Smoke & Air Quality
Smoke Emissions and Inventory
Most of the previous investigations on the relationship between PM2.5 chemical characteristics and wildfire focused on the predictions of particle components concentrations or future pollution scenarios. Little research has focused on trends analyses based on large temporal datasets. Our research addresses this gap by quantifying the long-term impacts of wildfires on ambient particulate carbon levels (organic carbon - OC and elemental carbon - EC) in the western U.S. over a long of 29 years (1988-2016). We quantified the past wildfire-related increases in EC and OC concentration using Generalized Additive Models (GAMs). We used a framework that derives “penalties” (wildfire penalty, in μg/m3 per year) for each season (warm and cold) by accounting for the differences of the β values between two models – adjusted (wildfire included as covariate in the model) and unadjusted model (wildfire is removed from the model). While the wildfire impact is incorporated into the unadjusted trends, the control by wildfire in the adjusted model removes the impact of inter-annual wildfire variation on EC and OC trends. Therefore, we considered that any differences between the unadjusted and wildfire-adjusted trends are entirely attributable to the impact of long-term wildfire changes. A positive penalty (beta-unadjusted > beta-adjusted) suggests that an increase in EC and OC is associated with long-term wildfire changes between 1988 and 2016. Wildfires increased in the warm season and decreased in the cold season. We estimated an annual increase of 20.106 km2 of area burned (95% CI: 20.103; 20.109) in the warm period. EC and OC concentrations increased during the warm and cold season. EC and OC concentrations had an annual decrease of 0.03 μg/m3 (95% CI: −0.14; 0.08) and 0.10 μg/m3 (95% CI: −0.21; 0.01), respectively. In the cold period, our analyses showed an increase of 0.05 μg/m3 (95% CI: −0.07; 0.17) and 0.07 μg/m3 (95% CI: −0.04; 0.19) per year for EC and OC, respectively. In the warm season, during the study period (1988-2016), the estimated total concentration change (total penalty) for EC was 0.003 μg/m3 (95% CI: 0.001 and 0.005) and for OC was 0.015 μg/m3 (95%CI: 0.008 and 0.022). In the cold season the penalties were statistically insignificant.