Emission of volatile organic compounds from domestic coal stove with the actual alternation of flaming and smoldering combustion processes

Tibetan Plateau is vulnerable to aromatic-related photochemical pollution and health threats: A case study in Lhasa

Anthropogenic aromatics play a key role in photochemical pollution and pose a serious threat to human health. Current knowledge on source characteristics of aromatics in the urban region of the Tibetan Plateau (TP), the "Third Pole" and ecologically sensitive area, remains limited. In this study, an intensive observation of 17 aromatic hydrocarbons was conducted in Lhasa, the cultural and economic center of TP, during the second Tibetan Plateau Scientific Expedition and Research in summer 2020. The results showed that the average concentration of aromatics in Lhasa (7.6 ± 7.4 ppbv) was unexpectedly higher than those in megacities such as Beijing, Shanghai, and Guangzhou. Tripled concentrations and corresponding ozone formation potential during pollution episodes were recorded. Further source apportionment using positive matrix factorization revealed that solvent usage (60.0 %) was the dominant source, which may be due to the extremely low atmospheric pressure. Vehicle exhaust (15.4 %), industrial emissions (12.8 %), fuel evaporation (6.2 %), and burning emissions (5.7 %) were also important sources. The concentration weighted trajectory analysis revealed that the observed high levels of aromatics were mainly driven by local anthropogenic emissions, rather than the regional transport by the Indian summer monsoon. Long-term exposure to aromatics in Lhasa was assessed to pose carcinogenic risks to the population, with the risks of benzene and ethylbenzene 5 times the criteria. Our results suggest that, given the magnified emissions of aromatics in this extreme environment (low atmospheric pressure and strong solar radiation), the implementation of targeted pollution controls is urgently needed to mitigate the aromatic-related photochemical pollution and health threats in TP.

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.

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.

VOC emission profiles from typical solid fuel combustion in Fenhe River Basin: Field measurements and environmental implication

This study examined volatile organic compounds (VOCs) emitted from the combustion of seven typical biomass fuel types in a traditional stove, elevated kang, and biomass furnace and from the combustion of three types of coal in coal furnaces. The results revealed that emission factors (EFs) of VOCs emitted from combustion processes ranged from 48.8 ± 29.1 mg/kg (for anthracite combustion in an outdoor boiler) to 5700 ± 6040 mg/kg (for sesame straw combustion in a traditional stove). Changing the fuel type engendered a more significant EF reduction (82.7%) than changing the stove type (51.8%). The emitted VOCs (including oxygenated VOCs, OVOCs) can be ordered as follows (in descending order) in terms of proportion: OVOCs > alkenes > aromatic VOCs > alkanes > halo hydrocarbons > alkynes. These results indicate solid fuel combustion processes warrant attention because they produce high OVOC emissions. The ozone formation potential (OFP) values derived for VOCs emitted from solid fuel combustion ranged from 5.83 ± 0.72 to 1910 ± 1750 mg/kg. Clean fuel and clean stove technologies both exhibited >80% efficiency levels in reducing OFP emissions (e.g., 80.6% reduction for the optimal fuel; 89.4% reduction for a clean stove). Therefore, the difference between VOC emission profiles from different combustion technologies should not be ignored. This study also noted substantial differences between VOC emissions from residential combustion and industrial combustion. Accordingly, attention should be paid to the local characteristics of fuels and stoves and to VOC emissions from residential combustion.

Using the carbon balance method based on fuel-weighted average concentrations to estimate emissions from household coal-fired heating stoves

In China, household coal burning accounts for a large proportion of primary fine particulate matter (PM_2.5), black carbon (BC), organic carbon (OC), polycyclic aromatic hydrocarbons (PAHs) and carbon monoxide (CO) emissions. Previous field investigations generally measured short-term emissions from heating coal stoves, which did not provide a full characterization of the actual conditions in most cases, or resulted in large uncertainties in the calculated emission factors (EFs). In this study, we propose a sampling design using a chimney partial-capture dilution system in the field measurement of household coal-fired heating stoves emissions during selected periods within the different burn phases and then using the carbon balance method (CBM) based on fuel-weighted average concentrations (FWAC) from the different burn phases to quantify emissions. We evaluated this proposed methodology by comparing the results with a laboratory total-capture dilution-tunnel system. Statistical analysis indicated that emissions measured during the selected burn cycle periods using the dilution sampling system can generally represent emissions at different burn phases; however, different dilution ratios can affect EFs for PM_2.5 and OC. EFs of air pollutants derived by CBM with FWAC are more representative of the actual emissions than simple average concentration (SAC) and time-weighted average concentrations (TWAC). In the field application, to quantify FWAC, it is suggested to determine the ratio of power in the jth burn phase (P_j) to that in the high power phase (P_H) of the stove, i.e., P_j/P_H values with the calorimeter. If measured P_j/P_H values are not available, the recommended value in this study is also suggested.

