FIREX Science Overview

Motivation

The combination of a warmer, drier climate with fire-control practices applied over the last century has produced a situation in which we can expect larger and more frequent fires in the U.S. and Canada. The 20th century saw fire suppression become the standard response to wildfires, especially in western North America; this has led to a buildup of fuels in forested areas, a breakdown in the natural ecology of forests, and risks to life and property associated with the development of the urban-wildland interface. Prescribing fires and allowing some naturally- occurring fires to burn are some of the management practices that can address the above problem [U.S. Department of Interior, 2014].

Fire is important for many ecosystems, but it also poses costly risks to human health and property. These risks have increased in recent decades due in part to population growth in the wildland urban interface [Westerling et al., 2006]. Extreme fire seasons attract mounting attention due to the increasing number of costly extreme wildfires that include: the 2016 fires that burned across 8 states in the southeast (48,158 ha); the 2016 Anderson Creek prairie fire that was the largest in Kansas history (161,874 ha); the 2016 Fort McMurray fire, which is the costliest fire in Canadian history ($2.7 B, 589,552 ha, 2400 structures destroyed); the 2004 Alaskan fire season (2.74 M ha), the largest in almost 80 years of Alaskan fire history and the extreme 2015 unusually- early-season Alaskan fires (2.07 M ha). Since 1960, total burned area in a single year has exceeded 3.6 M ha in the United States only 4 times – all of which occurred in last decade. Coupled with the direct threats to life and property, wildland fires have demonstrable detrimental air-quality related health impacts including aggravated asthma, chronic bronchitis, decreased lung function, congestive heart failure, and premature death [Rappold et al., 2011; Thelen et al., 2013].

Background and State of the Science

Fire impacts occur over wide time and distance scales, from local to global, via many complex, interdependent, and poorly understood processes. For example, primary fire emissions are affected by a wide variety of factors including fuel conditions (type, structure, quantity, and moisture content), fire intensity, and fire weather (cumulative temperature, relative humidity, wind speed and precipitation), which in turn can be rapidly and heterogeneously modified by fires as they burn. Over the life cycle of a fire, combinations of flaming and smoldering combustion lead to different emissions at different times and at different locations within a fire. These variables also influence plume rise and the subsequent transport and chemical evolution of fire emissions, which determine the secondary products (e.g. evolved gases and aerosol species). Wildfire initiation can be natural (by lightning) or human caused and prescribed fires are becoming a more frequent tool for land management (e.g., land clearing and agriculture). Fire growth is driven by weather conditions and is subject to the limitations of weather-based prediction. Fire activity can be predicted on a broad seasonal scale, but climatologies are inadequate to provide the detailed information needed to understand and predict fire impacts. This is especially true for impacts related to air quality, which depend on the intersection of fire emissions with populations and are sensitive to chemical transformations that can result when emissions from fires and anthropogenic sources combine.

The ubiquity of fire emissions is evident from previous airborne field studies. Some of the more recent missions observing these atmospheric impacts of fires are introduced here, followed by a more detailed explanation of state of the science organized by general subtopic. The international ICARTT study (2004) found strong biomass burning (BB) influence from Canadian and Alaskan fires in the northeast U.S. [Warneke et al., 2006], and NOAA's TEXAQS (2006) identified systematic differences in particle morphology between urban and biomass burning sources [Schwarz et al., 2008]. The international POLARCAT study (2008) focused on Arctic measurements, observed strong fire contributions in spring by Asian fires to arctic haze over Alaska [Warneke et al., 2009] and sampled local Canadian fire emissions during summer as well as unexpected fires in California, providing a broad cross section of fire emissions and impacts [Hecobian et al., 2011; H.B. Singh et al., 2012]. NOAA's SENEX (2013) acquired data on the relative contribution of BB to organic aerosols and gases in the southeast U.S. and provided the first airborne measurements of nighttime smoke [Zarzana et al., 2017], while the NASA/NSF DC3 (2012) campaign had the good fortune to encounter a smoke plume interacting with a deep convective tower [Apel et al., 2015] and evidence for the broad influence of convection on the ventilation of fire emissions [Huntrieser et al., 2016]. Fire sampling during NASA's SEAC4RS (2013) study enabled evaluation of the plume from the Rim Fire, a large wildfire in California [Peterson et al., 2015] and emissions from a collection of 15 small agricultural fires in the Mississippi River Valley [Liu et al., 2016].

