Modified Combustion Efficiency Research Articles

Smoldering Ignition and Transition to Flaming Combustion of Pine Needle Fuel Beds: Effects of Bulk Density and Heat Supply

The smoldering of pine needle fuel beds (PNBs) has been a common subject of research because of its importance in initiating the rekindling of forest floor fires. Experimental studies of the coupling effects of the bulk density and external heat supply on smoldering in PNBs have been scarce up to now. In this study, laboratory smoldering experiments were conducted to study the coupling effects of bulk density (30–55 kg m−3) and heat supply (ignition-off temperature Toff = 190 °C and 230 °C). Different ignition modes were observed under the same conditions, including non- ignition (NI), flaming ignition (FI), and the smoldering-to-flaming (StF) transition. The results in this study showed that the bulk density had distinct effects on different ignition modes: the increase in the bulk density facilitated the StF transition but impeded the FI. The coupling effects between the bulk density and heat supply became more intricate, especially at lower bulk densities and at a reduced heat supply. Additionally, a simple energy balance equation was established to explain the coupling effects of bulk density and heat supply on ignition behavior. The critical mass loss rate (MLR) for the StF transition ranged from 0.01 g s−1 to 0.03 g s−1, while the critical MLR for FI was 0.035 g s−1. The modified combustion efficiency (MCE) index for the StF transition decreased from approximately 79.6% to 70.1% as the density increased from 30 kg m−3 to 55 kg m−3. In contrast, the MCE for FI was approximately 90% across all the bulk densities. The StF transition delay time increased from 50 s at 30 kg m−3 to 1296 s at 55 kg m−3 when Toff = 230 °C. Further reduction in heat supply led to an increase in the delay time for the StF transition by diminishing the intensity of smoldering combustion. This work advances the fundamental understanding of how heat supply and bulk density impact smoldering ignition modes, ultimately aiding in the development of wildfire prevention strategies.

GAMBUT field measurement of emissions from a tropical peatland fire experiment: from ignition to spread to suppression

Background Accurate quantification of emissions from peatland wildfire is crucial for understanding their feedback to the atmospheric and Earth system. However, current knowledge on this topic is limited to a few laboratory and field studies, which report substantial variability in terms of the fire emission factors (EFs). Aims We aim to understand how emissions vary across the life cycle of a peatland fire. Methods In August/September 2018, we conducted the largest and longest to-date field-scale experimental burn on a tropical peatland in Sumatra, Indonesia. Field measurements of gas emissions from the fire experiment were conducted using an open-path Fourier transform infrared spectroscopy to retrieve mole fractions of 11 gas species. Key results For the first time, we calculated and reported EFs from 40 measurement sessions conducted over 2 weeks of burning, encompassing different fire stages (e.g. ignition, smouldering spread, and suppression) and weather events (e.g. rainfall). Our findings provide field evidence to indicate that EFs vary significantly among fire stages and weather events. We also observed that the heterogeneous physicochemical properties of peatland site (e.g. moisture content) influenced the EFs. We also found that modified combustion efficiency was highly sensitive to complex field variables and could introduce large uncertainties when determining the regimes of a peat fire. Conclusions and implications Further studies to investigate peat fire emissions are needed, and more comprehensive mapping of peatland heterogeneity and land use for emissions inventories, accounting for spatial and temporal variability in EFs since the initiation of a fire event is required.

A Numerical and Experimental Performance Assessments of an Improved Natural Draft Biomass Cook Stove

ABSTRACT This article analyses the performance of an efficiently designed biomass cook stove using standard performance parameters. The investigation was first conducted using mathematical modeling developed in the ANSYS Fluent software. The results of primary air and the temperature profiles inside the combustion chamber were found through simulation. It revealed that the flue gas left the combustion chamber with an average velocity of 1.7 m/s. The average pot bottom and fuel bed temperatures were 650 K and 1100 K, respectively. A copper coil was wrapped around the combustion chamber wall to recover its waste heat. The recovered waste heat was utilized to warm the water flowing through the copper coil. The heated water could be used for other domestic applications. The fabricated design of the improved stove was experimented with water boiling test. The maximum thermal efficiency achieved was 42% with a firepower of 8.25 kW, after incorporating the waste heat recovery system, corresponding to 7.5 L test. The overall efficiency, which is the product of the modified combustion efficiency and the maximum thermal efficiency, was found to be 41.50%. The performance was found to be significantly better than that of a commercial biomass cook stove. The developed model was also evaluated for indoor CO, CO2 and PM emissions. The highest levels of CO2 and CO were 940 ppm and 23 ppm. The average amount of PM1, PM2.5 and PM10 found out to be 18 µg/m3, 20 µg/m3 and 35 µg/m3 respectively.