Emission factors and chemical profile of I/SVOCs emitted from household biomass stove in China

Household combustion of biomass straw for cooking or heating is one of the most important emission sources of intermediate volatility and semi-volatile organic compounds (I/SVOCs). However, there are limited studies on the emission factors (EFs) and speciation profiles of I/SVOCs from household stoves burning biomass straw. In this study, experiments were conducted in a typical Chinese stove to test the EFs and species of I/SVOCs in three commonly used straws. It was revealed that EFs of I/SVOCs emitted from the burning of corn straw, rice straw, and wheat straw were 6.7, 1.9, and 9.8 g/kg, respectively, which accounted for 48.3 %, 36.8 %, and 48.6 % of total organic compounds emitted. Particulate organic compounds were dominated by ketones, oxygenated aromatics, acids, esters, and nitrogen-containing compounds, whereas the gaseous phase was dominated by aldehydes, acids, and aromatics. Although I/SVOCs only accounted for 18.1-23.6 % of the gaseous emissions from burning of straw, they represented 64.8-72.9 % of the secondary organic aerosol formation potential (SOAFP). The EFs of 16 priority polycyclic aromatic hydrocarbons (PAHs) were 362.0, 262.5, and 1145.2 mg/kg for corn straw, rice straw, and wheat straw, respectively, among which 3-ring and 4-ring PAHs were the main components. Thus, the results of this study provide new reliable I/SVOCs data that are useful for the development of an accurate emission inventory of organic compounds, simulation of secondary organic aerosol (SOA) formation, and health risk assessment.

Rapid increase in atmospheric glyoxal and methylglyoxal concentrations in Lhasa, Tibetan Plateau: Potential sources and implications

Glyoxal (Gly) and methylglyoxal (Mgly) are the intermediate products of several volatile organic compounds (VOCs) as well as the precursors of brown carbon and may play key roles in photochemical pollution and regional climate change in the Tibetan Plateau (TP). However, their sources and atmospheric behaviors in the TP remain unclear. During the second Tibetan Plateau Scientific Expedition and Research in the summer of 2020, the concentrations of Gly (0.40 ± 0.30 ppbv) and Mgly (0.57 ± 0.16 ppbv) observed in Lhasa, the most densely populated city in the TP, had increased by 20 and 15 times, respectively, compared to those measured a decade previously. Owing to the strong solar radiation, secondary formations are the dominant sources of both Gly (71%) and Mgly (62%) in Lhasa. In addition, primary anthropogenic sources also play important roles by emitting Gly and Mgly directly and providing abundant precursors (e.g., aromatics). During ozone pollution episodes, local anthropogenic sources (industries, vehicles, solvent usage, and combustion activities) contributed up to 41% and 45% in Gly and Mgly levels, respectively. During non-episode periods, anthropogenic emissions originating from the south of Himalayas also have non-negligible contributions. Our results suggest that in the previous decade, anthropogenic emissions have elevated the levels of Gly and Mgly in the TP dramatically. This study has important implications for understanding the impact of human activities on air quality and climate change in this ecologically fragile area.

Volatile organic compounds in wintertime North China Plain: Insights from measurements of proton transfer reaction time-of-flight mass spectrometer (PTR-ToF-MS)

The characteristics of wintertime volatile organic compounds (VOCs) in the North China Plain (NCP) region are complicated and remain obscure. VOC measurements were conducted by a proton transfer reaction time-of-flight mass spectrometer (PTR-ToF-MS) at a rural site in the NCP from November to December 2018. Uncalibrated ions measured by PTR-ToF-MS were quantified and the overall VOC compositions were investigated by combining the measurements of PTR-ToF-MS and gas chromatography-mass spectrometer/flame ionization detector (GC-MS/FID). The measurement showed that although atmospheric VOCs concentrations are often dominated by primary emissions, the secondary formation of oxygenated VOCs (OVOCs) is non-negligible in the wintertime, i.e., OVOCs accounts for 42% ± 7% in the total VOCs (151.3 ± 75.6 ppbV). We demonstrated that PTR-MS measurements for isoprene are substantially overestimated due to the interferences of cycloalkanes. The chemical changes of organic carbon in a pollution accumulation period were investigated, which suggests an essential role of fragmentation reactions for large, chemically reduced compounds during the heavy-polluted stage in wintertime pollution. The changes of emission ratios of VOCs between winter 2011 and winter 2018 in the NCP support the positive effect of "coal to gas" strategies in curbing air pollutants. The high abundances of some key species (e.g. oxygenated aromatics) indicate the strong emissions of coal combustion in wintertime of NCP. The ratio of naphthalene to C8 aromatics was proposed as a potential indicator of the influence of coal combustion on VOCs.

Hourly emission estimation of black carbon and brown carbon absorption from domestic coal burning in China

Residential coal combustion (RCC) emission demonstrates obvious daily variation, while no real-time estimation of air pollutants from RCC has been reported, as the limitation of hourly activity data and emission factors. With a dilution sampling system, a high-precision electronic balance, and an Aethalometer Model AE33, a real-time monitoring platform for RCC emission was established. Hourly emission factors (EFs) of BC and absorption emission factors (AEFs) of BrC from eleven kinds of chunk coals and nine kinds of honeycomb coals burning in China were obtained. The monthly and hourly coal consumption amounts were calculated with the activity data from literature reviews and a field survey. The first hourly BC and absorption cross section of BrC emission inventories from RCC were established in China. The historical emission trends (2003-2017) indicated that the policy has rapidly controlled the emission of BC and ACS_BrC from RCC in urban area (26.7% and 31.8% decreased, respectively in 2013). While in rural areas, their emission continually increased by 1.2% ~ 5.3% until more strict law enacted in 2017. Emissions of BC and ACS_BrC in winter seasons were 60.1 Gg and 1064.1 Gm², which accounted for 54.3% and 55.1% of the total BC and ACS_BrC emissions correspondingly. The peak values of hourly emission of BC and ACS_BrC (in 370 nm) normally appeared at 19:00-23:00, accounting for 43.0% and 41.5% of their total daily emission. The low emission periods were at cooking times including 7:00, 12:00, and 17:00 of a day and the whole emission of BC and ACS_BrC for the three periods accounted for 1.8% and 2.3% of their daily emission. This high-resolution BC and ACS_BrC emission inventories can be useful for future modeling works on the formation and evolution of a haze event, the smoke aging and transportation, as well as corresponding climate and human health effects.

