South Korea saw a 25 percent decline in airborne nitrogen dioxide levels between January and May from the previous three-year average, a lawmaker said Wednesday, attributing the decline to coronavirus lockdowns in China.

Rep. Jang Chul-min of the Democratic Party cited Korea Environment Corp. data available on AirKorea that showed Korea’s average concentrations of nitrogen dioxide, a key air pollutant, during the first five months of this year reached 0.017 parts per million, 25.4 percent less than the average of the corresponding periods from the past three years.

Airborne ozone levels, however, gained 2.2 percent to reach 0.0322 parts per million during the same period, the data showed.

While China enforced lockdowns in high-risk areas during those months, Korea did not, but still saw positive changes in air quality due to the impact of China’s actions, Rep. Jang said.

China reported a 41.7 percent drop in its nitrogen dioxide concentrations and a 14.5 percent rise in its ozone gas concentrations after a 113-day lockdown in its territory.

According to a study published in August in the Proceedings of the National Academy of Sciences of the United States of America, lockdowns tended to drag down nitrogen dioxide concentrations but had no direct effect on ozone levels.

The lawmaker said the nitrogen dioxide and ozone levels in Korea and China were correlated, as the data showed. He said the two neighboring countries should expand cooperation to mitigate air pollution, calling on the Korean government to step up efforts to get China to take action on air quality.

By Ko Jun-tae (ko.juntae@heraldcorp.com)