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The pore structure of organic matter (OM) is affected by the maturity and type of OM, and these exert an important control on the development of OM pores. However, it is often challenging to distinguish between autochthonous and secondary OM. In this study, different types of OM were distinguished by means of morphology and the form of its occurrence under scanning electron microscopy (SEM) observation. Pyrolyzed samples were used to obtain pore structures of autochthonous and secondary OM from a lacustrine shale from high to over mature stages. The SEM observations indicated that the secondary OM is porous, whereas the autochthonous OM is nonporous. Further, nitrogen adsorption data showed that nanopores in the autochthonous OM are blocked in non-extracted samples and reoccurred after extraction, whereas nanopores in the secondary OM remain open from high to over mature stages. Moreover, the pore structure, i.e., pore type and pore size, differed for autochthonous and secondary OM in the lacustrine shale. For instance, nanopores in the autochthonous OM were micropores (smaller than 1.5 nm); nanopores in the secondary OM were mesopores (ranging from 5 to 20 nm) and micropores. Nanopores in the autochthonous OM were formed at reflectance values (Ro) of 1.50%, but they were slightly destroyed at the over mature stage. Nanopores in the secondary OM were formed at 2.00% Ro and were preserved. Therefore, the development of OM nanopores in the lacustrine shale was synchronously affected by the type of OM and maturity. Furthermore, nanopores in the secondary OM were more developed than those in the autochthonous OM; thus, the OM nanopores at the high mature stage belonged to the autochthonous OM, and those at the over mature stage mainly belonged to the secondary OM. Besides, the nanopores in the autochthonous OM are easily blocked. Therefore, the secondary OM is important to the development of OM nanopores in the lacustrine shale at the over mature stage., Competing Interests: The authors declare no competing financial interest., (© 2022 The Authors. Published by American Chemical Society.)

Shale gas desorption and loss is a serious and common phenomenon in the Sichuan Basin. The characteristics, capability, and origin of shale gas desorption are significant for understanding the shale gas reservoir accumulation mechanism and guiding shale gas exploration. The shale gas of the Longmaxi Formation in the southeastern Sichuan Basin was studied based on a shale gas desorption simulation experiment, combined with mineral composition, total organic carbon, specific surface area, isothermal adsorption, and scanning electron microscope (SEM) data. Here, the shale gas desorption capability was quantitatively evaluated, and its controlling factors are discussed. The results show that the shale gas desorption process within the Longmaxi Formation varies significantly. The total time of the desorption process varies from 600 min to 4400 min, and it mainly occurs by the 98 °C desorption stage. The desorption capability of the lower Formation is markedly weaker than that of the upper Formation, and it is mainly determined by the shale properties. Organic matter (OM) is the most important controlling factor. As the OM content increases, the specific surface area, methane adsorption capacity, and OM pores increase, leading to a rapid decrease in shale gas desorption capability. In addition, feldspar exhibits a positive correlation with shale gas desorption capability due to its large pores but low specific surface area.

PAHs in five-stage size segregated aerosol particles were investigated in 2003 at urban and suburban sites of Beijing. The total concentration of 17 PAHs ranged between 0.84 and 152 ng m(-3), with an average of 116 ng m(-3), in urban area were 1.1-6.6 times higher than those measured in suburban area. It suggested a serious pollution level of PAHs in Beijing. PAHs concentrations increased with decreasing the ambient temperature. Approximately 68.4-84.7% of PAHs were adsorbed on particles having aerodynamic diameter 2.0 microm. Nearly bimodal distribution was found for PAHs with two and three rings, more than four rings PAHs, however, followed unimodal distribution. The overall mass median diameter (MMD) for PAHs decreased with increasing molecular weight. Diagnostic ratios and normalized distribution of PAHs indicated that the PAHs in aerosol particles were mainly derived from fossil fuel combustion. Coal combustion for domestic heating was probably major contributor to the higher PAHs loading in winter, whereas PAHs in other seasons displayed characteristic of mixed source of gasoline and diesel vehicle exhaust. Biomass burning and road dust are minor contributors to the PAHs composition of these aerosol particles. Except for source emission, other factors, such as meteorological condition, photochemical decay, and transportation from source to the receptor site, should to be involved in the generation of the observed patterns.