Evaluation of offline sampling for atmospheric C3-C11 non-methane hydrocarbons

The concentration variation of C3-C11 non-methane hydrocarbons (NMHCs) collected in several types of commercial flexible bags and adsorption tubes was systematically investigated using a gas chromatography-flame ionization detector (GC-FID) system. The percentage loss of each NMHC in the polyvinyl fluoride (PVF) bags was less than 5% during a 7-hr storage period; significant NMHCs loss was detected in aluminum foil composite film and fluorinated ethylene propylene bags. The thermal desorption efficiency of NMHCs for adsorption tubes filled Carbopack B and Carboxen1000 sorbents was greater than 95% at 300℃, and the loss of NMHCs in the adsorption tubes during 20-days storage at 4℃ was less than 8%. The thermal desorption efficiency for C11 NMHCs in the adsorption tube filled with Carbograph 1 and Carbosieve SⅢ absorbents was less than 40% at 300℃, and pyrolysis of the absorbents at 330℃ interfered significantly with the measurements of some alkenes. The loss of alkenes was significant when NMHCs were sampled by cryo-enrichment at -90℃ in the presence of O₃ for the online NMHC measurements, and negligible for enrichment using adsorption tubes at 25℃. Although O₃ scrubbers have been widely used to eliminate the influence of O₃ on NMHC measurements, the loss of NMHCs with carbon numbers greater than 8 was more than 10%. Therefore, PVF bags and adsorption tubes filled Carbopack B and Carboxen1000 sorbents were recommended for the sampling of atmospheric NMHCs.

Existence and Formation Pathways of High- and Low-Maturity Elemental Carbon from Solid Fuel Combustion by a Time-Resolved Study

Elemental carbon (EC) from various sources contains different sub-fractions with different properties; however, this variability poses several challenges for the accurate assessment of EC emission inventory. EC is defined using thermo-optical analysis (TOA), and its different fractions have different maturation and formation pathways. High- and low-maturity ECs have similar detection signals to those of Soot-EC and Char-EC in TOA. The emission characteristics of Soot-EC and Char-EC were affected by fuel composition and combustion temperatures. Biomass combustion generated more Char-EC than coal combustion, resulting in lower Soot-EC to Char-EC ratios. Soot-EC emissions always increased with an increasing temperature. Char-EC emissions increased with an increasing temperature at 300-900 °C in biomass combustion and decreased in coal combustion when the temperature was >600 °C, suggesting that the two ECs have different formation pathways. Time-resolved analyses of organic carbon (OC), EC, and polycyclic aromatic hydrocarbons showed that Char-EC was preferentially generated in the ignition stage with the rapid emission of OC through direct conversion of OC, whereas Soot-EC was preferentially generated during the flaming stage through gas-phase polymerization of small molecules generated from the decomposition of OC.

Chemical characterization of dissolved organic matter as disinfection byproduct precursors by UV/fluorescence and ESI FT-ICR MS after smoldering combustion of leaf needles and woody trunks of pine (Pinus jeffreyi)

Forested land plays an essential role in water supply across the United States (US). Smoldering commonly existing in wildfires contributes significantly to biomass consumption and gas emission, but its influence on source water quality has been rarely studied. Here, we investigated the impact of smoldering temperature (i.e., no burn, 250, 400, and 600 °C) on the nutrients, elements, and dissolved organic matter (DOM) of water extracts from the residues of the leaf needles and woody trunks of pine (Pinus jeffreyi) under the lab-simulated smoldering fire. Results showed the increase of pH and the yields of the dominated exchangeable cations of K+ and Mg2+, P, PO43--P, and SO42- with increasing temperature increasing from 250 to 600 °C, whereas significant decreases in the fraction of dissolved organic C in residue C with increasing temperature and the yields of dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) after burnings. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) presented consistent results with UV/fluorescence, suggesting that the unburned materials contained more biodegradable tyrosine/tryptophan/soluble microbial byproduct-like compounds with high molecular weight (MW), whereas the 600 °C-smoldering materials composed of more aromatic, humified, fulvic/humic acid-like, and oxidized compounds with a potentially high density of C=C bonds had less reactivity in forming trihalomethanes (THMs) and haloacetonitriles (HANs). Our study indicates the smoldering-dominated prescribed fire as a potential forest management strategy for reducing biomass fuel and disinfection byproducts (DBPs) precursors in source water from forested lands.

