Air Pollutants (continued) ◆ Regulated air pollutants China:before 2000,TSP,SO2,NOx;after 2001:PM1o,SO2,NO2 O3 and PM2.5 are also taken in some countries/regions Primary and secondary pollutants Directly emitted from sources or transformed in atmosphere,e.g. O in photochemical smog,fine particles (e.g.sulfates and nitrates), acid rain,... ◆Units ■Mass concentration inμg/m3ormg/m3 Volume concentration in %ppm and ppb by volumeAir Pollutants (continued) Regulated air pollutants  China: before 2000, TSP, SO2 , NOx ; after 2001: PM10, SO2 , NO2  O3 and PM2.5 are also taken in some countries / regions Primary and secondary pollutants  Directly emitted from sources or transformed in atmosphere, e.g.,  O3 in photochemical smog, fine particles (e.g. sulfates and nitrates), acid rain, … Units  Mass concentration in μg/m3 or mg/m3  Volume concentration in %, ppm and ppb by volume