Estimation and Spatiotemporal Analysis of NO2 Pollution in East Asia During 2001-2016

Ambient nitrogen dioxide (NO2) not only has adverse health effects on humans but also contributes to the production of two major secondary atmospheric pollutants, ozone (O-3) and fine particulate matter (PM2.5). In this study, surface NO2 concentrations in East Asia from 2001 to 2016 were estimated by combining an ensemble backpropagation neural network method, satellite NO2 column data, and reanalysis data. The estimated monthly and annual mean NO2 concentrations were well-correlated with the observations, with R (correlation coefficient) values of 0.89 and 0.91, respectively. Our results indicate that the NO2 concentrations in most areas of East Asia peaked during 2011-2013. The NO2 concentrations in autumn and winter, especially in the eastern and northern parts of China, were much higher than those in summer. In terms of population NO2 exposure, over 25 million South Korea residents (similar to 45% of the population) were exposed to NO2 concentrations higher than the 2005 World Health Organization's annual standard (40 mu g/m(3), similar to 22 ppbv at 25 degrees C) in 2015. In contrast, the entire populations of some developing countries, such as Vietnam, Cambodia, Myanmar, the Philippines, and Lao PDR, were exposed to NO2 concentrations less than 14 ppbv. Based on the estimation, NO2-related asthma cases in East Asia increased by 1.37% annually from 2001 to 2015, reaching 139,000 cases (95% confidence interval: 37,400-263,400) in 2015. NOx emission inventories vary from country to country in East Asia; thus, more targeted NOx emission-control policies are urgently required.

Automated summary

This study estimated the surface NO2 concentrations in East Asia from 2001 to 2016 and found that NO2 concentrations peaked during 2011-2013. In autumn and winter, especially in eastern and northern China, NO2 concentrations were significantly higher than in summer. Additionally, over 45% of South Korea's population was exposed to high levels of NO2, while some developing countries had lower exposure. Furthermore, NO2-related asthma cases in East Asia increased annually from 2001 to 2015.