Comparison of water-soluble and water-insoluble organic compositions attributing to different light absorption efficiency between residential coal and biomass burning emissions

Abstract. There are growing concerns about the climate impacts of absorbing organic carbon (also known as brown carbon, BrC) in the environment, yet its chemical composition and association with the light absorption capabilities remain poorly understood. This study characterized water-soluble and water-insoluble organic carbon (WSOC and WIOC) from residential solid fuel combustion at the molecular level and evaluated their quantitative relationship with mass absorption efficiency (MAE). The MAE values at λ = 365 nm from biomass burning were significantly higher than those from coal combustion (p < 0.05). Thousands of peaks were identified in the m/z range of 150–800, with the most intense ion peaks occurring between m/z 200–500 for WSOC and m/z 600–800 for WIOC, respectively. The CHO group predominated in the WSOC extract from biomass burning emissions, while sulfur-containing compounds (SOCs) including CHOS and CHONS were more intense in the WIOC extract, particularly from coal emissions. Emissions of the CHON group were positively correlated with the fuel nitrogen content (r = 0.936; p < 0.05), explaining their higher abundance in coal emissions compared to biomass. The SOC emissions were more predominant during flaming phases, as indicated by a positive correlation with modified combustion efficiency (MCE) (r = 0.750; p < 0.05). The unique formulas of coal combustion aerosols were in the lower H/C and O/C regions, with higher unsaturated compounds in the van Krevelen (VK) diagram. In the WIOC extract, coal combustion emissions contained significantly higher fractions of condensed aromatics (32 %–59 %) compared to only 4.3 %–9.7 % in biomass burning emissions. In contrast, the CHOS group in biomass burning emissions was characterized by larger condensed aromatic compound fractions than those in coal combustion. Moreover, the CHOS aromatic compound fractions were positively correlated with MAE values in both WSOC (r = 0.714; p < 0.05) and WIOC extracts (r = 0.929; p < 0.001), suggesting that these compounds significantly contributed to MAE variabilities across different fuels.

Design Optimization of an Improved Mud Cookstove Using Computational Fluid Dynamics

ABSTRACT The present study focuses on optimizing the design and performance of natural draft mud-based cookstove (MBC) using the CFD tool ANSYS Fluent. The study simulates the performance of the MBC over different levels of three key factors, i.e. grate height, pot gap, and secondary hole diameter, against the targeted response parameters, which include average flame temperature, thermal efficiency, and combustion efficiency. Two-dimensional (2D) simulations of a real-world prototype of MBC were performed using ANSYS Fluent, solving governing equations for mass, momentum, energy, and species transport throughout the computational domain and employing a pseudo-transient accelerated solver approach to achieve a steady state. Grid independence was established to ensure reliable simulation results. It was observed that an optimized response was obtained at the grate height of 30 mm, pot gap of 30 mm, and secondary hole diameter of 8 mm, wherein the average flame temperature of 887 K, thermal efficiency of 27.64%, and a modified combustion efficiency of 98.97% was observed. The achieved thermal efficiency complied with the BIS IS 13,152:2013 standard for natural draft cookstoves, classifying it as a Tier 2 cookstove according to the performance targets outlined in ISO/TR 19,867-3:2018. The combustion efficiency exceeded 0.97, indicating pure flaming combustion. A full-scale field prototype was fabricated and successfully validated through laboratory and field experiments.

