Residential Coal Combustion Research Articles

Characteristics and health risks assessment of PM2.5-bound heavy metals during winter in urban areas of northern China: A case study in Kaifeng

The health impact of heavy metals in atmospheric PM2.5 has garnered increasingly widespread attention. We have collected PM2.5 samples in a typical city (Kaifeng) within the Central Plains Urban Agglomeration in China during winter and measured the mass concentration of PM2.5-bound heavy metals. The pollution of As and Cr in the urban atmosphere requires significant attention. As PM2.5 concentrations increased, the enrichment factors (EFs) of Mn, Cu, Zn, As, and Pb also rose, suggesting a growing contribution from anthropogenic emissions. The analysis showed that the hazard quotient (HQ) for the non-heating and heating periods (HQ < 1) did not result in a cumulative non-carcinogenic health risk to humans. Regarding carcinogenic effects, As and Cr exhibit significant carcinogenic impacts on both children and adults (ELCR>1 × 10−6), indicating that the carcinogenic risks posed by As and Cr under PM2.5 exposure in Kaifeng could not be overlooked. It was found that industrial and biomass combustion are the primary sources of carcinogenic risk in Kaifeng city. From the non-heating to the heating period, the industrial carcinogenic risk increased from 37.12 % to 43.39 %, while the contribution of biomass burning remained at 25 %. This result was strongly correlated with the high proportions of heavy metal elements such as As, Mn, Pb, and Ni from the metal refinery industry. The results of this study revealed the equally important source of heavy metals, compared to coal combustion in North China Plain. In addition to residential coal combustion, industrial emissions are a major source of PM2.5-bound heavy metals in Kaifeng, contributing significantly to overall air pollution and providing a useful reference to mitigating human health risks in the area.

Dynamic evolution of particulate and gaseous emissions for typical residential coal combustion

Residential coal combustion still accounts for half of the heating energy consumption in many developing countries. The dynamic variation during the combustion process importantly determines the combustion facility design and appropriate air quality assessment, which was omitted in conventional studies. This study investigated the emissions of particulate and gaseous pollutants during the combustion process for typical coal types using online monitoring. During the first pyrolysis stage with temperature climbing, the organic aerosols (OA) and gases reached peak concentration. The second fierce combustion stage had the highest temperature and produced the highest cumulative emissions, particularly a substantial amount of black carbon for coals with higher volatile content. Using higher-quality coals will undoubtedly reduce PM emissions, by a factor of 10 from bituminous to anthracite coal. However, more ultrafine particles (d < 0.1 μm) from cleaner coal may pose additional health risks. Anthracite and honeycomb coal had approximately twice the energy content and emitted more CO2 per unit mass of fuel and had more persistent SO2 emissions throughout the burnout stage. The oxygenation of OA and organic gases remained increased during combustion, suggesting the pyrolysis products underwent oxidation before being emitted. The investigation of the coal combustion process suggests the importance of reducing volatiles to control PM emissions, but the potential negative synergistic effects between PM reduction and increased carbon emissions should also be considered.

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 &lt; 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 &lt; 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 &lt; 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 &lt; 0.05) and WIOC extracts (r = 0.929; p &lt; 0.001), suggesting that these compounds significantly contributed to MAE variabilities across different fuels.

Resolving emission factors and formation pathways of organic gaseous compounds from residential combustion of European brown coal

Residential combustion of brown coal can be an important source of ambient air pollution in areas with abundant brown coal deposits, such as Eastern Europe or China. The exhaust emission contents may vary regionally depending on the fuel composition, calling for detailed characterization of emissions from different coal types. In this work, the organic gaseous emissions of European brown coal combusted in a modern chimney stove -type residential appliance were measured by a proton transfer reaction time-of-flight mass spectrometer. Of three consecutive batches of brown coal briquettes, the first batch produced two-fold emission (144 ± 52 mg/MJ) of organic gaseous compounds (OGCs) compared to the later batches (71 ± 35 mg/MJ). The compositions between the batches were, however, relatively similar. Carbonyls accounted for 36 ± 3.0% of the identified emission factors, while aromatic hydrocarbons and oxygenated aromatic compounds contributed 19 ± 3.4% and 16 ± 1.8%, respectively. The complex and overlapping chemical processes within batch combustion were exposed by non-negative matrix factorization, giving insight into the temporal variation in the formation pathways of the OGCs. The OGCs were separated into five factors revealing the chemical fingerprints of the main processes leading to formation of, for example, substituted or single-ring aromatic hydrocarbons. Oxygenated aromatic compounds were related to a distinct factor, which was proposed to form specifically from decomposition of the lignin residues of the brown coal. OGCs from brown coal combustion were estimated to have notable secondary particle formation potential: in photochemical conditions, they may double the organic particulate emission, while reactions in dark conditions may lead to excessive nitrophenol formation.

