Wildfire Impacts on O₃ in the Continental United States Using PM_2.5 and a Generalized Additive Model (2018-2023)

Area of Science:

• Environmental Science
• Atmospheric Chemistry
• Air Quality Monitoring

Background:

• Wildfire smoke plumes, particularly from large events, are increasingly affecting air quality across the United States.
• Previous studies have indicated smoke's influence on air pollutants, but quantifying its contribution to health standard exceedances is crucial.

Purpose of the Study:

• To quantify the impact of wildfire smoke on daily concentrations of fine particulate matter (PM2.5) and maximum daily 8-hour average (MDA8) ozone (O3).
• To determine the contribution of smoke to days exceeding national health-based air quality standards for PM2.5 and O3.

Main Methods:

• Analysis of PM2.5 and satellite smoke plume data from approximately 600 US air monitoring stations (2018-2023).
• Statistical modeling (Generalized Additive Models) to estimate ozone contributions on smoke-impacted days using non-smoke day data as a baseline.
• Calculation of smoke's percentage contribution to exceedance days for PM2.5 and O3.

Main Results:

• Smoke was present on 14% of May-September days from 2018-2023, with notable increases in 2020, 2021, and 2023.
• Smoke-impacted days showed higher average PM2.5 (11 μg m⁻³) and MDA8 O3 (8 ppb) concentrations.
• Smoke accounted for 94% of PM2.5 exceedance days and 36% of O3 exceedance days, with an estimated average O3 contribution of 7.8 ± 6.0 ppb on smoke days.
• Wildfire smoke contributed to 25% of all US exceedance days over the study period, rising to 38% in 2023.

Conclusions:

• Wildfire smoke is a significant driver of US air quality standard exceedances for both PM2.5 and O3.
• The frequency and impact of smoke on air quality necessitate its consideration in air quality management and health impact assessments.
• Future air quality predictions and policy decisions must account for the growing influence of wildfire events.