Parameterizations of US wildfire and prescribed fire emission ratios and emission factors based on FIREX-AQ aircraft measurements

Abstract. Extensive airborne measurements of non-methane organic gases (NMOGs), methane, nitrogen oxides, reduced nitrogen species, and aerosol emissions from US wild and prescribed fires were conducted during the 2019 NOAA/NASA Fire Influence on Regional to Global Environments and Air Quality campaign (FIREX-AQ). Here, we report the atmospheric enhancement ratios (ERs) and inferred emission factors (EFs) for compounds measured on board the NASA DC-8 research aircraft for nine wildfires and one prescribed fire, which encompass a range of vegetation types. We use photochemical proxies to identify young smoke and reduce the effects of chemical degradation on our emissions calculations. ERs and EFs calculated from FIREX-AQ observations agree within a factor of 2, with values reported from previous laboratory and field studies for more than 80 % of the carbon- and nitrogen-containing species. Wildfire emissions are parameterized based on correlations of the sum of NMOGs with reactive nitrogen oxides (NOy) to modified combustion efficiency (MCE) as well as other chemical signatures indicative of flaming/smoldering combustion, including carbon monoxide (CO), nitrogen dioxide (NO2), and black carbon aerosol. The sum of primary NMOG EFs correlates to MCE with an R2 of 0.68 and a slope of −296 ± 51 g kg−1, consistent with previous studies. The sum of the NMOG mixing ratios correlates well with CO with an R2 of 0.98 and a slope of 137 ± 4 ppbv of NMOGs per parts per million by volume (ppmv) of CO, demonstrating that primary NMOG emissions can be estimated from CO. Individual nitrogen-containing species correlate better with NO2, NOy, and black carbon than with CO. More than half of the NOy in fresh plumes is NO2 with an R2 of 0.95 and a ratio of NO2 to NOy of 0.55 ± 0.05 ppbv ppbv−1, highlighting that fast photochemistry had already occurred in the sampled fire plumes. The ratio of NOy to the sum of NMOGs follows trends observed in laboratory experiments and increases exponentially with MCE, due to increased emission of key nitrogen species and reduced emission of NMOGs at higher MCE during flaming combustion. These parameterizations will provide more accurate boundary conditions for modeling and satellite studies of fire plume chemistry and evolution to predict the downwind formation of secondary pollutants, including ozone and secondary organic aerosol.

Emission Factors From Wildfires in the Western US: An Investigation of Burning State, Ground Versus Air, and Diurnal Dependencies During the FIREX‐AQ 2019 Campaign

AbstractEmission factors (EFs) are crucial in understanding the effects of wildfire emissions on air quality. We examined the variability of EFs of three wildfires (Nethker, Castle, and 204 Cow) during the 2019 Western US wildfire season using the Aerodyne Mobile Laboratory (AML) and compared them to previous studies. The AML sampling captured the high degree of variability present in wildfires, and we report results for a range of combustion conditions that is more extensive than previous field and laboratory studies. For instance, we captured emissions from freshly started flaming fuels and we report rare EF measurements at very high modified combustion efficiencies (MCEs); MCEs >0.9. Differences in emissions between AML‐observed wildfires were attributed to burning state/MCE rather than fuel type. A comparison of EFs versus MCE was made and linear fits were compared to previous observations to reveal important differences that incorporate these high MCEs. For some species, there remains an EF dependence on MCE at these high values, while others reach a minimum value and exhibit either no or a weak dependence above it. EF differences were found for many of the studied compounds when comparing ground‐based and airborne observations, with generally greater airborne EFs possibly due to photochemical oxidation. The largest differences were from monoterpenes and acetaldehyde. Comparisons were made between AML‐observed wildfires, aircraft observations, and the values in literature for EFs and emission ratios, with mixed agreement due to the high degree of variability caused by differences in MCE. Differences in MCE drove the diurnal EF differences.