Despite this wealth of fire sampling over the years, field studies dedicated specifically to the sampling and characterization of fires and their impacts from the point of emission have been lacking. This need is being met through recent efforts such as the DOE BBOP (2013) mission which was focused on smoke optical properties, but also identified, via morphological analysis, evidence for evolving brown carbon materials in fire plumes [Zhou et al., 2017]. Also, recent laboratory studies, e.g., NOAA's FIREX FIRE Lab 2016 study and the University of Montana led FLAME-4 study, produced some fuel specific emission factors (EFs) and smoke aging simulations [Koss et al., 2018]. FIREX-AQ will build directly on these contributions.

Below, broad science targets for the FIREX-AQ campaign are presented with background information and explanations of needs. Each target is associated with specific FIREX science questions.

Fuel-specific Emission Factors

Fuel-type-specific emission factors are one of the fundamental needs for prediction and assessment of wildfire emissions on the atmosphere, but the long list of factors influencing fire emissions creates a difficult statistical challenge. In an intercomparison of four unique approaches to estimating fire emissions in the United States, Al-Saadi et al. [2008] found that even though patterns were similar, monthly estimates of CO could vary by a factor of 10. Similar difficulties were encountered by Zhang et al. [2014] for estimates of smoke emissions over sub-Saharan Africa.

One demonstration of this challenge is provided by considering the observations that form the basis for recommended emission factors used in models. Akagi et al. [2011] provide an extensive review of these observations, which include airborne, ground-based, and laboratory sampling. Screening is applied to ensure that observations are fresh, meaning sampled emissions have cooled to ambient temperature but have undergone minimal photochemical processing. When assessing the contributions of airborne field observations, the resulting data are rather limited. This is due to the lack of airborne samples focused on near-field fire emission characterization. More traditionally, airborne field campaigns have documented fire impacts through diagnostic tracers (HCN, CH CN, K+) and plume interceptions at various distances downwind, often without detailed knowledge of the source. As a result, only eight airborne campaigns contribute to the Akagi et al. [2011] assessment of emission factors. For biomes relevant to North American wildfires, contributions are further limited to samples taken from 39 specific fire events (13 - boreal forest, 18 - temperate forest, 8 - chaparral). Airborne sampling of crop burning adds another 12 fires; hence only very limited statistics are available.

A good example of the current uncertainty in emission factors can be found in the recent work of Liu et al. [2016] comparing statistics from the recent SEAC4RS study with previous observations. Liu et al. analyzed fifteen crop fires in the Mississippi River Valley in 2013 sampled from the NASA DC-8. Emissions derived from these fires showed statistically significant differences from previously published emissions estimates, indicating that the distribution of possible emission factors has not been adequately quantified. This example applies only to crop burning, but other fuels suffer a similar paucity of observations.

While there is a modest amount of ground-based sampling and laboratory observations available to augment airborne data, there is a compelling need for more ambient observations near active fires. This need becomes more evident when looking at the suite of measurements collected during each field study included in the Akagi et al. assessment. The overlap in measurements is limited to a handful of constituents (CO2, CO, CH4, NO and/or NO2, C2H2). Measurements of other reactive hydrocarbons, tracers, and particulate emissions vary considerably between studies, leaving even fewer observations for estimating emission factors for many trace gas and particulate components. It is important to note that measurements of acetonitrile (CH3CN) are largely absent from these previous studies. CH3CN has emerged as the most reliable conservative tracer of biomass combustion, being widely measured in more recent airborne field studies to diagnose fire influence [de Gouw et al., 2003].

