Spatio-temporal variation and daily prediction of PM concentration in world-class urban agglomerations of China.

The contradiction between the development of urban agglomerations and ecological protection has long been a challenging issue. China has experienced an astonishing expansion of its urban scale in the past 40 years, and nearly 783 million of the nation's people now live in cities. Beijing-Tianjin-Hebei, the Yangtze River Delta and the Pearl River Delta have been prioritized to become world-class clusters by 2020. The health effects of air pollution in these three urban agglomerations are becoming increasingly formidable. Given these conditions, using the daily mean PM concentration in 40 cities from January 2014 to December 2016, this research explored the spatial-temporal characteristics of PM concentrations in these three urban agglomerations. The annual mean PM concentrations in Beijing-Tianjin-Hebei, the Yangtze River Delta and the Pearl River Delta are 35.39 µg/m, 53.72 µg/m and 78.54 µg/m, respectively. Compared with the other two urban agglomerations, abundant rainfall causes the Pearl River Delta to have the lowest PM level. Furthermore, a general regression neural network (GRNN) method is developed to predict the PM concentration in these clusters on the second day, with inputs including the average, maximum and minimum temperature; average, maximum and minimum atmosphere; total rainfall; average humidity; average and maximum wind speed; and the PM concentration measured 1 day ahead. The results indicate that the GRNN method can precisely predict the concentration level in these clusters, and it is especially useful for the Pearl River Delta, as the underlying influence mechanism is more specified in this cluster than in the others. Importantly, this 1-day-ahead forecasting of PM concentrations can raise awareness among the public to improve their precautionary behaviours and help urban planners to provide corresponding support.