Four seasons are very distinct based on localmeteorological characteristics of Tianjin. Four samplingperiods in 2008 were chosen to present winter–January 1stto 25th, spring–April 1st to 25th, summer–July 1st to 25th, andfall–October 1st to 25th, respectively.In the four sampling periods, daily PM2.5 and PM10samples were collected on 90 mm Pallflex #2500Quartz-fiber filters using middle-flow impact samplers (TH150AⅡ) operating at a flow rate of 100 L/min. The quartzfilters were pre-heated in a muffle furnace at 900°C for threehours before sampling to remove the residual carbon. Beforeand after sampling, the filters were equilibriumed in thedessicator (a temperature between 20°C and 23°C and arelative humidity (RH) between 35% and 45%) forforty-eight hours, and then weighed on an electronicmicrobalance with a ±1 μg sensitivity (Mettler Toledo,Switzerland) to determine the PM mass. Each filter wasweighted at least three times before and after sampling, andthe net mass was obtained by subtracting the pre-samplingweights from the post-sampling weights. Different amongreplicate weights were