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1. Evaluation and intercomparison of wildfire smoke forecasts from multiple modeling systems for the 2019 Williams Flats fire

   https://doi.org/10.5194/acp-21-14427-2021  

   Ye, Xinxin ; Arab, Pargoal ; Ahmadov, Ravan ; James, Eric ; Grell, Georg A. ; Pierce, Bradley ; Kumar, Aditya ; Makar, Paul ; Chen, Jack ; Davignon, Didier ; et al ( January 2021 , Atmospheric Chemistry and Physics)

   Abstract. Wildfire smoke is one of the most significant concerns ofhuman and environmental health, associated with its substantial impacts onair quality, weather, and climate. However, biomass burning emissions andsmoke remain among the largest sources of uncertainties in air qualityforecasts. In this study, we evaluate the smoke emissions and plumeforecasts from 12 state-of-the-art air quality forecasting systemsduring the Williams Flats fire in Washington State, US, August 2019, whichwas intensively observed during the Fire Influence on Regional to GlobalEnvironments and Air Quality (FIREX-AQ) field campaign. Model forecasts withlead times within 1 d are intercompared under the same framework basedon observations from multiple platforms to reveal their performanceregarding fire emissions, aerosol optical depth (AOD), surface PM2.5,plume injection, and surface PM2.5 to AOD ratio. The comparison ofsmoke organic carbon (OC) emissions suggests a large range of daily totalsamong the models, with a factor of 20 to 50. Limited representations of thediurnal patterns and day-to-day variations of emissions highlight the needto incorporate new methodologies to predict the temporal evolution andreduce uncertainty of smoke emission estimates. The evaluation of smoke AOD(sAOD) forecasts suggests overall underpredictions in both the magnitude andsmoke plume area for nearly all models, although the high-resolution modelshave a better representation of the fine-scale structures of smoke plumes.Themore »models driven by fire radiativepower (FRP)-based fire emissions or assimilating satellite AODdata generally outperform the others. Additionally, limitations of thepersistence assumption used when predicting smoke emissions are revealed bysubstantial underpredictions of sAOD on 8 August 2019, mainly over thetransported smoke plumes, owing to the underestimated emissions on7 August. In contrast, the surface smoke PM2.5 (sPM2.5) forecastsshow both positive and negative overall biases for these models, with mostmembers presenting more considerable diurnal variations of sPM2.5.Overpredictions of sPM2.5 are found for the models driven by FRP-basedemissions during nighttime, suggesting the necessity to improve verticalemission allocation within and above the planetary boundary layer (PBL).Smoke injection heights are further evaluated using the NASA LangleyResearch Center's Differential Absorption High Spectral Resolution Lidar(DIAL-HSRL) data collected during the flight observations. As the firebecame stronger over 3–8 August, the plume height became deeper, with aday-to-day range of about 2–9 km a.g.l. However, narrower ranges arefound for all models, with a tendency of overpredicting the plume heights forthe shallower injection transects and underpredicting for the days showingdeeper injections. The misrepresented plume injection heights lead toinaccurate vertical plume allocations along the transects corresponding totransported smoke that is 1 d old. Discrepancies in model performance forsurface PM2.5 and AOD are further suggested by the evaluation of theirratio, which cannot be compensated for by solely adjusting the smoke emissionsbut are more attributable to model representations of plume injections,besides other possible factors including the evolution of PBL depths andaerosol optical property assumptions. By consolidating multiple forecastsystems, these results provide strategic insight on pathways to improvesmoke forecasts.« less
2. Simulating the forest fire plume dispersion, chemistry, and aerosol formation using SAM-ASP version 1.0

   https://doi.org/10.5194/gmd-13-4579-2020  

   Lonsdale, Chantelle R. ; Alvarado, Matthew J. ; Hodshire, Anna L. ; Ramnarine, Emily ; Pierce, Jeffrey R. ( January 2020 , Geoscientific Model Development)

