INVESTIGATING NOX EFFECTS ON SOA FORMATION IN THE WESTERN UNITED STATES USING WRF-CHEM REGIONAL MODELING
EMSL Project ID
30394
Abstract
The proposed research investigates effects of human-produced air pollution on Earths climate, via the interaction of nitrogen oxides (NOx = NO2 + NO) with the chemistry of atmospheric aerosol formation. The focus will be on secondary organic aerosol (SOA), aerosol which is formed by the oxidation of volatile organic compounds (VOCs) in the atmosphere yielding condensable products. SOA makes up a major fraction of all organic aerosol, which constitutes ~20-50% of total fine aerosol mass over North America. However, its source strength is extremely poorly constrained, with estimates ranging from 12 to 900 Tg C year-1. Biogenic emissions constistute a major source of gas-phase organic compounds that can form SOA. Recent dark chamber studies show that the oxidation of biogenic volatile organic compounds (bioVOC) by NO3, a primarily nighttime reservoir of NOx, may form significant SOA. On the contrary, several chamber studies of the OH/NOx photochemistry of VOCs found that increased NOx depresses SOA yields. This poorly understood NOx/SOA interaction forms the focus of my proposed research.This research program will use the WRF-chem regional model to study NOx effects on aerosol formation and evaluate the impact of this interaction on atmospheric chemistry and climate change. We will first assess current WRF-chem model representation of NOx-SOA interactions, then isolate target areas of the chemistry and aerosol modules to improve the model. We will employ comparisons of this modified model output with surface and satellite observations to answer the following scientific questions: (1) In the western United States, where are the greatest measurement/model discrepancies in aerosol loading predicted by WRF-chem? Is there a NOx correlation? (2) In the current WRF-chem model, does increasing NOx enhance or depress aerosol formation? (3) Does nighttime oxidation of biogenic VOC by NO3 contribute significantly to ambient aerosol loading in areas where urban outflow interacts with forest emissions? (4) Does daytime photochemical bioRO2 + NO chemistry enhance or depress aerosol formation appreciably, under varying assumptions about partitioning of organic nitrate vs. peroxide products? (5) Does inclusion of organic nitrate formation from NO3 + bioVOC and/or bioRO2 + NO improve measurement / model agreement on NOy (= total reactive nitrogen oxides)?
Project Details
Project type
Large-Scale EMSL Research
Start Date
2008-10-07
End Date
2011-09-30
Status
Closed
Released Data Link
Team
Principal Investigator