Combustion Burning Research Articles

Experimental study on the performance of biohythane combustion in a porous radiant burner operated on submerged mode

Abstract Present energy consumption and environmental conditions have motivated researchers to explore renewable and alternative energy sources for cooking. Biohythane is a renewable fuel, that can be prepared by purifying biomethane and biohydrogen along with CO2, generated from the anaerobic digestion of biological sources like food waste and cow dung. The current research aims to analyze the combustion performances of biohythane in a double-layered porous radiant burner (PRB) made of silicon carbide and ceramic matrix. The experiment was conducted in the PRB by varying the input fuel range (thermal load) of 200-400 kW/m2, and the biohydrogen percentage of 5-20% in the biohythane for lean fuel-air mixture conditions. It was observed that the PRB performed steadily within the equivalence ratio of 0.55-0.76 and offered radiation efficiency of 41.39-89.93%, CO of 11-84 ppm, and NOX of 4-6.1 ppm. As the biohydrogen percentage increases from 5-20% in the biohythane, the temperature, radiation efficiency, and NOX have increased but the CO has decreased. Further, the temperature and NOX emission has increased due to the increase in thermal load and equivalence ratio, but the CO emission has increased with the increase in thermal load only and decreased due to the increase in equivalence ratio in the PRB. Moreover, the radiation efficiency has increased due to the increase in equivalence ratio only. Overall, the PRB offers efficient combustion of biohythane in the range of a low fuel-air combination.

Pyrogenic PAHs Have Different Biogeochemical Fates in the Eastern Indian Ocean.

Understanding the fate of polycyclic aromatic hydrocarbons (PAHs) in the deep ocean is crucial for elucidating the biogeochemical cycle of organic carbon under anthropogenic influences. In this study, surface sediments were collected from the deep sea of the Eastern Indian Ocean (water depth: 2161-4545 m) and analyzed for 29 semivolatile organic compounds (SVOCs), including parent PAHs and their alkylated derivatives, as well as source biomarkers. The target SVOCs (∑29SVOCs: 23.0-183 ng/g, ∑16PAHs: 11.3-93.3 ng/g) were mainly from pyrogenic sources, namely coal combustion, traffic emissions, and wood burning. The contributions from wood burning and coal combustion exhibited distinct trends with increasing total organic carbon contents, suggesting different dominant biogeochemical behaviors. Major fractions of PAHs from wood burning can be biodegraded or photodegraded, leading to a depletion-dominated fate in the water column. Conversely, PAHs from coal combustion showed an accumulation-dominated fate via their sedimentation due to their persistence and hydrophobicity. This study highlights the distinct biogeochemical fates of PAHs from biomass or fossil fuel combustion in deep oceans and has implications for the marine cycle of refractory organic carbon under anthropogenic impacts.

ANALYSIS OF THE EFFECT OF SWIRL FLAME SHAPING ON EMISSIONS FROM THE CO-FIRING OF AMMONIA AND METHANE

This paper presents experimental and numerical insights into the behaviour of lean swirl flames with co-combustion of ammonia and methane. In order to evaluate the accuracy of the emissions modelling for CH4/NH3/air preheated (473K) mixtures with an increasing share of ammonia, experimental investigations were performed, varying the share of ammonia up to 25% in the fuel and the equivalence ratio of air to fuel of 0.71. A burner featuring swirl outflow blades with a 30-degree angle of outflow and a convergent-divergent nozzle was employed in the experimental setup. In order to determine the size of the reaction zone, the concentrations of NO and CO along the probing radius inside the combustion chamber were measured. A complete geometry of the combustion chamber and burner was modelled with RSM and EDC models. The outcomes of the Okafor, Xiao, and San Diego mechanisms were compared to the test data. A further DES simulation was conducted to assess the potential applicability of the models. For the flames tested with 3D RSM, a good agreement was achieved for NO emissions. In the case of a fuel containing between 10% and 25% ammonia, the Okafor mechanism demonstrated the most favourable qualitative and quantitative agreement. The reactor volume, residence time and heat transfer conditions for the CRN reactor network were calculated using numerical CFD methods. A satisfactory correlation was observed between the calculated and experimental NO emissions, with a discrepancy of only 10%. In view of the considerable computational expense associated with the models employed and the high degree of accuracy demonstrated in the emission predictions, the 3D RSM simulation was deemed to be an appropriate means of modelling small-scale applications.

