China has proposed stricter standards for determining its air pollution index.

Currently China's index is derived from measurements of sulfur dioxide, nitrogen dioxide and other pollutants. But the government doesn't include data for the finest particle pollutants, those of 2.5 micrometers or less, known as PM2.5.

Experts say these ultra-fine particles, caused mostly by cars and coal burning, can easily penetrate the lungs and bloodstream.

Such particles account for more than half the weight of industrial dust in the air of northern China, Jinhua Daily newspaper reports.

In smog-blanketed Beijing, the U.S. Embassy has an air quality monitor to measure PM 2.5 particulates on the embassy compound and issues hourly pollution reports via its Twitter account. The embassy's air quality reports are considered more accurate than those provided by the Chinese government.

The embassy's index caught attention with a "crazy bad" determination on a day last November when levels of PM2.5 surged past 500, about 20 times higher than the guideline issued by the World Health Organization.

"The central government has the responsibility to protect residents' health," said Ma Jun, director and founder of the Institute of Public and Environmental Affairs of China's proposed air pollution reporting change, China Daily newspaper reports. "We need to improve the system now. Monitoring and publicizing the information on PM2.5 is the first step."

But Pan Xiaochuan, a professor with the School of Public Health at Peking University, said that ensuring the standards are reliable and effective would be difficult and a decision has yet to be made whether the PM2.5 standards should be based on a number concentration or a mass concentration.

"The ministry has considered adding PM2.5 into the national air quality standards for many years but hasn't done so. Decisions such as these may be the reason," Pan said.

To clear up smog-draped skies for the 2008 summer Olympics in Beijing, the Chinese government implemented a number of measures for the city in advance of the Games, including cutting vehicle traffic in half.

China aims to reduce energy intensity by 16 percent by 2015 while slashing 17 percent from the 2010 level of carbon dioxide emissions by 2015.

But a September report by the Netherlands Environmental Assessment agency and sponsored by the European Commission says that if current trends in China's emissions continue, it will overtake the United States by 2017 as the highest per capita emitter among the 25 largest emitting countries.