Chemical And Light Absorption Properties Of Brown Carbon Emitted From Residential Coal Combustion In China

Brown carbon?BrC?is a type of light absorbing organic carbon?OC?,which is strongly wavelength dependent and mainly absorbing light in the low wavelength visible and near ultraviolet regions.Coal combustion is an important source of atmospheric brown carbon?BrC?,but the relevant research is still in its infancy,The study of it's content,chemical and optical characteristics can further understand the impact of BrC to atmospheric environment and human health.In this study,six types of coal?Raw-coal chunks and Honey-comb briquettes?with different geological maturity were selected to produce the smoke particles.Then the characteristics of abundance,chemistry and light absorption properties of BrC fractions?WSOC?HULIS_w?ASOC?MSOC?were investigated,the main conclusions are as follows:?1?In this study,the relative percentages of the four types of BrC components?WSOC,HULIS_w,ASOC,MSOC?in smoke particles emitted from coal combustion were 4.33%-45.6%,2.25%-22.6%,3.16%-13.6%and 75.6%-98.2%respectively,indicating that coal combustion is an important source of atmospheric BrC.In addition,the results also indicated that the content of BrC in the particles varies with the types of extraction solvent,the maturity of the coal and the shape of the coal.For the same coal smoke sample,the amount of BrC fractions extracted by different solvents followed the order of MSOC>WSOC>ASOC and MSOC>WSOC+ASOC.The abundance of BrC?WSOC and ASOC?in coal combustion particles were also influenced by the maturity?R_o?of coal materials.The WSOC,HULIS_w and ASOC shows a“dumb-bell”trend as the maturity increased.However,the content of MSOC in the bituminous coal smoke particles did not exhibit significant changes,indicating that the BrC fraction extracted with methanol was not significantly affected by the maturity of coal samples.?2?Different BrC factions show similar UV-vis absorption characteristics,and their absorbance increases with the decreasing wavelength.The SUVA₂₅₄ value of BrC components extracted by different solvents always follows the following orders:MSOC>ASOC>HULIS_w>WSOC.The AAE value of WSOC is generally higher than MSOC and ASOC,indicating WSOC may have stronger wavelength dependence than MSOC and ASOC.As an important part of WSOC,HULIS_w has similar AAE values to the corresponding WSOC components.In addition,the WSOC and MSOC fractions in the low-mature coal smoke particles have relative lower SUVA₂₅₄ and higher S_R values.Compared with WSOC,both ASOC and MSOC have higher MAE₃₆₅ values,indicating that the latter has stronger light absorption capability.?3?The different types of BrC emitted from coal combustion have similar fluorescence characteristics.For example,all WSOC samples contain two major fluorescence peaks,A and B,while,there are also some differences:the detection of E peaks in YC-1 and YC-2 should be caused by differences in the chemical composition of coal.In addition,there are many similarities in the fluorescence spectra of BrC emitted from the combustion of coal with different maturity and shapes?raw coal chunks and honeycomb briquettes?indicated that coal maturity and shape have no significant effects on the fluorescence spectrum of the BrC fractions.?4?The results of ¹H NMR showed that the HULIS_w emitted from the combustion of coal samples contained relative high abundance of[H-C-C=]and[Ar-H]and relative low abundance of[C-H],[H-C-O],indicating that the HULIS_w emitted from coal combustion contained more aromatic structures and less aliphatic structures.The results of FT-ICR MS showed that the soot HULIS_w contains more S-containing substances,indicating that coal combustion may be an important source of S-containing components in atmospheric HULIS.Therefor,reducing emission from coal combustion can significantly reduce the S-containing componences in HULIS and their potential environmental and health impacts.?5?The results of Py-GC/MS showed that the pyrolysis products derived from soot particles emitted from the combustion of coal with different maturity were very similar.They were all dominated by aromatic compounds?58.1-92.0%?and including phenolic compounds?0.66-3.23%?,aliphatic hydrocarbon?0.21-9.57%?,furan compounds?1.42-2.57%?,S-containing compounds?NA-4.12%?and N-containing compounds?NA-3.91%?.These data indicating these soot particles were characterized with aromatic nuclei and/or oxygen-,nitrogen-containing units.In addation,the content of aromatic compounds in pyrolysis products of soot increased with the increasing coal maturity and the content of phenolic compounds exhibited a decreasing trend.The N-containing compounds were mainly contained in soot emitted from the combustion of low maturity coal samples,the S-containing compounds mainly contained in soot emitted from the combustion of coal with high maturity.