Experimental study of smouldering combustion and transient emissions from forest duff with dual layers

Smouldering combustion in wildfires is responsible for large amounts of carbon emissions and regional haze episodes. In the wildland, there are dual or multiple layers of forest duff with varying particle sizes, forming a non-homogeneous fuel system. However, understanding of the effects of the fuel heterogeneity on smouldering combustion is limited. In this study, we experimentally investigated the smouldering behaviour and gas emissions of forest duff consisting of dual layers with particle diameters ranging in three sizes (1 mm ≤ d1 < 2 mm, 0.425 mm ≤ d2 < 1 mm, and d3 < 0.425 mm). A comprehensive smouldering combustion rig was designed and built to simultaneously measure the mass loss, temperature profile, time-resolved gas concentration for 20 species, and visual and infrared imaging for 6 dual-layered duff samples (d1 - d1, d1 - d2, d1 - d3, d2 - d2, d2 - d3, d3 - d3) under a controlled environment. A terrace smouldering front structure was observed for dual-layered fuel beds with coarse duff particle (d1 and d2) staying in the upper layer (50% of the volume of an open-top reactor with dimensions of 20 × 20 × 10 cm), while a surface cracking phenomenon was observed for sample consisting of fine duff particles d3 - d3. Increases in the particle size at the lower-layer with a fixed d1 upper-layer particles were found to have a greater impact on the oxygen supply, leading to a higher lateral spread rate, a higher modified combustion efficiency (MCE), and a lower fire-averaged CO/CO2. In contrast, changes in the upper-layer particle size with a fixed d3 lower-layer particles have a greater impact on the heat transfer. These findings advance the scientific understanding of smouldering fires spreading in dual forest fuel system, ultimately contributing to the development of wildfire mitigating technologies.

Identification and Parametrization of Key Factors Affecting Levoglucosan Emission During Solid Fuel Burning.

Levoglucosan (LG) is a pyrolysis product of cellulose and hemicellulose at low combustion temperatures. However, LG release cannot be determined only by considering the contents of cellulose and hemicellulose exclusively due to the complexity of combustion processes and the physical-chemical properties of the fuel. This study detected the emission factors (EFs) of LG from 22 different solid fuel samples (including coal and biomass) by considering 18 different fuel properties and five combustion parameters. The average LGEFs during solid fuel burning varied in a range of 0.03-136 mg kg-1, with a magnitude difference of 1-4 orders. While the variations in cellulose (59.5-368 mg g-1) and hemicellulose (73.5-165 mg g-1) contents of fuel samples were only one- to 6-fold. A short combustion duration (<150 min) and a medium combustion temperature (200-400 °C) influenced by volatile and ash contents are crucial for the generation and accumulation of LG. A random forest coupled with the Akaike information criterion stepwise regression model successfully explained 96% of the total LG emission variation using three variables (ash content, cellulose content, and modified combustion efficiency). The ash content promoted coke formation and LG chain cracking by increasing the pyrolysis temperature and is considered the most important factor. The alkali metal in ash can reduce the energy barrier of intramolecular ring contraction reactions and inhibit the dehydration reactions, which led to additional heat being utilized by the competitive pathways of LG formation. This study provided a method to address the parametrization and release mechanisms of combustion source emissions.

Laboratory benchmark of low-cost portable gas and particle analysers at the source of smouldering wildfires

Background Smouldering wildfires emit large amounts of carbon, toxic gases and particulate matter (PM), posing health and environmental hazards. It is challenging to conduct field measurements on wildfire emissions, and available instruments are limited by high cost and low mobility. Aim Here, we contribute to solving this challenge by studying three commercial low-cost and portable air quality analysers (KANE101, SDS011 and FLOW) and comparing them with research-grade instruments (FTIR, PM Cascade Impactor and DustTrak). Methods A series of laboratory experiments on peat smouldering were conducted including the stages of ignition, spread and burnout to provide conditions of emission measurements near the source. Key results The gas analyser KANE101 accurately measured CO2 and allowed calculation of modified combustion efficiency (MCE). The FLOW air pollution sensor was found unsuitable for PM measurements near fire sources because of its narrow range. FLOW captured the variation of volatile organic compounds (VOCs), but measurements did not correlate well with NO2 measurements. The SDS011 PM sensor responded well in measuring PM10 in this study. Conclusions KANE101 and SDS011 can be used in the field after calibration to measure CO2/CO and PM. Implications This work provides a better understanding of how low-cost and portable emission sensors can be of use for wildfire measurements in the field.

