Wildfires are occurring with increasing frequency and intensity in the United States, and are a recognized large source of air pollutants. Particulate matter and particulate matter precursor emissions from wildfires impact not only human health, ecosystems, and visibility, but also the radiative balance of the planet through both direct and indirect forcing. Quantitative observational constraints on these emissions and their evolution are essential for advancing understanding of the role of fire in affecting past, present and future climate.
Rationale. The combustion chemistry occurring in wild and prescribed fires is complex and dynamic. Emissions vary strongly with fuel, fire phase (burning / smoldering), temperature, air/fuel ratio, and other factors. Downwind observations of aged plumes, relevant to human health and environmental issues, must be tied to the emissions at their source during the corresponding time period, to understand how those emissions evolved during transport. Further, field observations near the source provide a link to data from controlled lab studies. Thus, dedicated sampling of the source for extended periods, along with characterization of the evolution of emissions within the first few hours of aging, is a needed component of a comprehensive biomass burning field study.
Statement of work. We propose to conduct observations from an airborne laboratory, ideally the NOAA Twin Otter, with flight patterns aimed at dedicated source and near-field characterization. These measurements will be made as part of the FIREX [Fire Influence on Regional and Global Environments] study and will complement data from the NOAA P-3 as it samples the same emissions downwind after many hours of aging. We will determine the submicron nonrefractory aerosol composition with a high resolution time-of-flight aerosol mass spectrometer (HR-ToFAMS), and will obtain size distributions of black carbon with a single particle soot photometer (SP2). We have four specific objectives: (1) To characterize the composition of biomass burning aerosol sources, and, in particular, emission ratios and their variability, (2) To investigate the physical evolution of emissions in the near field, with emphasis on dilution effects, (3) To characterize the emission ratios of black carbon, and (4) To determine the contributions and variability in organic nitrate components of biomass burning aerosol in the near-field.