Biomass Burning Smoke and Its Influence on Clouds Over the Western U. S.

Abstract

Wildfires are abundant over the western United States during summer months, creating high concentrations of smoke aerosol particles that can impact health (Künzli et al., 2006) and produce complex effects on

Wildfire plumes in the Western US are reaching greater heights and injecting more aerosols aloft as wildfire activity intensifies

“…4 ) to climate impacts is drawn from recognition of the importance of altitude to extending the aerosol atmospheric lifetime 29 , 31 , 32 , enhancing the direct radiative effects of an absorbing aerosol layer 29 , 68 , and expanding the potential for impact on cloud processes. Recent aircraft-based observations indicate the ability of smoke aerosols to suppress downwind precipitation by acting as a source of cloud condensation nuclei, lowering the average cloud droplet size and staving off initiation of collision-coalescence 12 . Further, enhanced aerosol injection aloft increases the potential for regional-continental scale smoke transport.…”

“…Injection of a greater aerosol mass at higher altitudes, potentially into the upper troposphere—lower stratosphere, corresponds to an enhanced direct radiative effect given longer atmospheric lifetimes and increased absorption efficacy 9 , 29 , 31 , 32 , 68 . While less understood, there are also potential indirect effects related to aerosol-cloud microphysical interactions 12 , 13 , 34 . Though speculative, the potential for wildfire-derived aerosols to act as cloud condensation nuclei 13 and stave off initiation of rainfall 12 , 13 is further cause for concern given the risk of a positive feedback on wildfire activity.…”

“…While less understood, there are also potential indirect effects related to aerosol-cloud microphysical interactions 12 , 13 , 34 . Though speculative, the potential for wildfire-derived aerosols to act as cloud condensation nuclei 13 and stave off initiation of rainfall 12 , 13 is further cause for concern given the risk of a positive feedback on wildfire activity.…”

“…In terms of climate, aerosol loading from wildfires has a direct radiative impact in the form of absorption and scattering of incoming solar radiation by black carbon 9 , 10 and organic aerosols 11 , respectively. Additionally, wildfire emitted aerosols generate indirect radiative effects by altering cloud microphysics 12 , 13 .…”

Impacts of Simulated Contrail Processing and Organic Content Change on the Ice Nucleation of Soot Particles

“…After CO 2 , soot particles may exhibit the second largest direct radiative forcing globally (Bond et al., 2013), which may exceed that of CO 2 emitted by aircraft in aviation corridors (Lee et al., 2021). The impact of soot particles, particularly aviation soot, on climate relies on the particle ice nucleation (IN) ability in the cirrus regime by serving as ice nucleating particles (INPs), which modifies the microphysics of cirrus clouds (Cziczo & Froyd, 2014; Cziczo et al., 2013; Kärcher et al., 2021; Lohmann, 2002; Twohy et al., 2021) and thus changes the cloud optical properties and radiative forcing. However, the radiative forcing of aviation soot is reported to be poorly constrained as the simulated estimation spans a large range between a cooling and warming effect (McGraw et al., 2020).…”