Field based performance evaluation of optimized improved biomass mud cookstoves in rural India

The present work assesses the real-world performance of novel improved mud-based cookstoves (MBC) - Pavak 1 (P1) and Pavak 2 (P2) in a remote community in Khandwa, Madhya Pradesh, India. These MBC's were designed using multi-parameter optimization based on extensive laboratory testing. These MBCs are affordable and durable, and can be locally manufactured without compromising cooking quality, taste, or convenience while still meeting the Indian cookstove performance standards (BIS IS 13152 (Part 1): 2013) for emissions and efficiency. MBC's performance was compared to traditional stoves (TS) in accordance with the ISO 19869:2019 cookstove field testing protocol. 45 cooking sessions were captured (22 P1; 13 P2; 10 TS). Fuel-based emission factors (EF) for PM2.5 and CO were estimated using the carbon balance method. Results indicate reductions in PM2.5 (56% for P1 and 46% for P2) and CO emissions (15% for P1 and 0.85% for P2) compared to TS. Analysis of real-time modified combustion efficiencies showed that MBCs exhibited prolonged periods in pure flaming conditions compared to TS. A user perception survey was conducted in the intervention households to understand community acceptability. Our results demonstrate the potential for increased adoption rates, emphasizing the importance of information, education, and communication (IEC) programs to maximize health and climate benefits.

Impact of peri-urban forest fires on air quality and aerosol optical and chemical properties: The case of the August 2021 wildfires in Athens, Greece

Wildfires occurring near urban areas are known to have exceedingly detrimental impacts on the environment, air quality, economy and human health. In this framework, this study examines the effects of peri-urban forest fires on atmospheric chemical composition, and aerosol physical-optical properties in Athens, Greece, during August 2021. Satellite imagery and air mass trajectories showed advection of intense smoke plumes over Athens from three forest fires persisting for 10 days in the greater Athens area and in Central Greece (Euboea). During August 1–20, 2021, daily PM2.5 concentrations ranged from 8.9 to 78.7 μg m−3, and were associated with high OC levels (2.3–27.8 μg m−3), while BC and BCbb concentrations on smoke-impacted days were 2.6 μg m−3 and 1.0 μg m−3, respectively (2–3 times higher than August mean levels). During the peak of biomass burning (BB) smoke transport over Athens, daily-average scattering and absorption coefficients at short wavelengths maximized at 313 Mm−1 and 171 Mm−1, respectively. There was also a large impact of ambient BrC (brown carbon) absorption (60 Mm−1), while the OC/EC ratio exhibited characteristically low values (3–4), linked to flaming combustion (modified combustion efficiency of 0.97–0.99). The absorption Ångström exponent (1.38) and single scattering albedo (0.74) indicated highly absorbing BB aerosol, deviating from the normal summer patterns. BB-tracers like nssK+ displayed strong correlations with OC, EC and BC concentrations, as well as with scattering and absorption coefficients. However, forest fires drastically modified the levels of additional chemical species, with enhancements observed for Ca2+, NO3−, Cl−, and for organic aerosol (OA) components such as BBOA and less-oxidized oxygenated OA (LO-OOA). Since under climate change conditions, the Mediterranean is anticipated to experience a dramatic rise in the frequency and intensity of wildfires, the results highlight the necessity for prevention and mitigation policies to safeguard urban air quality.

Emission Factors for Crop Residue and Prescribed Fires in the Eastern US During FIREX‐AQ

AbstractAgricultural and prescribed burning activities emit large amounts of trace gases and aerosols on regional to global scales. We present a compilation of emission factors (EFs) and emission ratios from the eastern portion of the Fire Influence on Regional to Global Environments and Air Quality (FIREX‐AQ) campaign in 2019 in the United States, which sampled burning of crop residues and other prescribed fire fuels. FIREX‐AQ provided comprehensive chemical characterization of 53 crop residue and 22 prescribed fires. Crop residues burned at different modified combustion efficiencies (MCE), with corn residue burning at higher MCE than other fuel types. Prescribed fires burned at lower MCE (&lt;0.90) which is typical, while grasslands burned at lower MCE (0.90) than normally observed due to moist, green, growing season fuels. Most non‐methane volatile organic compounds (NMVOCs) were significantly anticorrelated with MCE except for ethanol and NMVOCs that were measured with less certainty. We identified 23 species where crop residue fires differed by more than 50% from prescribed fires at the same MCE. Crop residue EFs were greater for species related to agricultural chemical use and fuel composition as well as oxygenated NMVOCs possibly due to the presence of metals such as potassium. Prescribed EFs were greater for monoterpenes (5×). FIREX‐AQ crop residue average EFs generally agreed with the previous agricultural fire study in the US but had large disagreements with global compilations. FIREX‐AQ observations show the importance of regionally‐specific and fuel‐specific EFs as first steps to reduce uncertainty in modeling the air quality impacts of fire emissions.

