Downdrafts of Biomass Burning to Houston Enhanced by Local Convective Activity

In June 2023, an elevated smoke layer from record-breaking Canadian wildfires was transported across the eastern half of the United States, impacting air quality for millions of people. Houston, TX experienced a notable biomass burning (BB) event associated with this wildfire smoke from Jun 4 to 9, 2023. The vertical transport of this smoke layer down to the surface followed afternoon convective activity in the Houston urban area on Jun 6–8. Our monitoring sites at urban, rural, and coastal locations around Houston experienced different levels of wildfire smoke. Carbon monoxide, aerosol absorption, and the Absorption Ångström Exponent (AAE) revealed stronger smoke incursions overnight at the urban site. The average nighttime AAE during the BB event period was 1.28 with 384 ppbv of CO; by comparison, the monthly nighttime averages for Jun 2023 were 1.03 and 172 ppbv, respectively. Enhanced PM2.5 and NO2 coincided with BB tracers while higher ozone concentrations were observed the following day at downwind sites relative to the peak observed BB smoke sites. The nighttime NO2 for the BB event was also significantly higher than the monthly average with standard deviation for Jun 2023 (14.5 ppbv versus 5.19 ± 4.61 ppbv, respectively). Ozone concentrations peaked over 100 ppbv on Jun 9 driven by clear skies after the overnight high BB. Understanding the role of convective activity in enhancing the downdraft of BB plumes to the surface will improve assessment of the long-range impacts of wildfire smoke on urban populations.