Title: Insights into Ozone and PM2.5 Pollution: A Case Study in Spring China and Trend Analysis across the Continental United States
Abstract:
Ground-level Ozone (O3) and fine particulate matters (PM2.5) are two major pollutants, produced through complex photochemical processes involving nitrogen oxides (NOx=NO+NO2), volatile organic compounds (VOCs), and various radicals. Understanding this chemical system is crucial for effective mitigation strategies. This thesis leverages model simulations, and comprehensive ground- and satellite-based observations to gain insights into the underlying photochemistry of O3 and PM2.5 formation. This dissertation begins by exploring three observation-based pathways associated with nitrous acid (HONO) production, highlighting intrinsic relationships between NO2, particulate nitrate (pNO3) and nitric acid (HNO3). Our results reveal varying implications for O3 production. The conversion of HONO from pNO3 enhances regional O3 production, while the conversion of HONO from NO2 can reduce O3 sensitivity to NOx changes in polluted eastern China. Secondly, the comparison between satellite and ground-based multi-axis differential optical absorption spectroscopy (MAX-DOAS) measurements validates the use of satellite in assessing air pollution patterns, with better agreement observed for NO2 compared to formaldehyde (HCHO). Nonetheless, the TROPOspheric Monitoring Instrument (TROPOMI) HCHO still shows promising improvements compared to two Ozone Monitoring Instrument (OMI) products. Meanwhile, a bias ~30% between two OMI NO2 products are linked to the discrepancies between scattering weight profiles in two retrieval algorithms. In addition, regional effects, seasonal and historical trends of secondary organic carbon (SOC) across the continental United States (CONUS) through 2005-2020 are investigated using organic carbon (OC) and elemental carbon (EC) data from the Interagency Monitoring of PROtected Visual Environments (IMPROVE) network. We divided CONUS into six regions according to the correlations of OC concentrations among different sites. The regional mean secondary fractions vary from 22% to 40% and are consistent with co-located values reported by previous studies. With a consistent peak-in-summer seasonal pattern across all six regions, controlling factors for summertime SOC production for each region are investigated through a stepwise multiple linear regression. Furthermore, despite decreasing trends of anthropogenic emissions, as well as that of primary OC, significant decreasing trends in SOC are found only in eastern US in winter, and the southeast (SE) in summer. Accordingly, annual mean SOC fractions have been found to be significantly increasing except for SE. As anthropogenic emissions continue to decrease, SOC will most likely account for increasingly larger fractions of OC and PM2.5.
Date: Nov 14, 2023
Time: 3:30 PM ET
Location: ES&T L1114
Committee members:
Dr. Yuhang Wang (Advisor), Dr. Nga Lee (Sally) Ng, Dr. Lewis G. Huey, Dr. Jennifer Kaiser, and Dr. Rodney J. Weber