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.

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.

Black carbon (BC) is an important aerosol species because of its global and regional influence on radiative forcing and its local effects on the environment and human health. We have estimated the emissions of BC in China, where roughly one-fourth of global anthropogenic emissions is believed to originate. China's high rates of usage of coal and biofuels are primarily responsible for high BC emissions. This paper pays particular attention to the application of appropriate emission factors for China and the attenuation of these emissions where control devices are used. Nevertheless, because of the high degree of uncertainty associated with BC emission factors, we provide ranges of uncertainty for our emission estimates, which are approximately a factor of eight. In our central case, we calculate that BC emissions in China in 1995 were 1342 Gg, about 83% being generated by the residential combustion of coal and biofuels, We estimate that BC emissions could fall to 1224 Gg by 2020. This 9% decrease in BC emissions can be contrasted with the expected increase of 50% in energy use; the reduction will be obtained because of a transition to more advanced technology, including greater use of coal briquettes in place of raw coal in cities and towns. The increased use of diesel vehicles in the future will result in a greater share of the transport sector in total BC emissions. Spatially, BC emissions are predominantly distributed in an east-west swath across China's heartland, where the rural use of coal and biofuels for cooking and heating is widespread. This is in contrast Lo the emissions of most other anthropogenically derived air pollutants. which are closely tied to population and industrial centers. (C) 2001 Elsevier Science Ltd. All rights reserved.