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

Particulate polycyclic aromatic hydrocarbons in rural households burning solid fuels in Xuanwei County, Southwest China: occurrence, size distribution, and health risks

The study is about the size distribution and health risks of polycyclic aromatic hydrocarbons (PAHs) in indoor environment of Xuanwei, Southwest China particle samples were collected by Anderson 8-stage impactor which was used to gather particle samples to nine size ranges. Size-segregated samples were collected in indoor from a rural village in Xuanwei during the non-heating and heating seasons. The results showed that the total concentrations of the indoor particulate matter (PM) were 757 ± 60 and 990 ± 78 μg/m3 in non-heating and heating seasons, respectively. The total concentration of indoor PAHs reached to 8.42 ± 0.53 μg/m3 in the heating season, which was considerably greater than the concentration in the non-heating season (2.85 ± 1.72 μg/m3). The size distribution of PAHs showed that PAHs were mainly enriched in PMs with the diameter <1.1 μm. The diagnostic ratios (DR) and principal component analysis (PCA) showed that coal and wood for residential heating and cooking were the main sources of indoor PAHs. The results of the health risk showed that the total deposition concentration (DC) in the alveolar region (AR) was 0.25 and 0.68 μg/m3 in the non-heating and heating seasons respectively. Throughout the entire sampling periods, the lifetime cancer risk (R) based on DC of children and adults varied between 3.53 ×10-5 to 1.79 ×10-4. During the heating season, the potential cancer risk of PAHs in adults was significant, exceeding 10-4, with a rate of 96%.

Emissions of nitrated and oxygenated polycyclic aromatic hydrocarbons bound to coarse particles from solid fuel combustion

Parent polycyclic aromatic hydrocarbons (PAHs) emitted by residential sector have been well studied, however, data on PAHs derivatives such as nitrated PAHs (nPAHs) and oxygenated PAHs (oPAHs) are scarce. In this study, emission factors (EFs) of PM10-bound nPAHs and oPAHs from the combustion of eight different solid fuels in three different stoves in rural homes were measured in field, and a total of twelve fuel-stove combinations were included. Results showed that the field-based EFs for different fuel-stove combinations varied over three orders of magnitude, which ranged from 3.3 to 514 μg/kg and from 0.1 to 214 mg/kg for nPAHs and oPAHs, respectively. Biomass burning had 2.2 and 14.8 times higher EFs values of nPAHs and oPAHs compared with coal burning. The size distribution pattern of PAHs derivatives confirmed that they prefer to bind to fine particles. The composition profiles of nPAHs and oPAHs varied largely in different coals, while slightly in different biomasses. Furthermore, the nPAHs and oPAHs composition profiles varied largely from emission source to the nearby atmosphere, implying that the composition of PAHs derivative changed during small-scale transport process. Results from this study can fill in the data gap in PAHs derivative emissions from residential solid fuel combustion and help to evaluate the environmental and health impacts of residential solid fuel combustion.

Gas Particle Partitioning of PAHs Emissions from Typical Solid Fuel Combustions as Well as Their Health Risk Assessment in Rural Guanzhong Plain, China

Air pollutants from the incomplete combustion of rural solid fuels are seriously harmful to both air quality and human health. To quantify the health effects of different fuel-stove combinations, gas and particle partitioning of twenty-nine species of polycyclic aromatic hydrocarbons (PAHs) emitted from seven fuel-stove combinations were examined in this study, and the benzo (a) pyrene toxicity equivalent (BaPeq) and cancer risks were estimated accordingly. The results showed that the gas phase PAHs (accounting for 68-78% of the total PAHs) had higher emission factors (EFs) than particulate ones. For all combustion combinations, pPAHs accounted for the highest proportion (84.5% to 99.3%) in both the gas and particulate phases, followed by aPAHs (0.63-14.7%), while the proportions of nPAHs and oPAHs were much lower (2-4 orders of magnitude) than pPAHs. For BaPeq, particulate phase PAHs dominated the BaPeq rather than gas ones, which may be due to the greater abundance of 5-ring particle PAHs. Gas and particle pPAHs were both predominant in the BaPeq, with proportions of 95.2-98.6% for all combustion combinations. Cancer risk results showed a descending order of bituminous coal combustion (0.003-0.05), biomass burning (0.002-0.01), and clean briquette coal combustion (10^-5-0.001), indicating that local residents caused a severe health threat by solid fuel combustion (the threshold: 10^-4). The results also highlighted that clean briquette coal could reduce cancer risks by 1-2 orders of magnitude compared to bulk coal and biomass. For oPAH, BcdPQ (6H-benzo(c,d)pyrene-6-one) had the highest cancer risk, ranging from 4.83 × 10^-5 to 2.45 × 10^-4, which were even higher than the total of aPAHs and nPAHs. The dramatically high toxicity and cancer risk of PAHs from solid fuel combustion strengthened the necessity and urgency of clean heating innovation in Guanzhong Plain and in similar places.

