The chemical and absorptive characteristics of brown carbon emission from household coal combustion revealed by Guangzhou Institute of Geochemistry

Brown carbon (BRC) is a kind of organic carbon component in atmospheric aerosols, which has strong light absorption in the ultraviolet visible light band, and its absorption characteristics show significant wavelength dependence It widely exists in aerosol, cloud, fog, rain and other media As an important macromolecular organic matter, BRC can not only directly absorb and scatter solar radiation, but also affect the energy balance of the earth, the hygroscopic growth of particles, the formation of cloud condensation nodules and ice cores, and thus the atmospheric environment and climate change In addition, this kind of macromolecular organic matter can also induce the production of living oxygen substances, which is very harmful to human health There are many sources of BRC in the atmosphere, among which biomass and fossil fuel combustion are considered as the most important primary emission sources For a long time, China's energy structure has been based on coal resources as the main fuel According to the data of China's National Bureau of Statistics (2016), coal consumption (4000tg) accounts for 68% of China's total energy, of which 93tg is used as domestic fuel for cooking in winter and throughout the year (NBSC, 2016) The large-scale use of domestic coal leads to a large number of pollutant emissions, which has been highly concerned by relevant experts and carried out a lot of research However, these works are mainly focused on the emission of organic carbon, black carbon and polycyclic aromatic hydrocarbons, while the research on the emission of BRC from coal is relatively lack, and the emission characteristics are not well understood Recently, Dr Song Jianzhong, associate researcher of Peng Ping'an academician team of Guangzhou Institute of geochemistry, Chinese Academy of Sciences, and Dr Li Meiju selected coal with different maturity (bulk coal and honeycomb coal) to burn in the domestic coal furnace and collect the discharged particulate matter samples Different BRC components (water-soluble organic carbon (WSOC), water-soluble humus like substance (HULIS w), alkali soluble organic matter (ASoC) in the samples were analyzed ）The contents, chemical and optical characteristics of methanol dissolved organic matter (MSOC) have been studied systematically The following important knowledge has been obtained: (1) the combustion of domestic coal is an important emission source of atmospheric brown carbon, and its content and absorption characteristics are mainly affected by the maturity of coal, while the shape of coal has little influence In this study, the content of different BRC components such as WSOC, HULIS W and ASoC showed a "dumbbell type" trend with the increase of coal maturity (Figure 1) In addition, the absorption spectrum characteristics of different BRC components have a direct correlation with the maturity of coal For example, WSOC and MSOC components of low maturity coal emissions have relatively low absorption capacity Compared with WSOC, ASoC and MSOC have lower AAE value and higher Suva 254 and Mae 365 value, indicating that the latter has lower wavelength dependence and stronger aromaticity and light absorption ability Fig 1 emission characteristics of domestic coal combustion with different maturity (source: environ SCI Technical.) (2) molecular characteristics of WSOC and MSOC components were further studied by FT-ICR Ms, The influence of coal maturity on the molecular composition of emissions and the relationship between the molecular structure of organic matter and absorbability were discussed It is found that both WSOC and MSOC, the sources of domestic coal combustion, contain a series of complex organic macromolecules with M / Z distribution ranging from 150 to 600 The average molecular formula is C 14-16 h 16-18 o 4.5-5.6 n 0.17-0.33 s 0.66-0.88 (WSOC) and C 19-21 h 19-21 o 2.3-3.9 n 0.15-0.25 s 0.05-0.23 (MSOC), respectively Obviously, WSOC and MSOC have different molecular composition, WSOC contains more o and s, while MSOC contains more C and H According to the composition of elements, these organic compounds can be divided into CHO, Chon, chos and chons WSOC contains more S-containing compounds (chos and chons) (65 – 87%), while MSOC contains more CHO and Chon compounds (79 – 96%) Compared with the environmental samples, the water-soluble organic compounds emitted from the combustion of domestic coal contain significantly more S-containing compounds, indicating that coal combustion emissions may be an important source of sulfur-containing components in the atmosphere of HULIS It is worth noting that in the chos compounds, the O / s atomic ratio of more than 90% of the chos compounds is greater than 4, indicating the existence of a large number of organic sulfate structures Therefore, we think that domestic coal may be one of the important sources of sulfur compounds, especially organic sulfates It is also found that the molecular characteristics of organic matter are affected by coal maturity The macromolecular organic matter produced by low maturity coal combustion contains lower aromatic structure and more oxygen-containing polar groups In addition, the molecular characteristics of organic matter show a significant correlation with its absorbance, and organic components with high aromaticity, low O / C ratio and low polarity have strong absorbance In addition, in terms of molecular composition, CHO and Chon contribute a lot to the absorbability, especially Chon has a high absorbability Fig 2 Correlation Analysis of BRC molecular structure and absorbability (source: environ SCI Technical.) comprehensively, this study provides information on the optical and molecular characteristics of brown carbon emitted by household coal combustion, which is of great significance to better understand the impact of household coal combustion on atmospheric brown carbon The above achievements were published in the international journal Environmental Science & Technology (DOI: 10.1021 / ACS Est 9b04331), and were supported by NSFC (41390240, 41673117, 41473104) and National Key Laboratory of organic geochemistry.