Pyrogenic Skies: Photochemistry, heterogeneous chemistry and air quality impacts of wildfire smoke

As wildfires have increased in frequency and intensity across North America, their emissions have become a driver of regional air quality degradation. Biomass burning is a large source of ozone precursors, nitrogen oxides (NOx) and volatile organic compounds (VOCs), as well as particulate matter that impacts air quality directly and also drives heterogeneous chemical processes. Photochemistry within smoke plumes creates pyrogenic ozone over a variety of timescales, leading to short- and long-range transport and widespread increases in the ozone background. Mixing and entrainment of smoke that is rich in pyrogenic VOCs into NOx-rich urban areas alters regional photochemistry and can further enhance ozone production. However, aerosol loads associated with smoke layers may also suppress photochemistry. Heterogeneous chemistry in smoke plumes influences atmospheric composition through a different set of chemical cycles that affect both the lower and upper atmosphere. A series of recent airborne and ground-based field studies has investigated these chemical processes in biomass burning influenced air. These include the 2019 Fire Influence on Regional to Global Environments and Air Quality (FIREX-AQ), the 2022 California Fire Dynamics Experiment (CalFiDE), the 2023 Atmospheric Emissions and Reactivity Observed from Megacities to Marine Areas (AEROMMA) campaign, the 2024 Utah Summer Ozone study, and others. These studies provide new insights into the biomass burning influence on tropospheric ozone at all scales, from near field plume chemistry to the global remote troposphere, and from the continental background to local urban influence.

Speaker: Steven Brown, NOAA Chemical Sciences Laboratory