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COVID-19 (Corona Virus Disease 2019) is a severe respiratory syndrome currently causing a human global pandemic. The original virus, along with newer variants, is highly transmissible. Aerosol is a multiphase system consisting of the atmosphere with suspended solid and liquid particles, which can carry toxic and harmful substances; especially the liquid components. The degree to which aerosol can carry the virus and cause COVID-19 disease is of significant research importance. In this study, we have discussed the aerosol transmission as the pathway of SARS-CoV-2 (Severe Acute Respiratory Syndrome Coronavirus 2), and the aerosol pollution reduction as a consequence of the COVID-19 lockdown. The aerosol transmission routes of the SARS-CoV-2 can be further subdivided into proximal human-exhaled aerosol transmission and potentially more distal ambient aerosol transmission. The human-exhaled aerosol transmission is a direct dispersion of the SARS-CoV-2. The ambient aerosol transmission is an indirect dispersion of the SARS-CoV-2 in which the aerosol act as a carrier to spread the virus. This indirect dispersion can also stimulate the up-regulation of the expression of SARS-CoV-2 receptor ACE-2 (Angiotensin Converting Enzyme 2) and protease TMPRSS2 (Transmembrane Serine Protease 2), thereby increasing the incidence and mortality of COVID-19. From the aerosol quality data around the world, it can be seen that often atmospheric pollution has significantly decreased due to factors such as the reduction of traffic, industry, cooking and coal-burning emissions during the COVID-19 lockdown. The airborne transmission potential of SARS-CoV-2, the infectivity of the virus in ambient aerosols, and the reduction of aerosol pollution levels due to the lockdowns are crucial research subjects.

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Polycyclic aromatic hydrocarbons (PAHs) are toxic and hazardous volatile environmental pollutants that have been studied as possible major causative agents of lung cancer in Xuanwei. In this paper, indoor and outdoor PM2.5 samples were collected from two homes at different time periods in Hutou, the lung cancer epidemic area in Xuanwei. The results showed that PAH pollution levels from coal combustion in Xuanwei lung cancer epidemic area were significant. The mass concentrations of total PAHs, major carcinogenic compounds, and benzo[a]pyrene-based equivalent concentration (BaPeq) were significantly higher in the coal-using home than in the electricity-using home. For the coal-using home, the PAHs were mainly derived from coal combustion. For the electricity-using home, the PAHs might have been a combination of traffic and coal combustion sources. The human health risk due to inhalation exposure to the PAHs was represented by the incremental lifetime cancer risk (ILCR) of the inhalation exposure. The results showed that the indoor cancer risk for the coal-using home in Xuanwei is higher than that of the electricity-using home and much higher than that of Chinese megacities such as Beijing and Tianjin. Long-term exposure to indoor coal-burning environments containing high levels of PAHs may be one of the main reasons for the high incidence of lung cancer in Xuanwei.

To better understand the complex transformation mechanisms of pollutants in different phases in sluice-controlled river reaches (SCRRs), a multi-phase transformation model of water quality is proposed. This model mainly describes the interactions of the water body, suspended matter, deposited sediments, and organisms. Mathematical expressions were first derived to describe the mass transportation processes in different phases of the river system. The multi-phase transformation model in SCRRs was then established with defined physical mechanisms. Monitored data from the operation of Huaidian sluice were used to identify and validate the parameters of the transformation model and to simulate the spatial and temporal changes of pollutants in different phases. Four findings were made from the results. Firstly, the concentration values of pollutants in each phase in the upper and lower river reaches of the sluice are affected by flow, mode of sluice operation, and algal growth and enrichment. Secondly, the reaction processes in the upper and lower river reaches of the sluice indicate different dominant mechanisms according to the change in sluice operation. Thirdly, sluice operation leads to stronger exchanges between the water body and external materials because of the increased water disturbance. Fourthly, in the early period of the experiment, changes in the alga concentrations were mainly affected by water movement. In the later period, changes in the alga concentrations were mainly affected by the obstruction of the sluice in the upstream section, while these were affected by flow velocity, flow volume, and changes in nutrient concentration in the downstream section.

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