Call number: LD2668 .T4 1984 T78 / Master of Science

Exposure to ground-level ozone (O₃), which forms secondarily in the atmosphere, intensifies the risk of respiratory and cardiovascular diseases. Effective mitigation strategies require understanding the spatiotemporal variability of O₃ precursors, including nitrogen oxides (NOx) and volatile organic compounds (VOCs), as well as O₃ formation photochemistry. This thesis examines the concentrations of trace gases closely related to O₃ production, specifically nitrogen dioxide (NO₂, the dominant component of NOx) and formaldehyde (HCHO, a proxy for VOC reactivity), as well as photochemical conditions. I investigate how these factors differ on high-O₃ days, change diurnally, and respond to the temporal resolution of anthropogenic emissions. The focus is on the summer of 2018 due to the availability of trace gas retrievals from the TROPOspheric Monitoring Instrument (TROPOMI) and in situ measurements from field campaigns. I first investigate New York City (NYC) and the Baltimore/Washington D.C. area, where high O₃ levels frequently occur in summer. On high-O₃ days (when the maximum daily 8-hour average (MDA8) O₃ exceeds 70 ppb), tropospheric vertical column densities (VCDTrop) of HCHO and NO₂ increase in urban centers. The HCHO/NO2 VCDTrop ratio, proposed as an indicator of local surface O₃ production sensitivity to its precursors, generally rises due to a more pronounced increase in HCHO VCDTrop. This suggests a shift toward a more NOx-sensitive O₃ production regime that could enhance the effectiveness of NOx controls on the highest O₃ days. As retrievals of tropospheric trace gases from Low Earth Orbit (LEO) satellites like TROPOMI are limited to one overpass per day (early afternoon), I then analyze spatial variability in HCHO and NO₂ concentration diurnal patterns and connect changes in column densities with surface concentrations. Diurnal HCHO patterns indicate the impact of temperature-dependent VOC emissions, while a bimodal surface NO₂ pattern reflects diurnal patterns of local anthropogenic NOx emissions and boundary layer dynamics. Column concentration peaks generally occur about four hours after surface concentration peaks (morning for NO2 and midday for HCHO), highlighting the challenge of relating column densities to health-related surface concentrations. I also explore how the temporal resolution of anthropogenic emissions influences air pollution levels and diurnal variations. Surface NOx and O3 concentrations show different spatial patterns of change when switching from daily mean to hourly varying nitric oxide emissions. In urban areas of both the western and eastern CONUS, adding hourly NO emissions increases daytime emissions, leading to O₃ decreases, indicating NOx-saturated O₃ chemistry. In the western CONUS, monthly mean surface NO₂ increases, while in the eastern CONUS, characterized by shorter NO₂ lifetimes, NO₂ decreases. These sensitivities highlight the importance of accounting for diurnal changes when inferring emissions from concentrations. This thesis advances our understanding of O₃-NOx-VOC air pollution by exploring variations in both surface and column conditions across urban-rural gradients. It integrates in situ measurements, space-based observations, and modeling techniques and assesses advanced modeling tools for future applications. These findings support the future applications of geostationary satellite retrievals for continuous trace gas observation throughout daylight hours, supplementing the once-a-day LEO satellite data used in this thesis, with implications such as aiding source attribution and targeting cost-effective control measures for O₃ mitigation.