   Abstract. Biomass burning is a major source of trace gases andaerosols that can ultimately impact health, air quality, and climate.Global and regional-scale three-dimensional Eulerian chemical transportmodels (CTMs) use estimates of the primary emissions from fires and canunphysically mix them across large-scale grid boxes, leading to incorrectestimates of the impact of biomass burning events. On the other hand,plume-scale process models allow for explicit simulation and examination ofthe chemical and physical transformations of trace gases and aerosols withinbiomass burning smoke plumes, and they may be used to developparameterizations of this aging process for coarser grid-scale models. Herewe describe the coupled SAM-ASP plume-scale process model, which consists ofcoupling the large-eddy simulation model, the System for AtmosphericModelling (SAM), with the detailed gas and aerosol chemistry model, theAerosol Simulation Program (ASP). We find that the SAM-ASP version 1.0 modelis able to correctly simulate the dilution of CO in a California chaparralsmoke plume, as well as the chemical loss of NOx, HONO, and NH3within the plume, the formation of PAN and O3, the loss of OA, and thechange in the size distribution of aerosols as compared to measurements andprevious single-box model results. The newly coupled model is able tocapture the cross-plume vertical and horizontal concentration gradientsmore »asthe fire plume evolves downwind of the emission source. The integration andevaluation of SAM-ASP version 1.0 presented here will support thedevelopment of parameterizations of near-source biomass burning chemistrythat can be used to more accurately simulate biomass burning chemical andphysical transformations of tracegases and aerosols within coarser grid-scale CTMs.« less
3. Wildfire Smoke Observations in the Western United States from the Airborne Wyoming Cloud Lidar during the BB-FLUX Project. Part I: Data Description and Methodology

   https://doi.org/10.1175/JTECH-D-21-0092.1  

   Deng, Min ; Wang, Zhien ; Volkamer, Rainer ; Snider, Jefferson R. ; Oolman, Larry ; Plummer, David M. ; Kille, Natalie ; Zarzana, Kyle J. ; Lee, Christopher F. ; Campos, Teresa ; et al ( May 2022 , Journal of Atmospheric and Oceanic Technology)

   During the summer of 2018, the upward-pointing Wyoming Cloud Lidar (WCL) was deployed on board the University of Wyoming King Air (UWKA) research aircraft for the Biomass Burning Flux Measurements of Trace Gases and Aerosols (BB-FLUX) field campaign. This paper describes the generation of calibrated attenuated backscatter coefficients and aerosol extinction coefficients from the WCL measurements. The retrieved aerosol extinction coefficients at the flight level strongly correlate (correlation coefficient, rr > 0.8) with in situ aerosol concentration and carbon monoxide (CO) concentration, providing a first-order estimate for converting WCL extinction coefficients into vertically resolved CO and aerosol concentration within wildfire smoke plumes. The integrated CO column concentrations from the WCL data in nonextinguished profiles also correlate (rr = 0.7) with column measurements by the University of Colorado Airborne Solar Occultation Flux instrument, indicating the validity of WCL-derived extinction coefficients. During BB-FLUX, the UWKA sampled smoke plumes from more than 20 wildfires during 35 flights over the western United States. Seventy percent of flight time was spent below 3 km above ground level (AGL) altitude, although the UWKA ascended up to 6 km AGL to sample the top of some deep smoke plumes. The upward-pointing WCL observed a nearly equalmore »amount of thin and dense smoke below 2 km and above 5 km due to the flight purpose of targeted fresh fire smoke. Between 2 and 5 km, where most of the wildfire smoke resided, the WCL observed slightly more thin smoke than dense smoke due to smoke spreading. Extinction coefficients in dense smoke were 2–10 times stronger, and dense smoke tended to have larger depolarization ratio, associated with irregular aerosol particles.