An investigation of a multi-injector, premix/micromix burner burning pure methane to pure hydrogen

An investigation of a multi-injector, premix/micromix burner burning pure methane to pure hydrogen

Investigation of the Steam Injection Method Used to Reduce Emissions During Liquefied Petroleum Gas Combustion in an Atmospheric Burner

Investigation of the Steam Injection Method Used to Reduce Emissions During Liquefied Petroleum Gas Combustion in an Atmospheric Burner

Flow field and emission characterization of a novel enclosed jet-in-hot-coflow canonical burner

The jet-in-hot-coflow is a canonical combustion setup, which has been used in several studies to study Flameless/MILD combustion and auto-ignition of fuels. However, the NOx and CO emission measurements from these combustion setups were not possible due to the entrainment of laboratory air and a lack of a well-defined physical system limit. These limitations have been overcome by a new enclosed jet-in-hot-coflow setup. The combustor was operated by injecting a mixture of CH4-Air in the central jet, and the coflow comprised of hot products from CH4-Air combustion in burners upstream. The coflow composition was further controlled by adding diluents such as N2 and CO2. Measurements were done using stereoscopic particle image velocimetry, suction probe gas analysis, thermocouples, and chemiluminescence imaging. Increasing central jet velocity and equivalence ratio led to lower NOx and a reaction zone that enlarged and shifted downstream. The reduction in NOx emission was attributed to the returning mechanism. Adding CO2 and N2 as diluents in the coflow resulted in a longer combustion zone and reduced temperatures in the combustion chamber, leading to decreased NOx production and increased reburning. These experiments provide relevant flowfield and emissions data for modelers and help characterize combustion regimes such as Flameless/MILD.

Experimental Investigation on Compact Current Non Thermal Plasma Assisted Hydrocarbon Reforming Hydrogen Rich Gas

On-board vehicle hydrogen-rich gas extraction of gasoline reforming utilizing for fuel cells and GDI-engine lean burn combustion enhancement NOx trap applications. A non-thermal plasma discharge electrode that produces a reduce current, increased voltage 15kV source arc plasma fuel reformer is designed to operate at an arc frequency of 50 Hz. The operating factors gasoline equivalence ratio between 4 and 6.and electronically control by the fuel injector and eliminating ground spark plug plasma arc generation. The plasma arc non-thermal reformer gasoline converted into gas that contains partial oxidation contains combustible gases like hydrogen (H2), CO, non-combustible gases like CO2, N2, and a small quantity of H2O. The nonthermal plasma technology alternative for on-board hydrogen vehicle applications.

Experimental and numerical investigation of heat transfer modes on pot surfaces in a power range of a cooking porous burner

The investigation of convective and radiative heat transfers to a cooking pot in a porous burner, coupled with an analysis of the pot's bottom and side contributions to total heat transfer, remains an underexplored area of research. In this study, we adopt a comprehensive approach, combining experimental measurements and 3D numerical models, to explore the practical application of a Silicon carbide porous burner fueled with natural gas in cooking pots with power ranging from 12.15 kW to 31.04 kW. Three primary aspects are examined: differentiating between radiative and convective heat transfer contributions, investigating porous mixing characteristics, and analyzing the burner's thermal and combustion efficiencies. To facilitate this investigation, a dedicated test bench is meticulously designed and constructed, equipped with state-of-the-art measuring instruments to effectively monitor the thermal behavior of the heating process. The results reveal that the higher Damköhler number at higher power, driven by the dominance of chemical time over mixing time, accentuates the importance of chemical reactions in heat transfer to the pot. Moreover, increasing the power leads to a reduction in the burner's overall thermal efficiency, from 29.2% to 18.8%, due to a higher energy waste percentage, escalating from 45.12% at P = 12.15 kW to 65.31% at P = 31.04 kW. This increase in power also strengthens the downward movement of the flame and its detachment from the pot surface. The pot's bottom contribution to total heat transfer ranged from 76.7% to 95.5%, with convection alone accounting for over 98% in all cases. Consequently, optimizing the pot bottom geometry for the purpose of enhancing convection presents promising avenues for significantly boosting thermal efficiency. These findings highlight the potential of the investigated porous burner for efficient and clean combustion in cooking appliances.