Characterizing carbonaceous aerosols in residential coal combustion: Insights from thermal/spectral carbon analyzer coupled with photoionization mass spectrometry analysis

This study aims to identify unique signatures from residential coal combustion in China across various combustion conditions and coal types. Using a Thermal/Spectral Carbon Analyzer with a Photoionization Time-of-Flight Mass Spectrometer (TSCA-PI-TOF-MS), we focus on the optical properties and organic mass spectra of the emissions. Bituminous coal emerged as the primary emitter of total carbon, releasing 729 μg C/mg PM2.5 under smoldering and 894 μg C/mg PM2.5 under flaming. Carbon fractions mainly comprised OC1 and OC2, except for anthracite's dominance of EC1 under smoldering. Pyrolysis carbon absorption shifted from 405, 445 and 532 nm during smoldering to near-infrared bands (635–980 nm) during flaming for both bituminous and anthracite coal. Conversely, clean coal exhibited an inverse trend, attributed to additives enhancing oxygen-containing organic compounds and long-chain hydrocarbons released in charring process. Sample of bituminous coal began charring at OC3 step, while anthracite began earlier at OC2 step, particularly pronounced under flaming. Clean coal displayed unconventional charring at OC1 step under smoldering condition, producing signature compounds like butenal, methylfuran, furanylalcohol, and naphthol. The mass spectra of bituminous coal featured characteristic peaks, including m/z 192 (methylphenanthrene), 206, 220 (alkylated phenanthrenes), and 234 (retene). Anthracite coal showed a potential tracer at m/z 223, shifting from OC1 in smoldering to OC2 in flaming. Clean coal under flaming condition exhibited elevated levels of aromatic compounds, indicating potential toxicity, with peaks at m/z 178 (phenanthrene), 228 (chrysene/benz[a]anthracene), 234 (retene), 242 (methylchrysene), and 252 (benzo[a]pyrene, benzo[k]fluoranthene). Results also showed that the broader mass spectra range in the OC3 and OC4 steps across all coal types suggests that high-temperature pyrolysis promotes diversity. These findings contribute to refined source apportionment of carbon emissions from residential coal combustion and provide the scientific basis for the formulation of air pollution prevention strategies, crucial for coal-dependent regions.

More evidence on primary sulfate emission from residential coal combustion in northern China: Insights from the size-segregated chemical profile, morphology, and sulfur isotope

This study addresses the ongoing debate concerning the origin of ambient sulfate in northern China, and provides more evidence for primary sulfate from the perspective of source emission. An extensive field experiment was conducted, involving the collection of size-segregated particulate matter emitted under various coal types and combustion conditions for subsequent analysis. Our findings reveal that residential coal combustion (RCC) emits significant amounts of primary sulfate, constituting approximately 26.48 ± 15.43% of the particulate mass. Moreover, these emissions exhibit a strong association with NH4+, leading to the formation of stable ammonium sulfate compounds. The emission of sulfate is intricately linked to both coal quality and combustion conditions. Notably, the oversight of δ34S isotope enrichment in RCC particulate matter, which distinctly differs from the raw coal, introduces uncertainties in the quantitative assessment of sulfate sources and formation pathways. Therefore, more in-depth explorations are necessary to elucidate the precise processes involved in RCC sulfate transformation and to accurately determine its environmental impact.