Emission and spatialized health risks for trace elements from domestic coal burning in China

Residential coal combustion (RCC) emission exhibited obvious daily variation, while no real-time estimation of air pollutants from RCC has been reported, as the shortages of corresponding activity dataset and emission factors with high time resolution. A real-time monitoring platform for RCC emission was established. Hourly emission factors of 18 typed of TEs from eleven kinds of chunk coals and nine kinds of honeycomb coals burning in China were obtained. The monthly and hourly coal consumption amounts were calculated with reference and our field survey. Then the hourly TEs emission inventories from RCC were established in China. GEOS-Chem and Risk Quotients Models were utilized to map the spatialized health risks of hazardous elements, including the gridded hazard index and carcinogenic risk. The result indicated that the EFs of TEs would be underestimated if the tests only consider flaming conditions. Cu, K, Ca, Zn, and Co were the top five elements from RCC, with corresponding emission amounts as 1397.7, 1054.0, 676.0, 623.5 and 420 tons in 2017, respectively. K, Ti, Fe, Sn, and Sb showed hourly peak values under flaming dominated periods, accounting for 48.2%, 45.9%, 31.8%, 42.8%, and 33.8% of their daily emissions. Other elements (e.g., V, Co, As, Hg and Pb) exhibited higher emissions under smoldering dominated period in nighttime, accounting for 22.2%, 32.9%, 27.6%, 34.7%, and 28.4% of their daily emissions. TEs emission from RCC closely follows the habits of human daily cooking and heating activity. The national HI were lower than the acceptable level (HI ≤ 1) except Sichuan Province (up to 1.2). Higher carcinogenic risks (≥1 × 10^-6) occurred in parts of Sichuan, Shanxi, Hunan and Hubei, which were up to 2.0 × 10^-5. The high-resolution TEs emission inventories could be useful for future modeling works on the formation and evolution of air pollution and are helpful for human exposure assessment.

A critical review of pollutant emission factors from fuel combustion in home stoves

A large population does not have access to modern household energy and relies on solid fuels such as coal and biomass fuels. Burning of these solid fuels in low-efficiency home stoves produces high amounts of multiple air pollutants, causing severe air pollution and adverse health outcomes. In evaluating impacts on human health and climate, it is critical to understand the formation and emission processes of air pollutants from these combustion sources. Air pollutant emission factors (EFs) from indoor solid fuel combustion usually highly vary among different testing protocols, fuel-stove systems, sampling and analysis instruments, and environmental conditions. In this critical review, we focus on the latest developments in pollutant emission factor studies, with emphases on the difference between lab and field studies, fugitive emission quantification, and factors that contribute to variabilities in EFs. Field studies are expected to provide more realistic EFs for emission inventories since lab studies typically do not simulate real-world burning conditions well. However, the latter has considerable advantages in evaluating formation mechanisms and variational influencing factors in observed pollutant EFs. One main challenge in field emission measurement is the suitable emission sampling system. Reasons for the field and lab differences have yet to be fully elucidated, and operator behavior can have a significant impact on such differences. Fuel properties and stove designs affect emissions, and the variations are complexly affected by several factors. Stove classification is a challenge in the comparison of EF results from different studies. Lab- and field-based methods for quantifying fugitive emissions, as an important contributor to indoor air pollution, have been developed, and priority work is to develop a database covering different fuel-stove combinations. Studies on the dynamics of the combustion process and evolution of air pollutant formation and emissions are scarce, and these factors should be an important aspect of future work.

A comparison investigation of atmospheric NMHCs at two sampling sites of Beijing city and a rural area during summertime

Atmospheric non-methane hydrocarbons (NMHCs) were measured synchronously at an urban site of Beijing city (BJ) and a rural site of Dongbaituo (DBT) in Hebei province from 1 July to 15 August 2016. The average concentration of the total NMHCs (TNMHCs) at DBT site were about a factor of 1.3 higher than that at BJ site. Ethane, ethylene, propane, acetylene, butane, isobutane, toluene and isopentane were the common species in the top ten NMHCs at the two sampling sites, and the contributions of the top ten NMHCs to TNMHCs at BJ and DBT sites were 65.6% and 75.1%, respectively. The diurnal variations of TNMHCs at BJ site exhibited one peak during the morning rush hours, whereas two peaks occurred at DBT site during the period from 3:00 to 8:00 (UTC/GMTC8). Based on the correlation coefficients of typical NMHCs pairs and the positive matrix factorization (PMF) results, the gasoline exhaust was found to be the dominant source (38.8%) for atmospheric NMHCs in Beijing, while coal combustion made the largest contribution (32.3%) at the rural site. Atmospheric ozone production over the BJ site was found to be NMHCs-sensitive, while it was in the transition regime at DBT site. Additionally, the largest contributions of atmospheric NMHCs groups to the ozone formation potential at BJ and DBT sites were alkenes and aromatics, with the proportions of 35.8% and 38.6%, respectively.

Effects of Molecular Properties on Adsorption of Six-Carbon VOCs by Activated Carbon in a Fixed Adsorber

Gravimetric adsorption equipment with a microbalance was used to measure the adsorption of volatile organic compounds (VOCs) by activated carbon from 288 to 313 K. VOCs [n-hexane, cyclohexane, 1-hexene, 2-methylpentane, 3-methylpentane, 2,2-dimethylbutane, acetone, butanone, and 2-pentanone (Pentan-2-one)] were used as adsorbates in the adsorption system. Considering the geometric barrier, the critical diameter, and the boiling point, the adsorption capacities for six-carbon (C₆) alkane isomers decrease in the order of n-hexane, 3-methylpentane, and 2-methylpentane. The adsorbates, including nonpolar or weakly polar substances, and substances with smaller geometric obstacles and smaller molecular weights, were more easily adsorbed by the activated carbon. However, the dipole-dipole interactive force at higher pressures resulted in a higher adsorption capacity for 1-hexene than for n-hexane. Both polarity and molecular size should be considered in the analysis of the adsorption of ketones by activated carbon. The adsorption equilibrium constants decreased with increases in temperature because a higher temperature was unfavorable for adsorption. The results for the Toth adsorption isotherm model fitted by the adsorption data showed that the experimental data and the Toth adsorption isotherm model were consistent with each other, as evidenced by the low deviation between the experimental data and those from the fitted model.