Update of the present decomposition mechanisms of ammonia: A combined ReaxFF, DFT and chemkin study

Ammonia, a promising carbon-free fuel, offers significant potential for reducing carbon emissions. The decomposition of NH3 is crucial for improving NH3 combustion, yet its mechanisms remain unclear. This study uses ReaxFF simulations, density functional theory (DFT), and Chemkin calculations to explore NH3 decomposition and refine the Konnov mechanism. Our results show that the NH3 to N2 conversion is highly temperature-dependent. At high temperatures, the pathway is NH3→NH2→N2H4→N2H2→N2. As temperature decreases, the N2H pathway becomes more significant, shifting the reaction to NH3→NH4→NH2→N2H→N2 pathway. Additionally, temperature affects H dissociation: at lower temperatures, NH3 to NH2 follows NH3→NH4→NH2, while the NH4 pathway's influence diminishes with rising temperatures. The updated Konnov mechanism improves NH3 decomposition prediction accuracy by about 72.79% and enhances predictions of decomposition rates and intermediate formations (NH, NH2, NH4). This research advances the understanding of NH3 decomposition mechanisms and is vital for optimizing burners for efficient and stable NH3 combustion.

Ammonia Sprays for Combustion: A Review

Ammonia is a globally transported chemical used for a variety of applications, most notably, the production of fertiliser. Over the past decade, attention has been afforded to the use of ammonia as an energy carrier, coupling global supply of renewable energy to demand regions. Ammonia’s advantages as an energy carrier include its ease of liquefaction and established international transportation routes; overcoming its low reactivity, excessive production of nitrogen oxides and its toxicity remain as challenges. For energy applications, fuel delivery is a critical aspect of effective combustion in boilers, burners and engines. Due to its adaptable phase change characteristics, ammonia fuel may be injected as a liquid or vapour, each with respective advantages or disadvantages. The focus of this review concerns the characterisation of liquid ammonia fuel injection for combustion, including recent research findings from experimental and simulation studies. Liquid ammonia injection can result in the highly dynamic so-called ‘flashing’ or ‘flash boiling’ phenomena. Research findings have been drawn from other related applications such as accidental hazardous releases. Bespoke optical experimental rigs together with diagnostic techniques and two-phase computational fluid dynamics (CFD) simulations have enabled studies of the flashing jets under various initial or final conditions, with recent work also examining ammonia spray combustion. The review concludes with an insight into future trends and requirements for liquid ammonia combustion. Reciprocating engines for marine propulsion are cited as potential early adopters of ammonia energy.

Substantial CO2 uptake by biomass ashes under natural condition in China

A considerable amount of biomass ashes, resulting from agricultural waste field burning, wildfire, and solid biofuel incineration, is typically discarded in field or stored in dumps, where the alkaline oxides (CaO, MgO) they contain undergo carbonation and weathering-erosion processes over extended periods, continuously absorbing CO2 from the atmosphere and soil. However, their CO2 absorption behavior under natural conditions remains insufficiently explored in China. Using life cycle assessment (LCA) and material flow analysis (MFA) methods, this study developed a CO2 absorption analysis model for biomass ashes under natural conditions. We estimated the CO2 absorption of 9 different types of biomass ash from 1950 to 2022 through Monte Carlo uncertainty simulation. The results show that biomass ashes in China absorbed approximately 24.17Mt/year (95 % CI, 11.10–43.56) of CO2 under nature conditions, with the annual average CO2 uptake showing a steady increase from 1950 to 2022. The total CO2 uptake reached 856.85Mt (95 % CI, 368.73–1526.01) over these decades, mainly due to the significant contribution of biomass ash produced by domestic straw burning and fuelwood combustion, which accounted for 51.97 % and 22.08 %, respectively. Our findings highlight the substantial carbon sink benefits of biomass ash, providing valuable insights for further studies on carbon cycles in natural ecosystems and the potential integration of biomass ash in Carbon Capture, Utilization, and Storage (CCUS) technologies.

