Hourly emission amounts and concentration of water-soluble ions in primary particles from residential coal burning in rural northern China.

Residential coal burning (RCB) stands as an important contributor to ambient pollutants in China. For the effective execution of air pollution control policies, it is essential to maintain precise emission inventories of RCB. The absence of hourly emission factors (EFs) combined with the inaccuracies in the spatial-temporal distribution of activity data, constrained the quality of residential coal combustion emission inventories, thereby impeding the estimation of air pollutant emissions. This study revised the hourly EFs for PM2.5 and water-soluble ions (WSIs) emitted from RCB in China. The hourly emission inventories for PM2.5 and WSIs derived from RCB illustrate the diurnal fluctuations in emission patterns. This study found that the emissions of PM2.5, NH4+, Cl-, and SO42- showed similar emission features with emission of 106.8 Gg, 1417.6, 356.8, and 5868.5 ton in erupt period. The results provide basic data for evaluating RCB emission reduction policies, simulating particles, and preventing air pollution in both sub-regions and time periods. The spatial emission and simulated concentration distribution of PM2.5 and WSIs indicated that emission hotspot shifted from North China Plain (NCP) to Northeast region in China. The emissions in China were well-controlled in '2 + 26' region (R28) priority region, with hotspots decreasing by 99.6% in BTH region. The RCB became the dominant contributor to ambient PM2.5 with a ratio in the range of 16.2-23.7% in non-priority region.

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.

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.

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.

Socioeconomic and Demographic Associations with Wintertime Air Pollution Exposures at Household, Community, and District Scales in Rural Beijing, China.

The Chinese government implemented a national household energy transition program that replaced residential coal heating stoves with electricity-powered heat pumps for space heating in northern China. As part of a baseline assessment of the program, this study investigated variability in personal air pollution exposures within villages and between villages and evaluated exposure patterns by sociodemographic factors. We randomly recruited 446 participants in 50 villages in four districts in rural Beijing and measured 24 h personal exposures to fine particulate matter (PM2.5) and black carbon (BC). The geometric mean personal exposure to PM2.5 and BC was 72 and 2.5 µg/m3, respectively. The variability in PM2.5 and BC exposures was greater within villages than between villages. Study participants who used traditional stoves as their dominant source of space heating were exposed to the highest levels of PM2.5 and BC. Wealthier households tended to burn more coal for space heating, whereas less wealthy households used more biomass. PM2.5 and BC exposures were almost uniformly distributed by socioeconomic status. Future work that combines these results with PM2.5 chemical composition analysis will shed light on whether air pollution source contributors (e.g., industrial, traffic, and household solid fuel burning) follow similar distributions.

Investigating the relationship between mass concentration of particulate matter and reactive oxygen species based on residential coal combustion source tests.

Particulate matter (PM) has been considered to be closely related to human health, especially fine particulate matter. However, whether PM mass concentration alone is a good indicator for health impact remains a challenging question. In this study, emissions from residential coal combustion (RCC), one of the important PM sources in northern China, were tested to examine the relationship between the emission factors of particle-generated reactive oxygen species (ROS) (EFROS) and PM (EFPM). A total of 24 combinations of source tests were conducted, including eight types of coal with different geological maturities (two anthracites and six bituminous) burned in three types of stoves (one honeycomb coal stove, one old chunk stove, and one new chunk stove). Here, ROS was defined as generated hydroxyl radical (·OH) by PM, and results showed EFROS from 24 residential coal combustion varied greatly by nearly 20 times. EFROS ranged 0.78-14.85 and 2.99-12.91 mg kg-1 for the emissions from honeycomb and chunk coals, respectively. Moreover, the correlation between EFROS and EFPM was significantly positive in honeycomb coal emissions (r = 0.82, p < 0.05), but it was insignificant in chunk coal emissions (r = 0.07, p > 0.05). For honeycomb coal emissions, organic carbon (OC) was quite abundant in PM and it might be the predominant contributor to both EFPM and EFROS, resulting in a strong and positive correlation. For chunk coal emissions, high EFROS was mainly related to relatively high metal emissions in AN and LVB, while the metals were not major components in PM, leading to a poor correlation between EFPM and EFROS. Therefore, this study revealed that PM was not always positively correlated with ROS from residential coal burning, and the relationship was mainly determined by the compositions of PM, suggesting PM mass concentration alone may not be the best indicator for assessing health impacts.

Refined source apportionment of residential and industrial fuel combustion in the Beijing based on real-world source profiles.

