Seoul has consistently exceeded the national limits on toxic air pollutants for a decade, according to research released Wednesday.

The report by the Seoul Development Institute said that the amount of nitrogen dioxide in Seoul exceeded the national limit from 2000 to 2009.

Nitrogen dioxide is a toxic pollutant which can cause respiratory problems and other health problems including bronchitis, pneumonia and asthma.

The institute found that air near high-traffic areas, mainly roads, was between 49 parts per billion and 57 parts per billion NO2. Residential areas were measured to have somewhere between 34-38 parts per billion. All exceeded the national limit of 30 parts per billion.

“Despite the city’s aggressive efforts to reduce the level of nitrous oxides (NOx) released into the atmosphere, it does not seem to have had a great effect on the levels,” said researchers.

“The levels of nitrogen dioxide in the air are at a standstill because of the ease on smog regulation for diesel vehicles which has increased its numbers, though diesel engines have higher smog emission levels.”

According to the U.S. Environmental Protection Agency, the U.S. has seen a 38 percent decrease in its national average nitrogen dioxide levels.

The government data shows that in 2010, 90 percent of the sites measured had less than 17 parts per billion of the gas.

By Robert Lee (robert@heraldcorp.com)