Improved estimation of rural residential coal emissions considering coal-stove combinations and combustion modes

Rural residential coal combustion (RRCC) has detrimental effects on air quality, climate, and human health. There are large uncertainties regarding emissions from RRCC owing to the lack of consideration of several key factors (e.g. combination modes of coal and stoves, combustion modes, and high temporal resolution). In this study, we provided a new estimation framework for RRCC emissions through a case study in the Beijing-Tianjin-Hebei (BTH) region, China. The emission estimations were improved according to four aspects, namely (1) coal-specific and stove-specific coal consumption was calculated based on face-to-face field interviews of 6700 valid volunteers/households covering 288 villages in 50 counties; (2) the influences of combustion modes (flaming and smoldering modes) on emissions were considered; (3) emissions of different fuel-stove combinations were estimated based on coal, stove, and combustion mode-specific RRCC consumption and localised emission factors; and (4) a method for emission estimation with high temporal resolution (1 h) was developed. The results indicated that RRCC emitted 413.6 kt SO₂, 55.7 kt NO_x, 5717.3 kt CO, 149.4 kt VOCs, 167.1 kt PM_2.5, 18.2 kt EC, 32.5 kt OC, and 8.2 kt NH₃ in 2016. The combination of bituminous coal and an advanced coal stove was the most significant contributor (20.7-71.8%) to various pollutant emissions. Coal combusted under the flaming mode contributed to most (81.9%) of the total coal consumption, and thus emitted the majority (50.8-99.8%) of pollutants, except for VOCs. Meanwhile, that under the smoldering mode only accounted for 18.1% of the total consumption, but contributed 49.2% and 74.7% of the CO and VOCs emissions, respectively. Two clear emission peaks occurred at approximately 7:00-9:00 and 18:00-20:00. The detailed coal consumption and emissions with high temporal and spatial resolution can provide sound data for further research on rural environmental issues and scientific support to pollution control strategies.

Fuel Aromaticity Promotes Low-Temperature Nucleation Processes of Elemental Carbon from Biomass and Coal Combustion

Significant elemental carbon (EC) emissions from low-temperature solid fuel combustion cannot be explained by classical mechanisms ascribing EC to higher-temperature condensation (> 850 °C). The importance of fuel composition in promoting EC nucleation was investigated by studying EC and polycyclic aromatic hydrocarbon (PAH) formation at multiple-ignition temperatures (300-900 °C) using fuels with different aromatic contents (i.e., straw, wood, and coal). Biomass and coal combustion at 300 °C can produce substantial EC containing a large amount of soot-EC, a known high-temperature condensation product, possibly because aromatics reduce EC nucleation barriers, corresponding to the increasing ratios of soot-EC to char-EC from straw to coal (1.22 to 3.61). High- to low-molecular-weight PAH ratios in biomass combustion were four times lower than those in coal combustion, resulting in different EC formation atmospheres. Specifically, 31.4% of PAHs from biomass combustion were indene, compared to only 0.24% for coal, indicating that resonance-stabilized hydrocarbon-radical chain reactions dominated EC nucleation in biomass combustion. Five- to six-membered PAH ratios were always higher than one in biomass combustion but increased significantly from 0.5 to 2 with increasing temperature in coal combustion, indicating that PAHs generated through aromatic decomposition in coal could form EC through van-der-Waals forces and phenyl addition/cyclization-based covalent bonding at low and high temperatures, respectively.

Impact of rural residential coal combustion on air pollution in Shandong, China

Rural residential coal combustion (RRCC) for household heating is a potentially important source of air pollution. However, little research has been done on the environmental impacts of RRCC. This study therefore investigated the impacts of RRCC on air pollution based on detailed household heating data obtained from intensive face-to-face interviews in Shandong province, China. The total contributions and specific contributions of coal, stoves, and coal-stove combinations to air pollution were simulated using the WRF-CAMx-PSAT model. The RRCC for heating had a considerable impact on air pollution, contributing 36.1, 9.1, and 16.1% of atmospheric SO₂, NO_x, and PM_2.5 in winter, respectively. Different coal-stove combinations had different impacts on air pollution and mitigation efficiencies. The combination of bituminous coal and advanced coal stoves was the dominant contributor to air pollution, comprising 60.3-68.8% of the total RRCC contribution to different air pollutants. Sensitivity analyses indicated that bituminous coal burnt in a traditional stove had the highest mitigation efficiency (0.67 μg·m^-3/10 kt) for atmospheric PM_2.5 pollution, 4.1 times higher than that of anthracite briquette coal burnt in advanced coal stoves. Moreover, although RRCC is a near-surface emission source, it contributed considerably to regional pollution. Non-local RRCC emissions accounted for 21.8-74.6, 15.5-72.3, and 35.3-79.9% of the total contribution to SO₂, NO_x, and PM_2.5 in different cities, respectively. The findings of this study improve understanding on the environmental impacts of rural emissions and can provide scientific support for the formulation of effective air pollution mitigation strategies.