Physico-chemical Characteristics and Evolution of NR-PM1 in the Suburban Environment of Seoul

In South Korea, particulate matter (PM) is generated from various emission sources, including domestic air pollutants and long-range transport. Effective air quality policies require an understanding of the chemical characteristics of PM and differences between urban and non-urban areas (suburban and background areas). We analyzed the chemical characteristics of non-refractory submicron aerosols (NR-PM1) in Yongin City, a suburban area southeast of Seoul, using a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) in spring/summer. In spring/summer, photochemical reactions resulted in the highest proportion of Organic Aerosol (OA) among NR-PM1. Positive matrix factorization (PMF) revealed four OA sources: Primary OA and Secondary OA (Oxidized Primary OA (OPOA), Less Oxidized Oxygenated OA (LO-OOA), and More Oxidized Oxygenated OA (MO-OOA)). OPOA was formed from the oxidation of emissions from biomass burning and coal combustion; LO-OOA and MO-OOA were correlated with inorganic compounds and influenced by long-range transport. The majority of OA was SOA (82%). High temperatures and humidity accelerated the conversion of SO2 to SO42−, resulting in the proportion of SO42−, second only to OA. Despite favorable conditions for nitrate formation in ammonium-rich conditions, the proportion of NO3− was relatively low due to the decomposition of NH4NO3 into gaseous NH3 and HNO3 at high temperatures. This indicated that while ammonium-rich conditions are conducive to NH4NO3 production, elevated temperatures lead to its decomposition, resulting in lower NO3− concentrations in spring/summer. In the case study, for the case associated with long-range transport, the PM concentration increased due to inorganic compounds such as NO3− and SO42−. Conversely, in cases of domestic air stagnation, the concentration of PM increased primarily due to the presence of OA. These findings provide crucial insights for air quality management in suburban areas and can guide policies to reduce PM levels in spring and summer.

Experimental study on reliable combustion of a 15-kw sofc exhaust gas burner across a wide range of operating conditions

The exhaust gas burner, a critical component of a solid oxide fuel cell (SOFC) thermal management system, is essential for the stable and reliable operation of the entire system. This study establishes a test bench that simulates the gas composition and temperature of the fuel cell stack anode and cathode gases and conducts comprehensive experimental research on an exhaust gas burner used in a 15-kW SOFC power generation system. The experimental results show that the burner has the operational characteristic of reliable combustion over a wide range of excess air ratios. The burner can achieve stable and reliable combustion under low-flow ignition, steam injection, reforming, and power-generation conditions with excess air ratios of 29–45, 21–28, 23–37, and 11–27, respectively. Rapid changes in the excess air ratio did not lead to combustion instability; for example, during power generation, an increase of 47.6% in the excess air ratio resulted in a 3.5% decrease in the burner outlet temperature. However, under the steam injection condition, with an excess air ratio of 28 and a steam-to-carbon ratio of 3, the temperature decreased significantly. The burner also exhibited low-pressure loss, with a maximum anode exhaust pressure drop of only 233 Pa. Furthermore, the burner exhibited excellent performance during condition transitions, although a certain time delay occurred in the temperature response to the flow rate changes.

