GAW Report No. 205 - IGAC Project

CHAPTER 3 - ASIAIn the case of PM 10 , a series of stringency has been implemented since the annual meanstandard was implemented in 1993. The annual mean dropped from 80 µg m -3 in 1993, to 70 µg m -3in 2001 and lastly, to 50 µg m -3 in 2007 (Figure 49). The annual mean standard for PM 10 wasexceeded in 2001-2002 and in 2007.Particularly in 2002, the annual mean PM 10 concentration has almost levelled off with the1995 PM 10 , mainly due to the extraordinarily severe Asian dust event that happened on that year.For Pb, the annual mean levels have always been met, and the trend linearly decreased from 1993to 2004 at 0.01 µg m -3 yr -1 (Figure 50). This is expected trend due to the worldwide shift to unleadedgasoline.Figure 48 - Frequency of Ozone exceedances per year in SeoulFigure 49 - Annual mean concentrations of PM10 in Seoul (1995-2007)116