To evaluate the effect of temporary emissions control measures on air quality during the 2016 G20 Summit held in Hangzhou, China, an intensive field campaign was conducted with focus on aerosol chemistry and gaseous precursors from 15 August to 12 September, 2016. The concentrations of fine particles were reduced during the intense emission control stages, of which the reduction of carbonaceous matters was mostly responsible. This was mainly ascribed to the decreases of secondary organic aerosols via the suppression of daytime peak SOC formation. Although the regional joint control was enacted extending to the Yangtze River Delta region, the effect of long-range transport on the air quality of Hangzhou was ubiquitous. Unexpectedly high NOx concentrations were observed during the control stage when the strictest restriction on vehicles was implemented, owing to the contribution from upstream populous regions such as Jiangsu and Shandong provinces. In addition, the continental outflow via sea breeze triggered a short pollution episode on the first day of the G20 Summit, resulting in a significant enhancement of the nitrogen/sulfur oxidation rates. After the Summit, all the air pollutants evidently rebounded with the lifting of various control measures. Overall, the fraction of secondary inorganic aerosols (SNA) in PM 2.5 increased as relative humidity increased, but not for the concentrations of PM 2.5 . Aerosol components that had distinctly different sources and formation mechanisms, e.g. sulfate/nitrate and elemental carbon, showed strong correlations exclusively during the regional/long-range transport episodes. The SNA/EC ratios, which was used as a proxy for assessing the extent of secondary inorganic aerosol formation, were found significantly enhanced under transport conditions from northern China. This study highlighted that the emission control strategies were beneficial for curbing the particulate pollution whereas the regional/long-range transport may offset the local emission control effects to some extent.