Characterization of gas and particle emissions from open burning of household solid waste from South Africa

Abstract. Open burning of household and municipal solid waste is a frequent practice in many developing countries. Due to limited resources for collection and proper disposal, solid waste is often disposed of in neighborhoods and open-burned in piles to reduce odors and create space for incoming waste. Emissions from these ground-level and low-temperature burns cause air pollution, leading to adverse health effects among community residents. In this study, laboratory combustion experiments were conducted to characterize gas and particle emissions from 10 waste categories representative of those burned in South Africa: paper, leather/rubber, textiles, plastic bottles, plastic bags, vegetation (with three different moisture content levels), food discards, and combined materials. Carbon dioxide (CO2) and carbon monoxide (CO) were measured in real time to calculate modified combustion efficiencies (MCEs). MCE is used along with video observations to determine fuel-based emission factors (EFs) during flaming and smoldering phases as well as the entire combustion process. Fuel elemental composition and moisture content have strong influences on emissions. Plastic bags have the highest carbon content and the highest combustion efficiency, leading to the highest EFs for CO2. Textiles have the highest nitrogen and sulfur content, resulting in the highest EFs for nitrogen oxides (NOx) and sulfur dioxide (SO2). Emissions are similar for vegetation with 0 % and 20 % moisture content; however, EFs for CO and particulate matter (PM) from the vegetation with 50 % moisture content are 3 and 20–30 times, respectively, those from 0 % and 20 % moisture content. This study also shows that neglecting carbon in the ash and PM can lead to significant overestimation of EFs. Results from this study are applicable to emission inventory improvements as well as air quality management to assess the health and climate effects of household-waste open burning.

The hygroscopic properties of biomass burning aerosol from Eucalyptus and cow dung under different combustion conditions

Aerosols hygroscopic growth is of current interest due to its effect on atmospheric light scattering and extinction. Knowledge of hygroscopic properties is essential for predicting the effect of aerosol on cloud formation, regional visibility, climate impact, and lung deposition. Previous studies have used surrogate components of complex aerosol; and the application to complex multi-component aerosol like biomass burning aerosol is limited. We report aerosol hygroscopicity parameter of biomass burning aerosol derived from Eucalyptus and cow dung in a humidified smog chamber using two techniques: (1) measuring extinction hygroscopic enhancement factor f(RH) of aerosol using a cavity ring down spectrometer and deriving the hygroscopicity parameter using empirical equations and (2) directly using a Cloud Condensation Nuclei Counter (CCNC). Based on repeated measurements of the same fuel under different burning conditions, quantified by the modified combustion efficiency (MCE), we found that aerosol hygroscopicity depends on both fuel types and to some extent on burning conditions. For similar MCE, cow dung has a consistently larger value of hygroscopicity compared to Eucalyptus. Hygroscopicity measurements ranged from 0.024 to 0.577 for MCE measurements that ranged from 0.73 to 0.99. Specifically, sub-saturated hygroscopicity parameter values for cow dung are 0.024–0.131 and Eucalyptus are 0.012–0.300, while supersaturated hygroscopicity parameter values for cow dung are 0.071–0.577 and Eucalyptus are 0.021–0.494. There is a clear increase in hygroscopicity with increasing MCE for supersaturated cow dung measurements using CCNC but the dependence of kappa on MCE is generally inconclusive.