Necessary CO2 emissions improvement based on rural residential coal/stove-specific coal combustion and prefectural-differentiation synergistic effect of pollutants and carbon emission reduction

Rural residential coal combustion (RRCC) is an important CO2 emission source in rural areas and these emissions vary greatly by coal and stove types. The lack of CO2 emission estimations for different coal-stove combinations restricts refinement and region-differentiated synergistic reduction of pollution and CO2 emissions from RRCC. This study established the coal and stove specific CO2 emissions inventory of RRCC based on investigated coal combustion of various coal and stove types, taking the region of Hebei in China as an example. The synergistic reduction effect of CO2 and pollutants was evaluated using 4 emission reduction scenarios. CO2 emission was 67.4% higher than estimates of RRCC based on the Statistical Yearbook and IPCC emission factors. The combination of bituminous coal and an advanced coal stove was the greatest contributor (62.1%) to CO2 emissions. Bituminous coal burnt in home Arcola has the highest per capita hourly and per unit calorific value CO2 emission, 2.3 and 2.4 times higher than the combination of anthracite briquette coal and pit coal stove and the combination of bituminous coal and an advanced coal stove, respectively. Except for NOx and CO, the coal-stove combination with the lowest per capita hourly and per unit calorific value emissions is anthracite briquette coal and an advanced coal stove. Scenario analysis shows that updated coal stoves feature the highest pollutant emission reduction, but greater CO2 and NOX emissions. For individual cities, synergistic pollution and carbon reduction is seen in Tangshan and Qinhuangdao, and organic carbon, CO, and SO2 have better synergistic positive reduction with CO2, while NOX has shown a negative effect with CO2 in other cities with the best coal and stove update scenario. Compared with the coal and stove update scenario, emission reduction effects with clean fuel substitution varies across cities. This study is helpful to understand the possible non-synergy of pollutant and CO2 reduction in the process of RRCC management. Attention should be given to issues related to the synergistic control plan of pollution and CO2 reduction for RRCC with local adaptation.

Indoor PM from residential coal combustion: Levels, chemical composition, and toxicity

Indoor air quality is crucial for human health due to the significant time people spend at home, and it is mainly affected by internal sources such as solid fuel combustion for heating. This study investigated the indoor air quality and health implications associated with residential coal burning covering gaseous pollutants (CO, CO2 and total volatile organic compounds), particulate matter, and toxicity. The PM10 chemical composition was obtained by ICP-MS/OES (elements), ion chromatography (water-soluble ions) and thermal-optical analysis (organic and elemental carbon). During coal combustion, PM10 levels were higher (up to 8.8 times) than background levels and the indoor-to-outdoor ratios were, on average, greater than unity, confirming the existence of a significant indoor source. The chemical characterisation of PM10 revealed increased concentrations of organic carbon and elemental carbon during coal combustion as well as arsenic, cadmium and lead. Carcinogenic risks associated with exposure to arsenic exceeded safety thresholds. Indoor air quality fluctuated during the study, with varying toxicity levels assessed using the Aliivibrio fischeri bioluminescence inhibition assay. These findings underscore the importance of mitigating indoor air pollution associated with coal burning and highlight the potential health risks from long-term exposure. Effective interventions are needed to improve indoor air quality and reduce health risks in coal-burning households.

Regulation of open straw burning and residential coal burning around urbanized areas could achieve urban air quality standards in the cold region of northeastern China