Design method and experimental study on a novel self-sustaining internal combustion burner

Peak shaving represents a particular challenge with regard to coal-fired power plants, as methods to achieve stable, high-efficiency, and low-nitrogen-oxide combustion at ultralow loads remain unavailable. In this study, based on analysis of the ignition mechanism, heating mode, and theory of preheating method, we proposed a novel pulverized coal full-time self-sustaining internal combustion burner by combining the processes of plasma ignition, reverse jetting, and multi-stage ignition. A flame stability model for the burner's recirculation zone was established using the temperature change rate of the recirculation zone as a criterion. The ignition position of the stable self-sustained combustion of the pulverized coal gas stream was determined under various working conditions, and the length of the ignition core stage, a component of the burner inside which the pulverized coal gas stream achieves stable self-sustained combustion, was determined based on the calculated maximum ignition position; a self-sustaining internal combustion burner was then designed based on the ascertained length. Subsequently, we established an experimental system for the self-sustaining internal combustion burner and conducted tests in the load range of 25 %–100 %. Notably, the results of the pulverized coal self-sustained ignition position experiment were consistent with the computational results of the model. The self-sustaining internal combustion burner offers a quick start–stop feature, with the pulverized coal able to achieve stable self-sustained combustion after the plasma igniter shuts off. The resultant gas-phase products exiting the burner met the boiler's concentration requirements for enhanced nitrogen reduction, and the burner exhibited good anti-interference properties. The influence of the pulverized coal gas stream velocity and concentration on the self-sustained ignition was expounded. Under the experimental conditions, an optimal concentration range was ascertained for stable ignition of the pulverized coal gas stream, with the ignition position gradually advancing backward with increasing gas stream velocity. Together, our findings highlight the potential of the proposed burner design to support clean and efficient pulverized coal combustion in coal-fired power plants.

Review of gliding arc plasma assisted ignition and combustion for gas turbine application

Abstract The potential of gliding arc plasma-assisted ignition and combustion technology to enhance ignition and combustion performance is attracting increasing attention from the scientific community. A multitude of experimental studies have been conducted by scientists and engineers on its application in gas turbine combustors. This paper presents a review of the research conducted on gliding arc plasma-assisted ignition and combustion over the past five years. Gliding arc plasma exerts a multitude of effects on combustion processes. These effects can be broadly categorized as follows: (1) reduction in ignition delay time; (2) expansion of ignition and lean blowout boundaries; (3) enhancement of ultra-lean burning combustion and low-temperature flame stability; (4) improvement in combustion efficiency; (5) reduction in pollutant emissions; (6) augmentation of stability of unstable fuels such as ammonia. Finally, a prospection on the application of gliding arc plasma assisted ignition and combustion technology in gas turbine combustor is presented.

Combustion and heat release characteristics of micron aluminum with extremely large specific surface area obtained by L-malic acid surface corrosion

Aluminum (Al) particles are widely used in propellants, thermite and pyrotechnics. However, commonly used micro Al has drawbacks such as agglomeration, high ignition temperature and slow burning rate, making its energy potential not fully exploited in applications. Therefore, exploring pathways to enhance the combustion of Al particles has become the focus at present. Herein, L-malic acid (LMA) was used to corrode the surface of Al particles to obtain a sample (named LMAl) with an average specific surface area of 11.456 m2/g (corresponding to Al particles with a diameter of 194 nm). The particle size distribution of LMAl did not change significantly compared to pristine Al. The XPS results showed that a small amount of LMA and corrosion products remained on the surface of the LMAl particles. Thermal analysis tests showed that the thermal oxidation rate and efficiency of LMAl was dramatically higher than that of pristine Al. Compared with the pristine Al, the combustion characterization parameters of LMAl such as combustion intensity, ignition delay time, maximum combustion temperature, mass burning rate and combustion efficiency were all improved. This trend was maintained after blending the ammonium perchlorate (AP). The condensed combustion products (CCPs) of Al revealed a large number of agglomerates and unburned Al particles. While many broken particles and tentacle-like structures were found in the CCPs of LMAl. Overall, compared to Al, the combustion of LMAl is significantly enhanced. The thermal reaction and combustion behaviors of the two are quite different. This study provides new insights into improving the ignition and combustion of Al.