There continues to be significant progress in defining and quantifying the detailed chemistry of BB emissions as analysis methods applied to these measurements continue to evolve in sophistication. Examples of recent new findings include measurements of isocyanic acid (HNCO) emissions and the observation of nitrous acid (HONO) as a consistent product of fires in both the laboratory and field at levels of 5-30% of NOx [Burling et al., 2010; Roberts et al., 2010]. There has also been increased effort to obtain detailed information on the semi-volatile organic compounds (SVOCs) that are an abundant class of secondary organic aerosol (SOA) precursors in fires. Attempts to reconcile the VOC emissions from fires with the observed SOA formation have shown that unidentified SVOCs, while perhaps only 20-50% of the VOC emitted [Hatch et al., 2014; Stockwell et al., 2014], can have a disproportionately large effect on the amount of SOA estimated by models [Jathar et al., 2014; McMeeking et al., 2014]. Recent laboratory work has led to the recognition that the relative amounts of BC and organic carbon aerosol (OC) emitted are strongly relevant to the optical properties because of light-absorbing OC aerosol (also called "Brown Carbon", BrC) [Saleh et al., 2014]. Recently, new analytical techniques were deployed during the FIREX Fire Lab 2016 experiment in Missoula, MT to characterize fire emissions in more detail. One example is that Koss et al., [2017] determined a significant fraction of volatile organic compounds (VOCs) and semivolatile VOCs (SVOCS) that were previously unidentified in emissions of North American wildfires. Over 90% of the mass detectable by a PTR-ToF-MS instrument were identified. In addition, a better process-level understanding of the emissions of trace gases was established: it was found that the variability in VOC emissions can be explained using the temperature of the pyrolysis and that the VOC emissions can be parameterized using a high and a low temperature pyrolysis factor that is independent of the fuel burned [Sekimoto et al., 2018]. These laboratory-determined emission factors and process understanding has yet to be applied to ambient measurements.

FIREX-AQ will provide ambient observations to complement these recent laboratory measurements using a near-comprehensive suite of chemical and aerosol measurements. The resulting information will broaden the characterization of fire emissions and be used to refine and improve emission inventories. These measurements will be critical to addressing science question #1 and associated sub-elements

Emission Estimates using Satellites

Fire emissions can be estimated using the burned area, fuel loading, fuel consumption and compound-specific emission factors discussed above. The routine (or operational) determination of these parameters (except the emissions factors) relies on satellite observations in combination with information on ecosystem types [Friedl et al., 2010; Giglio et al., 2003; Giglio et al., 2006].

Burned area estimates are derived from a variety of satellite data products (GOES and MODIS). These estimates have the advantage of being able to detect after the fires by collecting observations over a period of time that includes multiple satellite overpasses, thus increasing the chance to observe locations free of cloud cover [Giglio et al., 2006; Giglio et al., 2009; Roy et al., 2008; Roy et al., 2005]. For instance, the MODIS burned area product is diagnosed from the 8-day surface reflectance product, providing information at 500m resolution. While this fine spatial resolution is adequate for large Western wildfires, it is not sufficient for detecting many small agricultural fires in the Southeast [McCarty et al., 2009]. Geostationary satellites were shown to capture more small fires, even though the instrument resolution was low, simply due to the fact that the instruments were overhead when small (brief) fires were burning [Al-Saadi et al., 2008; Soja et al., 2009].

Active fire detection based on satellite observations in the infrared offer complementary information capable of detecting such small fires, but at coarser resolution (1 km) and only when fires are actively burning and unobscured by clouds at the time the satellite is overhead. In an analysis of fire detection products over the U.S., McCarty concluded that 65% of active fire detections in croplands were not accompanied by a burned area detection. This number rose to 70% in the southeast. While these detections are valuable for detecting small cropland fires, they were found to add only 4% to total burned area estimated from the MODIS burned area product. Focusing more generally on small fires, Randerson et al. [2012] came to a different conclusion based on a global analysis of the same MODIS 500 m burned area products and 1 km active fire detections. Using a set of scaling factors developed to assign a burned area estimate to active fire detections lacking coincident burned area detections, it was estimated that small fires increase global burned area by 26%. As with emissions factors, the disparity in these results places emphasis on the need to validate information on the contribution of small fires to overall emissions. It is important to note that other satellite products (e.g., GOES-16, VIIRS, Landsat8/OLI) are now available, offering higher spatial resolution, more frequent coverage, and greater spectral information than was available for these previous studies.