Air quality issues in Northeast China are concerning due to the significant seasonal atmospheric pollution and typical climatic, geographic and industrial structure characteristics of the area. However, urban air quality managers are having great difficulty achieving targeted pollution control goals in the time allotted due to limited studies in the region. In this study, using the city of Siping in Jilin Province as a case study, we analysed the cause of seasonal atmospheric pollution, developed a high-resolution emissions inventory for major atmospheric pollutants and simulated urban air quality improvements under projected emission control scenarios to select a reasonable source control scheme to inform urban air quality management planning in the region. Years with available air quality data (2014–2020) were divided into three periods, i.e., a weak control period (WCP: 2014–2017), an enhanced control period (ECP: 2018–2019) and the COVID-19 period (CDP: 2020). The annual PM2.5, PM10, SO2 and NOx emissions varied by 62∼46 μg·m−3, 103∼76 μg·m−3, 27∼22 μg·m−3 and 46∼41 μg·m−3, respectively, during the WCP; the emissions decreased to 37 μg·m−3, 69 μg·m−3, 11 μg·m−3 and 34 μg·m−3, respectively, during the ECP and to 33 μg·m−3, 61 μg·m−3, 11 μg·m−3 and 33 μg·m−3, respectively, during the CDP, which reached the limits of the Ambient Air Quality Standard of China (level II, 35 μg·m−3, 70 μg·m−3, 60 μg·m−3 and 50 μg·m−3). The PM2.5 and PM10 indices exceeded the standards, mainly in late autumn (October and November) and in the middle of winter (January and February). Based on comprehensive data analysis of the spatiotemporal air quality and the local high-resolution emissions inventory, straw burning, stationary combustion (especially for coal burning) and vehicle emissions were the main pollution sources in late autumn, and continuous adverse weather conditions were the dominant factors in severe pollution days during the middle of winter. In addition, the urban air quality of Siping was also affected by pollutant transport from the northwest (the city of Songyuan in Jilin Province), northeast (the city of Changchun in Jilin Province) and south (the city of Tieling in Liaoning Province) according the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model. Strict straw-burning policy was implemented in autumn during the ECP and CDP, which significantly improved the air quality from that of the WCP, with an AQI reduction of 31.58 %. However, the planned burning policy was not well-implemented, resulting in more days of moderate or heavy pollution. Using 2017 as the base year, scenarios were simulated in which feasible source control measures were set (namely, straw-burning control, the elimination of small boilers in urbanized areas, staggered peak heating measures and a 50 % reduction in residential bulk coal burning around urbanized areas and suburban areas), and the concentrations of PM2.5 and PM10 were projected to decline by more than 29.79 %, meeting the urban air quality standards. This study highlights the importance of combining straw burning regulation in no-burning areas, limited burning areas and residential coal-burning substitution around urbanized areas to improving the air quality in cold regions.

Sources and composition of elemental carbon during haze events in North China by a high time-resolved study

Despite the implementation of stringent emission reduction measures in the past year, severe winter haze events still occurred frequently in North China, with only marginal decreases observed in elemental carbon (EC) concentrations. EC not only constitutes a fraction of particle mass but also interacts with boundary layer and influences haze formation. Given the complex composition of EC, characterizing its sources and composition during haze processes is challenging yet crucial for understanding haze formation and evolution. Here, hourly-resolution PM2.5 samples were collected during three different haze event (P1-P3) in the North China Plain to investigate dynamic changes in EC source across different haze processes. The average EC concentrations and char/soot ratios were 9.94 ± 4.80 μgC·m−3, 14.5 ± 6.93 μgC·m−3, 15.9 ± 5.54 μgC·m−3, and 2.42 ± 0.98, 2.70 ± 0.88, 2.61 ± 0.95 for P1, P2 and P3, respectively. Backward trajectory analysis showed distinct variations in EC concentration and composition under the influence of different air masses during the three haze events, with local air masses influenced days exhibiting higher EC concentrations and char/soot ratios. The char/soot ratio based diagnostic method suggested that EC was predominantly influenced by coal combustion and vehicle emissions. Further positive matrix factorization analysis suggested that biomass burning and residential coal combustion were the main contributors of EC (58 %) and played a dominant role in driving variations in EC concentrations during haze episodes. Potential source contribution function analysis results highlight that local biomass burning and residential coal combustion could be major reason for the EC elevation in different haze events. Our results provide valuable insights into the sources and composition of EC during haze events, facilitating the implementation of effective measures for mitigating both EC and PM pollution.

Residential combustion of coal: Effect of the fuel and combustion stage on emissions

Worldwide coal is still used for household heating purposes not only because it is available and cheap but also due to behavioural issues. Regional variability in fuels and combustion appliances make accurate emission estimates from this source hard to achieve. In the present study, gaseous (CO, VOCs, SO2 and NOX) and particulate matter (TSP) emission factors (EFs) were determined for Spanish household coal combustion covering three commercial coals and distinct combustion stages and mimicking usage patterns in real households. TSP samples were analysed to determine water-soluble inorganic ions, metal(loid)s, and organic and elemental carbon (OC and EC). Additionally, the morphology of the emitted particles was also characterised.CO (3.43–169 g kg−1), NOX (1.29–6.00 g kg−1) and SO2 (8.96–22.3 g kg−1) EFs showed no trend regarding the combustion stage or coal type tested. On the other hand, VOC, TSP and EC EFs were higher for the ignition/devolatilisation combustion stage, regardless of the fuel tested. TSP EFs (0.085–1.08 g kg−1) increased with increasing coal volatile matter while the opposite trend was recorded for VOC emissions (0.045–3.39 gC kg−1).TSP carbonaceous matter was dominated by EC while OC represented a small fraction of the particulate mass emitted (less than 8 %wt.). Inorganic compounds composed an important fraction of the TSP samples. Sulphate particulate mass fractions (8.66–22.9 %wt.) appeared to increase with coal S-content. Coal combustion released particles with diverse morphologies, including silicate-rich particles, ferro- and glassy-spheres. This study provides novel emission factors to update emission inventories of residential coal combustion. Additionally, detailed chemical profiles were obtained for source apportionment.

