Differences in Ozone and Particulate Matter Between Ground Level and 20 m Aloft are Frequent During Wintertime Surface‐Based Temperature Inversions in Fairbanks, Alaska
Meeta Cesler‐Maloney, William R. Simpson, Tate Miles, Jingqiu Mao, Kathy S. Law, Tjarda Roberts
Abstract
Abstract During winter in Fairbanks, Alaska, fine particulate matter (PM 2.5 ) accumulates to large concentrations at breathing level; yet little is known about atmospheric composition aloft. To investigate vertical differences of pollutants, we measured PM 2.5 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 PM 2.5 at 3, 6, 9, and 11 m AGL on a tower to quantify surface‐based temperature inversions (SBIs) and near‐surface PM 2.5 gradients. We defined SBIs as data with an 11 m minus 3 m temperature difference greater than 0.5°C. We observed the largest differences in PM 2.5 and O 3 when SBIs were present. During SBIs, PM 2.5 accumulated to large concentrations at 3 m but to a lesser extent at 20 m, demonstrating reduced vertical mixing. During SBIs, the median PM 2.5 concentration was 4.8 μg m −3 lower at 20 m than at 3 m. When PM 2.5 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.