Air quality is a global public health challenge with regionally-specific drivers and control strategies. Variations in meteorology and climate coupled with emission source types and atmospheric chemical processes lead to diverse air quality impacts at regional scale. This session solicits submissions from observational and modeling studies on air pollution in different regions around the world. Observational studies that include remote sensing, in-situ measurements, analysis from recent field intensives or a combination of these approaches are encouraged. Laboratory studies of important atmospheric chemical processes and progress toward the development of chemical mechanisms are also of interest. Modeling studies that use observations and laboratory data to improve predictive skills of air quality are welcome. Relevant air quality issues include, but are not limited to, near-surface ozone, fine particles, hazardous air pollutants, emerging/understudied pollution sources, smoke from wild and prescribed fires, visibility, regional haze, air quality-climate interactions, emissions and trends, and inequities in pollutant exposure and health impacts.

Natural Surface Emissions Dominate Anthropogenic Emissions Contributions to Total Gaseous Mercury (TGM) at Canadian Rural Sites

680

Analyzing the Meteorology Driven Spatial-temporal Variability in Transportation Air Quality Impacts on Neighboring Communities

Quantification of PM_2.5 concentrations Reduction during Rainfall due to Below-cloud scavenging based on Observational data and Meteorology-chemistry model.

685

Quantifying NO_x Emissions in the Colorado Front Range during AMMBEC

Clara Jean Lietzke, Univ. of Colorado Boulder, Boulder, CO; and V. Osorio, C. N. Silver, M. Muter, C. F. Lee, W. A. Brewer, S. S. Brown, X. Ren, B. McDonald, S. Wang, S. Baidar, and R. Volkamer

Nighttime oxidation of monoterpenes (MT) via the nitrate radical (NO₃) and ozone (O₃) contributes to the formation of secondary organic aerosol (SOA). This study uses observations in Atlanta, Georgia from 2011–2022 to quantify trends in nighttime production of NO₃ (PNO₃) and O₃ concentrations and compare to model outputs from the EPA’s Air QUAlity TimE Series Project (EQUATES). We present urban-suburban gradients in nighttime NO₃ and O₃ concentrations and quantify their fractional importance (F) for MT oxidation. Both observations and EQUATES show a decline in PNO₃, with modeled PNO₃ declining faster than observations. Despite decreasing PNO₃, we find that NO₃ continues to dominate nocturnal boundary layer (NBL) MT oxidation (F_NO3 = 60%) in 2017, 2021, and 2022, which is consistent with EQUATES (F_NO3 = 80%) from 2013–2019. This contrasts an anticipated decline in F_NO3 based on prior observations in the nighttime residual layer, where O₃ is the dominant oxidant. Using two case studies of heatwaves in summer 2022, we show that extreme heat events can increase NO₃ concentrations and F_NO3, leading to short MT lifetimes (<1 h) and high gas-phase organic nitrate production. Regardless of the presence of heatwaves, our findings suggest sustained organic nitrate aerosol formation in the urban SE US under declining NO_x emissions, and highlight the need for improved representation of extreme heat events in chemistry-transport models and additional observations along urban to rural gradients.

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