The North China Plain (NCP) and the Yangtze River Delta (YRD) in China have been experiencing severe particulate matter (PM) pollution problems associated with the rapid economic growth and the accelerated urbanization. In this study, hourly mass concentrations of PM 2.5 and PM 10 during June 1st–August 31st, 2013 were collected in 13 cities located in or adjacent to the NCP region and 20 cities located in the YRD region. The overall average PM 2.5 and PM 10 concentrations were 77.0 μg/m 3 and 136.2 μg/m 3 in the NCP region, respectively, and 42.8 μg/m 3 and 74.9 μg/m 3 in the YRD region, respectively. The frequencies of occurrence of concentrations exceeding the China's Ambient Air Quality Standard (AAQS) (BG3095-12) Grade I standards were 83% for PM 2.5 and 93% for PM 10 in the NCP region, and 51% for PM 2.5 and 66% for PM 10 in the YRD region. Strong temporal correlation for both PM 2.5 and PM 10 between cities within 250 km was frequently observed. PM 2.5 was found to be negatively associated with wind speed. On the PM 2.5 episode days (when the 24 h PM 2.5 concentration is greater than 75 μg/m 3 ), average PM 2.5 concentrations were 2–4 times greater compared to the non-episode days. The PM 2.5 to PM 10 ratio increased from 0.50 (0.57) on the non-episode days to 0.64 (0.64) on the episode days in the NCP (YRD) region. No distinct weekday/weekend difference was observed for PM 2.5 , PM 10 , and other gaseous pollutants (CO, SO 2 , NO 2 , and O 3 ) in all cities. The results presented in this paper will serve as an important basis for future regional air quality modeling and source apportionment studies.