Seoul has undergone dramatic changes over the past decade. It has become one of the most popular destinations in Asia. City streets are filled with tourists and foreign students flock to Seoul’s universities to spend a semester or year or just to stay for the summer.

Well, looking back on the past several years there is also one noticeable change, on the negative side. The air quality in the city has deteriorated significantly in a short time frame, and we have reached the point where checking the air quality index is now a daily routine for many Seoulites.

Fine particle advisories have gone from occasional to frequent. In fact, it does not require any official index or advisory: People can see particle-laden smog or haze more often when they walk or drive in the city.

They start to appreciate the clean sky after a rain or strong winds. It has been some time that yellow dust from the Gobi Desert has become a fixture every April, but the fine particle phenomenon is quite recent and different.

According to the Environmental Performance Index 2016, an outcome of joint research conducted by Yale School of Forestry & Environment and Yale Law School, Korea’s air quality ranks 173rd out of 180 countries surveyed. For air quality rankings, they measured exposure to fine particulate matter and nitrogen dioxide.

Korea is only followed by Myanmar, Pakistan, Laos, Nepal, India, China and Bangladesh, in the order of the rankings from 174 to 180. Among developed states, Korea is surely ranked at the bottom by a wide margin. The nation’s startling ranking shows the urgency of the matter and the wrong direction of air quality control policy.

Many of us have wondered what has caused such a noticeable deterioration in a short period of time. Speculation has been rife about outside factors, such as the inflow of polluted air from neighboring countries. Recent studies signal that the deteriorating environmental conditions have more to do with homegrown reasons than exogenous factors.

The United States Environmental Protection Agency notes that the main culprits of creation and accumulation of small particles in the air are emissions from fossil fuel combustion, which produces NO2. NO2 then mixes with other compounds in the air such as ammonia and moisture to create small particles.

These particles are then inhaled to penetrate the lungs. So, the key to tackling small airborne particles is to reduce emissions from cars and fossil fuel burning facilities.

Nonetheless, Korea has seen steadily robust activities of coal power plants along the west coast and a continued increase of diesel fuel vehicles over the past several years. The realization is now spreading that the policies to facilitate coal power plants and diesel automobiles are to blame for the fast deterioration of air quality in the Seoul metropolitan area.

The nation’s Green Growth Policy of 2009 even included “clean diesel” in the eco-friendly business category requiring governmental support, showing how much the air quality control scheme was off target.

A misguided lenient approach toward diesel vehicles led to the scrapping of the plan to impose environment-improvement charges for these vehicles and introduction of support measures. Together with consumers’ strong interest in fuel efficiency, the percentage of diesel cars on the road increased from 18.5 percent in 2010 to 44.7 percent in 2015.

Even after the disclosure of environmental test manipulation by some automakers in 2015, the sales of diesel vehicles have not changed that much, due to the reduced price of these cars and their tempting fuel efficiency.

A policy change is long overdue. Without a strong commitment by the government to improve air quality, the situation will only deteriorate. It will not be too long before, as in Beijing today, expatriates living in Seoul receive additional allowance from employers to compensate their suffering from air pollution.

Lee Jae-min is a professor of law at Seoul National University. — Ed.

By Lee Jae-min