Rapid transformation of wildfire emissions to harmful background aerosol

Abstract

Wildfires are a significant source of organic aerosol during summer, with major impacts on air quality and climate. However, studies in Europe suggest a surprisingly low (less than 10%) contribution of biomass burning organic aerosol to average summertime fine particulate matter levels. In this study we combine field measurements and atmospheric chemical transport modeling, to demonstrate that the contribution of wildfires to fine particle levels in Europe during summer is seriously underestimated. Our work suggests that the corresponding contribution has been underestimated by a factor of 4–7 and that wildfires were responsible for approximately half of the total OA in Europe during July 2022. This discrepancy with previous work is due to the rapid physicochemical transformation of these emissions to secondary oxidized organic aerosol with an accompanying loss of its organic chemical fingerprints. These atmospheric reactions lead to a regionally distributed background organic aerosol that is responsible for a significant fraction of the health-related impacts caused by fine particles in Europe and probably in other continents. These adverse health effects can occur hundreds or even thousands of kilometers away from the fires. We estimate that wildfire emissions are responsible for 15–22% of the deaths in Europe due to exposure to fine particulate matter during summer.

Formation and chemical evolution of SOA in two different environments: A dual chamber study

“…1 where it increased by 0.04. During the experiments, when SOA was formed, PMF analysis (Paatero and Tapper, 1994) in the ambient revealed that the less oxidized organic aerosol factor (LO-OOA) was dominating while the more oxidized factor (MO-OOA) had low levels at the time (Vasilakopoulou et al, 2023). This indicates that the corresponding air masses were less aged.…”

“…transported over long distances and biogenic emissions in the Eastern Mediterranean. It combined both chamber experiments and ambient measurements (Vasilakopoulou et al, 2023;Matrali et al, 2024). Situated at an elevation of 1300 meters above sea level, the site was positioned at the chalet atop the Pertouli ski resort (39° 32'44"N 21° 29'55"E), in the middle of a sprucefir forest.…”

“…PMF analysis revealed that the biogenic oxidized factor accounted for 23% of the total, the rest being less-oxidized OA (37%) and more-oxidized OA (40%) (Vasilakopoulou et al, 2023). Detailed analysis of the latter suggested that it was mostly a result of rapid chemical aging and transport of wildfire emissions, originating hundreds of kilometres away from the site (Vasilakopoulou et al, 2023). However, biogenic SOA was also present in the less-oxidized OA, and some could be even included in the more oxidized OA.…”

“…The higher potential of SOA formation observed in the Po Valley (compared to Pertouli, where SOA was practically formed in only one experiment) suggests that the anthropogenic VOCs have a higher potential to form later generation products, enhancing the mass of secondary material in the OA. Part of the explanation for the high SOA formation potential observed in the Po Valley could also be the contribution of less aged biomass burning OA emissions in this area (Saarikoski et al, 2012;Paglione et al, 2020), estimated to contribute about 25% of the OA during the FAIRARI campaign, compared to the very aged OA in Pertouli (Vasilakopoulou et al 2023).…”

Aged and obscured wildfire smoke associated with downwind health risks

“…Due to the photochemically-aged features of the smoke reaching NYC, our real-time trace metal measurements were key to identifying and constraining wildfire influences, especially for lowintensity or long-range transported aged smoke episodes (Vasilakopoulou et al, 2023). Potassium is often one of the most abundant metals in biomass burning aerosol emissions (Reid et al, 2005),…”