By quantifying the absorption of black carbon (BC), brown carbon (BrC) and the lensing effect, we found that BrC dominates the total absorption at 450 nm, and the largest absorption contribution proportion of BrC could reach 78.3% during heavy pollution. The average absorption enhancement (E-abs) at 530 nm was only 1.38, indicating that BC is not coated well here. The average value of the absorption Angstrom exponent (AAE) between 450 nm and 530 nm was 5.3, suggesting a high concentration of BrC in Wangdu. CHN+ was the greatest contributor to the light absorption of molecules detected in MSOC with a proportion of 12.2-22.4%, in which the polycyclic aromatic nitrogen heterocycles (PANHs) were the dominant compounds. The C6H5NO3 and its homologous series accounted for 3.0-11.3%, and the C15H9N and its homologous series, including one C16H11N and three C17H13N compounds, accounted for 5.1-12.3%. The absorption of these PANHs is comparable to that of nitro-aromatics, which should attract more attention to the impact of climate radiative forcing.

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

Particulate black carbon (BC) affects global warming by absorbing the solar radiation, by affecting cloud formation, and by decreasing ground albedo when deposited to snow or ice. BC has also a wide variety of adverse effects on human population health. In this article we reviewed the BC emission factors (EFs) of major anthropogenic sources, i.e. traffic (incl. marine and aviation), residential combustion, and energy production. We included BC EFs measured directly from individual sources and EFs derived from ambient measurements. Each source category was divided into sub-categories to find and demonstrate systematical trends, such as the potential influence of fuel, combustion technologies, and exhaust/flue gas cleaning systems on BC EFs. Our review highlights the importance of society level emission regulation in BC emission mitigation; a clear BC emission reduction was observed in ambient studies for road traffic as well as in direct emission measurements of diesel-powered individual vehicles. However, the BC emissions of gasoline vehicles were observed to be higher for vehicles with direct fuel injection techniques (gasoline direct injection) than for vehicles with port-fueled injection, indicating potentially negative trend in gasoline vehicle fleet BC EFs. In the case of shipping, a relatively clear correlation was seen between the engine size and BC EFs so that the fuel specific BC EFs of the largest engines were the lowest. Regarding the BC EFs from residential combustion, we observed large variation in EFs, indicating that fuel type and quality as well as combustion appliances significantly influence BC EFs. The largest data gaps were in EFs of large-scale energy production which can be seen crucial for estimating global radiative forcing potential of anthropogenic BC emissions. In addition, much more research is needed to improve global coverage of BC EFs. Furthermore, the use of existing data is complicated by different EF calculation methods, different units used in reporting and by variation of results due to different experimental setups and BC measurement methods. In general, the conducted review of BC EFs is seen to significantly improve the accuracy of future emission inventories and the evaluations of the climate, air quality, and health impacts of anthropogenic BC emissions.

Fuel combustion provides basic energy for the society but also produces CO2 and incomplete combustion products that threaten human survival, climate change, and global sustainability. A variety of fuels burned in different facilities expectedly have distinct impacts on climate, which remains to be quantitatively assessed. This study uses updated emission inventories and an earth system model to evaluate absolute and relative contributions in combustion emission-associated climate forcing by fuels, sectors, and regions. We showed that, from 1970 to 2014, coal burned in the energy sector and oil used in the transportation sector contributed comparable energies consumed (24 and 20% of the total) but had distinct climate forcing (1 and 40%, respectively). Globally, coal burned for energy production had negative impacts on climate forcing but positive effects in the residential sector. In many developing countries, coal combustion in the energy sector had negative radiative forcing (RF) per unit energy consumed due to insufficient controls on sulfur and scattering aerosol levels, but oils in the transportation sector had high positive RF values. These results had important implications on the energy transition and emission reduction actions in response to climate change. Distinct climate efficiencies of energies and the spatial heterogeneity implied differentiated energy utilization strategies and pollution control policies by region and sector.

