Diesel cars are being blamed as the main culprit of the chronic fine dust pollution in the country, but studies indicate that diesel construction equipment is also a big part of the problem, according to experts on Friday.

A tally from the Ministry of Land, infrastructure and Transport showed South Korea had 450,482 registered construction equipment as of end-March, 67 percent of them forklifts and excavators. The majority, experts say, use diesel fuel for cost and efficiency reasons, releasing dust and microdust particles and nitrogen oxide into the air.

A report released by the Seoul Institute last year estimated that nearly one-third of dust and microdust emissions in the capital city came from operating construction machines. The figure, however, excludes dump trucks and concrete mixer trucks that are blamed for up to half of dust and NOx polluting Seoul's air.

The number of registered construction equipment in Gyeonggi Province, adjacent to Seoul, is about double that of the capital city at 82,714.

State rules are in place to control noxious emissions by these machines. A regulation is in place for machines being sold after October last year to meet the strictest requirements of the U.S.

Environmental Protection Agency. New dump trucks and concrete mixer trucks have been required since 2004 to follow the European Union's Euro 6 standards.

But the older machines are exempt from these standards, creating a big loophole in any attempts to control the emissions.

The report from the Seoul Institute said that as of 2013, 55 percent of the registered construction equipment were more than 10 years old, putting them outside of the regulations.

Choi Yoo-jin, the author of the report, said construction machines have higher emissions levels than diesel passenger cars because of their bigger engines.

"The older the engine, the higher the emissions," Choi said.

"The lifespans of these machines are also longer than regular vehicles'."

Some experts, including professor Lee Ho-geun at Daeduk College in Daejeon, south of Seoul, say the problem is that there is no viable alternative to using diesel engines when it comes to construction equipment.

"These machines need high power engines. They have no choice but to use diesel," Lee said.

"Rather than going for hurried measures to bring down the emissions level, we have to find a practical solution, like banning operations of these machines during commuting hours and weekends," he said.

Choi of the Seoul Institute recommended that stricter rules be applied to smaller construction sites as well.

"Large-scale sites that are assessed for their environmental impact ban the entry of aged equipment in order to control fine dust emissions," Choi said. "One possible solution is to put such practice to use at all smaller construction sites." (Yonhap)