Dwindling aromatic compounds in fine aerosols from chunk coal to honeycomb briquette combustion

With the implementation of clean coal policy in China, the chunk coal has been gradually replaced by honeycomb briquette in domestic energies. In this study, the molecular composition of fine particles (PM_2.5) from chunk coal and honeycomb briquette combustion is characterized using the Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS). More than 6000 molecular formulae were detected in each PM_2.5 sample. A remarkable decrease in unsaturation and aromatic compounds was found from chunk coal to honeycomb briquette derived aerosols. Around 73.6% of the unique CHON compounds in chunk coal are considered to have aromatic structures, while it decreased to 7.3% in honeycomb briquette. Most of these nitroaromatics detected only in chunk coal are highly carcinogenic and mutagenic with 4-6 rings. Moreover, the aromatic compounds in sulfur-containing compounds also showed a significant decrease. Meanwhile, because of the perforated shape and the additives added during the production of honeycomb briquettes, there are more heteroatoms-containing molecules released from honeycomb briquette combustion, which are highly functional compounds with high molecular weight, high degree of oxidation, and low volatility. Our results provide molecular level evidence that the transformation from chunk coal to honeycomb briquette can effectively reduce the emission of aromatic compounds, which is beneficial to assessing and reducing the impacts to climate change as well as human health.

An overlooked source of nanosized lead particles in the atmosphere: Residential honeycomb briquette combustion

Atmospheric lead (Pb) pollution has attracted long-term and widespread concerns due to its high toxicity. The definite source identification of atmospheric Pb is the key step to mitigate this pollution. Here, we first report an overlooked source of atmospheric nanosized Pb particles using transmission electron microscopy and bulk sample analyses, finding that residential honeycomb briquette combustion emits large numbers of nanosized Pb-rich particles. We found that 33.7 ± 19.9 % of primary particles by number from residential honeycomb briquette combustion contains the crystalline Pb particles. These Pb-rich particles range in size from 14 to 956 nm with a mean diameter of 117 nm. Compared with raw coal chunks, honeycomb briquette combustion could emit less carbonaceous particles, but largely increase nanosized Pb particle emissions. This result is attributed to two key factors: (1) higher Pb content in honeycomb briquette (63.6 μg g^-1) than that in coal chunk (8.5 μg g^-1), and (2) higher Pb release rate for honeycomb briquette (62.3 %) caused by honeycomb structure than that for coal chunk (20.1 %). This study highlights that atmospheric and health implications of high emissions of toxic nanosized Pb from honeycomb briquette should be paid more attention in future research on ambient and indoor airs.

Emissions of particulate PAHs from solid fuel combustion in indoor cookstoves

Residential solid fuel combustion is a major emission source of PAHs (polycyclic aromatic hydrocarbons) in most developing countries, including China; however, accurate estimates of PAH emissions are often challenged by limited real-world emission factors (EFs) under field conditions, which can hardly be repeated in laboratory-controlled tests. In this study, a series of field measurements was conducted to determine the emissions of 28 PAHs from different fuel-stove combinations. A total of 14 fuel-stove combinations were studied. The total EFs of 28 PAHs (EF_PAH28), on the basis of fuel mass, ranged from 20.7 to 535 mg/kg, with relatively lower EFs for coal than for biomass. Biomass burning in gasifier stoves had lower PAH EFs and fewer toxic PAH species than biomass burning in traditional brick stoves. Fuel type was a significant factor affecting PAH emissions, while stove difference had a relatively smaller influence. Much higher EFs were found from these field tests than from the idealized laboratory tests, which indicated significant underestimation in inventories based on the laboratory-based EFs. Biomass and coal had different profiles, with larger intra-fuel variations in coal than those in biomass. Highly variable values of some, though not all, commonly used isomer ratios indicated substantial biases in source apportionment relying on single or simple ratios without correction, and the MCE was found to be significantly corrected with some ratios.

