Shortwave-Absorbing Aerosols and their Interactions with Clouds
24 October 2022
1:30 PM - 3:30 PM
Paquita Zuidema, Yan Feng, Arthur Sedlacek
Biomass-burning aerosols (BBA) represent complex mixtures of black and brown carbon that include organic aerosols, distinguishing them from the soot emitted by fossil fuels. The aerosol chemical composition, irrespective of source, continues to evolve, affecting the aerosol’s optical and cloud-nucleating properties in time-dependent ways. New developments are occurring in understanding single-particle properties, mixing state, brown carbon formation, and interactions with clouds, including BBA as cloud condensation and ice-nucleating particles. Longer-term trends in shortwave aerosol absorption are becoming better known and modeling efforts are improving in representing BBA and the impact on cloud microphysics and thermodynamics. New DOE campaigns such as TRACER, SAIL, and the recent CACTI campaign add additional perspectives to that gleaned from more mature campaigns such as LASIC, ACE-ENA, HI-SCALE, and BBOP. We invite all attendees with relevant material, spanning lab studies, field campaign observations, and analyses and modeling efforts.
The session was organized to lead up to a discussion on valuable low-hanging next steps for the relevant research community. As such, the session began with a longer invited talk by Manish Shrivastava on the status of aerosol representation within the E3SM model. This was followed by 12 presentations of approximately 5 minutes each, divided into an ‘observational’ section and a ‘bridging observations to modeling’ section. The presentations focused more on the aerosol issues than on aerosol-cloud interactions. While many of the presentations were motivated by LASIC observations, laboratory studies focusing more on US western wildfires, and field study results from the Amazon were also discussed.
The presentations overall focused more on aerosol processes occurring near the emission source, than on the processes dominating the overall radiative forcing after more than one day of transport. Manish’s presentation highlighted that the photolytic process his group has recently implemented into E3SM is primarily active at higher altitudes (>5km). Model experimentation has also revealed that simple biomass-burning organic aerosol (BBOA)->secondary OA conversions work as well as more complex multi-generational representations for semi/intermediate volatility aerosols. Also noteworthy was that significant progress has occurred in characterizing the link between brown carbon chemistry and optical properties, and in the evolution of BB aerosols in long-range transport from both observational and modeling studies. Overall, the presentations indicated an increased articulation in the language used to describe BBA processes compared to even just five years ago.
BBA processes are complex and vary with scale, from local, to regional, to global. Much has been learned over the past decade, though primarily on the near-source regime. Given the significant expertise distributed over many institutions and concerns over the increased wildfire aerosol emissions, the timing is good for assessing productive future directions within the ARM/ASR communities as well as coordination with other agencies on climate impact of wildfires.
We think a workshop that encompasses expertise both inside and outside the DOE ASR community would be useful.
The session was well attended, with an intellectually diverse community clearly interested in moving research forward on the chemical, physical, optical, and cloud-nucleating processes active across the full BBA life cycle. As such, the conveners are proposing a community workshop to assess measurement and modeling gaps more comprehensively and to identify the most fruitful ways forward to address the gaps. A short (two-page) white paper is currently being prepared in support of the workshop.
See ‘Decisions’. We expect the workshop we hope to hold to produce a white paper that can help inform further decision-making on field work and model improvement.
See ‘Decisions/Future Plans’. In addition, a new collaboration has begun between LANL and LASIC/ORACLES/CLARIFY scientists, in which the campaign absorption enhancements and black carbon coating-to-core thicknesses are being included in an extended analysis based on Lee et al. 2022, https://doi. org/10.1029/2022GL099334