Double Trouble of Air Pollution by Anthropogenic Dust.

With urbanization worldwide in recent decades, anthropogenic dust (AD) emissions due to heavy urban construction and off-road vehicle use have been increasing. Its perturbations on urban air pollution at the global scale are still unclear. Based on observations, we found that a high urban AD optical depth is often accompanied by severe non-dust aerosol optical depth in the planetary boundary layer (PBL), both magnitudes even comparable. To investigate the causes, an AD emission inventory constrained by satellite retrievals is implemented in a global climate model. The results show that AD-induced surface radiative cooling of up to -15.9 ± 4.0 W m-2 regionally leads to reduced PBL height, which deteriorates non-dust pollution, especially over India and northern China, in addition to the tremendous direct AD contribution to pollutants. The estimated global total premature mortality due to AD is 0.8 million deaths per year and is more severe in populous regions.

Impact of city lockdown on the air quality of COVID-19-hit of Wuhan city.

A series of strict lockdown measures were implemented in the areas of China worst affected by coronavirus disease 19, including Wuhan, to prevent the disease spreading. The lockdown had a substantial environmental impact, because traffic pollution and industrial emissions are important factors affecting air quality and public health in the region. After the lockdown, the average monthly air quality index (AQI) in Wuhan was 59.7, which is 33.9% lower than that before the lockdown (January 23, 2020) and 47.5% lower than that during the corresponding period (113.6) from 2015 to 2019. Compared with the conditions before the lockdown, fine particulate matter (PM2.5) decreased by 36.9% and remained the main pollutant. Nitrogen dioxide (NO2) showed the largest decrease of approximately 53.3%, and ozone (O3) increased by 116.6%. The proportions of fixed-source emissions and transported external-source emissions in this area increased. After the lockdown, O3 pollution was highly negatively correlated with the NO2 concentration, and the radiation increase caused by the PM2.5 reduction was not the main reason for the increase in O3. This indicates that the generation of secondary pollutants is influenced by multiple factors and is not only governed by emission reduction.