane during the ICARTT experiment. The addition of cloud processing to CMAQ improved agreement between modeled OC and measured water-soluble organic carbon (WSOC) for all flights. SOA formation through cloud processing was negligible in certain areas and substantial in others. For the August 14^th experiment specifically designed to investigate clouds, half (5 μg/m³) of the SOA was formed through cloud processing. This work suggests that cloud processing is a substantial contributor to SOA formation in the Northeastern US , at least on days with substantial cloud cover.

To further improve the treatment of cloud chemistry in CMAQ, a Rosenbrock solver has been incorporated into a test version of CMAQ and is now ready for testing. This solver has already been tested using a box model approach. Good agreement with AQCHEM (within 1% for all predicted species) was obtained in box model runs except during rain events (i.e., as long as the wet deposition code is not called).

Future Activities:

In the subsequent reporting periods we will analyze and interpret the results of methylglyxal and glyoxal (+·OH) experiments conducted with and without HNO₃ and conduct more such experiments. We will also carry out the work that comprises Objective 2. We will continue to work with our EPA collaborator, Annmarie Carlton, who is improving the treatment of aqueous chemistry in the CMAQ model.

Journal Articles on this Report : 4 Displayed | Download in RIS Format

Publications Views
Other project views:	All 46 publications	16 publications in selected types	All 16 journal articles

Publications
Type	Citation	Project	Document Sources
Journal Article	Altieri KE, Seitzinger SP, Carlton AG, Turpin BJ, Klein GC, Marshall AG. Oligomers formed through in-cloud methylglyoxal reactions: chemical composition, properties, and mechanisms investigated by ultra-high resolution FT-ICR mass spectrometry. Atmospheric Environment 2008;42(7):1476-1490.	R833751 (2008) R833751 (2009) R833751 (2010) R833751 (Final) R831073 (Final)	Full-text: Science Direct-Full Text HTML Exit Abstract: Science Direct-Abstract Exit Other: Science Direct-Full Text PDF Exit
Journal Article	Altieri KE, Turpin BJ, Seitzinger SP. Oligomers, organosulfates, and nitroxy organosulfates in rainwater identified by ultra-high resolution electrospray ionization FT-ICR mass spectrometry. Atmospheric Chemistry and Physics Discussions 2008;8(5):17439-17466.	R833751 (2008)	Full-text: Atmospheric Chemistry and Physics PDF Exit Abstract: Atmospheric Chemistry and Physics Exit
Journal Article	Carlton AG, Turpin BJ, Altieri KE, Seitzinger SP, Mathur R, Roselle SJ, Weber RJ. CMAQ model performance enhanced when in-cloud secondary organic aerosol is included:comparisons of organic carbon predictions with measurements. Environmental Science & Technology 2008;42(23):8798-8802.	R833751 (2008) R833751 (2009) R833751 (2010) R833751 (Final) R831073 (Final)	Abstract from PubMed Full-text: ES&T-Full Text HTML Exit Abstract: ES&T-Abstract Exit Other: ES&T-Full Text PDF Exit
Journal Article	Ervens B, Carlton AG, Turpin BJ, Altieri KE, Kreidenweis SM, Feingold G. Secondary organic aerosol yields from cloud-processing of isoprene oxidation products. Geophysical Research Letters 2008;35(2):L02816 (5 pp.).	R833751 (2008) R833751 (2009) R833751 (2010) R833751 (Final) R831073 (Final)	Full-text: Wiley-Full Text PDF Exit Abstract: Wiley-Abstract & Full Text HTML Exit

Supplemental Keywords:

SOA, secondary organic aerosol, PM2.5, cloud processing, isoprene, ambient air

Progress and Final Reports:

Original Abstract

The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.