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Wildfires are an increasing source of emissions into the air, with health effects modulated by the abundance and toxicity of individual species. In this work, we estimate reactive organic compounds (ROC) in western U.S. wildland forest fire smoke using a combination of observations from the 2019 Fire Influence on Regional to Global Environments and Air Quality (FIREX-AQ) field campaign and predictions from the Community Multiscale Air Quality (CMAQ) model. Standard emission inventory methods capture 40–45% of the estimated ROC mass emitted, with estimates of primary organic aerosol particularly low (5–8×). Downwind, gas-phase species abundances in molar units reflect the production of fragmentation products such as formaldehyde and methanol. Mass-based units emphasize larger compounds, which tend to be unidentified at an individual species level, are less volatile, and are typically not measured in the gas phase. Fire emissions are estimated to total 1250 ± 60 g·C of ROC per kg·C of CO, implying as much carbon is emitted as ROC as is emitted as CO. Particulate ROC has the potential to dominate the cancer and noncancer risk of long-term exposure to inhaled smoke, and better constraining these estimates will require information on the toxicity of particulate ROC from forest fires.

Increased throughput and container ship backlogs at the ports of Los Angeles and Long Beach due to supply chain disruptions related to the COVID-19 pandemic caused a significant increase in the number of ships near the California coast, leading to concerns about increased air pollution exposure of nearby communities. We use a combination of satellite-based observations from TROPOMI and ground-based observations from routine surface monitoring sites with chemical transport model results to analyze the changes in NO2and PM2.5in the Los Angeles Basin during a period in 2021 when the number of ships was at its peak. Using simulations to account for meteorological effects, changes are apportioned to emissions and meteorology. The largest emission-related changes in column NO2occurred immediately east of the ports where emission-related NO2increased by 28% compared to the baseline (2018–2019 average). In Central Los Angeles, emission reductions led to a 10% decrease in NO2during the same period. Emission-related PM2.5increased by 0.7 μg m−3on average with a maximum increase of 4.5 μg m−3in the eastern part of Basin. The emission/meteorology attribution method presented here provides a novel approach to quantify emission-influenced changes in air quality that are consistent with observations and suggests that both NO2and PM2.5were elevated in parts of the Los Angeles area during a period of increased port activity.

US background (US-B) ozone (O3) is the O3that would be present in the absence of US anthropogenic (US-A) emissions. US-B O3varies by location and season and can make up a large, sometimes dominant, portion of total O3. Typically, US-B O3is quantified using a chemical transport model (CTM) though results are uncertain due to potential errors in model process descriptions and inputs, and there are significant differences in various model estimates of US-B O3. We develop and apply a method to fuse observed O3with US-B O3simulated by a regional CTM (CMAQ). We apportion the model bias as a function of space and time to US-B and US-A O3. Trends in O3bias are explored across different simulation years and varying model scales. We found that the CTM US-B O3estimate was typically biased low in spring and high in fall across years (2016–2017) and model scales. US-A O3was biased high on average, with bias increasing for coarser resolution simulations. With the application of our data fusion bias adjustment method, we estimate a 28% improvement in the agreement of adjusted US-B O3. Across the four estimates, we found annual mean CTM-simulated US-B O3ranging from 30 to 37 ppb with the spring mean ranging from 32 to 39 ppb. After applying the bias adjustment, we found annual mean US-B O3ranging from 32 to 33 ppb with the spring mean ranging from 37 to 39 ppb.