Zhixin Xue

Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


Atmospheric and Earth Science

Committee Chair

Sundar A. Christopher

Committee Member

John R. Christy

Committee Member

Qingyuan Han

Committee Member

Udaysankar Nair

Committee Member

Pawan Gupta


Air quality--United States--Measurement, Wildfires--Environmental aspects--United States, Wildfires--Canada--Remote sensing


In recent years, frequent and widespread wildfires in Canada have become the “new normal” during summer, which degrades the U.S. air quality significantly. Smoke from wildfires in British Columbia and Alberta can be transported by northwesterly winds to the U.S. and cause health issues to vulnerable populations, which also increases the health costs to the country. During the fire season, daily PM2.5 in cities along the smoke transport path in the United States can increase 5 to 10 times compared to pre-fire values. This research examined different processes affecting smoke's vertical and horizontal transport and quantified the increase in fine particulate matter (PM2.5) in the U.S. caused by Canadian wildfires. The mid-visible Multi-Angle Implementation of Atmospheric Correction (MAIAC) satellite-derived Aerosol Optical Depth (AOD) is used in conjunction with a Chemistry Transport Model (CTM) to develop a seamless aerosol product without gaps. Then meteorological variables associated with transport processes are selected along with the filled AOD product to assess the surface pollution using geographically weighted regression (GWR) and random forest (RF) models. Simulations are performed with and without fire emissions in Canada to quantify the increase in PM2.5. We found that synoptic pressure systems are the main factor for the horizontal transport of Canadian smoke, and the lifting of aerosols from a low-pressure system contributes to the long distances of the transport path. Our results indicate that smoke aerosols caused significant pollution changes in over half of the United States. We estimate that nearly 29 states have increased PM2.5 during the fire-active year and that 15 of these states have PM2.5 concentrations more than two times that of the inactive year. Furthermore, these fires increased the daily mean surface PM2.5 concentrations in Washington and Oregon by 38 to 259 μ gm-3, posing significant health risks, especially to vulnerable populations. The data and analysis developed in this research will be helpful to decision-makers, epidemiologists, ecologists, and others interested in particulate matter air quality data sets.



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