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Background: Hygiene behaviors in public toilets are important to prevent the transmission of infectious diseases, especially during the pandemic. All through the novel coronavirus (COVID-19) pandemic, governments in many countries published guidance on personal hygiene for the general population to prevent disease transmission. This study aimed to investigate improvements in residents' hygiene awareness and behaviors in public toilets before and during the pandemic.Methods: We recruited 316 residents between November and December 2018 before the pandemic, and 314 residents between December 2020 and January 2021 during the pandemic in the same study sites in Hangzhou, a well-developed city in China. Residents' hygiene behaviors in public toilets, hygiene awareness, risk perception, and sociodemographic factors were collected. Bivariate analysis and multivariable logistic regressions were used to test the differences between the two rounds. We conducted an observational study to record the provision of hygiene amenities at toilets during the pandemic.Results: After controlling for sociodemographic factors (gender, marital status, age, education level, and monthly household income), compared with respondents recruited before the pandemic, respondents recruited during the pandemic were more likely to perceive the risks of infection when using public toilets (aOR = 1.77, 95%CI [1.20, 2.60]), and were more likely to be aware of the risks of touching contaminated toilet facilities (aOR = 1.72, 95%CI [1.17, 2.54]) and the risks of not using soap to wash one's hands after using the toilet (aOR = 1.93, 95%CI [1.38, 2.72]). They were more likely to always clean their toilet seat with alcohol (aOR = 1.88, 95%CI [1.01, 3.51]), wash hands with soap (aOR = 1.52, 95%CI [1.09, 2.10]) and dry their hands with a dryer (aOR = 1.78, 95%CI [1.16, 2.71]), but they were less likely to always wash their hands after using the toilets (aOR = 0.57, 95%CI [0.32, 1.00]). Among 70 public toilets observed, 9 provided alcohol for toilet seat disinfection, 52 provided soap, 33 provided paper towels, and 41 had working hand dryers.Conclusions: Despite the overall improvement, residents' hygiene behaviors in public toilets and the supply of hygiene amenities were still suboptimal during the pandemic. Further hygiene education and an adequate supply of hygiene amenities in public toilets are needed to promote residents' hygiene behaviors. [ABSTRACT FROM AUTHOR]

Air pollution in megacities represents one of the greatest environmental challenges. Our observed results show that the dramatic NOx decrease (77%) led to significant O3 increases (a factor of 2) during the COVID‐19 lockdown in megacity Hangzhou, China. Model simulations further demonstrate large increases of daytime OH and HO2 radicals and nighttime NO3 radical, which can promote the gas‐phase reaction and nocturnal multiphase chemistry. Therefore, enhanced NO3− and SO42− formation was observed during the COVID‐19 lockdown because of the enhanced oxidizing capacity. The PM2.5 decrease was only partially offset by enhanced aerosol formation with its reduction reaching 50%. In particular, NO3− decreased largely by 68%. PM2.5 chemical analysis reveals that vehicular emissions mainly contributed to PM2.5 under normal conditions in Hangzhou. Whereas, stationary sources dominated the residual PM2.5 during the COVID‐19 lockdown. This study provides evidence that large reductions in vehicular emissions can effectively mitigate air pollution in megacities. Plain Language Summary: Megacities in developing countries such as China and India are facing severe air pollutions. There are still large uncertainties in quantifying the sources of fine particles at the citywide scale due to the synergetic effects of complex aerosol chemistry and transboundary transport. The COVID‐19 lockdown led to the lowest intensity of human activities in recent decades, which provides a unique opportunity to gain insights into the relationship between emission sources and aerosol chemistry. The COVID‐19 lockdown led to significant decreases of PM10, PM2.5, CO, SO2, and NOx, whereas O3 increased by more than a factor of 2 in megacity Hangzhou, China. The filter‐based PM2.5 chemical analysis and model simulation show that although enhanced oxidizing capacity promoted the secondary aerosol formation during the COVID‐19 lockdown, the PM2.5 concentrations still largely decreased by 50%, in which NO3− had the largest decrease of 68% whereas SO42− only decreased by 5%. This result indicates that the reduction in vehicular emissions contributed significantly to the PM2.5 decrease during the COVID‐19 lockdown. We highlight that to mitigate air pollution in megacities, regulations on vehicular emissions, deeper energy and industrial restructuring, and regional joint‐controls should be taken in the future. Key Points: Air pollutants PM10, PM2.5, NOx, CO, and SO2 decreased whereas O3 increased during the COVID‐19 lockdown in megacity HangzhouEnhanced NO3− and SO42− formation caused by the enhanced oxidizing capacity partially offset the decrease of PM2.5 in megacity HangzhouThe contribution of vehicular emissions to PM2.5 was over stationary sources under normal conditions in megacity Hangzhou [ABSTRACT FROM AUTHOR]