Breakout Summary Report
ARM/ASR User and PI Meeting
19 - 23 March 2018
Biomass burning aerosol processes: Integrating ASR/ARM field and laboratory studies to inform E3SM parameterizations
21 March 2018
1:30 PM - 3:30 PM
40
M. Dubey, S. Jathar, M. Shrivastava, J. Jimenez, A. Aiken, Q. Zhang, J. Fast & R. Zaveri
21 March 2018
1:30 PM - 3:30 PM
40
M. Dubey, S. Jathar, M. Shrivastava, J. Jimenez, A. Aiken, Q. Zhang, J. Fast & R. Zaveri
Breakout Description
The session reports on the state-of-the-art knowledge of carbonaceous aerosol (CA) processes from biomass burning (BB) to facilitate their representation in models. We will highlight BB CA process findings from ARM/ASR campaigns that span all scales: LASIC, ISDAC, GoAmazon, HiLat, and BBOP, along with laboratory studies that harness advanced instrumentation. Our focus is on fundamental chemical and microphysical processes determining the dynamic BB CA properties as they age that include: (1) Secondary organic aerosol formation from intermediate volatility organic compounds, (2) Light-absorbing aerosol properties (tar balls, UV absorption, coating enhancement, photochemical bleaching, and cloud processing effects), and (3) Water uptake and its effect on aerosol lifetime, clouds, and snow albedo. Mechanistic findings on BB CA life cycle elucidated using process-level modeling of field data (WRF-MOSAIC and PartMC) will be highlighted. Finally, methods to represent BB CAs in DOE’s high-resolution Community Atmosphere Model models will be discussed. Our goal is to create a forum for dialogue among the ASR/ARM process-level community to advance DOE’s Energy Exascale Earth System Model (E3SM) effectively.We invite campaign leads, experimentalists, and modelers to submit 1-2 slides on their key findings to the conveners for brief (<5 minutes) presentations. A group discussion will follow and findings will be integrated into a breakout report for the working groups.
Main Discussion
The session discussed recent observational and modeling findings (ARM and other agencies) on biomass burning carbonaceous aerosol (BBCA) across aging timescales to assess gaps and inform strategies to develop model parameterizations for E3SM. Two overview talks discussed secondary organic formation (SOA) from BB emissions from modeling and observational perspectives. Large uncertainties in global BBA SOA source exist with multiple estimates ranging from 0 to 95 Tg/year. Two global model studies report ranges of 44 to 95 Tg/y and 3 to 26 Tg/y. The variation could result from different treatments of semi- and intermediate volatility organic compounds and their SOA mass yields. Estimates based on aircraft fire plume observations (1 to 15 Tg/y) differ from smog chamber extrapolations (0 to 68 Tg/y). Chamber measurements have errors from complexities of particle and vapor wall losses that are ill understood. Fire plume studies from aircraft and mountain top sites show a constant net ΔOA/ΔCO with age and no net OA production. However, the degree of oxidation increases with aging, suggesting that SOA formation is balanced by dilution and evaporation of primary organic aerosols (POA) in the field. The CESM global model suggests large amount of SOA formation from biomass burning is needed to match aircraft-based organic aerosol measurements during the ARCTAS field campaign. Ongoing work using the E3SM model shows that either 3-5 times higher SOA or a factor of 2-3 higher POA emissions from biomass burning are needed to bring model-predicted AOD into agreement with satellite observations. Gaps in understanding of SOA and POA are too large to quantify their individual model contributions to the AOD that is biased low. The high particle/gas ratio in BB emissions relative to urban emissions should result in lower SOA production. However, reactive organic gases in BB plumes and more dynamic chemical regimes could promote SOA formation. Finally, if these OA-specific emissions are missing, models should also under-predict CO and VOCs. Strategies to prioritize studies and solve these problems included: (1) Model sensitivity studies using simplified treatments of BB SOA pathways and POA emissions for sensitivity studies (e.g., GEOS-Chem, MOZART), (2) Detailed chemical analysis of field data of fresh and aged biomass burning plumes, (3) Carefully planned laboratory studies that address particle and vapor wall-loss issues, and (4) Develop detailed mechanisms based on laboratory results and validated by field observations for use in climate models (E3SM).
The second half of the session discussed the optical and microphysical properties of BBOAs from recent measurements that demonstrated that they are much more complex than models assume. Observations show mixing state alters optical properties of black and brown carbon (BC, BrC) from BB in a highly dynamic and nonlinear manner. The importance of tar balls that make up 40% mass in fire plumes is now recognized, but their properties remain uncertain. Tar balls can be related to BBOA-3 (highly aged BBOA) determined in aged BB plumes using PMF analysis of AMS measurements. This chemical analysis could help resolve the observations of relatively constant ΔOA/ΔCO and increase in BBOA oxidation in fire plumes (BBOP). African BBOAs transported over long range and measured on Ascension Island exhibited low SSA and AAE, indicating they have high BC (LASIC). Mixing state analysis of models show that H2O coatings make the largest contribution to enhanced absorption by BC. However, they have not been experimentally measured due to instrumental gaps that recent advances in humidified scattering and extinction can overcome.
Key Findings
BBCA representations are a key gap in climate models. E3SM is poised to address them, but POA, SOA, BC, and BrC and their properties need to be better understood for this. Model sensitivity studies should help us evaluate the global significance of BBOA. Coordinated analysis of laboratory and field data and more follow-up studies are needed to develop predictive process understanding of BBCA life cycle in E3SM.Issues
Time and resource constraints to facilitate integration within ASR and with E3SM.Needs
Focus group framework to interact with CCRD regional/global modeling programs.Decisions
Coordinated laboratory and field studies field and model analysis across scales are needed to determine the POA and SOA production, evolution, and properties of BBOAs. A strategy for interactions between experimentalists and modelers –- over a range of scales for effective BBOA process discovery and insertion into models -- was developed.