Along with burned area, the amount of fuel consumed must also be determined. The amount of fuel contained in unique ecosystems can vary by 2 orders of magnitude, and the amount of fuel available (dry enough) to burn in each ecosystem varies with fire weather or fire danger conditions. McRae et al. (2006) demonstrated that even in the same ecosystem, the amount of fuel consumed by a fire can vary by an order of magnitude, dependent on the fuel conditions and fire severity. This adds credence to the value of accumulating statistics and connecting the ground to the atmosphere by connecting multiple-agency field campaigns.

More recently, Fire Radiative Power (FRP) and Fire Radiative Energy (FRE) have been related to fuel consumption [Charles Ichoku et al., 2008; Wooster et al., 2005], and FRE has been suggested as a methodology to estimate fire emissions from the top down [C. Ichoku and Ellison, 2014; C. Ichoku and Kaufman, 2005]. As these approaches have matured, their application has been hampered by a lack of quantitative validation data for fire energetics.

Satellite trace-gas retrievals of unprecedented spatial resolution will also be available during FIREX-AQ with an opportunity to evaluate TROPOMI observations of NO2, CH2O, CO, and CH4. Observations from other satellites (e.g., MOPITT, AIRS, IASI) will also be useful for constraining trace gas emissions from fires. These satellites will provide additional value in diagnosing the extent of mixing between fire and anthropogenic emissions affecting air quality. Satellite retrievals are relevant to many FIREX-AQ science topics, and are specifically called out in science question #6, which addresses this explicitly.

Optical Properties of Smoke

Smoke is one of the most prominent and visible aspects of BB. Smoke is primarily comprised of gaseous and aerosol constituents including BC, BrC, OC, and mineral dust, all of which have critical climate, health, and air quality impacts. The aerosol, controlling most of the optical properties, evolves due to dilution, coagulation, and chemical processing on time scales of seconds to days [Vakkari et al., 2014]. Fire smoke has many impacts on the atmosphere; depending on the relative amounts of OC and BC/BrC, surface albedo and altitude, it can either heat or cool the atmosphere; it can provide ice and water active aerosols; affect visibility and air quality; be transported over global scales. BB is the largest source of black carbon to the atmosphere [Bond et al., 2013] and a singularly important source of BrC [Saleh et al., 2014]. There is evidence that fires produce BC particles coated with particulate organic matter in a manner that enhances some of their optical properties, specifically short wavelength absorption by "lensing" [Lack et al., 2012]. However, the net direct forcing effect of all aerosol species generated by BB is currently believed to be small while uncertain [Bond et al., 2013].

The optical properties of smoke are relevant to science questions #3 - 6, as they determine the effects of smoke on visibility and climate, and influence interpretation of satellite retrievals. To the degree that FIREX-AQ determinations of smoke's intensive properties (including optical properties) can be linked more generally to smoke emissions globally, this topic could have meaning for understanding fires' wider impacts.