Carbonaceous particles are an important radiative forcing agent in the atmosphere, with large temporal and spatial variations in their concentrations and compositions, especially in remote regions. This study reported the delta C-14 and delta C-13 of total carbon (TC) and water-insoluble particulate carbon (IPC) of the total suspended particles (TSP) and PM2.5 at a remote site of the eastern Tibetan Plateau (TP), a region that is influenced by heavy air pollution from Southwest China. The average organic carbon and elemental carbon concentrations of TSP samples in this study were 3.20 +/- 2.38 mu g m(-3) and 0.68 +/- 0.67 mu g m(-3), respectively, with low and high values in summer and winter, respectively. The fossil fuel contributions of TC in TSP and PM2.5 samples were 18.91 +/- 7.22% and 23.13 +/- 12.52%, respectively, both of which were far lower than that in Southwest China, indicating the importance of non-fossil contributions from local sources. The delta C-13 of TC in TSP samples of the study site was -27.06 +/- 0.96 parts per thousand, which is between the values of long-range transported sources (e.g., Southwest China) and local biomass combustion emissions. Therefore, despite the contribution from the long-range transport of particles, aerosols emitted from local biomass combustion also have an important influence on carbonaceous particles at the study site. The findings of this work can be applied to other remote sites on the eastern TP and should be considered in related research in the future.

The Tibet Autonomous Region in China is a unique place with high altitude and special Tibetan culture. The residents have different living habits and domestic fuels from those in other parts of China, however, knowledge on the emission characteristics of local residential fuels remain poorly understood until now. In this study, nine popular residential fuels in the Tibet are burned in situ to study the aerosol chemical compositions, mass spectral signatures, and emission characteristics from their burning emissions. Overall, emissions of particulate and gaseous pollutants depend strongly on the burning conditions, in addition to the fuel constituents themselves. Burning the biofuels of yak dung, WeiSang mixture fuels, and two powdery Tibetan incenses with relatively low combustion efficiencies can emit large amounts of CO and aerosols, especially organic aerosols (>90%) with large diameters. In contrast, burning of wood, coal, ghee lamp, stick-like Tibetan incense, and diesel can release abundant CO2 but fewer aerosols from their flaming combustion. A comprehensive database consisting of the high-resolution mass spectra of organics and emission factors of multiple chemical components are established. Distinctly different mass spectral signatures are found among the different fuels, in particularly those unique Tibetan biofuels. All these findings have significant implications for the identification of aerosol sources, compilation of pollutant emission inventories, and assessment of potential environment effects in this remote region.

Coal consumed in domestic cooking and heating in rural areas of China is considered as a major source of air pollution. To efficiently represent the emission of coal burnt for residential living at various combustion regimes, four coal samples are selected for combustion experiments in the simulated air state at three different temperatures in a drop-tube furnace system in this study. Size-segregated particulate matter in flue gas from combustion of the four coal samples at different temperatures were collected by a TISCH-type Andersen eight-stage impact sampler operating synchronously with the furnace system. The emission factors of the particulate matter samples show that OC2 and OC3 are the main carbonaceous products of bituminous coal and lignite combustion. It is also found that the particulate matter from lignite flue gas contains EC1 in a large proportion and a small amount of highly-refractory EC2 and EC3 from bituminous coals. Meanwhile, in order to evaluate the light-absorption of organic carbon in particulate matter, the mass absorption cross efficiency (alpha/rho) is investigated. The clear-sky radiative transfer model shows that BrC emitted from low-temperature burning leads to even positive top-ofatmosphere radiative forcing at surfaces with an albedo of 0.19. In the 300-700 nm spectral band, the simple forcing efficiency (SFE) of particulate matter sampled significantly decreases as combustion temperature and coal maturity increase. The particulate matter presents a high SFE in the range of 0.4-1.1 mu m in terms of particle size.