Emission inventory of air pollutants from residential coal combustion over the Beijing-Tianjin-Hebei Region in 2020

Emission inventory of air pollutants from residential coal combustion over the Beijing-Tianjin-Hebei Region in 2020

Multiple pathways for the formation of secondary organic aerosol in the North China Plain in summer

Abstract. Secondary organic aerosol (SOA) has been identified as a major contributor to fine particulate matter (PM2.5) in the North China Plain (NCP). However, the chemical mechanisms involved are still unclear due to incomplete understanding of its multiple formation processes. Here we report field observations in summer in Handan of the NCP, based on high-resolution online measurements. Our results reveal the formation of SOA via photochemistry and two types of aqueous-phase chemistry, the latter of which include nocturnal and daytime processing. The photochemical pathway is the most important under high-Ox (i.e., O3 + NO2) conditions (65.1 ± 20.4 ppb). The efficient SOA formation from photochemistry (Ox-initiated SOA) dominated the daytime (65 % to OA), with an average growth rate of 0.8 µgm-3h-1. During the high-relative-humidity (RH; 83.7 ± 12.5 %) period, strong nocturnal aqueous-phase SOA formation (aqSOA) played a significant role in SOA production (45 % to OA), with a nighttime growth rate of 0.6 µgm-3h-1. Meanwhile, an equally fast growth rate of 0.6 µgm-3h-1 of Ox-initiated SOA from daytime aqueous-phase photochemistry was also observed, which contributed 39 % to OA, showing that photochemistry in the aqueous phase is also a non-negligible pathway in summer. The primary-related SOA (SOA attributed to primary particulate organics) and aqSOA are related to residential coal combustion activities, supported by distinct fragments from polycyclic aromatic hydrocarbons (PAHs). Moreover, the conversion and rapid oxidation of primary-related SOA to aqSOA were possible in the aqueous phase under high-RH conditions. This work sheds light on the multiple formation pathways of SOA in ambient air of complex pollution and improves our understanding of ambient SOA formation and aging in summer with high oxidation capacity.

Insight into the contributions of primary emissions of sulfate, nitrate, and ammonium from residential solid fuels to ambient PM2.5

Understanding the primary emissions of sulfate (SO42−), nitrate (NO3−), and ammonium (NH4+) (SNA) from solid fuels (coal and biomass) combustion is important to study their roles in haze formation and particle growth. In this study, direct emissions of SNA and other inorganic ions (including Na+, K+, Mg2+, Ca2+, and Cl−) in fine particulate matter (PM2.5) from residential coal combustion (RCC) and biomass burning (BB) were quantified through combustion chamber experiments. Emission factors (EFs) of the total quantified ions for the five types of solid fuels are in the range of 178–3880 mg/kg, accounting for 5.8%–41.1% of the emitted PM2.5 mass. The average proportions of SO42−, NO3−, and NH4+ in PM2.5 emitted from RCC are 3.7%, 0.9%, and 1.0%, respectively, in comparison to 1.3%, 0.8%, and 0.1%, respectively, for BB. Despite the variations of SNA proportions seen among the solid fuel types, SO42− is the most dominating inorganic ion, consistent with the emission profiles shown in other literatures. Similar mass fraction and its range of SO42− are found between RCC and ambient in the northern cities, implying that the primary emission from RCC is a significant source contributor to atmospheric SO42−, particularly in wintertime. According to the EFs and mass fractions of SNA determined for the solid fuels, the contribution of secondary formation to atmospheric SO42− should be overestimated in ambient PM2.5 source apportionment.

