Contribution of Large Wildfire Events and Burn Severity Classes to Air Pollution in California in 2018

Wildfire smoke represents a growing threat to air quality and public health. The newly available Wildfire Burn Severity and Emissions inventory (WBSE) provides emissions estimates for individual large wildfires in California at a finer spatial resolution and for a longer historical record than global inventories. For the 2018 wildfire season, we utilized daily emissions from WBSE and the Fire INventory from NCAR (FINNv2.5) with atmospheric modeling to simulate fire-derived fine particulate matter (PM_2.5) concentrations at 16 California receptors. Simulated concentrations with WBSE and FINNv2.5 were significantly correlated with station observations at 11 receptors, but the strength of correlations varied. We leveraged WBSE’s event-based framework and burn severity classification to quantify contributions of individual wildfires and burn severity classes to fire-derived PM_2.5 pollution. We found that the top ten largest fires in our modeling period accounted for nearly all fire-derived PM_2.5 pollution at our receptors. Most fire-derived PM_2.5 came from moderate or high severity burned areas. Multiple fires contributed to almost all poor air quality days, and all had contributions from 3 to 4 burn severity classes. WBSE is a promising open-source inventory for event-based emissions and multiple emission scenarios for future climate change and land management.

A new wildfire emissions inventory is applied to atmospheric modeling and compared with station observations. With the inventory’s novel event-based framework and burn severity data, we found that the top ten wildfires, mainly the top two, and the moderate and high severity burned areas accounted for most air pollution at our receptors for the 2018 California wildfire season.