The light absorption black carbon (BC) and brown carbon (BrC) are two important sources of uncertainties in radiative forcing estimate. Here we investigated the light absorption enhancement (E-abs) of BC due to coated materials at an urban (Beijing) and a rural site (Gucheng) in North China Plain (NCP) in winter 2019 by using a photoacoustic extinctiometer coupled with a thermodenuder. Our results showed that the average (+/- 1s) E-abs was 1.32 (+/- 0.15) at the rural site, which was slightly higher than that at the urban site (1.24 +/- 0.15). The dependence of E-abs on coating materials was found to be relatively limited at both sites. However, E-abs presented considerable increases as a function of relative humidity below 70%. Further analysis showed that E-abs during non-heating period in Beijing was mainly caused by secondary components, while it was dominantly contributed by enhanced primary emissions in heating season at both sites. In particular, aerosol particles mixed with coal combustion emissions had a large impact on E-abs (>1.40), while the fresh traffic emissions and freshly oxidized secondary OA (SOA) had limited E-abs (1.00-1.23). Although highly aged or aqueous-phase processed SOA coated on BC showed the largest E-abs, their contributions to the bulk absorption enhancement were generally small. We also quantified the absorption of BrC and source contributions. The results showed the BrC absorption at the rural site was nearly twice that of urban site, yet absorption Angstrom exponents were similar. Multiple linear regression analysis highlighted the major sources of BrC being coal combustion emissions and photochemical SOA at both sites with additional biomass burning at the rural site. Overall, our results demonstrated the relatively limited winter light absorption enhancement of BC in different chemical environments in NCP, which needs be considered in regional climate models to improve BC radiative forcing estimates. (C) 2021 Elsevier B.V. All rights reserved.

Under typical Chinese wintry rural conditions, dominating individual coal heating would emit lots of the fine fraction of ambient aerosol exclusively including carbonaceous particulate matter. In this study, a specified drop tube furnace system is employed to simulate experimentally particle matter emitted during individual coal combustion. Emphatically, the effects of coal types, oxygen concentration and combustion ambient on the formation characteristics of carbonaceous aerosols in the flue gas were discussed. It was found that the fraction of organic carbon (OC) and elemental carbon (EC) in the flue gas produced by bituminous coal combustion was lower than that of lignite. Meanwhile, with the increase of oxygen concentration, the production of OC and EC decreased, but the sensitivity of EC to oxygen concentration was higher than that of OC, which indicated that the formation mechanism of OC and EC is extremely different. Noticeable, the Absorption Angstrom Exponent (AAE) of methanol-soluble organic carbon (MSOC) is higher than that of water-soluble organic carbon (WSOC), which indicates that a large amount of methanol-soluble but water-insoluble brown carbon has strong light absorption capacity between 330 nm and 550 nm, and its light absorption capacity tends to be in the short-wave region. The mass absorption efficiency (MAE) of brown carbon produced by coal combustion (0.1-1 m(2)/gC) is similar to that of atmospheric aerosol (0.3-1.8 m(2)/gC), which indicates that the contribution of brown carbon emitted from coal combustion to the light absorption capacity of atmospheric aerosol should not be underestimated.

Understanding of carbonaceous aerosols from different combustion sources and their optical properties are important to better understand atmospheric aerosol sources and estimate their radiative forcing. In this study, eight organic carbon (OC) and elemental carbon (EC) sub-fractions and light absorption properties of EC are investigated using thermal/optical method and compared among six typical solid and liquid fossil fuel combustion sources (e.g., coal combustion, industry, power plant, diesel and gasoline vehicle, and ship emissions) and within each source type, with consideration of different fuel types and combustion conditions. The results indicate that OC and EC sub-fraction distributions and mass absorption efficiency of EC (MAE(EC)) are sensitive and specific to sources, fuels, combustion and operating conditions. The differences in carbon fractions and AE(EC) between solid and fossil fuel source emissions are statistically significant (p < 0.05). The average MAE(EC) from liquid fossil fuel sources (7.9 +/- 3.5 m(2)/g) are around1.5-fold higher than those from solid fossil fuels (5.3 +/- 4.0 m(2)/g). Correlation analysis indicates that light attenuation of EC positively correlates with EC1 and EC2 fractions with correlation coefficients (r) around 0.6, while negatively correlates with the percentages of OC2 and OC3 in total carbon. Inter-comparisons of distributions of carbon sub-fractions and MAE(EC) from different coal samples indicate the tested new stoves and honeycomb-like shape may contribute to lower EC emission factors but with stronger light absorptivity of EC, suggesting curbing short-lived pollutants (e.g., EC) with improvement of coal stoves and clean coal at current stage might not always result in co-benefits of air quality and climate.