Transport, Transformation and Plume Chemistry

The impact of wildfires on regional- to global-scale atmospheric chemistry depends on the physical and chemical transformations that take place as fire emissions are transported, diluted, and exposed to chemical oxidants. Ozone and other oxidants can be formed along the way, and particle mass-loadings can grow or shrink [Akagi et al., 2012]. In addition, toxic gas and particle materials that have health impacts can be both formed and destroyed. Not all the factors that govern these processes are well understood, and individual fire plumes can have very different behaviors. Fire emissions contain a number of unusual compounds, some of which may have specific health effects [Roberts et al., 2011], and more compounds are being discovered as more sophisticated analytical techniques have been applied [Stockwell et al., 2014]. Fundamental atmospheric chemical behavior of some of these compounds is often unknown. Mueller et al (2016) used a PTR-ToF-MS to detect previously unreported compounds in a small understory fire in Georgia and successfully modelled some of these newly reported compounds, but still was not able to model several compounds with current chemical mechanisms. The FIREX FireLab 2016 results of smoke aging reactors were used to further update the chemical mechanisms of furan-type compounds and was able to model a much larger set of compounds. Yet still a large fraction of the initial reactivity remains unaccounted for in the updated chemical mechanism.

Photooxidation of the NOx and VOCs emitted by fire plumes shows complex behavior, sometimes leading to production of ozone and sometimes not [Jaffe and Wigder, 2012]. The reasons for this complexity are not understood and may have to do with how fast the plume was lofted and cooled, how efficiently NOx was converted to products such as peroxyacetyl nitrate (PAN), or whether the fire had substantial amounts of radical precursors such as HONO or carbonyls. What is clear is that fire emissions often have broad-scale impacts on ozone formation [Pfister et al., 2006; Wotawa and Trainer, 2000], especially when mixed with urban emissions [H.B. Singh et al., 2012], and can be decisive factors in triggering air quality exceedances.

The physical and chemical processes governing the transformation of particles in BB plumes is quite complex, with evidence of both loss and gain of particle mass, and rapid atmospheric oxidation [Vakkari et al., 2014]. Mass can be lost as smoke is diluted due to the physical equilibration of semi-volatile compounds [Robinson et al., 2007]. Oxidation of both gas and particle phase compounds due to reaction with HOx radicals (daytime) and NO3 radicals, N2O5, and ClNO2 (nighttime) can lead to mass loss or gain, and changes in the optical properties. The chemistry and surface coating properties of particles emitted by fires evolve as these physical and chemical changes take place and affect the optical, cloud nucleation, and toxicological properties of the particles. The chemical transformation of fire-sourced pollutants is the main focus of science question #2.

Plume Injection Heights

Another critical parameter needed to improve forecasts of fire emission transport, lifetime, chemistry, and impacts is plume injection height, namely the distribution in altitude space at which fire emissions are entrained into the boundary layer, the free troposphere, and even the lower stratosphere. By far, the most determinations of plume-height statistics are based on satellite retrievals [Paugam et al., 2016]. Currently there are two satellite instruments that are capable of capturing plume injection height: the Multi-angle Imaging SpectroRadiometer (MISR); and the Cloud-Aerosol LIdar with Orthogonal Polarization (CALIOP). Both of these instruments provide essential and unique information. MISR has a larger swath width, thus a greater ability to estimate near-fire plumes, and the MISR plume database is mature [Kahn et al., 2008; Martin et al., 2012; Nelson et al., 2013]. However, MISR is on Terra with a morning overpass, while smoke plumes occur most often in the late afternoon; their heights can also vary diurnally. MISR also requires distinct smoke edges to estimate plume height and large smoke plumes can fill the MISR field of view such that a distinct smoke boundary cannot be observed. CALIOP (active lidar, 30 m vertical resolution for height, 60 m vertical resolution of plume density via backscatter), paired with a back-trajectory model, can enhance the MISR morning database, by characterizing afternoon plumes [Omar et al., 2009]. While useful for historical context, CALIOP will not be available in 2019; however, the Cloud-Aerosol Transport System (CATS) onboard the International Space Station is another lidar that may prove useful.

Some parameterizations of fire plume injection height take into account the atmospheric stability appropriate for each fire, as well as the availability of latent energy via water vapor which strongly affect plume height. Plume injection height will be directly observed during FIREX-AQ for a large number of fires and meteorological conditions, providing information relevant to science questions #2, 3, and 6.