Kinetic Properties of Combustion and Pyrolysis of Masson Pine with Synergistic Flame Retardancy by GUP-APP-silica Sol

ABSTRACT In order to investigate the effect of guanylurea phosphate-ammonium polyphosphate-silica sol on the combustion and pyrolysis characteristics of Masson Pine, UL-94 horizontal and vertical burner, LOI tester, cone calorimeter, and thermogravimetric analysis were used to study the flame retardant wood, and Coats-Redfern model was used to analyze its pyrolysis kinetics. The results showed that the combined use of guanylurea phosphate-ammonium polyphosphate-silica sol had a significant synergic flame retardant effect on Masson pine. When the mass ratio of guanylurea phosphate, ammonium polyphosphate, and silica sol was 2:1:1, the heat release rate and total heat release of flame retardant pine were decreased by 54.7% and 44.7% compared with pure Masson pine, and the LOI was increased by 77.8% compared with the control group. In addition, the addition of silica sol in the flame retardant reduces the effect of flame retardant on the mechanical properties of wood. Raman analysis of carbon layer showed that the R-value of char residue decreased by 5% and 13% when the mass fraction ratio of guanylurea phosphate, ammonium polyphosphate, and silica sol was 5:1:2 and 2:1:1, respectively, indicating that the compound flame retardant effectively promoted the conversion of amorphous carbon into graphite structure. The TG results of the 5:1:2 and 2:1:1 ratios of guanylurea phosphate, ammonium polyphosphate, and silica sol groups showed that the pyrolysis temperature of flame-retardant pine advanced by about 100°C at the heating rate of 15 ℃/min, and the final char residue rate and apparent activation energy were 15.22%, 18.61%, 24.35 kJ/mol, and 23.76 kJ/mol, respectively. These results indicated that the synergistic flame retardant system of guanylurea phosphate-ammonium polyphosphate-silica sol reduced the apparent activation energy of pine pyrolysis, effectively inhibited the pyrolysis of Masson Pine, and enhanced the thermal stability, char forming ability, and flame retardant property.

Effects of Wire-Wrapping Patterns and Low Temperature on Combustion of Propellant Embedded with Metal Wire

Incorporating silver wires into propellant has emerged as a highly effective strategy for enhancing propellant burning rates, a technique extensively deployed in the construction of numerous fielded sounding rockets and tactical missiles. Our research, employing a multi-faceted approach encompassing thermogravimetric-differential scanning calorimetry measurements (TG-DSC), combustion diagnoses, burning rate tests, and meticulous collection of condensed combustion products, sought to elucidate how variations in silver wire quantity and winding configuration impact the combustion properties of propellants. Our findings underscore the remarkable efficacy of double tightly twisted silver wire in significantly boosting propellant burning rates under ambient conditions. Moreover, at lower temperatures, the reduced gap between the propellant and silver wire further magnifies the influence of silver wire on burning rates. However, it is noteworthy that the relationship between burning speed and combustion efficiency is not deterministic. While a smaller cone angle of the burning surface contributes to heightened burning rates, it concurrently exacerbates the polymerization effect of vapor phase aluminum particles, consequently diminishing propellant combustion efficiency. Conversely, propellants configured with sparsely twinned silver wires exhibit notable enhancements in combustion efficiency, despite a less pronounced impact on the burning rate attributed to the larger cone angle of the burning surface. Remarkably, these trends persist at lower temperatures. Based on the principle of heat transfer balance, a theoretical model for the combustion of propellants with wire inserts is developed. The reliability of this theoretical model is validated through a comparison of calculated values with experimental data. Our research outcomes carry significant implications for guiding the application and advancement of the silver wire method in solid propellants for solid rocket motors, offering valuable insights to inform future research and development endeavors in this domain.

