Variations of source and aerosol composition over ten years: Implications for Clean Air Action Plan in a rapidly developing megacity.

A long-term (2007-2016) particulate matter dataset measured at multiple sites in Chengdu, an expanding megacity in southwest China, was analyzed. The trends of particulate chemical compositions and source apportionment were used to evaluate and review the effectiveness of source-specific control policies and measures in Atmospheric Pollution Prevention and Control Action Plan (APPCAP). The concentration of particulate matter decreased significantly, and most aerosol components changed synchronously with particulate matter. The results of advanced three-way factor analysis model suggested that six sources were resolved at three sites: coal combustion, vehicle, crustal dust, cement, sulfate, nitrate and secondary organic matter. Secondary source, including secondary organic carbon (SOC), sulfate, nitrate, and ammonium (SNA), was always the main pollution source in this region. Dust, including cement and crustal dust, was important primary source. Encouragingly, coal combustion had been significantly controlled after APPCAP. The central site represented the higher contribution of vehicles, nitrates and SOC, while north and eastern sites showed the higher contribution of sulfate, coal combustion and dust. Many evidence points to substantial alterations in the physicochemical attributes of Chengdu's atmosphere. The rising proportion of nitrate and the transition of the atmospheric environment from ammonia-poor to ammonia-rich conditions highlight the necessity for the next phase of particulate matter control to focus intensively on the management of NH₃ and NO. China's APPCAP could provide useful experience for vast developing countries and other urbanizing and industrializing regions to strike a balance between social development and environmental protection.