Residential and industrial emissions are considered as dominant contributors to ambient fine particulate matter (PM2.5) in China. However, the contributions of residential and industrial fuel combustion are difficult to distinguish because specific source indicators are lacking. In this study, real-world source testing was performed on residential coal, biomass and industrial combustion, industrial processes, and diesel and gasoline vehicle source emissions in the Beijing-Tianjin-Hebei region, China. PM2.5 emission factors and chemical profiles, including 97 compositions (e.g., carbonaceous matter, water-soluble ions, elements, EPA priority polycyclic aromatic hydrocarbons (EPAHs), methyl PAHs (MPAHs), and n-alkanes) were obtained for the aforementioned sources. The results showed high OC1, OC2, fluoranthene, methyl fluoranthene, and retene in emissions from residential coal combustion, high OC3, sulfate, Ca, and iron abundance in emissions from industrial combustion, and high Pb and Zn loadings in emissions from industrial processes. Furthermore, specific diagnostic ratios were determined to distinguish between residential and industrial fuel combustion. For example, the ratios of MPAHs/EPAHs (>1) and Mfluo/Fluo (>5) can be used as fingerprinting ratios to distinguish residential coal combustion from other sources. Finally, 1-h resolution refined source apportionments of PM2.5 were conducted in Beijing during two haze events (EP1 and EP2) with a chemical mass balance (CMB) model based on the localized real-world source profiles established in this study. Source apportionment results of CMB showed that the contributions of industrial and residential fuel combustion were 19.4% and 30.8% in EP1 and 26.8% and 18.1% in EP2, respectively, which were comparable to the results of the positive matrix factorization model (R2 = 0.82). This study provides valuable information for the successful and accurate determination of the contributions of residential and industrial fuel combustion to ambient PM2.5.

Source profiles of molecular structure and light absorption of PM2.5 brown carbon from residential coal combustion emission in Northwestern China.

Residential coal combustion is a prominent source of brown carbon (BrC) aerosols, but knowledge of their molecular structures and optical absorption were limited, which have notable used in ambient BrC source identification and radiative forcing calculation. In this study, the Fourier transform-ion cyclotron resonance mass spectrometry combined with partial least squares regression analysis as well as Fourier transform infrared spectroscopy analysis were used to insight the molecular compounds and structures of BrC from anthracite and bituminous coal combustions between traditional and improved stoves. The absorption Ångström exponents (AAE) and mass absorption efficiency (MAE) values for the BrC emitted from the combinations of bituminous were both 1.2-2.5 times lower than those of anthracite, interpreting that the BrC from the anthracite emissions had greater light-absorbing capacity. In contrast, the emission factor of light absorption (EFAbs) at 365 nm for the bituminous coal combusted in the traditional stove was the highest among all the tested scenarios, which revealed that the incomplete combustion of bituminous coal could emit more BrC. It was noted that primary BrC emitted from the coal combustion with traditional stoves contains higher aromaticity groups of C-C and C＝O and higher S containing organics, whereas more aliphatic groups were found in BrC using the improved stoves. N-containing (CHON and CHONS) compounds were dominated in the total molecular formula of BrC, whereas the sum of CHON and CHO groups had high double-bond equivalent (DBE) values contributed 53.5%-87.1% to the total BrC absorption. Moreover, for CHOS, the lowest of estimated molecular absorption, DBE, and DBE/C should attribute to the non-chromophoric or weak absorptive S-containing compounds. This study supplied an effective evaluation method to compare BrC emissions and their absorption for coal combustion on regional scale.

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.

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 ACSBrC 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 ACSBrC in winter seasons were 60.1 Gg and 1064.1 Gm2, which accounted for 54.3% and 55.1% of the total BC and ACSBrC emissions correspondingly. The peak values of hourly emission of BC and ACSBrC (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 ACSBrC for the three periods accounted for 1.8% and 2.3% of their daily emission. This high-resolution BC and ACSBrC 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.

Competing PM2.5 and NO2 holiday effects in the Beijing area vary locally due to differences in residential coal burning and traffic patterns.