The pollution levels, variation characteristics, sources and implications of atmospheric carbonyls in a typical rural area of North China Plain during winter

Atmospheric carbonyls were measured at a typical rural area of the North China Plain (NCP) from November 13 to December 24, 2017 to investigate the pollution characteristics, sources and environmental implications. Fifteen carbonyls were detected, and formaldehyde, acetaldehyde and acetone accounted for about 81% at most. The concentration of the total carbonyls in heavily polluted days was twice more than that in clean days. In contrast to other carbonyls, m-tolualdehyde exhibited relatively high concentrations in the clean days in comparison with the polluted days. The ratios of three principal carbonyls to CO showed similar daily variations at different pollution levels with significant daytime peaks. Multiple linear regression analysis revealed that the contributions of background, primary and secondary sources to three principal carbonyls showed similar variation trends from the clean level to the heavily polluted level. The OH formation rate of formaldehyde showed a similar variation trend to its photodegradation rate, reaching the peak value at noon, which is important to maintain relatively high OH levels to initiate the oxidation of various gas-phase pollutants for secondary pollutant formation at the rural site. OH radical consumption rate and ozone formation potential (OFP) calculations showed that formaldehyde and acetaldehyde were the dominant oxidative species among measured carbonyls. As for OH radical consumption, n-butyraldehyde and m-tolualdehyde were important contributors, while for ozone formation potential, n-butyraldehyde and propionaldehyde made significant contributions. In addition, the contribution of carbonyl compounds to secondary organic aerosol (SOA) formation was also important and needs further investigation.

Characteristics of fresh and aged volatile organic compounds from open burning of crop residues

Open burning of crop residues is a major source of volatile organic compounds (VOCs), which contribute substantially to the formation of secondary organic aerosols (SOAs) in the atmosphere. An integrated system of combustion chamber coupled with potential aerosol mass (PAM) reactor was used to demonstrate the emission characteristics of fresh and aged VOCs (corresponding to 2- and 7-day atmospheric aging) from the burning of rice, maize, and wheat straws. The average emission factor (EF) of quantified non-methane VOCs (NMVOCs) emitted from the straw (fresh) was 1.82 ± 0.41 g/kg and wheat straw had the highest EFs. The EF residues of quantified NMVOCs decreased considerably after photo-oxidation in PAM. Stronger oxidation condition (7-day aging) produced a 57.2% decline in NMVOC EFs, compared with 42.3% decline during 2-day atmospheric aging. The largest declines were observed in the alkenes group: 82.6% and 66.2% after 7- and 2-day aging, respectively, which is consistent with their high reactivity toward oxidation with ozone and hydroxyl radical (OH). Aromatic compounds mainly reacted with OH, and their EFs decreased 59.1% on average. Alkanes were much less reactive, and their EFs only decreased an average of 29.8% after the oxidation processes. Considerable SOAs formation was observed in the fine particulate matter (PM_2.5) filter samples collected after the oxidation of isoprene, benzene and toluene. The moderate to strong correlations between isoprene and isoprene-derived SOAs, between benzene and toluene with nitrophenols, and between toluene and aromatic acids demonstrate that the VOCs were degraded in the reactions with oxidative radicals, producing active contributors to SOAs formations.

Volatile organic compounds emissions from traditional and clean domestic heating appliances in Guanzhong Plain, China: Emission factors, source profiles, and effects on regional air quality

Solid (biomass and coal) fuels burned for residential heating are major sources of atmospheric volatile organic compounds (VOCs). In this study, VOC samples were collected in-situ from chimneys in 10 typical heating scenarios in rural areas of the Guanzhong Plain. A modified SUMA canister approach was then employed, followed by gas chromatography/mass spectrometry analysis. Emission factors (EFs) (as received basis) of targeted non-methane VOCs (NMVOCs) varied from 90.3 ± 29.3 to 12300 ± 1510 mg kg^-1 in descending order of fuel wood > maize straw > bitumite ≫ anthracite (p < 0.05). Both clean stove and coal briquetting technologies effectively reduced VOC EFs compared with traditional heating methods. The EFs of methane (CH₄) had similar characteristics to those of NMVOCs. However, they yielded different correlations with CO because of their differing mechanisms of formation. Coefficient of divergence (CD) values showed that a semi-gasifier has a limited effect on changing VOC profiles compared with a traditional stove using the same fuels. However, different types of fuel produce CD values over 0.50, which should therefore be classified as different sub-categories in source apportionment models. Correlation analysis showed that volatile matter content (V%) and modified combustion efficiency (MCE) were the two primary factors influencing NMVOC and CH₄ emissions. A stepwise linear regression analysis showed that V%, MCE, and element nitrogen content (N%) can be used to predict total VOC (TVOCs, including CH₄ and NMVOCs) emissions with regression coefficients of 0.23, -72.8 and -6.53, respectively (R² = 0.92, p < 0.001). Ozone formation potential (OFP) EFs from burning solid fuel ranged from 72 to 18680 mg kg^-1, with an approximate 50% contribution from alkenes. VOCs from burning solid fuel were equivalent to 62 to 22200 mg kg^-1 secondary organic aerosol formation potential (SOAP), most of which (>95%) were contributed by aromatics. A semi-gasifier and coal briquettes were effective in reducing TVOC emissions, even when used in conjunction with a traditional stove and fuels. It is estimated that over 15,000 ton year^-1 emissions can be reduced in Guanzhong Plain by adopting a semi-gasifier and coal briquettes, resulting in a 57,000 and 65,000 ton year^-1 reduction of OFP and SOAP emissions, respectively. These results demonstrate that the use of clean heating technologies in Guanzhong Plain has considerable potential in relation to emissions reduction and thus provides a feasible solution to mitigate VOCs and related secondary pollutants emitted by residential solid fuel burning.