Regional and Nighttime Atmospheric Chemistry and Impacts

Wildfires have profound impacts on regional air quality due to their promotion of photochemical ozone production, emission of particle pollution of both primary and secondary origin, and emission of toxic materials. These impacts are often the most immediate acting on populations and ecosystems and are a high priority for consideration when making decisions on fire management, i.e., when to plan prescribed burns and when to allow naturally-initiated fires to burn. The research needed to understand and manage these impacts is one of the more challenging aspects of wildfire research, as it involves understanding all of the smaller-scale processes detailed above: fire weather, emissions, and transport and transformation. This information must then be incorporated into models that can be used to make policy decisions on all timescales, from the immediate: e.g. fire management and health advisories, mid-term: air quality waiver, to the long- term: ecosystem and urban-wildland interface management. Meeting the stricter National Ambient Air Quality Standards (NAAQS) for ozone and other criteria pollutants will require better understanding and prediction of fire impacts (along with long-range transport of pollution from other parts of the world).

Night-time plume evolution, air quality impacts, and exposure have not been studied in detail previously. Due to lower temperatures at nighttime the combustion efficiency of fires is generally lower than during the daytime and as a result smoke does not get lifted as high at night. A common pattern for western wildfire smoke is to accumulate in valleys overnight and often fires only "blow up" in late afternoon/evening. Regions with concentrated smoke from these sudden low-altitude intensifications are often visible in satellite images close to the fires or hundreds of miles downwind of their source on following days. Nighttime dilution and chemistry will play a role in downwind impacts of these plumes. The smoke that accumulates in valleys leads to impacts and high exposure closer to the sources. These varying scenarios need investigation with a combination of mobile laboratory and small aircraft platforms.

Night flights may be particularly useful in constraining emission factors for highly reactive gases such as carbonyl compounds and nitrous acid (HONO) [Selimovic et al., 2018] that will undergo rapid photolysis during the day but should be longer lived at night. This rapid photolysis makes these compounds difficult to constrain from daytime observations but they are important to understanding of fire plume chemistry due to increased radical production. Therefore, night-time fire plume sampling may serve to provide robust emission factors for such compounds.

The regional impacts and nighttime emission and chemical transformation of fires are the main focus of science question #3.

Global Distributions and Impacts

The impacts of wildfires are mostly associated with short-term climate forcers; ozone and aerosols including BC, BrC and OC. Global climate impacts of BB result from its truly massive contributions to aerosol optical depth (AOD) over large areas. Regions such as the Arctic and the cloud decks of South America are uniquely sensitive to BB emissions and to secondary processes, such as cloud and ice nucleation that can magnify the radiative impact of the emissions. The research needed to advance our understanding of these impacts is broad on both spatial and temporal scales, and relates to a wide spectrum including BB inventories, satellite fire detection, chemical evolution of gaseous species, aerosol microphysical and optical properties, proper integration into models, interactions with warm, mixed phase, and ice clouds, and effects on the vertical structure of the thermal profile. For example, current fire emissions inventories undercount small fires and domestic BB because they are based on satellite fire detection schemes that have limited resolution and therefore regional airborne measurements of fire products are invaluable in assessing inventories. Improving the integration of wildfires and BB into global models requires more detailed emission estimates at finer spatial scales and better understanding of how to represent these emissions in relatively coarse-resolution treatment after significant chemical processing and dilution. These efforts will require combining new chemical details from emission measurements, new insights about chemical and physical transformation of smoke, supported by observations from the next generation of satellites.

The global impacts and climate relevant properties of fires are the main focus of science questions #4 and #5.

