Reactive nitrogen partitioning fuels contribution of Canadian wildfire
plumes to U.S. ozone air quality
Abstract
Accurately quantifying wildfire impacts on ozone air quality is
challenging due to complex physical and chemical processes in wildfire
smoke. Here we use measurements from the 2018 WE-CAN aircraft campaign
to parameterize emissions of reactive nitrogen (NOy) from wildfires into
PAN (37%), NO3- (27%), and NO (36%) in a global chemistry-climate
model with 13 km horizontal resolution over the contiguous US. The NOy
partitioning, compared with emitting all NOy as NO, reduces model ozone
bias in near-fire smoke plumes sampled by the aircraft but significantly
enhances ozone downwind when Canadian smoke plumes reach cities in
Washington state, Utah, Colorado, and Texas. Using multi-platform
observations, we identify the smoke-influenced days with daily maximum
8-h average (MDA8) ozone of 70-85 ppbv in Spokane, Salt Lake City,
Denver and Dallas. On these days, mixing of wildfire smoke into urban
pollution enhance simulated MDA8 ozone by 10–20 ppbv.