Schematic of various coupled meteorological and chemical processes within wintertime PCAPs. Figure is not to scale. Importantly, stable nocturnal inversions can be extremely shallow (tens of meters) and elevated inversions can also be present depending on the large-scale synoptic flow.
(bottom left) Elevation map of the western United States showing selected air quality monitoring sites (black dots) that exhibit winter maxima in PM2.5. Colored markers show three sites that are highlighted in the top panel. Rings show the approximate ranges of a large research aircraft (P-3 or C-130) based out of Salt Lake City or smaller aircraft (Twin Otter) based out of either Salt Lake City, UT, or Fresno, CA. (top) Daily PM2.5 at Salt Lake City, UT, and Bakersfield, CA, from 1999 to 2020. The dashed lines are the 24-h U.S. National Ambient Air Quality Standards (NAAQS) for PM2.5 of 35 µg m−3. Gray shaded areas indicate November–February. (bottom right) Median, 25th and 75th percentile, and 10th and 90th percentile PM2.5 at Salt Lake City, UT, and Bakersfield, CA, for each day of year from the record in the top panel. Dashed lines indicate the NAAQS, as in the top panel.
