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To understand the characteristics of chemical components and dicarboxylic acids, oxocarboxylic acids and α‐dicarbonyls in atmospheric aerosols at underground coal fire environment, we collected fine aerosols (PM2.5) from Wuhai, Inner Mongolia, North China, where the underground coal fire often occurs. PM2.5 samples were analyzed for the measurements of carbonaceous components, stable carbon isotopic composition (δ13C) of total carbon, and molecular distribution and compound‐specific δ13C of diacids, oxoacids and α‐dicarbonyls. Oxalic acid (C2) was the most abundant species, accounting for 43.2%–63.1% (avg. 50.8%) of total diacids, followed by phthalic acid (Ph) (13.7%). Azelaic acid (C9) was the third most (7.4%) abundant, followed by succinic (C4) and malonic (C3) acids. Significant correlations of C2 diacid with glyoxylic (ωC2) and 3‐oxopropanoic (ωC3) acids and C3 diacid and their δ13C implied that diacids and related compounds were mainly derived from the underground coal fire emissions and subsequent in situ secondary formation. Based on molecular distribution, seasonal pattern and linear relations of C9 diacid with C2, C3, ωC2 and ωC3 as well as with Ph acid and total diacids, together with the comparability and similarity of its δ13C (−27.0 ± 0.9‰) with that of Ph acid and organic matter in coals, respectively, we found that the C9 diacid has been mainly derived from its precursors such as unsaturated fatty acids emitted from underground coal fires and their subsequent in situ photochemical oxidation. However, further research is needed to confirm such an importance of coal combustion for azelaic acid loading in atmospheric aerosols. Plain Language Summary: Fine aerosols in the atmosphere cause high uncertainty in radiative forcing of the Earth's climate system and have become one of the serious environmental risk factors, causing more than 6 million premature deaths annually. The atmospheric environment over the underground coal fire field is different from that in urban area, because the emission of inorganic gaseous species, volatile organic compounds and particulates that consist oxygen‐containing organic species and polycyclic aromatic hydrocarbons and their subsequent photochemical oxidation processes are relatively larger at the coal fire field. Our study on fine aerosols from underground coal fire field at Wuhai, North China showed a rather large abundance of dicarboxylic acids associated with a specific partitioning from the coal fires compared to observations from other environments including an unusual abundance of azelaic acid. Key Points: The characteristics of diacids in atmospheric aerosols at underground coal fire environment have been investigatedAzelaic acid could be applied in evaluating the coal combustion influence on secondary organic aerosols in the atmosphereC2 was mainly derived from underground coal fire emissions and their subsequent in situ photochemical oxidation [ABSTRACT FROM AUTHOR]

Water-soluble organic carbon (WSOC) in the cryosphere can significantly influence the global carbon cycle and radiation budget. However, WSOC in the snowpack has received little scientific attention to date. This study reports the fluorescence characteristics, absorption properties, and radiative effects of WSOC based on 34 snow samples collected from sites in northeastern China. A significant degree of regional WSOC variability is found, with concentrations ranging from 0.5±0.2 to 5.7±3.7µ g g -1 (average concentration: 3.6±3.2µ g g -1). The three principal fluorescent components of WSOC are identified as (1) the high-oxygenated humic-like substances (HULIS-1) of terrestrial origin, (2) the low-oxygenated humic-like substances (HULIS-2) of mixed origin, and (3) the protein-like substances (PRLIS) derived from autochthonous microbial activity. In southeastern Inner Mongolia (SEIM), a region dominated by desert and exposed soils, the WSOC exhibits the highest humification index (HIX) but the lowest fluorescence (FI) and biological (BIX) indices; the fluorescence signal is mainly attributed to HULIS-1 and thus implicates soil as the primary source. By contrast, the HIX (FI and BIX) value is the lowest (highest), and the percentage of PRLIS is the highest in the remote area of northeastern Inner Mongolia (NEIM), suggesting a primarily biological source. For south and north of northeastern China (SNC and NNC), both of which are characterized by intensive agriculture and industrial activity, the fluorescence signal is dominated by HULIS-2, and the HIX, FI, and BIX values are all moderate, indicating the mixed origins for WSOC (anthropogenic activity, microbial activity, and soil). We also observe that, throughout northeastern China, the light absorption of WSOC is dominated by HULIS-1, followed by HULIS-2 and PRLIS. The contribution of WSOC to albedo reduction (average concentration: 3.6 µ g g -1) in the ultraviolet–visible (UV–Vis) band is approximately half that of black carbon (BC average concentration: 0.6 µ g g -1). Radiative forcing is 3.8 (0.8) W m -2 in old (fresh) snow, equating to 19 % (17 %) of the radiative forcing of BC. These results indicate that WSOC has a profound impact on snow albedo and the solar radiation balance. [ABSTRACT FROM AUTHOR]

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Lake eutrophication seriously threatens water quality and human health. Under continuous global warming and intensified human activity, increasing attention is being paid to how lake trophic status responds to climate change and anthropogenic impacts. Based on the sedimentary organic matter (SOM) molecular composition determined by the Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) technology, and combined with the SOM stable nitrogen isotopes (δ15N org), we studied how lake trophic status and ecology respond to both climatic changes and anthropogenic impacts of the past 500 yrs at Lake Daihai, Inner Mongolia. The results show that the relative abundance of lipids, proteins, and carbohydrates in lake sediments kept relatively low before AD ∼1850, and increased gradually thereafter, especially after AD ∼1950, suggesting that the lake trophic status was low before AD ∼1850, but obviously increased during the past one more century. On the other hand, the relative abundance of allochthonous condensed aromatics and vascular plant-derived polyphenols compounds gradually decreased after AD ∼1850, which is most likely due to the intensified land-use changes in the catchment. Our results show that the SOM molecular composition is more sensitive to trace the land-use changes than the δ15N org ratios, suggesting a potential use of this technique to trace even earlier human land uses (e.g., during the prehistorical times) in a catchment. The results of this study suggest that intensified land-use change, increased discharges of human sewage and industrial wastewater, cropland runoff, and concentrated effects caused by lake level drops may have combinedly increased nutrient concentration and accelerated lake eutrophication at Lake Daihai. Therefore, proper policy is necessary to slow down anthropogenic impacts and limit further eutrophication for lakes like Lake Daihai. • SOM molecular composition reveals a 500-yr eutrophication history of Lake Daihai. • Land-use changes clearly alter SOM molecular composition since AD1850. • Intensified human activities obviously accelerated eutrophication after AD 1950. [ABSTRACT FROM AUTHOR]