Indoor air pollution from the household combustion of coal: Tempo-spatial distribution of gaseous pollutants and semi-quantification of source contribution

Coal is a widely used solid fuel for cooking and heating activities in rural households, whose incomplete combustion in inefficient household stoves releases a range of gaseous pollutants. To evaluate the impact of coal combustion on indoor air quality, this study comprehensively investigated the indoor air pollution of typical gaseous pollutants, including formaldehyde (HCHO), carbon dioxide (CO2), carbon monoxide (CO), total volatile organic compounds (TVOC), and methane (CH4), during coal combustion process in rural households using online monitoring with high tempo-spatial resolution. The indoor concentrations of gaseous pollutants were considerably elevated during the coal combustion period, with the indoor concentrations being significantly higher than those in courtyard air. The levels of several gaseous pollutants (CO2, CO, TVOC, and CH4) in indoor air were much higher during the flaming phase than the de-volatilization and smoldering phases, while HCHO peaked in the de-volatilization phase. The gaseous pollutant concentrations mostly decreased from the room ceiling to the ground level, while their horizontal distribution was relatively uniform within the room. It was estimated that coal combustion accounted for about 71 %, 92 %, 63 %, 59 %, and 21 % of total exposure to indoor CO2, CO, TVOC, CH4, and HCHO, respectively. Improved stove combined with clean fuel could effectively lower the concentrations of CO2, CO, TVOC, and CH4 in indoor air and reduce the contributions of coal combustion to these gaseous pollutants by about 21–68 %. These findings help better understand the indoor air pollution resulting from residential coal combustion and could guide the development of intervention programs to improve indoor air quality in rural households of northern China.

More water-soluble brown carbon after the residential “coal-to-gas” conversion measure in urban Beijing

The implementation of air pollution reduction measures has significantly reduced the concentration of atmospheric fine particles (PM2.5) in Beijing, among which the “coal-to-gas” conversion measures may play a crucial role. However, the effect of this conversion measure on brown carbon (BrC) is not well known. Here, the chemical composition of BrC in humic-like fraction (HULIS-BrC) and water-insoluble fraction (WI-BrC) were characterized for ambient PM2.5 samples collected in Beijing before and after the “coal-to-gas” conversion measure. After the conversion measure, the number of HULIS-BrC compounds increased by ~14%, while the number of WI-BrC compounds decreased by ~8%. The intensity of over 90% of HULIS-BrC compounds also increased after the conversion measure, and correspondingly the O/C ratios of CHO and CHON compounds in HULIS-BrC fraction generally increased with the increase of intensity ratios after/before the conversion measure, indicating that there were more water-soluble highly oxygenated BrC compounds after “coal-to-gas” conversion measure. On the contrary, the intensity of more than 80% of WI-BrC compounds decreased after the conversion measure, and the O/C ratios of CHO and CHON compounds in WI-BrC fraction generally decreased with the decrease of intensity ratios after/before the conversion measure, indicating that after the “coal-to-gas” conversion measure the water-insoluble low oxygenated BrC compounds decreased. This work sheds light on the differences in the chemical composition of BrC between before and after the “coal-to-gas” conversion measure and suggests that future studies on the residential coal combustion BrC and secondary BrC deserve further exploration.

Photochemical Aging Induces Changes in the Effective Densities, Morphologies, and Optical Properties of Combustion Aerosol Particles.

Effective density (ρeff) is an important property describing particle transportation in the atmosphere and in the human respiratory tract. In this study, the particle size dependency of ρeff was determined for fresh and photochemically aged particles from residential combustion of wood logs and brown coal, as well as from an aerosol standard (CAST) burner. ρeff increased considerably due to photochemical aging, especially for soot agglomerates larger than 100 nm in mobility diameter. The increase depends on the presence of condensable vapors and agglomerate size and can be explained by collapsing of chain-like agglomerates and filling of their voids and formation of secondary coating. The measured and modeled particle optical properties suggest that while light absorption, scattering, and the single-scattering albedo of soot particle increase during photochemical processing, their radiative forcing remains positive until the amount of nonabsorbing coating exceeds approximately 90% of the particle mass.