The holiday effect is a useful tool to estimate the impact on air pollution due to changes in human activities. In this study, we assessed the variations in concentrations of fine particulate matter (PM2.5) and nitrogen dioxide (NO2) during the holidays in the heating season from 2014 to 2018 based on daily surface air quality monitoring measurements in Beijing. A Generalized Additive Model (GAM) is used to analyze pollutant concentrations for 34 sites by comprehensively accounting for annual, monthly, and weekly cycles as well as the nonlinear impacts of meteorological factors. A Saturday effect was found in the downtown area, with about 4% decrease in PM2.5 and 3% decrease in NO2 relative to weekdays. On Sundays, the PM2.5 concentrations increased by about 5% whereas there were no clear changes for NO2. In contrast to the small effect of the weekend, there was a strong holiday effect throughout the region with average increases of about 22% in PM2.5 and average reductions of about 11% in NO2 concentrations. There was a clear geographical pattern in the strength of the holiday effect. In rural areas the increase in PM2.5 is related to the proportion of coal and biomass consumption for household heating. In the suburban areas between the Fifth Ring Road and Sixth Ring Road there were larger reductions in NO2 than downtown which might be due to decreased traffic as many people return to their hometown for the holidays. This study provides insights into the pattern of changes in air pollution due to human activities. By quantifying the changes, it also provides insights for improvements in air quality due to control policies implemented in Beijing during the heating season.

[Investigation on the Emission Difference of Air Pollutants from Common Residential Coal Stoves and Suggestions for Emission Reduction].

To explore the difference in the emission of air pollutants from coal stoves, five new and common residential coal stoves (square briquette, baffled heat exchange, heating and cooking integrated gasification positive burning, and gasification reverse burning stove) were selected. The emission level of major air pollutants was determined using simulated combustion in the laboratory for quantitatively evaluating the environmental effects of different coal stoves. Moreover, the factors and reasons for the differences were identified, and suggestions for the reduction of emission were proposed. The results showed that: ① the emissions of air pollutants from different coal stoves were significantly different; the heating and cooking integrated stove had the largest emission intensity (2.9 kg ·t-1) of air pollutants (SO2, NOx, and TSP), which was 1.6 times of the average value, and the square briquette stove had the lowest emission level, which was 65% of the average value. ② The emissions of gaseous pollutants from the coal stoves in different combustion stages also showed evident differences. In the high-fire stage, the NOx emission concentration of the square briquette stove was 0.49 mg ·m-3, which was 45%-72% lower than that of the other stoves; the SO2 emission concentration of the gasification reverse burning stove was 1.38 mg ·m-3, which was 28% lower than that of the other stoves. ③ The application technology and combustion type were the main factors affecting the emission levels of the coal stoves. The stove with square briquette technology and gasification reverse burning technology could have great environmental benefit. However, the cost of the two stoves was 20 and 18 thousand yuan, respectively, which was clearly higher than that of the other types of stoves. ④ Considering the difference in the emission of air pollutants from the different stoves, it was suggested to adopt differentiated economic policy and strict emission and product standards, promoting the use of energy-saving and environment-friendly coal stoves to reduce the emission of air pollutants from coal-fired stoves.

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, NOx, and PM2.5 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 PM2.5 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, NOx, and PM2.5 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.

Pollution levels, composition characteristics and sources of atmospheric PM2.5 in a rural area of the North China Plain during winter.

The pollution levels, composition characteristics and sources of atmospheric PM2.5 were investigated based on field measurement at a rural site in the North China Plain (NCP) from pre-heating period to heating period in winter of 2017. The hourly average concentrations of PM2.5 frequently exceeded 150 µg/m3 and even achieved 400 µg/m3, indicating that the PM2.5 pollution was still very serious despite the implementation of stricter control measures in the rural area. Compared with the pre-heating period, the mean concentrations of organic carbon (OC), element carbon (EC) and chlorine ion (Cl-) during the heating period increased by 20.8%, 36.6% and 38.8%, accompanying with increments of their proportions in PM2.5 from 37.5%, 9.8% and 5.5% to 42.9%, 12.7% and 7.2%, respectively. The significant increase of both their concentrations and proportions during the heating period was mainly ascribed to the residential coal combustion. The proportions of sulfate, nitrate and ammonium respectively increased from 9.9%, 10.9% and 9.0% in nighttime to 13.8%, 16.2% and 11.1% in daytime, implying that the daytime photochemical reactions made remarkable contributions to the secondary inorganic aerosols. The simulation results from WRF-Chem revealed that the emission of residential coal combustion in the rural area was underestimated by the current emission inventory. Six sources identified by positive matrix factorization (PMF) based on the measurement were residential coal combustion, secondary formation of inorganic aerosols, biomass burning, vehicle emission and raising dust, contributing to atmospheric PM2.5 of 40.5%, 21.2%, 16.4%, 10.8%, 8.6% and 2.5%, respectively.

Parent, alkylated, oxygenated and nitro polycyclic aromatic hydrocarbons from raw coal chunks and clean coal combustion: Emission factors, source profiles, and health risks.

