서울의 대기 중 이산화질소(NO₂) 저감 둔화 원인 분석 및 대응방안

NO₂concentration in Seoul has not been improved in spite of implementing various NOx emission control policies. In this study, the reasons for the slow reduction of NO₂ concentration were investigated through comparing control measures of developed cities, both successfully managing NO2 and poorly managing NO2, with Seoul’s. Also, NO₂ characteristics in Seoul was analyzed in prospective of primary NO₂ emission issue, which has been actively discussed in Europe. The most effective policy for NO₂control in California and Tokyo, where NO₂has been improved consistently, was to introduce much stricter NOx emission standards for diesel vehicles than in London and Seoul. Introducing strict emission standards results in a low penetration rate of diesel vehicles known as larger NOx emitters than gasoline vehicles, which prevents fundamentally NOx emissions. In addition, Tokyo controlled both NOx and PM by implementing ‘Vehicle NOx?PM law’ in 2001, and a policy discouraging polluted diesel vehicles from being driven in Tokyo and surrounding area in 2003. Increasing proportion of primary NO₂emission, originating from modern diesel-technology vehicles with DPF and DOC for the purpose of reducing PM emissions, has been observed and considered an importance reason for the slower reduction of NO₂concentration in urban cities of Europe with high penetration rates of diesel vehicles. The result of primary NO₂emission analysis from 2000 to 2010 for Seoul shows that the proportion of primary NO₂in the vehicular NOx emission is in a range of 11~32% for monthly averages and 15~21% for yearly averages. This proportion of primary NO₂emission is high enough to be related to the slower reduction of NO₂concentration in Seoul as for many cities in Europe. Therefore, we conclude that one important reason for the slower reduction of NO₂ concentration in Seoul is the increasing penetration of diesel vehicles with the primary NO₂emission issue due to the relaxed NOx emission standards for diesel vehicles. In order to control NO₂concentration in Seoul, it is necessary to decrease the primary NO₂emissions as well as total NOx emissions. Considering diesel vehicles major emission sources of both NOx and PM, policies reducing all of PM, NOx, and primary NO₂emissions should be preferentially implemented. With this principle in mind, several policy suggestions are made. Also, laws and regulations related to vehicle emission standard, vehicle emission inspection and DPF certification should be revised in advance.