Characterizing Meteorological Patterns for Oregon's Winter Elevated PM_2.5 Concentrations from 2000-2023

Valleys and basins are uniquely susceptible to the buildup of air pollution during the wintertime due to cool, dense air pooling under favorable meteorological conditions, a common occurrence in the Intermountain West. In Oregon, wintertime anthropogenic air pollution is primarily from woodburning stoves and heaters and although efforts have been made to reduce wintertime pollution, stagnation events continue to result in decreased air quality. This analysis aims to understand the relationship between air pollution in six Oregon counties and the associated meteorology in the cool season (November-March) using a 2000-2023 climatology. This is completed through a composite analysis using key meteorological variables of days below the 10th and above the 80th, 90th and 99th percentile of PM2.5 concentrations in six counties, and a regression analysis between each county's PM2.5 concentrations and these key meteorological variables. Both analyses reveal that 500-hPa geopotential height anomalies, indicative of ridge amplification over the western U.S., along with positive sea level pressure anomalies over and to the northwest of Oregon, are commonly associated with high concentrations of PM2.5. Temperature anomalies are characterized by negative values in the basin/valley recording the high PM2.5, with positive values in the surrounding higher terrain reflecting a low-level temperature inversion. Precipitation anomalies are negative across Oregon, associated with the upper-level ridging and atmospheric stability. The methodology of this analysis could be expanded to a larger geographic area to further diagnose the interactions between meteorological patterns and orography in modulating PM2.5 concentrations with the potential inform forecasts of unhealthy air quality during air stagnation events.