Particulate matter pollution over China and the effects of control policies

China is one of the regions with highest PM_2.5 concentration in the world. In this study, we review the spatio-temporal distribution of PM_2.5 mass concentration and components in China and the effect of control measures on PM_2.5 concentrations. Annual averaged PM_2.5 concentrations in Central-Eastern China reached over 100μgm^-3, in some regions even over 150μgm^-3. In 2013, only 4.1% of the cities attained the annual average standard of 35μgm^-3. Aitken mode particles tend to dominate the total particle number concentration. Depending on the location and time of the year, new particle formation (NPF) has been observed to take place between about 10 and 60% of the days. In most locations, NPF was less frequent at high PM mass loadings. The secondary inorganic particles (i.e., sulfate, nitrate and ammonium) ranked the highest fraction among the PM_2.5 species, followed by organic matters (OM), crustal species and element carbon (EC), which accounted for 6-50%, 15-51%, 5-41% and 2-12% of PM_2.5, respectively. In response to serious particulate matter pollution, China has taken aggressive steps to improve air quality in the last decade. As a result, the national emissions of primary PM_2.5, sulfur dioxide (SO₂), and nitrogen oxides (NO_X) have been decreasing since 2005, 2006, and 2011, respectively. The emission control policies implemented in the last decade could result in noticeable reduction in PM_2.5 concentrations, contributing to the decreasing PM_2.5 trends observed in Beijing, Shanghai, and Guangzhou. However, the control policies issued before 2010 are insufficient to improve PM_2.5 air quality notably in future. An optimal mix of energy-saving and end-of-pipe control measures should be implemented, more ambitious control policies for NMVOC and NH₃ should be enforced, and special control measures in winter should be applied. 40-70% emissions should be cut off to attain PM_2.5 standard.