Residential coals are still inevitable using in developing areas in China. Clean coal briquettes, normally using alkaline substance such as lime or red mud (RM) as the additive, were helpful in pollution emission reduction even without changes of stoves. Studies of atmospheric polycyclic aromatic hydrocarbons (PAHs) emission characteristics from RM clear coal combustion were limited. In this study, emission factors (EFs), sources profiles, and health risks of polycyclic aromatic hydrocarbons (PAHs) in PM2.5 were investigated for raw coal chunks and clean coal (with red mud) through combustion experiments. EFs of total PAHs were found to be 160.1 ± 100.9 mg·kg-1 and 19.4 ± 6.1 mg·kg-1 for bituminous and anthracite raw coal chunks (B-C and A-C), respectively. EFs values were highest for parent PAHs (p-PAHs), followed by oxygenated PAHs (o-PAHs), alkylated PAHs (a-PAHs), and nitro PAHs (n-PAHs). EFs of p-PAHs account for 80% and 52% of total PAHs emissions for B-C and A-C, respectively, while those for o-PAHs are 22.9% and 44.9%, demonstrating residential coal combustion as a significant primary source for p-PAHs and o-PAHs. Clean coals were developed through cold-press technology with red mud (RM) as additive, and clean coals with RM contents of 10% are referred to as B-10% (bituminous) and A-10% (anthracite). Compared to raw coals chunks, EFs were reduced from 128.1, 2.5, 29.3 mg·kg-1 and 161.8 µg·kg-1 to 83.5, 1.3, 16.4 mg·kg-1 and 102.2 µg·kg-1 by B-10%, and from 10.1, 0.6, 8.7 mg·kg-1 and 20.6 µg·kg-1 to 11.9, 0.2, 2.4 mg·kg-1 and 15.3 µg·kg-1 by A-10% for p-PAHs, o-PAHs, a-PAHs and n-PAHs, respectively. Diagnostic ratios of 5-Nitroacenaphthene / Acenaphthene (0.02-0.05 for coal, 0.0002 for biomass) can be used to separate residential coal and biomass burning in source analysis. When B-C was replaced by B-10%, both noncancer (0.58 to 0.33 for male, 1.65 to 0.95 for female in hazard quotient) and cancer risks (5.68 × 10-4 to 2.73 × 10-4 for male, 2.63 × 10-3 to 1.27 × 10-3 for female) can be reduced. o-PAHs should be paid more attention because of its high cancer risks caused by 6H-Benzo(C,D)Pyrene-6-One (1.74 × 10-5 for male, 8.07 × 10-5 for female), which are even more than the total risks caused by n-PAHs (3.59 × 10-7 for male, 1.66 × 10-6 for female). Results from this study highlighted the environment and health effects of PAHs originated from residential coal combustion, and proposed an effective way by using clean coal to alleviate the associated negative impacts.

Dual-modelling-based source apportionment of NOx in five Chinese megacities: Providing the isotopic footprint from 2013 to 2014.

In China, nitrate (NO3-) becomes the main contributor to fine particles (PM2.5) because the emissions of its precursor, nitrogen oxides (NOx), were not recognized and controlled well in recent years. In this work, sources, conversion, and geographical origin of NOx were interpreted combining the isotopic information (δ15N and δ18O) of NO3- and dual modelling at five Chinese megacities (Beijing, Shanghai, Guangzhou, Wuhan and Chengdu) during 2013-2014. Results showed that the δ15N-NO3- values (n = 512) ranged from -12.3‰ to +22.9‰, and the average δ18O-NO3- value was +83.4‰ ± 17.2‰. The isotopic compositions both had a rising tendency as ambient temperature dropped, attributing largely to the source changes. Bayesian model indicated the percentage for the OH pathway of NOx conversion had a clear seasonal variation with a higher value during summer (58.0% ± 9.82%) and a lower value during winter (11.1% ± 3.99%); it was also significantly correlated with latitude (p < 0.01). Coal combustion was the most important source of NOx (31.1%-41.0%), which was geographically derived from North China and other south-central developed regions implied by Potential Source Contribution Function (PSCF). Apart from Chengdu, mobile sources was the second largest contributor to NOx. This source was extensive but uniformly distributed all around the typical urban agglomerations of China. Biomass burning and microbial processes shared similar source areas, mostly originating from the North China Plain and Sichuan Basin. Based on the NOx features, we infer that residential coal combustion was the primary source of heavy PM2.5 pollution in Chinese megacities. Controlling the source categories of these regional priorities would help mitigate atmospheric pollution in these areas.

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 PM2.1 and PM1.1, 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.

[Source Apportionment of PM2.5 in Suburban Area of Beijing-Tianjin-Hebei Region in Autumn and Winter].