Objectives

Fire emissions in the US are approximately half from Northwestern wildfires and half from prescribed fires that burn mostly in the Southeast US. Wildfires burn slightly more fuel and therefore have overall larger emissions, but prescribed fires dominate the area burned and the number of fires. FIREX-AQ will investigate both wild and prescribed fires. Wildfires generally result in exposures with larger pollution concentrations over larger areas, and cause both local and regional air quality impacts. Their emissions are often transported thousands of miles and can impact large regions of the US at a time. Prescribed fires are usually smaller and less intense than most wildfires but occur more frequently and throughout the whole year. They are usually ignited during periods that minimize population expose and air quality impacts, but can cause regional backgrounds to increase, are generally in closer proximity to populations, and are responsible for a large fraction of the US PM2.5 emissions. To date agricultural fire outputs are still poorly represented in emission inventories. The overarching objective of FIREX-AQ is to provide measurements of trace gas and aerosol emissions for wildfires and prescribed fires in great detail, relate them to fuel and fire conditions at the point of emission, characterize the conditions relating to plume rise, follow plumes downwind to understand chemical transformation and air quality impacts, and assess the efficacy of satellite detections for estimating the emissions from sampled fires.

US fire emissions

Monthly area burned and PM2.5 emissions for wild (WF) and prescribed (RX) fires in the US. Wildfires consume more fuel, but prescribed fires account for the majority of the area burned in the US.

  1. Sampling of Wildfires with Multiple Coordinated Aircraft

  2. A primary objective of FIREX-AQ is to combine near and far-field observations to understand emissions, chemical evolution, transport and evaluate downwind impacts of wildfires in coordination with interagency partners. The airborne component of the FIREX-AQ effort, centered on the deployment of the NASA DC-8 with potentially two complementarily outfitted NOAA Twin Otters, will sample wildfire plumes from near the point of emission to downwind on a regional scale. These efforts will provide data to understand the influence of fire emissions on the atmospheric composition with continuity from initial emissions to evolved impacts far from the source. Wildfire plumes frequently affect many people directly by exposing population centers with large concentrations of pollutants, both close to the fires and potentially far downwind. Fire plumes affecting populated areas will be given priority in designing flight plans for sampling.

    Partners from the Joint Fire Science Program (JFSP) will use their knowledge of ground conditions for fuel and fire characterization to advise on the best targets for airborne fire plume sampling. The NASA DC-8 has the ability to explore an extremely wide range of emission age and will coordinate with the NOAA Twin Otter instrumented aircraft that are focused on narrower ranges of emission age with complimentary payloads. For example, a Twin Otter will sample individual fires throughout the day to understand the diurnal changes of fire emissions and fire plumes at night to investigate the nighttime chemical evolution of fire plumes. Further, Twin Otters will generally be able to obtain higher spatial resolution measurements and undertake more focused studies of rapidly evolving chemical evolution over shorter spatial scales than the DC-8 instruments.

  3. Sampling of Prescribed Fires to Build Statistics

  4. A second objective for FIREX-AQ is to exploit the range and endurance of the NASA DC- 8 to sample a large number of small mostly prescribed fires to build statistics on emission factors and fuels, plume rise, satellite detectability, and integrated impacts for these types of sources.

    Small fire activity will occur within the reach of the DC-8 every day during the deployment period. Thus, this objective will take priority when large wildfire activity is not occurring. Confidence that the DC-8 can adequately accomplish this objective comes from its demonstrated performance in sampling fifteen small agricultural fires during the recent SEAC4RS campaign. Given the modest amount of flight time dedicated to small fire sampling during SEAC4RS, it is expected that many more fires can be sampled during FIREX-AQ. This objective provides the best opportunity to build on the needed statistics for the variables described above and complements emission factor work of the FireLab study recently conducted by NOAA in advance of the joint field study in 2019. For best results, this objective requires liaison with state and local authorities to anticipate when and where to expect burning as well as to obtain ground-level data to the extent possible for understanding the fuel and conditions under which burning occurred. JFSP partners will be consulted for such advice, but funding for participation by an expert to assist in monitoring small fire activity and gathering information on ground conditions at sampled locations is also possible. The information gathered from small fires will also provide an opportunity to assess current satellite detection capabilities and reduce uncertainty in the contribution of small fires to total emissions.

For further information, download the FIREX-AQ White Paper PDF file