An attribution of the low single-scattering albedo of biomass burning aerosol over the southeastern Atlantic

Abstract. Aerosol over the remote southeastern Atlantic is some of the most sunlight-absorbing aerosol on the planet: the in situ free-tropospheric single-scattering albedo at the 530 nm wavelength (SSA530 nm) ranges from 0.83 to 0.89 within ORACLES (ObseRvations of Aerosols above CLouds and their intEractionS) aircraft flights from late August–September. Here we seek to explain the low SSA. The SSA depends strongly on the black carbon (BC) number fraction, which ranges from 0.15 to 0.4. Low organic aerosol (OA)-to-BC mass ratios of 8–14 and modified combustion efficiency values &gt;0.975 point indirectly to the dry, flame-efficient combustion of primarily grass fuels, with back trajectories ending in the miombo woodlands of Angola. The youngest aerosol, aged 4–5 d since emission, occupied the top half of a 5 km thick plume sampled directly west of Angola with a vertically consistent BC:ΔCO (carbon monoxide) ratio, indicating a homogenization of the source emissions. The younger aerosol, transported more quickly off of the continent by stronger winds, overlaid older, slower-moving aerosol with a larger mean particle size and fraction of BC-containing particles. This is consistent with ongoing gas condensation and the coagulation of smaller non-BC particles upon the BC-containing particles. The particle volumes and OA:BC mass ratios of the older aerosol were smaller, attributed primarily to evaporation following fragmentation, instead of dilution or thermodynamics. The CLARIFY (CLoud–Aerosol–Radiation Interaction and Forcing: Year 2017) aircraft campaign sampled aerosols that had traveled further to reach the more remote Ascension Island. CLARIFY reported higher BC number fractions, lower OA:BC mass ratios, and lower SSA yet larger mass absorption coefficients compared to this study's. Values from one ORACLES 2017 flight, held midway to Ascension Island, are intermediate, confirming the long-range changes. Overall the data are most consistent with continuing oxidation through fragmentation releasing aerosols that subsequently enter the gas phase, reducing the OA mass, rather than evaporation through dilution or thermodynamics. The data support the following best fit: SSA530nm=0.801+0055⋅(OA:BC) (r=0.84). The fires of southern Africa emit approximately one-third of the world's carbon; the emitted aerosols are distinct from other regional smoke emissions, and their composition needs to be represented appropriately to realistically depict regional aerosol radiative effects.

Ground solar absorption observations of total column CO, CO2, CH4, and aerosol optical depth from California's Sequoia Lightning Complex Fire: emission factors and modified combustion efficiency at regional scales

Abstract. With global wildfires becoming more widespread and severe, tracking their emissions of greenhouse gases and air pollutants is becoming increasingly important. Wildfire emissions have primarily been characterized by in situ laboratory and field observations at fine scales. While this approach captures the mechanisms relating emissions to combustion phase and fuel properties, their evaluation on regional-scale plumes has been limited. In this study, we report remote observations of total column trace gases and aerosols during the 2020 wildfire season from smoke plumes in the Sierra Nevada of California with an EM27/SUN solar Fourier transform infrared (FTIR) spectrometer. We derive total column aerosol optical depth (AOD), emission factors (EFs) and modified combustion efficiency (MCE) for these fires and evaluate relationships between them, based on combustion phase at regional scales. We demonstrate that the EM27/SUN effectively detects changes in CO, CO2, and CH4 in the atmospheric column at ∼10 km horizontal scales that are attributed to wildfire emissions. These observations are used to derive total column EFCO of 120.5±12.2 and EFCH4 of 4.3±0.8 for a regional smoke plume event in mixed combustion phases. These values are consistent with in situ relationships measured in similar temperate coniferous forest wildfires. FTIR-derived AOD was compared to a nearby AERONET (AErosol RObotic NETwork) station and observed ratios of XCO to AOD were consistent with those previously observed from satellites. We also show that co-located XCO observations from the TROPOspheric Monitoring Instrument (TROPOMI) satellite-based instrument are 9.7±1.3 % higher than our EM27/SUN observations during the wildfire period. Finally, we put wildfire CH4 emissions in context of the California state CH4 budget and estimate that 213.7±49.8 Gg CH4 were emitted by large wildfires in California during 2020, about 13.7 % of the total state CH4 emissions in 2020. Our work demonstrates a novel application of the ground-based EM27/SUN solar spectrometers in wildfire monitoring by integrating regional-scale measurements of trace gases and aerosols from smoke plumes.

