Impact of emission control strategy on NO2 in urban areas of Korea

Long-term trend in nitrogen dioxide (NO2) levels was analyzed from 16 urban roadside (U-RS) locations in 7 major cities along with 5 reference background areas in Korea over an 11-year period (1998–2008). These NO2 data were examined after being grouped into periods I (1998–2000) and II (2001–2008) in light of the major emission control strategy such as the natural gas vehicle supply (NGVS) program initiated since June 2000. There were contrasting signals between Seoul (capital) and others. Although the long-term trends were dominantly toward decline from most stations (5 out of 7) in Seoul, an increasing trend was dominant in other cities (7 out of 9 stations). A line of evidence collected in this study indicated that NO2 levels and the emission ratio of NO2 to NOx (f(NO2)) in U-RS sites have gradually decreased over the years due to the combined effects of various control efforts (e.g., the implementation of NGVS and the use of low emission diesel engines).