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1. Biomass burning nitrogen dioxide emissions derived from space with TROPOMI: methodology and validation

   https://doi.org/10.5194/amt-14-7929-2021  

   Griffin, Debora ; McLinden, Chris A. ; Dammers, Enrico ; Adams, Cristen ; Stockwell, Chelsea E. ; Warneke, Carsten ; Bourgeois, Ilann ; Peischl, Jeff ; Ryerson, Thomas B. ; Zarzana, Kyle J. ; et al ( January 2021 , Atmospheric Measurement Techniques)

   Abstract. Smoke from wildfires is a significant source of air pollution, which can adversely impact air quality and ecosystems downwind. With the recently increasing intensity and severity of wildfires, the threat to air quality is expected to increase. Satellite-derived biomass burning emissions can fill in gaps in the absence of aircraft or ground-based measurement campaigns and can help improve the online calculation of biomass burning emissions as well as the biomass burning emissions inventories that feed air quality models. This study focuses on satellite-derived NOx emissions using the high-spatial-resolution TROPOspheric Monitoring Instrument (TROPOMI) NO2 dataset. Advancements and improvements to the satellite-based determination of forest fire NOx emissions are discussed, including information on plume height and effects of aerosol scattering and absorption on the satellite-retrieved vertical column densities. Two common top-down emission estimation methods, (1) an exponentially modified Gaussian (EMG) and (2) a flux method, are applied to synthetic data to determine the accuracy and the sensitivity to different parameters, including wind fields, satellite sampling, noise, lifetime, and plume spread. These tests show that emissions can be accurately estimated from single TROPOMI overpasses.The effect of smoke aerosols on TROPOMI NO2 columns (via air mass factors, AMFs) is estimated, and these satellitemore »columns and emission estimates are compared to aircraft observations from four different aircraft campaigns measuring biomass burning plumes in 2018 and 2019 in North America. Our results indicate that applying an explicit aerosol correction to the TROPOMI NO2 columns improves the agreement with the aircraft observations (by about 10 %–25 %). The aircraft- and satellite-derived emissions are in good agreement within the uncertainties. Both top-down emissions methods work well; however, the EMG method seems to output more consistent results and has better agreement with the aircraft-derived emissions. Assuming a Gaussian plume shape for various biomass burning plumes, we estimate an average NOx e-folding time of 2 ±1 h from TROPOMI observations. Based on chemistry transport model simulations and aircraft observations, the net emissions of NOx are 1.3 to 1.5 times greater than the satellite-derived NO2 emissions. A correction factor of 1.3 to 1.5 should thus be used to infer net NOx emissions from the satellite retrievals of NO2.« less
2. Dilution and Photooxidation Driven Processes Explain the Evolution of Organic Aerosol in Wildfire Plumes

   https://doi.org/10.1039/D1EA00082A  

   Akherati, Ali ; He, Yicong ; Garofalo, Lauren A ; Hodshire, Anna L ; Farmer, Delphine ; Kreidenweis, Sonia M ; Permar, Wade ; Hu, Lu ; Fischer, Emily V ; Jen, Coty N ; et al ( June 2022 , Environmental Science: Atmospheres)

   Wildfires are an important atmospheric source of primary organic aerosol (POA) and precursors for secondary organic aerosol (SOA) at regional and global scales. However, there are large uncertainties surrounding the emissions and physicochemical processes that control the transformation, evolution, and properties of POA and SOA in large wildfire plumes. We develop a plume version of a kinetic model to simulate the dilution, oxidation chemistry, thermodynamic properties, and microphysics of organic aerosol (OA) in wildfire smoke. The model is applied to study the in-plume OA in four large wildfire smoke plumes intercepted during an aircraft-based field campaign in summer 2018 in the western United States. Based on estimates of dilution and oxidant concentrations before the aircraft first intercepted the plumes, we simulate the OA evolution from very close to the fire to several hours downwind. Our model results and sensitivity simulations suggest that dilution-driven evaporation of POA and simultaneous photochemical production of SOA are likely to explain the observed evolution in OA mass with physical age. The model, however, substantially underestimates the change in the oxygen-to-carbon ratio of the OA compared to measurements. In addition, we show that the rapid chemical transformation within the first hour after emission is driven bymore »higher-than-ambient OH concentrations (3×10 6 -10 7 molecules cm -3 ) and the slower evolution over the next several hours is a result of lower-than-ambient OH concentrations (<10 6 molecules cm -3 ) and depleted SOA precursors. Model predictions indicate that the OA measured several hours downwind of the fire is still dominated by POA but with an SOA fraction that varies between 30% and 56% of the total OA. Semivolatile, heterocyclic, and oxygenated aromatic compounds, in that order, were found to contribute substantially (>90%) to SOA formation. Future work needs to focus on better understanding the dynamic evolution closer to the fire and resolving the rapid change in the oxidation state of OA with physical age.« less
3. 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
4. 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
5. Atmospheric evolution of emissions from a boreal forest fire: the formation of highly functionalized oxygen-, nitrogen-, and sulfur-containing organic compounds

   https://doi.org/10.5194/acp-21-255-2021  

   Ditto, Jenna C. ; He, Megan ; Hass-Mitchell, Tori N. ; Moussa, Samar G. ; Hayden, Katherine ; Li, Shao-Meng ; Liggio, John ; Leithead, Amy ; Lee, Patrick ; Wheeler, Michael J. ; et al ( January 2021 , Atmospheric Chemistry and Physics)

   Abstract. Forest fires are major contributors of reactive gas- and particle-phaseorganic compounds to the atmosphere. We used offline high-resolution tandemmass spectrometry to perform a molecular-level speciation of gas- andparticle-phase compounds sampled via aircraft from an evolving boreal forestfire smoke plume in Saskatchewan, Canada. We observed diversemultifunctional compounds containing oxygen, nitrogen, and sulfur (CHONS),whose structures, formation, and impacts are understudied. Thedilution-corrected absolute ion abundance of particle-phase CHONS compoundsincreased with plume age by a factor of 6.4 over the first 4 h ofdownwind transport, and their relative contribution to the observedfunctionalized organic aerosol (OA) mixture increased from 19 % to 40 %.The dilution-corrected absolute ion abundance of particle-phase compoundswith sulfide functional groups increased by a factor of 13 with plume age,and their relative contribution to observed OA increased from 4 % to40 %. Sulfides were present in up to 75 % of CHONS compounds and theincreases in sulfides were accompanied by increases in ring-bound nitrogen;both increased together with CHONS prevalence. A complex mixture ofintermediate- and semi-volatile gas-phase organic sulfur species wasobserved in emissions from the fire and depleted downwind, representingpotential precursors to particle-phase CHONS compounds. These resultsdemonstrate CHONS formation from nitrogen- and oxygen-containing biomass burningemissions in the presence of reduced sulfur species. In addition, theyhighlight chemical pathways thatmore »may also be relevant in situations withelevated emissions of nitrogen- and sulfur-containing organic compounds fromresidential biomass burning and fossil fuel use (e.g., coal), respectively.« less