Ongoing reductions in oxides of nitrogen concentrations ([NOx] = nitric oxide ([NO]) + nitrogen dioxide ([NO2])) throughout the continental United States (U.S.) have important implications for tropospheric ozone (O3) and reactive oxidized nitrogen chemistry (NOy ≈ NOx + nitric acid (HNO3) + particle nitrate (pNO3) + peroxy nitrates (PNs) + alkyl nitrates (ANs)). Specifically, decreasing [NOx] concentrations have likely (1) increased the sensitivity of O3 to the [NOx] level, and (2) affected NOy speciation and partitioning. An understanding of the impacts of continued [NOx] reductions is needed to inform current and future air pollution control strategies, especially since the National Ambient Air Quality Standard (NAAQS) for O3 was lowered from 75 to 70 parts per billion (ppb) in 2015. The lower O3 NAAQS has made it more difficult for areas downwind of urban areas characterized by complex emissions (e.g., New York City) to be in O3 attainment.
To evaluate the above effects of [NOx] reductions in the northeast U.S., four analyses were performed and are presented in this dissertation. First, the observed and Community Multiscale Air Quality (CMAQ) model-predicted ozone production efficiency (OPE) were assessed at Pinnacle State Park (PSP, rural site) in Addison, New York (NY), and Queens College (QC, urban site) in Flushing, NY, from June-September 2016 and August-September 2016, respectively. CMAQ-predicted and observed OPEs were often in poor agreement at PSP and in reasonable agreement at QC, with model-predicted (observed) OPEs ranging from approximately 5-11 (10-13) at PSP and 4-7 (6-8) at QC. Second, observed summertime (May-September) OPEs and their relationship to ambient [NOx] concentrations were determined at PSP, QC, and Whiteface Mountain Summit (WFMS, rural site) in Wilmington, NY from 2000-2017, 2011-2018, and 2015-2017, respectively. The OPE at PSP and QC increased in response to [NOx] reductions, and the OPE was highest at WFMS, the more remote site with lower [NOx] concentrations. Third, the importance of surface nitrate (= HNO3 + pNO3) photolysis as a NOx source (i.e., “re-noxification”) was studied at PSP and QC during selected spring, summer, and winter case studies occurring from 2016-2018. Re-noxification due to surface nitrate photolysis may have noticeably contributed to the [NOx] concentration during some winter periods at PSP, but not during summer. At QC, re-noxification was likely a negligible contributor to the ambient [NOx] concentration during spring, summer, and winter, indicating that [NOx] concentrations are largely influenced by anthropogenic NOx emissions. Fourth, NOy speciation and partitioning were studied using continuous NOx, HNO3, pNO3, PNs, ANs, and total NOy measurements made at QC and PSP from September 2016-October 2018 and June 2016-September 2018, respectively. Both datasets yielded NOy budget closure results that were either fully or largely explained by the measurement uncertainties, suggesting that NOx, HNO3, pNO3, PNs, and ANs are representative of ambient NOy in urban and rural New York.
|Commitee:||Lu, Sarah, Zhou, Xianliang, Keesee, Robert|
|School:||State University of New York at Albany|
|Department:||Atmospheric and Environmental Sciences|
|School Location:||United States -- New York|
|Source:||DAI 81/11(E), Dissertation Abstracts International|
|Subjects:||Atmospheric Chemistry, Atmospheric sciences|
|Keywords:||Nitrogen oxides, Ozone, Ozone production efficiency, Re-noxification, Reactive oxidized nitrogen|
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