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The continuous methane emission from the coal piles is associated with many environmental problems and safety risks, in large storage facility. The methane emission parameters of coal piles and the concentration distribution characteristics of methane, which are the basis of ventilation design, are rarely reported in large storage facilities. In this study, based on the mass-transfer diffusion theory, desorption-concentration gradient method for determining methane emission parameters of coal piles in large facilities is proposed. In this method, firstly, the coal pile methane diffusion coefficient was deduced by conducting the coal particles absorption-desorption experiments and the particle-size distribution. Then, combing the diffusion coefficient and methane concentration-gradient on the coal pile surface, the coal pile methane diffusion flux was calculated. Further, when methane diffusion flux was utilized as the source item for CFD calculations, the results were consistent with the onsite measured values, which demonstrated the accuracy of this method. The CFD simulation results show that methane has diffusion characteristics that adhere upward along the slope of the coal pile and converge on the coal ridge. The methane flow reaches the dome upwards, where a higher concentration is formed. Both the coal pile volume and the methane diffusion flux will affect the concentration distribution of methane in large storage facility. For a larger diffusion flux, the explosion limit will be exceeded, and measures need to be taken to eliminate the safety risk. These findings provide principal data and analysis guide for optimized design of ventilation performance in closed industrial building. •Diffusion coefficients of coal pile methane was deduced based on the particle-size distribution and desorption method. •Desorption-concentration gradient method is proposed to solve methane diffusion flux in large storage facility. •Measurement-verified CFD method can be used for methane concentration distribution. •Methane adhesion diffusion and concentration distribution in large storage facilities are presented. •Larger methane emission rate, the methane in large storage facility will exceed the explosion limit. [ABSTRACT FROM AUTHOR]

In order to investigate the effects of the Coronavirus Disease 2019 (COVID-19) lockdown on air quality in cities in southwest China, a single particle aerosol mass spectrometer (SPAMS) and other online equipments were used to measure the air pollution in Chengdu, one of the megacities in this area, before and during the lockdown period. It was found that the concentrations of fine particulate matter (PM 2.5), nitric oxide (NO), nitrogen dioxide (NO 2), sulfur dioxide (SO 2) and carbon monoxide (CO) decreased by 38.6%, 77.5%, 47.0%, 35.1% and 14.1%, respectively, while the concentration of ozone (O 3) increased by 57.5% from the time before to the time during lockdown. All particles collected during the study period could be divided into eight categories: biomass burning (BB), coal combustion (CC), vehicle emissions (VE), cooking emissions (CE), Dust, K-nitrate (K–NO 3), K-sulfate (K–SO 4) and K-sulfate-nitrate (K-SN) particles, and their contributions changed significantly after the beginning of lockdown. Compared to before lockdown, the contribution of VE particles experienced the largest reduction (by 14.9%), whereas the contributions of BB and CE particles increased by 7.0% and 7.3%, respectively, during the lockdown period. Regional transmission was critical for pollution formation before lockdown, whereas the pollution that occurred during the lockdown period was caused mainly by locally emitted particles (such as VE, CE and BB particles). Weighted potential source contribution function (WPSCF) analysis further verified and emphasized the difference in the contribution of regional transmission for pollution formation before and during lockdown. In addition, the potential source area and intensity of the particles emitted from different sources or formation mechanisms were quite different. • Single aerosol particles during the COVID-19 lockdown were measured based on SPAMS. • The lockdown caused reductions in PM 2.5 , NO, NO 2 , SO 2 and CO, while increase in O 3. • Vehicle emission particles decreased the most (by 14.9%) during lockdown period. • Pollution formation mechanism before and during lockdown was completely different. [ABSTRACT FROM AUTHOR]