[Chemical Constituents and Sources of PM2.5 Around the Wuhan Military Games Period].

Hourly monitoring datasets of PM2.5 mass concentration and associated chemical compositions were used to investigate the variations in their mass concentrations before, during, and after the 7th Military World Games held in Wuhan. Furthermore, the source analysis was conducted through PMF combined with the backward trajectory and concentration weighted trajectory cluster analysis. The study revealed the variations in PM2.5 compositions and sources around the Wuhan Military Games period and their response to local and surrounding regional control measures. This can provide a reference for regional precise prevention and control of PM2.5. Under the influence of emission reduction measures, PM2.5 mass concentration during the control period [(31.3±12.0) µg·m-3] decreased by 14.7% compared with that before the control period, whereas the secondary components were obviously formed, in which sulfate, nitrate, and ammonium(SNA) increased by 25.6% in total. After the control period, owing to the decrease in humidity and the influence of the northwest air mass, the mass concentration of SNA decreased by 36.9%, whereas the mass concentration of mineral elements increased by 4.7 times. The source apportionment results indicated that there was no significant difference between the vehicle emissions before and after the control(P<0.05). Compared with that in the non-control period, the contributions of industrial emission and coal burning decreased by 68.1% and 43.7%, respectively, whereas the contribution of secondary inorganic aerosol increased by 89.5%. With the lack of large-scale control of vehicle emissions, the mass concentrations of NO3- and NOx increased by 6.13 µg·m-3 and 3.56 µg·m-3, respectively. The vehicle emissions peaked at 21:00 [(10.9±3.67) µg·m-3], reflecting the emissions of cargo vehicles, which were only allowed to pass at night during the control period. With the banning of ship navigation, the ship emission in the middle and lower reaches of the Yangtze River significantly decreased(48.8%). There were also high values of fugitive dust and industrial emissions near the Anhui section of the Yangtze River waterway, which reflected the dense distribution of industrial activities and road transportation along the Yangtze River. After the control period, the fugitive dust increased by 6.6 times, and the source areas were mainly distributed in Xiangyang and Jingmen.

Covid-19: Early Cases and Disease Spread.

The emergence and global spread of the Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) is critical to understanding how to prevent or control a future viral pandemic. We review the tools used for this retrospective search, their limits, and results obtained from China, France, Italy and the USA. We examine possible scenarios for the emergence of SARS-CoV-2 in the human population. We consider the Chinese city of Wuhan where the first cases of atypical pneumonia were attributed to SARS-CoV-2 and from where the disease spread worldwide. Possible superspreading events include the Wuhan-based 7th Military World Games on October 18-27, 2019 and the Chinese New Year holidays from January 25 to February 2, 2020. Several clues point to an early regional circulation of SARS-CoV-2 in northern Italy (Lombardi) as soon as September/October 2019 and in France in November/December 2019, if not before. With the goal of preventing future pandemics, we call for additional retrospective studies designed to trace the origin of SARS-CoV-2.

Impact of short-term control measures on air quality: A case study during the 7th Military World Games in central China.

The 7th Military World Games held in Wuhan (WH) in Oct 2019 provided an opportunity to clarify the impact of short-term control measures on air quality. Fine particulate matters (PM2.5) were collected in WH, Huangshi (HS), and Huanggang (HG) during the control (Oct 13-28, 2019) and non-control periods (Oct 29- Nov 5, 2019). The results showed that air quality was good during the control period, with the concentrations of PM2.5 and gaseous pollutants being below the Grade Ⅱ of China Ambient Air Quality Standard. Concentrations of PM2.5 and its major chemical components in the control period were significantly lower than those in the non-control period, with reductions ranging from 17% (trace elements) to 46% (elemental carbon). However, higher contributions of secondary components such as SO42-, NO3-, NH4+ and secondary organic carbon (SOC) to PM2.5 were observed during the control period, suggesting the important role of secondary transformation. Potential source contribution function (PSCF) of PM2.5 showed that the main source regions were potentially located in surrounding cities Hubei Province, but regional transport can't be ignored. Six sources were identified by positive matrix factorization (PMF) for both control and non-control period. The contributions of combustion emissions and vehicle emissions were amplified in the control period, while the contribution of construction dust increased significantly when the control measures ended. Emission reductions contributed more to PM2.5 concentration decrease in WH (55%) than that in HS (51%) and HG (49%), which was consistent with the stricter control measures implemented in WH. These results indicated that short-term controls were effective at lowering PM2.5 concentration. However, the elevated contributions of secondary aerosols and the influence of regional transport on the study areas also need to be paid attention for air quality improvement in the future.