Fine particles from village air in northern China in winter: Large contribution of primary organic aerosols from residential solid fuel burning

Rural residential emissions contribute significantly to regional air pollution in China, but our understanding on how residential solid fuel burning influences the village outdoor air quality is limited. In this study, we compared the fine particulate matter (PM_2.5) composition and individual particle characteristics from 11 to 18 January 2017 at a village and an urban site in northern China. At the village site, each day was divided into four periods: cooking (07:30-10:00; 16:00-17:00), daytime (10:00-16:00), heating (17:00-24:00), and midnight (00:00-07:30) periods. The highest PM_2.5 concentration occurred during the cooking period (236 ± 88 μg m^-3), which was characterized by high concentrations of K⁺ and abundant primary OM-K particles (i.e., organic matter mixed with K-salts) emitted from residential biomass burning. The second highest PM_2.5 concentration was found during the heating period (161 ± 97 μg m^-3), and the PM_2.5 contained abundant spherical primary OM particles (i.e., tarballs) emitted from residential coal burning. The primary emissions from residential solid fuel burning resulted in 75% of the village OM by mass consisting of primary OM and 67% of the village aerosol particles by number internally mixing with primary OM particles. The village PM_2.5 composition was different from that of the urban PM_2.5, with the former containing more OM (47% vs 32%) and less secondary inorganic ions (30% vs 46%). Individual primary OM-K and tarballs were abundant in the village air. These results suggest a large contribution of village residential emissions in the winter to village air pollution. Our study highlights that the residential health in villages of northern China should be paid more attention because of high PM_2.5 concentrations and abundant toxic particles during the cooking and heating periods per day in winter.

First High-Resolution Emission Inventory of Levoglucosan for Biomass Burning and Non-Biomass Burning Sources in China

Levoglucosan (LG) emitted from non-biomass burning (non-BB) sources has given rise to biased or even unreasonable source identification results when adopting LG as a distinct marker of biomass burning (BB). The estimation of LG emission and its spatiotemporal variation for various sources are the keys to reducing uncertainty. This study first developed a LG emission inventory for China from 25 sub-type sources belonging to eight categories, with a 3 km × 3 km spatial resolution and monthly distribution. The total LG emission in 2014 was 145.7 Gg. Domestic BB and open BB contributed 39.2 and 34.3% of the total emission. Non-BB sources, including municipal solid waste burning (9.7%), firework burning (9.6%), meat cooking (5.4%), domestic coal burning (1.5%), ritual item burning (0.2%), and industrial coal burning (0.1%), contributed to 26.5% of the total emission. LG emission varied spatially and temporally. Non-BB sources have a significant spatiotemporal impact on BB source contributions, even in high BB emission regions or in sowing, harvesting, and winter heating seasons. The local BB contributions have been substantially overestimated by 4.28-369% in previous studies, wherein LG was solely referred to as the BB source. By 2018, LG emission from BB might decrease to 63.9% of its total emission. This high-resolution LG emission inventory can be greatly useful for source identification studies in China. It also supports future research on the modeling of smoke aging and pollution control.

Parent, alkylated, oxygenated and nitrated polycyclic aromatic hydrocarbons in PM2.5 emitted from residential biomass burning and coal combustion: A novel database of 14 heating scenarios

To characterize the emissions of polycyclic aromatic hydrocarbons (PAHs) from residential biomass burning and coal combustion in field environments, smoke samples were collected from the combustion of six types of biomass in heated kangs and four types of coal in traditional stoves and semi-gasifier stoves. The emission factors (EFs) of the total PAH were in the range of 84.5-344 mg/kg for biomass burning, with lower EFs for biomass with higher densities, and in the range of 38.0-206 mg/kg for coal combustion, with lower EFs for coals with higher maturity. Moreover, EFs were lower from high-density biomass fuels (wood trunk, 84.5 ± 11.3 mg/kg) than low-maturity coals (bituminous coal, 206 ± 16.5 mg/kg). Parent, oxygenated, alkylated, and nitrated PAHs accounted for 81.1%, 12.6%, 6.2%, and 0.1%, respectively, of the total-PAH EFs from biomass burning, and 84.7%, 13.8%, 1.4%, and 0.1%, respectively, of the total-PAH EFs from coal combustion. PAH source profiles differed negligibly between biomass fuels but differed significantly between bituminous coal and anthracite coal fuels. The characteristic species of sources were phenanthrene, 9-fluorenone, and 2-nitrobiphenyl for biomass burning, and were phenanthrene, benzo[ghi]perylene, 1,4-naphthoquinone, and 2-nitrobiphenyl for coal combustion. The ratios of benzo[b]fluoranthene/(benzo[b]fluoranthene + benzo[k]fluoranthene) were 0.40-0.45 for biomass burning and 0.89-0.91 for coal combustion, and these significantly different values constitute unique markers for distinguishing these fuels in source apportionment. Benzo[a]pyrene-equivalent factor emissions were 2.79-11.3 mg/kg for biomass and 7.49-41.9 mg/kg for coal, where parent PAHs contributed 92.0%-95.1% from biomass burning and 98.6%-98.8% from coal combustion. Total-PAH emissions from residential heating were 1552 t across Shaanxi province, to which wheat straw (445 t) in biomass burning and bituminous coal (438 t) in coal combustion were the highest contributors. Results from this study provide crucial knowledge for the source identification of PAHs as well as for the design of abatement strategies against pollutant emissions.