A Comprehensive Assessment of Clean Coal Fuels for Residential Use to Replace Bituminous Raw Coal

Residential coal combustion is a major source of air pollution in developing countries, including China. Indeed, precisely measuring the real-time emission of major air pollutants is often challenging and can hardly be repeated at a lab-scale. In this study, for the first time, two clean coals initiated from raw bituminous coal were burned for real-time estimation of air pollution characteristics and their thermal efficiencies in different stoves. Moreover, thermodynamic equilibrium simulations were investigated for slagging parameters using Factsage 7.1 at reaction temperature 800~1600 °C. Results revealed that the firepower of clean coals (Briquetted coal and Semi-coke) was much higher (2.2 kW and 2.1 kW) than raw coal (1.8 kW) in a traditional stove. However, the thermal efficiencies were remarkably increased (13.3% and 13.5%) in an improved stove for briquetted coal and semi-coke, respectively. The emission of major air pollutants including carbon monoxide (CO), sulfur dioxide (SO2), particulate matter (PM), polycyclic aromatic hydrocarbons (PAHs), non-methane hydrocarbons (NMHCs) from both coal and semi-coke was significantly reduced. Thermodynamic equilibrium calculations indicate that briquetted coal is not susceptible to slagging under the reaction conditions in the household stove. The current study provides guidance for the selection of alternative and efficient clean coal fuels in rural areas for household purposes coupled with public health and safety.

Atmospheric ammonia in the rural North China Plain during wintertime: Variations, sources, and implications for HONO heterogeneous formation

Atmospheric ammonia (NH3) plays an important role in secondary inorganic aerosol formation. Understanding the temporal variations, sources, and environmental influences of NH3 is conducive to better formulate PM2.5 pollution control strategies for policy-makers. Here, we performed a comprehensive field campaign with the measurements of NH3 and related parameters at a rural site of the North China Plain (NCP) in winter of 2017. The results showed that residential coal combustion contributed dominantly to NH3 during the entire observation period, resulting in the obviously high average concentration of NH3 (31.2 ± 24.6 ppbv). The sensitivity tests of pH-NHx during the three different pollution periods suggested that the rural site was always in the NHx-rich atmosphere where high levels of NHx increased the particle pH inefficiently. Nevertheless, the particle pH still elevated by 1.5–2.2 units at the excessive NHx levels during the three pollution periods. In addition, the HONO/NO2 ratios were found to correlate linearly with NH3 concentrations, implying the acceleration effect of NH3 on HONO production from NO2 heterogeneous reactions. After considering the NH3-enhanced uptake coefficient of NO2 in the nocturnal HONO budget, the unknown source of HONO could be fully explained. Therefore, more attentions should be given for effective emission control of NH3 to improve air quality throughout the NCP, especially in the rural areas.

PM2.5 source apportionment using organic marker-based chemical mass balance modeling: Influence of inorganic markers and sensitivity to source profiles

A Chemical Mass Balance (CMB) model has been applied to source apportionment of PM2.5 in the Chinese megacity of Chengdu. The study explored the sensitivity of the CMB model to the adoption of different organic source profiles, and to the use of organic markers only (OM-CMB), compared with using a combination of organic and inorganic markers (IOM-CMB). A comprehensive comparison of OM-CMB and IOM-CMB shows that PM2.5 mass concentrations from gasoline vehicles, diesel vehicles, industrial coal combustion, biomass burning, cooking, and SOA which shared same markers in the two methods are in fair to good agreement between the two methods, with the relative biases ranging from 2.2% to 17.3%. The average contributions of sulfate and nitrate sources are more sensitive to the choice of model because inorganic ions were not inputted directly into the OM-CMB. The temporal variations of PM2.5 contributions from sulfate, nitrate, SOA, gasoline vehicles, and biomass burning, characterized by unique markers and low collinearity, were in good agreement between the OM-CMB and IOM-CMB results with the Pearson's r above 0.91 (p < 0.01). However, resuspended dust estimates from OM-CMB had a relatively weak correlation with that from IOM-CMB (Pearson's r = 0.73, p < 0.01), due to the different tracers used. When replacing the source profile for industrial coal combustion with that for residential sources, the contributions of resuspended dust and residential coal combustion were higher, and the contributions of other sources were lower compared with the result for the industrial coal combustion. Different source profiles for gasoline vehicles showed considerable sensitivity of the model to the choice of source profile, even when using data from within a single emissions study. Our results emphasize the value of combining inorganic and organic tracers in minimizing error, and in using up-to-date locally-relevant source profiles in source apportionment of PM.