The water-insoluble organic carbon in PM2.5 of typical Chinese urban areas: light-absorbing properties, potential sources, radiative forcing effects, and a possible light-absorbing continuum

Abstract. Water-insoluble organic carbon (WIOC) constitutes a substantial portion of organic carbon (OC) and contributes significantly to light absorption by brown carbon (BrC), playing pivotal roles in climate forcing. China is a hotspot region with high levels of OC and BrC, but information regarding the sources and light-absorbing properties of WIOC on a national scale remains scarce. Here, we investigated the light-absorbing properties and sources of WIOC in 10 representative urban cities in China. On average, WIOC made up 33.4 ± 7.66 % and 40.5 ± 9.73 % of concentrations and light absorption at 365 nm (Abs365) of extractable OC (EX-OC), which includes relatively hydrophobic OC (WIOC and humic-like substances, HULIS-C) and hydrophilic OC (non-humic-like substances, non-HULIS-C). The mass absorption efficiency of WIOC at 365 nm (MAE365) was (1.59 ± 0.55 m2 (g C)−1) comparable to that of HULIS (1.54 ± 0.57 m2 (g C)−1) but significantly higher than non-HULIS (0.71 ± 0.28 m2 (g C)−1), indicating that hydrophobic OC possesses a stronger light-absorbing capacity than hydrophilic OC. Biomass burning (31.0 %) and coal combustion (31.1 %) were the dominant sources of WIOC, with coal combustion sources exhibiting the strongest light-absorbing capacity. Moreover, employing the simple forcing efficiency (SFE300–700 nm) method, we observed that WIOC exhibited the highest SFE300–700 nm (6.57 ± 5.37 W g−1) among the EX-OC fractions. The radiative forcing of EX-OC was predominantly contributed by hydrophobic OC (WIOC – 39.4 ± 15.5 % and HULIS – 39.5 ± 12.1 %). Considering the aromaticity, sources, and atmospheric processes of different carbonaceous components, we propose a light-absorbing carbonaceous continuum, revealing that components enriched with fossil sources tend to possess stronger light-absorbing capacity, higher aromatic levels, increased molecular weights, and greater recalcitrance in the atmosphere. Reducing fossil fuel emissions emerges as an effective means of mitigating both gaseous (CO2) and particulate light-absorbing carbonaceous warming components.

Compositions and sources of fluorescent water-soluble and water-insoluble organic aerosols

Brown carbon (BrC), the light-absorbing component of organic aerosols, plays a significant role in climate change and atmospheric photochemistry. However, the water-insoluble fractions of BrC have not been extensively studied, limiting the assessment of the overall climate effects of BrC. In this study, water-soluble and -insoluble organic carbon (i.e., WSOC and WIOC) in wintertime aerosols in Hefei were subsequently fractionated, and their fluorescence properties were comparatively investigated with the excitation–emission matrix method. WIOC contributing 57.1 % was the major component of organic carbon. WSOC with the largest contribution from humic-like regions exhibited a redshift compared to WIOC. Three humic-like substances (HULIS) with different oxidation degrees and one protein-like substances (PRLIS) were identified as the major fluorescent components by the parallel factor analysis. WSOC had more highly oxygenated HULIS, whereas low-oxygenated HULIS dominated WIOC. Nighttime WIOC contained more less-oxygenated species. The positive matrix factorization analysis suggested that biomass burning (43 %) was the largest source of both fluorescent WSOC and WIOC. Coal combustion contributed much more to fluorescent WIOC (40 %), whereas secondary formation contributed more to fluorescent WSOC (12 %). During aerosol pollution episodes, the increase in fluorescence efficiency was much greater for WIOC (25 %) than for WSOC (12 %), and WSOC and WIOC experienced a redshift and blueshift in emission wavelength, respectively. WSOC had more highly oxygenated HULIS, while WIOC had more less-oxygenated HULIS in aerosol episodes than the non-episodic periods. In addition, aerosol pollution was accompanied by the increased contributions of biomass burning and coal combustion to both fluorescent WSOC and WIOC, while the decreased relative contribution of secondary formation to fluorescent WSOC. Our findings highlighted the different fluorescence properties, compositions and sources of fluorescent WSOC and WIOC, providing a comprehensive view of BrC aerosols.