Long-range transported North American wildfire aerosols observed in marine boundary layer of eastern North Atlantic

Journal Article · Mon Apr 06 00:00:00 EDT 2020 · Environment International

DOI:https://doi.org/10.1016/j.envint.2020.105680· OSTI ID:1608365

Zheng, Guangjie; Sedlacek, Arthur J.; Aiken, Allison C.; Feng, Yan; Watson, Thomas B.; Raveh-Rubin, Shira; Uin, Janek; Lewis, Ernie R.; Wang, Jian

Wildfire is a major source of biomass burning aerosols, which greatly impact Earth climate. Tree species in North America (NA) boreal forests can support high-intensity crown fires, resulting in elevated injection height and longer lifetime (on the order of months) of the wildfire aerosols. Given the long lifetime, the properties of aged NA wildfire aerosols are required to understand and quantify their effects on radiation and climate. Here we present comprehensive characterization of climatically relevant properties, including optical properties and cloud condensation nuclei (CCN) activities of aged NA wildfire aerosols, emitted from the record-breaking Canadian wildfires in August 2017. Despite the extreme injection height of ~12 km, some of the wildfire plumes descended into the marine boundary layer in the eastern North Atlantic over a period of ~2 weeks, owing to the dry intrusions behind mid-latitude cyclones. The aged wildfire aerosols have high single scattering albedos at 529 nm (ω₅₂₉; 0.92–0.95) while low absorption Ångström exponents (Å_abs) at 464 nm/648 nm (0.7–0.9). In comparison, Å^abs of fresh/slightly aged ones are typically 1.4–3.5. This low Å_abs529 and low Å_abs~110 nm diameter) with thick non-absorbing coatings. The accelerated descent of the wildfire plume also led to strong increase of CCN concentration at the supersaturation levels representative of marine low clouds. The hygroscopicity parameter, κ_CCN, of the aged wildfire aerosols varies from 0.2 to 0.4, substantially lower than that of background marine boundary layer aerosols. However, the high fraction of particles with large diameter (i.e., within accumulation size ranges, ~100–250 nm) compensates for the low values of κ, and as a result, the aged NA wildfire aerosols contribute more efficiently to CCN population. These results provide direct evidence that the long-range transported NA wildfires can strongly influence CCN concentration in remote marine boundary layer, therefore the radiative properties of marine low clouds. Given the expected increases of NA wildfire intensity and frequency and regular occurrence of dry intrusion following mid-latitude cyclones, the influence of NA wildfire aerosols on CCN and clouds in remote marine environment need to be further examined.

• Research Organization: Los Alamos National Laboratory (LANL), Los Alamos, NM (United States); Brookhaven National Laboratory (BNL), Upton, NY (United States); Argonne National Laboratory (ANL), Argonne, IL (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Biological and Environmental Research (BER); Israel Science Foundation (ISF); National Aeronautics and Space Administration (NASA)
• Grant/Contract Number: AC02-06CH11357; SC0012704; 1347/18; 89233218CNA000001; SC0020259
• OSTI ID: 1608365
• Alternate ID(s): OSTI ID: 1630860; OSTI ID: 1642406; OSTI ID: 1659107
• Report Number(s): LA-UR-19-29685; BNL-216183-2020-JAAM; S0160412019326480; 105680; PII: S0160412019326480
• Journal Information: Environment International, Journal Name: Environment International Vol. 139 Journal Issue: C; ISSN 0160-4120
• Publisher: Elsevier
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
earth sciences
North American wildfires
dry intrusion
long-range transport
optical properties
cloud condensation nuclei activity
marine low clouds