Quantifying Long‐Term Seasonal and Regional Impacts of North American Fire Activity on Continental Boundary Layer Aerosols and Cloud Condensation Nuclei

Abstract

An intimate knowledge of aerosol transport is essential in reducing the uncertainty of the impacts of aerosols on cloud development. Data sets from the U.S. Department of Energy (DOE) Atmospheric Radiation Measurement platform in the Southern Great Plains region (ARM-SGP) and the National Aeronautics and Space Administration (NASA) Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2), showed seasonal increases in aerosol loading and total carbon concentration during the spring and summer months (2008-2016) which was attributed to fire activity and smoke transport within North America. The monthly mean MERRA-2 surface carbonaceous aerosol mass concentration and ARM-SGP total carbon products were strongly correlated (R = 0.82, p < 0.01) along with a moderate correlation with the ARM-SGP cloud condensation nuclei (N CCN) product (0.5, p~0.1). The monthly mean ARM-SGP total carbon and N CCN products were strongly correlated (0.7, p~0.01). An additional product denoting fire number and coverage taken from the National Interagency Fire Center (NIFC) showed a moderate correlation with the MERRA-2 carbonaceous product (0.45, p < 0.01) during the 1981-2016 warm season months (March-September). With respect to meteorological conditions, the correlation between the NIFC fire product and MERRA-2 850-hPa isobaric height anomalies was lower (0.26, p~0.13) due to the variability in the frequency, intensity, and number of fires in North America. An observed increase in the isobaric height anomaly during the past decade may lead to frequent synoptic ridging and drier conditions with more fires, thereby potentially impacting cloud/precipitation processes and decreasing air quality. Plain Language Summary Aerosols have complex impacts on cloud development and air quality. This study seeks to illustrate and quantify climatological trends and impacts of carbonaceous smoke aerosols generated from fire activity in North America. In the presence of rising air motion (e.g., updrafts) and sufficient moisture, the smoke aerosols can become cloud condensation nuclei (CCN). The CCN eventually become cloud droplets which gather together to form clouds which may or may not precipitate depending on available moisture and updraft strength. Long-term, surface-based observation data from the Department of Energy (DOE) Atmospheric Radiation Measurement facility in the Southern Great Plains region (ARM-SGP), the National Aeronautics and Space Administration (NASA) Second-Generation Modern-Era Retrospective Analysis for Research and Applications (MERRA-2) product, and the National Interagency Fire Product show the regional and seasonal behavior and transport of the smoke aerosols derived from fires in the United States, Mexico, and Canada. Since 2010, during the warm season months (March-September), numerous fires due to anomalously dry weather patterns have been observed in North America and likely increased the amount of carbonaceous smoke aerosols and potentially CCN, though the overall atmospheric aerosol burden ha...

Assessing Radiative Impacts of African Smoke Aerosols Over the Southeastern Atlantic Ocean

“…The total aerosol number concentration (N a ) is a derived product calculated from scanning mobility particle sizer bin measurements whose particle sizes range from 40 to 700 nm (Barrett et al, 2022). Daily averaged AOS measurements which include N CCN values taken at a supersaturation of 0.2% are used in this study (Logan et al, 2020). This study focuses on cases where σ sp and N CCN values exceed 20 Mm 1 and 200 cm 3 , respectively, to demarcate the transition between clean and polluted conditions (Logan et al, 2018(Logan et al, , 2020.…”

“…Daily averaged AOS measurements which include N CCN values taken at a supersaturation of 0.2% are used in this study (Logan et al, 2020). This study focuses on cases where σ sp and N CCN values exceed 20 Mm 1 and 200 cm 3 , respectively, to demarcate the transition between clean and polluted conditions (Logan et al, 2018(Logan et al, , 2020. The fine mode fraction (FMF) is calculated as the daily averaged ratio of the 1-10 μm size cuts of σ sp at the green wavelength and differentiates influences from biomass burning (FMF > 0.4) and marine aerosols (FMF << 0.4) in this study.…”

“…In addition, persistent high pressure systems facilitate large scale subsidence and drought. These conditions can lead to an increase in wildfire activity which is conducive to carbonaceous aerosol generation and will likely continue to increase in the near term (Hallar et al., 2017; Logan et al., 2020). It should be noted that cloud development is impacted because carbonaceous smoke CCN typically auto‐convert into small cloud droplets which compete for available water vapor in strongly polluted environments (Adebiyi & Zuidema, 2018; Kacarab et al., 2020; Zheng et al., 2020).…”

“…Carbonaceous aerosols derived from biomass burning via natural and anthropogenic activities have extensive global source regions (Che et al, 2022). Numerous studies have examined the relationship between biomass burning aerosols and their ability to readily activate as cloud condensation nuclei (CCN) with respect to aerosol transport and regional/seasonal variability (Gallo et al, 2023;Logan et al, 2020;McCoy et al, 2021;Redemann et al, 2021;Zheng et al, 2022). In addition, persistent high pressure systems facilitate large scale subsidence and drought.…”