Unraveling atmospheric physics and chemistry of long-range transport of pollutants: Development of novel tools and methods

Long-range transport (LRT) of pollutants causes changes in background concentrations of pollutants (e.g., ozone, O3; and nitrogen dioxide, NO2) and alarming high peaks of unhealthy criteria pollutants (e.g., particulate matter, PM; and carbon monoxide, CO) in downwind regions. As the chemical composition of outflow over a region or continent can significantly affect the air quality downwind, information about LRT must be reliable. In the first chapter of this dissertation, we introduce a semi-Lagrangian chemical transport model to verify the direct source-receptor link of pollution during LRT. To validate the developed model, we investigate the CO transport from neighboring regions to Seoul Metropolitan Area in East Asia. By identifying the trajectories of CO concentrations, one can use the results from the developed model to directly link strong potential sources of pollutants to a receptor. Then we expand upon the designed Lagrangian framework to study a more acknowledged phenomenon in East Asia, the transboundary LRT of PM2.5 from the North China Plain (NCP) region to South Korea during springtime. In the second chapter, we redesigned the Lagrangian model into a diagnostic tool for the Community Multiscale Air Quality Modeling System (CMAQ) to track concentrations of PM through their transport. Our results shed light on the impact of nitrate and sulfate from various parts of the NCP region to South Korea during the high peaks of PM2.5. In the third chapter, we introduced a physics-based convective mixing scheme and explored the impact of implementing this scheme in CMAQ on the LRT of pollutants. Results revealed the potential of the new scheme to substantially increase or decrease CO concentrations at different altitudes. On some days, the updrafts and downdrafts played a significant role in changing CO concentrations (50 ppb) at various altitudes, however, on other days, the LRT was a major process responsible for differences in CO levels (100 ppb). In the final chapter of this dissertation, we analyzed the physics and chemistry of a wildfire plume through its transport from the fire initiation area to the downwind region. In this study, we assimilated satellite retrievals (i.e., column NO2, formaldehyde, and Aerosol Optical Depth) and meteorological variables to constrain model results to achieve the best possible simulation. We observed the formation and dissipation of O3 plumes (~ 80-90 ppb) and their precursors in the wildfire area and changes in O3 concentrations (~5-15 ppb) and O3 regimes in the downwind region.