Organic-containing Aerosols and Their Radiative Impacts in the Upper Troposphere and Lower Stratosphere

Aerosols in the upper troposphere and lower stratosphere (UT/LS) modify global radiative budget by scattering and absorbing solar shortwave and terrestrial longwave radiation, as well as affecting the cloud life cycle by acting as ice nuclei. Climate impacts of aerosols are greatly influenced by their microphysics, chemical composition, and mixing states. While considerable progress has been made, there remain important open questions regarding these properties of UT/LS aerosols, especially for the organic-containing aerosols. Organic components have long been disregarded for stratospheric aerosols, although aircraft studies have shown that they account for 5-50% of particle mass in the lower stratosphere. Notably, extensive organic aerosols were introduced into the UT/LS due to recent Australian and Canadian severe wildfire events.

The presentation will first discuss the composition dependence of stratospheric aerosol radiative forcing, with a specific focus on the refractive index of organics and their mixing states with ubiquitous sulfuric acid. Subsequently, laboratory work on the measurement and prediction of optical properties of organic aerosols will be showcased. Lastly, the presentation will highlight in situ measurements of aerosol concentration, size distribution, and chemical composition in the UT/LS during DCOTSS airborne mission with NASA ER-2 high-altitude aircraft. A few encounters of wildfire smoke from pyrocumulonimbus (pyroCb) events occurred in the upper troposphere. Microphysical processes and radiative impacts of pyroCb smoke aerosols will be discussed. Offline composition and morphology analysis of impactor aerosol samples from the DCOTSS mission will also be presented.