Measurement report: Emission factors of NH3 and NHx for wildfires and agricultural fires in the United States

Abstract. During the 2019 Fire Influence on Regional to Global Environments and Air Quality (FIREX-AQ) study, the NASA DC-8 carried out in situ chemical measurements in smoke plumes emitted from wildfires and agricultural fires in the contiguous United States. The DC-8 payload included a modified proton-transfer-reaction time-of-flight mass spectrometer (PTR-ToF-MS) for the fast measurement of gaseous ammonia (NH3) and a high-resolution time-of-flight aerosol mass spectrometer (AMS) for the fast measurement of submicron particulate ammonium (NH4+). We herein report data collected in smoke plumes emitted from 6 wildfires in the Western United States, 2 prescribed grassland fires in the Central United States, 1 prescribed forest fire in the Southern United States, and 66 small agricultural fires in the Southeastern United States. Smoke plumes contained double to triple digit ppb levels of NH3. In the wildfire plumes, a significant fraction of NH3 had already been converted to NH4+ at the time of sampling (≥2 h after emission). Substantial amounts of NH4+ were also detected in freshly emitted smoke from corn and rice field fires. We herein present a comprehensive set of emission factors of NH3 and NHx, with NHx=NH3+NH4+. Average NH3 and NHx emission factors for wildfires in the Western United States were 1.86±0.75 g kg−1 and 2.47±0.80 g kg−1 of fuel burned, respectively. Average NH3 and NHx emission factors for agricultural fires in the Southeastern United States were 0.89±0.58 and 1.74±0.92 g kg−1, respectively. Our data show no clear inverse correlation between modified combustion efficiency (MCE) and NH3 emissions. The observed NH3 emissions were significantly higher than measured in previous laboratory experiments in the FIREX FireLab 2016 study.

The Characteristics of Gas and Particulate Emissions from Smouldering Combustion in the Pinus pumila Forest of Huzhong National Nature Reserve of the Daxing’an Mountains

Smouldering combustion can emit a large amount of CO2, CO and particulate matter (PM). Moisture content is an important factor of the emission characteristics. As the hot spot of forest smouldering combustion, the gas and particulate emissions of the Huzhong National Nature Reserve with different moisture contents are discussed herein. The emission factors (EF) of CO2 and CO were 100.71 ± 39.14 g/kg and 11.76 ± 3.89 g/kg, respectively. The EF of PM2.5, PM4 and PM10 were 87.11 ± 19.47 g/kg, 353.37 ±159.25 g/kg and 602.59 ± 276.80 g/kg, respectively. PM2.5 accounted for 16.59 ± 5.25% of the PM, and PM4 and PM10 were 54.03 ± 13.46% and 91.00 ± 10.81%, respectively. There was no significant difference in the EF of CO2 and CO with different moisture contents, nor in the EF of PM2.5, but there was a significant difference in the EF of PM4 and PM10 with different moisture contents. In addition, the peak of CO2 and CO appeared at 2~3 h; the peak of PM2.5 lagged behind that of PM4 and PM10. According to the regression analysis, experimental expressions were obtained for the modified combustion efficiency (MCE) and the EF of PM.

Emissions of Particulate and Previously Ignored Gaseous Phosphorus from Coal and Biomass Combustion in Household Stoves

The biogeochemistry of phosphorus (P) strongly affects the primary productivity of terrestrial and ocean ecosystems. However, the global P budget is imbalanced, and the lack of experimental evidence-based P emissions from combustion sources is one important reason for this imbalance. Here, we evaluated P emissions in both the particulate and gaseous phases and assessed the P mass balance (MB) to verify the reliability of emission factors (EFs) measured directly from the burning of biomass and coal. The EFs of P released into the air from coal combustion ranged from 31.5 to 337.4 μg/g, with 8.4%–63.4% present in the gaseous phase, while for biomass burning, the EFs ranged from 63.2 to 866.5 μg/g, with 2.1%–69.5% as gaseous P. The MB results indicated that nearly half of fuel P was emitted into the air, but this fraction varied from 10% to 83% for the different fuels. The modified combustion efficiency (MCE) was not significantly correlated with the total emitted P. The previously ignored gaseous P is assessed for the first time, and this study provides experimental evidence reporting a gaseous P fraction of 2.1%–69.5% of the fuel P, which is important in reducing uncertainties in the imbalanced P budget.