Size-segregated emission factors and health risks of PAHs from residential coal flaming/smoldering combustion

Residential coal combustion is one of the main sources of ambient polycyclic aromatic hydrocarbons (PAHs). Updating its emission estimation is limited by the shortages of emission factors, especially for them in different particle sizes and from different combustion conditions. PAH emission factors (EFs) for nine size-segregated particle segments emitted from smoldering and flaming combustion of residential coals (four kinds of raw coals (RCs) and three kinds of honeycomb coal briquettes (HCBs)) were obtained in China, using a dilution sampling system. EFs of PAHs for the flaming and smoldering of HCB ranged from 1.32 to 2.04 mg kg^-1 and 0.35 to 5.36 mg kg^-1, respectively. The EFs of PAHs for RC flaming combustion varied from 0.50 to 218.96 mg kg^-1. About 53.5-96.4% and 47.4-90.9% of PAHs concentrated in PM_2.1 and PM_1.1, respectively. Different fuel types and combustion conditions strongly affected the PAH EFs. The PAH EF for the RC was 0.3 times that for HCB in Guizhou, which implied that PAH EFs for RC combustion were not always higher than those from HCB burning. For different combustion conditions, the PAH EFs from flaming were more than 2.5 times higher than those from smoldering for HCB except in the Anhui region. Results indicated that current PAH EFs may not be universal, which may bias the establishment of control policies for toxic pollutants emitted from domestic coal burning. On average, 73.2 ± 15.5% of total PAH potential toxicity risks were concentrated in submicron particles. More size-segregated PAH EFs for residential coal combustion should be investigated considering combustion conditions with a uniform sampling method in China.

Time-Resolved Intermediate-Volatility and Semivolatile Organic Compound Emissions from Household Coal Combustion in Northern China

Coal combustion in low-efficiency household stoves results in the emission of large amounts of nonmethane organic compounds (NMOCs), including intermediate-volatility compounds (IVOCs) and semivolatile organic compounds (SVOCs). This conceptual picture is reasonably well established, however, quantitative assessment of I/SVOC emissions from household stoves is rare. We used a proton-transfer-reaction time-of-flight mass spectrometer (PTR-ToF-MS) to quantify the emissions of organic gases from a typical Chinese household coal stove operated with anthracite and bituminous coals. Most NMOCs (approximately 64-88%) were dominated by hydrocarbons and emitted during the ignition and flaming phases. The ratio of oxidized hydrocarbons increased during the flaming and smoldering stages due to the elevated combustion efficiency. The average emission factors of NMOCs were 121 ± 25.7 and 3690 ± 930 mg/kg for anthracite and bituminous coals, respectively. I/SVOCs contributed to approximately 30% of the total emitted NMOC mass during bituminous coal combustion, much higher than the contribution of biomass burning (approximately 1.5%). Furthermore, I/SVOCs may contribute over 70% of the secondary organic aerosol (SOA) mass formed from gaseous organic species emitted as a result of bituminous coal combustion. This study highlights the importance of inventorying coal-originated I/SVOCs when conducting SOA formation simulation studies.

Volatile organic compounds from residential solid fuel burning in Guanzhong Plain, China: Source-related profiles and risks

Characteristics of indoor volatile organic compounds (VOCs) and their health risks were investigated in kitchens and bedrooms during the heating season in rural Guanzhong Plain, China. Toxic-VOC concentrations in kitchens with traditional wood (299 ± 38.8 μg m^-3) and liquefied petroleum gas (LPG) stoves (187 ± 54.6 μg m^-3) were considerably higher than those in bedrooms. High levels of toxic VOCs in traditional kitchens were strongly correlated with wood combustion (R = 0.72). The coefficient of determination of VOC profiles between the kitchen and wood combustion was 0.27, indicating that VOCs in traditional kitchens are mainly derived from wood combustion. For women, who do most of the cooking, noncancer risk from exposure to toxic VOCs could reach 7600 and 2550 in traditional and LPG kitchens, respectively. Noncancer risks were much lower in bedrooms than in kitchens, but still two orders of magnitude higher than the United States Environmental Protection Agency (USEPA) threshold. Cancer risk from exposure to VOCs for women was 8.98 × 10^-4 and 1.67 × 10^-4 in both traditional and LPG kitchens, respectively, and ranged from 2.51 × 10^-6 to 3.85 × 10^-5 in bedrooms-all exceeding the USEPA threshold. Thus, during the heating season indicated that the rural Guanzhong residents were exposed to toxic VOCs from indoor heating and cooking at levels higher than the recommended safety levels. Moreover, traditional cooking and heating styles in rural Guanzhong need to be urgently updated to improve the indoor air quality for residents.

