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Project Number:
 
12-012
Title:
 
Interactions Between Organic Aerosol and NOy: Influence on Oxidant Production
Lead PI:
 
Lea Hildebrandt-Ruiz
Institution(s) Represented:
 
The University of Texas at Austin - Lea H. Ruiz, ENVIRON International - Greg Yarwood
AQRP Project Manager:
 
Dave Sullivan
TCEQ Project Liaison:
 
Mark Estes
Awarded Amount:
 
$148,835.00

Abstract
 Interactions Between Organic Aerosol and NOy: Influence on Oxidant Production
 
In rural areas where emission rates of NOx (NO + NO2) are relatively low, ozone formation can be sensitive to secondary NOx sources such as decomposition of organic nitrates (R-ONO2). AQRP project 10-042 provided experimental evidence for NOx production when organic nitrates degrade by OH reaction and photolysis. Implementing NOx production from OH reaction with organic nitrates causes regional ozone increases that are large enough to affect model agreement with ozone observations. This implies that organic nitrates are less available to NOx recycling than previous experiments suggested. We are investigating the hypothesis that uptake of organic nitrates into secondary organic aerosol (SOA) reduces the amount of NOx recycled by organic nitrate photolysis and OH reaction.
 
The first task in this project is to add the uptake of organic nitrates by SOA to the Comprehensive Air quality Model with extensions (CAMx). The conceptual model of Perraud et al. (2012) is followed, in which organic nitrate molecules stick to aerosol surfaces and become irreversibly buried by accretion of SOA. Results of this initial modeling work is then used to design laboratory chamber experiments in which organic nitrates are formed from the oxidation of VOCs in the presence of NOx and the distribution of organic nitrates between the gas and particle phases is observed. New chemistries and mechanisms inferred from the experimental data are then tested by including them in a box model of the chamber experiments before they are implemented in CAMx. Finally, the partitioning of organic nitrates between the gas- and particle phase is observed in natural aerosol by conducting ambient measurements near Houston.




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Publications & Citations
Conference presentations: C. Faxon, J. Bean, L. Hildebrandt Ruiz. Evidence of atmospheric chlorine chemistry in Conroe, TX: Regional implications. American Chemical Society Southwest Regional Meeting, November 2013, Waco, TX. J. Bean, C. Faxon, L. Hildebrandt Ruiz. Atmospheric processing of pollutants in the Houston Region: First insights from DISCOVER-AQ. American Chemical Society Southwest Regional Meeting, November 2013, Waco, TX. L. Hildebrandt Ruiz, J. Bean, G. Yarwood, B. Koo, U. Nopmongcol. Formation and Gas-Particle Partitioning of Organic Nitrates: Influence on Ozone Production. American Association for Aerosol Research Annual Meeting, October 2013, Portland, OR. Planned publications: C. Faxon, J. Bean and L. Hildebrandt Ruiz. Preliminary title "Significant Inland Concentrations of ClNO2 Detected in Conroe TX during DISCOVER-AQ 2013". Submission planned for August 2014. J. Bean, C. Faxon and L. Hildebrandt Ruiz. Manuscript summarizing particle-phase measurements from DISCOVER-AQ. Submission planned for late 2014.