To identify the main sources of PM2.5 in Beijing-Tianjin-Hebei (BTH) region, PM2.5 samples were collected at four suburban sites in BTH region during autumn and winter in 2014-2015. Source apportionment of PM2.5 was conducted using the chemical mass balance model (CMB). It shows that the main sources of PM2.5 in autumn and winter were secondary aerosols (36%-58%), traffic (8%-26%), residential coal combustion (8%-16%), and biomass burning (5%-16%). Secondary nitrate was the most important source of PM2.5 at most sites during autumn and winter (11%-27%). The source apportionment at different pollution levels indicates that the coherence of the increasing trend of different sources among the four sites were much more obvious in autumn than in winter. Also, the increasing contribution of secondary sources (47.2-115.7 µg·m-3) was much higher than that of primary sources (29.5-43.4 µg·m-3) in autumn, but such trend was not significant in winter. The total contribution of coal combustion at suburban sites was quite similar to that in urban sites, but in suburban areas residential coal combustion dominates the contribution from coal combustion. Thus, it is very necessary for suburban areas of the BTH region to control emissions from residential coal combustion.

[Emission Factors of Heavy Metals in Size-resolved Particles Emitted from Residential Coal Combustion].

Based on a dilution sampling system and domestic burning tests, size-segregated particles emitted from burning of three kinds of honeycomb coals (in view of flaming and smoldering burning conditions) and four kinds of raw coals, were collected by cascade impactors (FA-3). The contents of V, Cr, Mn, Co, Ni, Cu, Zn, As, Cd, Sb, and Pb were analyzed to get their emission factors (EFs) in different particle size fractions. Results indicated that:① Zn and Pb dominated the emitted mass of heavy metals from chunk (53.16%-65.76%) and honeycomb (96.08% in 0.43 µm) during the flaming combustion condition. However, the emission of Ni was increased from 30.70% to 52.36% in the smoldering condition. Thus, combustion condition may affect the composition of heavy metals in particle matters. ② In the flaming condition, both chunk and honeycomb emission factors of heavy metals were concentrated under 1.1 µm, while the larger sized particles in the range of 5.8-10 µm were distributed. So, heavy metal components may shift to the larger size of the particles at lower combustion temperatures. ③ Fine particle matters(PM) was divided into three categories based on the size distribution of 11 kinds of heavy metal emission factors. The maximum emission values of As and V fell under the PM size category of 5.8-10 µm. The fourth cycle transition metal elements, such as Cr, Mn, Cu, Ni, and Co, fell in the range of 1.1-2.1 µm and these elements represented similar emission characteristic features. Other elements, such as Pb, Sb, Cd, and Zn, were concentrated in sizes less than 0.43 µm. ④ The additive in the honeycomb during the process may import several kinds of heavy metals and may change the combustion temperature, which remodels the mechanism of heavy metal emission. Thus, honeycomb coal may emit different heavy metals under different combustion conditions.The heavy metal emission mechanism during honeycomb coal combustion needs further investigation and the emission reduction effects (especially of heavy metals) needs to be re-estimated.

Chemical nature of PM2.5 and PM10 in Xi'an, China: Insights into primary emissions and secondary particle formation.

In Xi'an, a city that frequently experiences serious PM pollution in northern China, 1476 PM10 and 1464 PM2.5 valid daily filter samples were collected at six sites from December 2014 to November 2015 and analyzed for 29 species. The annual mean PM10 and PM2.5 concentrations were 149.4 ±â€¯93.1, 108.0 ±â€¯70.9 µg/m3, respectively. Organic carbon (OC) is the predominant PM2.5 component while crustal material predominated in PM10. Sulfate concentrations, which was the largest component in Xi'an PM in previous studies, were lower than nitrate. Winter sulfate, OC, and elemental carbon (EC) have decreased since 2003, while nitrate remained constant in recent years and the ratio of NO3-/SO42- increased from 0.4 in 2006 to 1.3 in 2014. This result suggests that the motor vehicle contribution to PM has increased relative to coal-fired power plant emissions over the past decade. The mass fractions of crustal material, sulfate, and EC in PM2.5 decreased as the PM2.5 concentrations increased from "clean" days (<50 µg/m3) to the highest values, while nitrate significantly increased. Despite forming through secondary reactions, the high concentrations of SOC and SO42- in winter are attributed to primary emissions and particularly to residential heating and cooking with coal. Primary SOC and SO42- accounted for 33% and 42% of their total PM2.5 concentrations in winter, respectively. Therefore, control measures applied to these primary sources can substantially improve air quality.