BEIJING (Reuters) - China’s heavily polluted capital, Beijing, plans to reduce air pollution levels by 15 percent by 2015 and 30 percent by 2020 through phasing out old cars, relocating factories and planting new forests, state media said on Thursday.

Smoke billows from the chimneys of a power plant during sunrise in Jiaxing, Zhejiang province December 23, 2011. REUTERS/Stringer

The level of air pollution in the capital varies, depending on winds. But a cocktail of smokestack emissions, vehicle exhaust, dust and aerosols have at times blanketed Beijing in a pungent, beige shroud for days on end over the past few months, and has even forced the cancellation of flights.

Many Beijing residents complain on the Internet that official figures greatly underestimate the problem and say they only trust readings from the U.S. Embassy, which has its own measurement based on U.S. standards. Those readings appear much grimmer than those of the city government’s.

In an effort to assuage those complaints, the city last month began to disclose the amount of tiny pollution particles in the air of 2.5 micrometers or less in diameter, known as

PM2.5.

State radio said on its website the city government would cut PM2.5 levels by 15 percent by 2015 compared with 2010 levels, and cut overall air pollution levels by 30 percent over the same period.

Chinese experts had earlier criticized as “unscientific” a single monitoring point on the roof of the U.S. Embassy, which releases hourly air quality data via a widely followed Twitter feed.

China previously only disclosed readings of pollutant particles that are 10 micrometers in diameter or larger.

Doctors warn that the tiny floating PM 2.5 particles can settle in the lungs more easily and cause respiratory problems and other illnesses.

“After 2020, the Beijing Environment Bureau will not rest in its efforts to continue improving air quality,” state radio said.

Xinhua news agency said 1.6 million old and polluting vehicles will be taken off the roads by 2020, and that all cement factories would be closed by then.

“By 2020, the government is expected to limit the city’s annual total consumption of coal within 10 million tonnes, 62 percent less than the amount estimated to be consumed by the end of 2015,” Xinhua said.

“From now on, heavy-polluting and energy-consuming companies in the oil refining, petrochemical, cement, iron and steel industries will not be allowed to open new plants or expand their current workplaces,” it said.

The city will also plant 133,000 hectares of new forests, the report added.