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4. Wildfire Smoke Observations in the Western United States from the Airborne Wyoming Cloud Lidar during the BB-FLUX Project. Part II: Vertical Structure and Plume Injection Height

   https://doi.org/10.1175/JTECH-D-21-0093.1  

   Deng, Min ; Volkamer, Rainer M. ; Wang, Zhien ; Snider, Jefferson R. ; Kille, Natalie ; Romero-Alvarez, Leidy J. ( May 2022 , Journal of Atmospheric and Oceanic Technology)

   The western U.S. wildfire smoke plumes observed by the upward-pointing Wyoming Cloud Lidar (WCL) during the Biomass Burning Fluxes of Trace Gases and Aerosols (BB-FLUX) project are investigated in a two-part paper. Part II here presents the reconstructed vertical structures of seven plumes from airborne WCL measurements. The vertical structures evident in the fire plume cross sections, supported by in situ measurements, showed that the fire plumes had distinct macrophysical and microphysical properties, which are closely related to the plume transport, fire emission intensity, and thermodynamic structure in the boundary layer. All plumes had an injection layer between 2.8 and 4.0 km above mean sea level, which is generally below the identified boundary layer top height. Plumes that transported upward out of the boundary layer, such as the Rabbit Foot and Pole Creek fires, formed a higher plume at around 5.5 km. The largest and highest Pole Creek fire plume was transported farthest and was sampled by University of Wyoming King Air aircraft at 170 km, or 2.3 h, downwind. It was associated with the warmest, driest, deepest boundary layer and the highest wind speed and turbulence. The Watson Creek fire plume intensified in the afternoon with stronger COmore »emission and larger smoke plume height than in the morning, indicating a fire diurnal cycle, but some fire plumes did not intensify in the afternoon. There were pockets of relatively large irregular aerosol particles at the tops of plumes from active fires. In less-active fire plumes, the WCL depolarization ratio and passive cavity aerosol spectrometer probe mass mean diameter maximized at a height that was low in the plume.

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5. Emission factors of long-lived volatile organic compounds from the 2019–2020 Australian wildfires during the COALA campaign

   https://doi.org/10.5194/acp-2021-742  

   Mouat, A. P. ; Paton-Walsh, C. ; Simmons, J. B. ; Ramirez-Gamboa, J. ; Griffith, D. W. ; Kaiser, J. ( January 2021 , Atmospheric chemistry and physics discussion)

   In 2019/2020, Australia experienced its largest wildfire season on record. Smoke covered hundreds of square kilometers across the southeastern coast and reached the site of the 2020 COALA (Characterizing Organics and Aerosol Loading over Australia) field campaign in New South Wales. Using a subset of nighttime observations made by a proton-transfer-reaction time-of-flight mass spectrometer (PTR-ToF-MS), we calculate emission ratios (ERs) and factors (EFs) for 21 volatile organic compounds (VOCs). We restrict our analysis to VOCs with sufficiently high lifetimes to be minimally impacted by oxidation over the ~8 h between when the smoke was emitted and when it arrived at the field site. We use oxidized VOC to VOC ratios to assess the total amount of radical oxidation: maleic anhydride/furan to assess OH oxidation, and (cis-2-butenediol + furanone)/furan to assess NO3 oxidation. We compare ERs calculated from the freshest portion of the plume to ERs calculated using the entire nighttime period. Finding good agreement between the two, we are able to extend our analysis to VOCs measured in more chemically aged portions of the plume. Our analysis provides ERs and EFs for 9 compounds not previously reported for temperate forests in Australia: acrolein, pentanones/methylbutanal, methyl propanoate, methyl methacrylate, propene, maleic anhydride, benzaldehyde, methylmore »guaiacol, and methylbenzoic acid. We compare our results with two studies in similar Australian biomes, and two studies focused on US temperate forests. We find mixed agreement for EFs presented from previous studies of Australian wildfires, and generally good agreement with studies focused on fires in the Western US. This suggests that comprehensive field measurements of biomass burning VOC emissions in other regions may be applicable to Australian temperate forests.« less