Spatial and temporal distribution characteristics of haze days and associated factors in China from 1973 to 2017

In recent years, more haze days have been detected with the intensification of air pollution in China. Haze is a serious environmental problem that is influencing human health. This study focuses on revealing the spatial and temporal distribution characteristics of haze, haze formation factors, and health risks in China since the reform and opening-up. The purpose of this study is to provide a reference for haze governance and develop suggestions for public health. In this study, haze was identified by visibility and meteorological data from 1973 to 2017. Haze days and visibility on haze days were calculated during this period. By using standard deviation ellipse analysis and principal component regression, we calculated the variation of the haze barycenter, standard deviation in the haze area, and contribution rates of the main influencing factors in nine typical regions. Haze seasonal variation and health risk assessment were also analysed in this study. The results show that the changes in haze in China present as five periods: 1973-1979,1980-1989,1990-2001, 2002-2010, and 2011-2017. Haze days in the majority of typical cities in central and eastern China show a tendency of growth or fluctuating growth, and the variation intensified after the 1990s. In most areas, there were about 100 haze days, and the visibility on haze days was approximately 7 km until 2017. The main body of the haze area in China is approximately a diamond-shaped pentagon with BEIJING, CHENGDU, NANNING, GUANGZHOU, and SHANGHAI as the apexes. In addition, GANSU and northeast China are also influenced by haze. The haze situation in typical areas has grown since 1973. The haze centres tended to move outwards, especially from 2002-2010, which was a turning point for haze variation. For most regions, pollutant emissions as well as economic and governance factors were the main contributing factors. Haze has obvious seasonal variation in China. Haze in winter is the heaviest, and then haze in autumn, summer and spring becomes relatively mild. The haze health risk increased sharply and expanded from 1973 to 2017. High- and extremely high-risk areas are still concentrated in the diamond region of the haze area and have expanded along or surround main traffic lines and major cities. Through analysis of the contributions of haze factors in various regions of China, this study suggests that the most important means of haze governance comprise four aspects: I) a reduction of exhaust emissions, II) the implementation of green consumption, travel, and behaviour concepts, III) enhanced governance, and IV) urbanization that is as balanced as possible; furthermore, the development of cities such as enclaves should be promoted to avoid health risks to large cities.