What We Are Learning from COVID-19 for Respiratory Protection: Contemporary and Emerging Issues.

Infectious respiratory diseases such as the current COVID-19 have caused public health crises and interfered with social activity. Given the complexity of these novel infectious diseases, their dynamic nature, along with rapid changes in social and occupational environments, technology, and means of interpersonal interaction, respiratory protective devices (RPDs) play a crucial role in controlling infection, particularly for viruses like SARS-CoV-2 that have a high transmission rate, strong viability, multiple infection routes and mechanisms, and emerging new variants that could reduce the efficacy of existing vaccines. Evidence of asymptomatic and pre-symptomatic transmissions further highlights the importance of a universal adoption of RPDs. RPDs have substantially improved over the past 100 years due to advances in technology, materials, and medical knowledge. However, several issues still need to be addressed such as engineering performance, comfort, testing standards, compliance monitoring, and regulations, especially considering the recent emergence of pathogens with novel transmission characteristics. In this review, we summarize existing knowledge and understanding on respiratory infectious diseases and their protection, discuss the emerging issues that influence the resulting protective and comfort performance of the RPDs, and provide insights in the identified knowledge gaps and future directions with diverse perspectives.

The Spring Festival Effect: The change in NO2 column concentration in China caused by the migration of human activities

The Spring Festival is the most important holiday in China, and human activity and population mobility may contribute greatly to air quality. According to the satellite-based tropospheric nitrogen dioxide (NO2) column and ground-based observational concentration of NO2 in megacities from 2013 to 2018 around the Spring Festival, we found that NO2 concentration obviously decreases, presenting a “tide phenomenon”, particularly in the megacities, with the tropospheric NO2 column density decreasing by 31.8%–44.5%. The tropospheric NO2 column density in Beijing decreased by 41.6% and rebounded by 22.3% after the festival. Vehicle sources were among the important causes of NOx emissions in the megacities, and traffic intensity decreased significantly during the festival. As the coronavirus disease 2019 (COVID-19) pandemic progresses, the traffic intensity in urban areas is decreasing significantly, with the tropospheric NO2 column density decreasing by 56.2% and rebounding by only 6.8% in 2020, without the “tide phenomenon”.