Differences in Ozone and Particulate Matter Between Ground Level and 20 m Aloft are Frequent During Wintertime Surface-Based Temperature Inversions in Fairbanks, Alaska

During winter in Fairbanks, Alaska, fine particulate matter (PM2.5) accumulates to large concentrations at breathing level; yet little is known about atmospheric composition aloft. To investigate vertical differences of pollutants, we measured PM2.5 and ozone (O-3) at 3 and 20 m above ground level (AGL) in Fairbanks during winter (November 2019-March 2020). We measured temperature and PM2.5 at 3, 6, 9, and 11 m AGL on a tower to quantify surface-based temperature inversions (SBIs) and near-surface PM2.5 gradients. We defined SBIs as data with an 11 m minus 3 m temperature difference greater than 0.5 degrees C. We observed the largest differences in PM2.5 and O-3 when SBIs were present. During SBIs, PM2.5 accumulated to large concentrations at 3 m but to a lesser extent at 20 m, demonstrating reduced vertical mixing. During SBIs, the median PM2.5 concentration was 4.8 mu g m(-3) lower at 20 m than at 3 m. When PM2.5 concentrations were large at 3 m, O-3 was often completely chemically removed (titrated) but was still present at 20 m. During SBIs, the O-3 mixing ratio was more than 2 nmol mol(-1) larger at 20 m than at 3 m in 48% of the data. Results show that during SBIs, pollution in Fairbanks is mixed to altitudes below 20 m AGL and that the oxidation regime of the atmosphere changes from 3 to 20 m AGL as large differences in O-3 mixing ratios were measured during SBIs.

Automated summary

This study investigates the vertical differences of PM2.5 and O-3 concentrations in the atmosphere of Fairbanks, Alaska during winter. The results show that pollution is mixed to altitudes below 20 m AGL during surface-based temperature inversions, leading to significant differences in pollutant concentrations between 3 m and 20 m AGL. Additionally, the oxidation regime of the atmosphere changes with different O-3 mixing ratios during surface-based temperature inversions.