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Abstract. Fires emit a substantial amount of non-methane organic gases (NMOGs), theatmospheric oxidation of which can contribute to ozone and secondaryparticulate matter formation. However, the abundance and reactivity of thesefire NMOGs are uncertain and historically not well constrained. In thiswork, we expand the representation of fire NMOGs in a global chemicaltransport model, GEOS-Chem. We update emission factors to Andreae (2019) andthe chemical mechanism to include recent aromatic and ethene and ethyne modelimprovements(Bateset al., 2021; Kwon et al., 2021). We expand the representation of NMOGs byadding lumped furans to the model (including their fire emission andoxidation chemistry) and by adding fire emissions of nine species alreadyincluded in the model, prioritized for their reactivity using data from the Fire Influence on Regional to Global Environments (FIREX) laboratory studies. Based on quantified emissions factors, we estimatethat our improved representation captures 72 % of emitted, identified NMOGcarbon mass and 49 % of OH reactivity from savanna and temperate forestfires, a substantial increase from the standard model (49 % of mass,28 % of OH reactivity). We evaluate fire NMOGs in our model withobservations from the Amazon Tall Tower Observatory (ATTO) in Brazil, Fire Influence on Regional to Global Environments and Air Quality (FIREX-AQ) and DC3 in the US, andmore »Arctic Research of the Composition of theTroposphere from Aircraft and Satellites (ARCTAS) in boreal Canada. We show that NMOGs,including furan, are well simulated in the eastern US with someunderestimates in the western US and that adding fire emissions improves ourability to simulate ethene in boreal Canada. We estimate that fires provide15 % of annual mean simulated surface OH reactivity globally, as well as morethan 75 % over fire source regions. Over continental regions about half ofthis simulated fire reactivity comes from NMOG species. We find that furansand ethene are important globally for reactivity, while phenol is moreimportant at a local level in the boreal regions. This is the first globalestimate of the impact of fire on atmospheric reactivity.« less

Abstract. The evolution of organic aerosol (OA) and aerosol sizedistributions within smoke plumes is uncertain due to the variability inrates of coagulation and OA condensation/evaporation between different smokeplumes and at different locations within a single plume. We use aircraftdata from the FIREX-AQ campaign to evaluate differences in evolving aerosolsize distributions, OA, and oxygen to carbon ratios (O:C) between and withinsmoke plumes during the first several hours of aging as a function of smokeconcentration. The observations show that the median particle diameterincreases faster in smoke of a higher initial OA concentration (>1000 µg m−3), with diameter growth of over 100 nm in 8 h – despite generally having a net decrease in OA enhancementratios – than smoke of a lower initial OA concentration (<100 µg m−3), which had net increases in OA. Observations of OA and O:Csuggest that evaporation and/or secondary OA formation was greater in lessconcentrated smoke prior to the first measurement (5–57 min afteremission). We simulate the size changes due to coagulation and dilution andadjust for OA condensation/evaporation based on the observed changes in OA.We found that coagulation explains the majority of the diameter growth, withOA evaporation/condensation having a relatively minor impact. We found thatmixing between the core and edges of the plume generally occurred ontimescalesmore »of hours, slow enough to maintain differences in aging betweencore and edge but too fast to ignore the role of mixing for most of our cases.« less

Abstract. Fires emit sufficient sulfur to affect local and regional airquality and climate. This study analyzes SO2 emission factors andvariability in smoke plumes from US wildfires and agricultural fires, as well as theirrelationship to sulfate and hydroxymethanesulfonate (HMS) formation.Observed SO2 emission factors for various fuel types show goodagreement with the latest reviews of biomass burning emission factors,producing an emission factor range of 0.47–1.2 g SO2 kg−1 C.These emission factors vary with geographic location in a way that suggeststhat deposition of coal burning emissions and application ofsulfur-containing fertilizers likely play a role in the larger observedvalues, which are primarily associated with agricultural burning. A 0-D boxmodel generally reproduces the observed trends of SO2 and total sulfate(inorganic + organic) in aging wildfire plumes. In many cases, modeled HMSis consistent with the observed organosulfur concentrations. However, acomparison of observed organosulfur and modeled HMS suggests that multipleorganosulfur compounds are likely responsible for the observations but thatthe chemistry of these compounds yields similar production and loss rates asthat of HMS, resulting in good agreement with the modeled results. Weprovide suggestions for constraining the organosulfur compounds observedduring these flights, and we show that the chemistry of HMS can alloworganosulfur to act as an S(IV) reservoir under conditions of pH > 6 andmore »liquid water content>10−7 g sm−3. This canfacilitate long-range transport of sulfur emissions, resulting in increasedSO2 and eventually sulfate in transported smoke.« less

Oceans emit large quantities of dimethyl sulfide (DMS) to the marine atmosphere. The oxidation of DMS leads to the formation and growth of cloud condensation nuclei (CCN) with consequent effects on Earth’s radiation balance and climate. The quantitative assessment of the impact of DMS emissions on CCN concentrations necessitates a detailed description of the oxidation of DMS in the presence of existing aerosol particles and clouds. In the unpolluted marine atmosphere, DMS is efficiently oxidized to hydroperoxymethyl thioformate (HPMTF), a stable intermediate in the chemical trajectory toward sulfur dioxide (SO 2 ) and ultimately sulfate aerosol. Using direct airborne flux measurements, we demonstrate that the irreversible loss of HPMTF to clouds in the marine boundary layer determines the HPMTF lifetime ( τ HPMTF < 2 h) and terminates DMS oxidation to SO 2 . When accounting for HPMTF cloud loss in a global chemical transport model, we show that SO 2 production from DMS is reduced by 35% globally and near-surface (0 to 3 km) SO 2 concentrations over the ocean are lowered by 24%. This large, previously unconsidered loss process for volatile sulfur accelerates the timescale for the conversion of DMS to sulfate while limiting new particle formation inmore »the marine atmosphere and changing the dynamics of aerosol growth. This loss process potentially reduces the spatial scale over which DMS emissions contribute to aerosol production and growth and weakens the link between DMS emission and marine CCN production with subsequent implications for cloud formation, radiative forcing, and climate.« less

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

Dimethyl sulfide (DMS), emitted from the oceans, is the most abundant biological source of sulfur to the marine atmosphere. Atmospheric DMS is oxidized to condensable products that form secondary aerosols that affect Earth’s radiative balance by scattering solar radiation and serving as cloud condensation nuclei. We report the atmospheric discovery of a previously unquantified DMS oxidation product, hydroperoxymethyl thioformate (HPMTF, HOOCH 2 SCHO), identified through global-scale airborne observations that demonstrate it to be a major reservoir of marine sulfur. Observationally constrained model results show that more than 30% of oceanic DMS emitted to the atmosphere forms HPMTF. Coincident particle measurements suggest a strong link between HPMTF concentration and new particle formation and growth. Analyses of these observations show that HPMTF chemistry must be included in atmospheric models to improve representation of key linkages between the biogeochemistry of the ocean, marine aerosol formation and growth, and their combined effects on climate.