Emission characteristics of 99 NMVOCs in different seasonal days and the relationship with air quality parameters in Beijing, China

In recent years, the haze incidents have occurred frequently in China. Therefore, more attention should be taken in comprehensively determination and analysis of the extended-ranges of volatile organic compounds (VOCs). Here, up to 99 non-methane VOCs (NMVOCs), including not frequently reported partial halocarbons and oxygenated VOC (OVOC) species, were monitored in atmosphere of Beijing. The mean concentration of total NMVOC (TNMVOC) decreased in the order of winter polluted days (216.05 μg m^-3) > summer polluted days (127.01 μg m^-3) > summer normal days (95.63 μg m^-3) > winter normal days (50.25 μg m^-3). The ethane to n-butane, ethylene to 1-butene, BTEX, acetaldehyde, acetone, n-hexanal, dichloromethane, chloroform and 1,2-dichloroethane, were determined to be the main composition in their respective alkane, alkene, aromatic, OVOC and halocarbon classes. The minor propylbenzene, diethylbenzene, ethyltoluene, and trimethylbenzene isomer ratios were within the narrow range of 1.3-3.21. Generally, the most abundant NMVOCs were alkanes in winter but OVOCs in summer. TNMVOC significantly positively correlated with PM₁₀, PM_2.5, CO, RH, SO₂ (winter), NO₂ (winter), but negatively with windspeed, SSD and PRS (winter). The opposite correlation was observed between TNMVOC and O₃ in winter and summer. There was no meaningful correlation between TNMVOC and T, PRS (summer), SO₂ (summer) and NO₂ (summer). 3D surface graphs, built by MATLAB, were drawn to investigate the relationship between PM_2.5 and NMVOC taking air quality parameters into account. The PM_2.5 concentration increased non-linearly as TNMVOC concentration increased, with various surface graphs. Unlike other air quality parameters, O₃ affected the relationship differently between winter and summer. The findings presented herein may provide a new train of thought for occurrence of haze.

Air pollutant emissions and mitigation potential through the adoption of semi-coke coals and improved heating stoves: Field evaluation of a pilot intervention program in rural China

Pollutant emissions from incomplete combustion of raw coal in low-efficiency residential heating stoves greatly contribute to winter haze in China. Semi-coke coals and improved heating stoves are expected to lower air pollutant emissions and are vigorously promoted by the Chinese government in many national and local plans. In this study, the thermal performance and air pollutant emissions from semi-coke combustion in improved heating stoves were measured in a pilot rural county and compared to the baseline of burning raw coal to quantify the mitigation potential of air pollutant emissions. A total of five stove-fuel combinations were tested, and 27 samples from 27 different volunteered households were obtained. The heating efficiency of improved stoves increased, but fuel consumption appeared higher with more useful energy output compared to traditional stoves. The emission factors of PM_2.5, SO₂, and CO₂ of semi-coke burning in specified improved stoves were lower than the baseline of burning raw coal chunk, but no significant NOx and CO decreases were observed. The total amount of PM_2.5 and SO₂ emissions per household in one heating season was lower, but CO, CO₂, and NOx increased when semi-coke coal and specified improved stoves were deployed. Most differences were not statistically significant due to the limited samples and large variation, indicating that further evaluation would be needed to make conclusions that could be considered for policy.

Characterization of Gas-Phase Organics Using Proton Transfer Reaction Time-of-Flight Mass Spectrometry: Residential Coal Combustion

Residential coal combustion is a significant contributor to particulate urban air pollution in Chinese mega cities and some regions in Europe. While the particulate emission factors and the chemical characteristics of the organic and inorganic aerosol from coal combustion have been extensively studied, the chemical composition and nonmethane organic gas (NMOG) emission factors from residential coal combustion are mostly unknown. We conducted 23 individual burns in a traditional Chinese stove used for heating and cooking using five different coals with Chinese origins, characterizing the NMOG emissions using a proton transfer reaction time-of-flight mass spectrometer. The measured emission factors range from 1.5 to 14.1 g/kg_coal for bituminous coals and are below 0.1 g/kg_coal for anthracite coals. The emission factors from the bituminous coals are mostly influenced by the time until the coal is fully ignited. The emissions from the bituminous coals are dominated by aromatic and oxygenated aromatic compounds with a significant contribution of hydrocarbons. The results of this study can help to improve urban air pollution modeling in China and Eastern Europe and can be used to constrain a coal burning factor in ambient gas phase positive matrix factorization studies.

The Human Exposure Potential from Propylene Releases to the Environment

A detailed literature search was performed to assess the sources, magnitudes and extent of human inhalation exposure to propylene. Exposure evaluations were performed at both the community and occupational levels for those living or working in different environments. The results revealed a multitude of pyrogenic, biogenic and anthropogenic emission sources. Pyrogenic sources, including biomass burning and fossil fuel combustion, appear to be the primary contributors to atmospheric propylene. Despite a very short atmospheric lifetime, measurable levels could be detected in highly remote locations as a result of biogenic release. The indoor/outdoor ratio for propylene has been shown to range from about 2 to 3 in non-smoking homes, which indicates that residential sources may be the largest contributor to the overall exposure for those not occupationally exposed. In homes where smoking takes place, the levels may be up to thirty times higher than non-smoking residences. Atmospheric levels in most rural regions are typically below 2 ppbv, whereas the values in urban levels are much more variable ranging as high as 10 ppbv. Somewhat elevated propylene exposures may also occur in the workplace; especially for firefighters or refinery plant operators who may encounter levels up to about 10 ppmv.