FIREX Organic Aerosol Science Questions

  1. What are the emissions of organic aerosol and aerosol precursors from North American fires?
    • What is the composition of the aerosol emissions?
    • What are the nitrate, organics or sulfate emissions? Are there significant emissions of inorganics such as chloride?
    • What is the composition, volatility, and implications of previously unidentified species including SVOCs, IVOCs, and BC, BrC and OC aerosols?
    • Which are the most important VOCs and SVOCs for SOA production? Can their oxidation products be detected in BBOA (similar to IEPOX-SOA)?
    • What are the BB OA tracer compounds emissions?
  2. How does SOA form in biomass burning plumes?

    Fires emit a large variety of VOCs and SVOCs, many of which are very reactive and can lead to the formation of low volatility compounds (LVOCs) that can condense and form SOA. The oxidation of isoprene to form SOA has been studied in detail recently: the main pathways involve the formation and subsequent uptake of LVOCs such as isoprene epoxydiols. Many LVOCs are highly oxidized and can now be detected in the atmosphere with new techniques such as I--CIMS or NO3-CIMS. Their condensed phase products have also been detected with HR-AMS (for example IEPOX-SOA). Although isoprene is globally the most important precursor for SOA production, the VOCs emitted from biomass burning will also be a globally important due to their quantity and variety. For one example, benzenediols have recently been identified as major biomass burning emissions and their oxidation with OH and NO3 can form compounds such nitrocatechols that readily partition into the particle phase as one of the major SOA components in BB SOA. Understanding the importance of individual VOCs and their SOA formation pathways are critical to understand the mechanisms of SOA formation, which will lead to improved understanding of the climate and air quality impacts from BB.

    Isoprene SOA yield is likely controlled by the sulfate, aerosol water, and NOx availability. BB fuel-type strongly affects SOA yield, where some fuels produce large amounts of SOA with aging, while others generate emissions that can even loose aerosol mass with aging. The processes and precursor VOCs that control SOA formation for BB is largely unknown.

    Specific questions:

    • What are the formation mechanisms for secondary species (ozone, SOA and sulfate) and what environmental or chemical conditions control their relative importance?
    • What drives the SOA formation: sulfate, water content or SVOC condensation?
    • Is there evaporation and condensation of SVOCs with dilution in the plume?
    • What is the production and loss of LVOCs and how important are those for SOA production?
    • What is the average oxidation state of the organic aerosol components, after emission and as a function of age?
    • How much “aerosol bleaching” takes place and how does the index of refraction and density change with aging?
    • How does the chemical transformation change with meteorological conditions?
    • How do nighttime chemical transformations involving NO3, N2O5 and O3 influence the composition and evolution of SOA in the BB plumes?
    • How important is nighttime chemistry for production of secondary organic aerosol and brown carbon aerosol in smoke?
    • How important is the formation of organic aerosol from aqueous-phase processes?
  3. What is the large-scale impact of BB OA from North American fires?
    • How strongly is the SOA composition and distribution over North America influenced by BB?
    • How far afield does SOA form from BB?
    • What are the extinction, absorption and CCN properties of BB aerosol as a function of smoke age on hours to days time scale?
    • What types of nitrogen-containing species are found in BBOA? How do they affect optical properties?
    • How does aerosol mixing state and morphology affect optical properties of fresh and aged smoke?
    • What role does brown carbon and coatings on black carbon particles play in the optical properties of smoke?
    • What fraction of the organic aerosol is primary versus secondary at various time scales?
    • How well do regional and global models predict SOA from BB?