| Humic Like Substances?HULIS?is an important component of water soluble organic carbon?WSOC?in PM2.5.From sunny days to highly polluted days,the intervention of HULIS to particle interface reactions will lead to a sudden increase of organic matter in aerosols,a sharp decline in visibility,and will deteriorate environment and climate and endanger human health.Therefore,it is very necessary to analyze the structure,content and source of HULIS.The TOC-V/TNM-1 analyzer was used to determine the HULIS concentrations in PM2.5samples.The HULIS solution was obtained by water extraction of aerosol samples followed with HLB column separation.The annual average concentration of HULIS-C was 13.25±2.56?g/m3 in Wenjiang District of Chengdu.Seasonal concentration trends are winter>spring>autumn?summer.The levels were higher than those in coastal cities such as Guangzhou,Hong Kong and Shanghai,and also higher than Beijing.Correlation analysis suggests that HULIS is positively associated with WSOC and AQI,and negatively associated with atmospheric visibility.This study used full-wavelength UV-Vis scanning to characterize of HULIS in seasonal PM2.5 aerosols from Wenjiang District,Chengdu.The study found that the structure of HULIS is similar between spring and summer,and between autumn and winter.Compared with the spring and summer,the maximum absorption wavelength of the HULIS ultraviolet spectrum in the autumn and winter has been blue-shifted.It is speculated that the content of sulfur and nitrogen in HULIS in spring and summer is higher than that in autumn and winter samples.Using the molar absorption coefficient?,the average molecular weights of HULIS in spring,summer,autumn and winter samples are estimated to be 690±26?633±25?658±26 and 671±34 Da,respectively.The average molecular weight of HULIS throughout the whole year is 663±33 Da.Seven obvious absorption peaks can be found in the FTIR spectrogram of HULIS for PM2.5 samples.The peaks are interpreted as absorption of alcohol O-H(3600 cm-1),carboxy O-H(3200 cm-1),carboxy C=O(1710 cm-1),organonitrate(1630 cm-1,1280 cm-1),alkane(1400 cm-1),and organosulfate(876 cm-1).Another weak absorption(1570 cm-1)produced by lignin was also be observed in the FTIR spectrogram of HULIS.Liquid Chromatography?LC?was used to analysis the HULIS in PM2.5 aerosols from Wenjiang District of Chengdu.Two groups of aliphatic chain compounds and two groups of benzene-containing compounds were found in LC chromatograms.The seasonal variation trend of aliphatic chain compounds A1 is:autumn>winter>spring>summer.It is speculated that the chain hydrocarbon A1 may be produced by the combustion of anthropogenic biomass.Meanwhile,the seasonal variation trend of aliphatic chain compounds A2 is:autumn>summer>winter>spring.It is speculated that the chain hydrocarbon A2 may be the secondary organic matter formed by the oxidation of natural source VOCs.Moreover,it can be regarded that benzene-containing compounds B1 is the compounds containing a single benzene ring,and benzene-containing compounds B2 is the compounds containing multi benzene rings.The seasonal variations of B1 and B2 are different.The average concentration of B1 in winter is the highest,indicating that B1 may be related to coal heating.On the contrary,the average concentrations of B2 in spring,autumn and summer are higher than that in winter,implying that B2 may be related to vehicle exhaust.We also used ion chromatography to determine water soluble ions in PM2.5.We found the association between HULIS and K+is the best,Meanwhile,associations between HULIS and Cl-and between HULIS and NO3-are fairly good.HULIS in atmospheric PM2.5 in Wenjiang District of Chengdu is mainly affected by biomass burning and coal combustion. |
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