Only 9 percent of people in China live in an environment that meets the national air quality standards, according to a scientific journal article.
The article, published in a scientific journal of the Nature Publishing Group Scientific Reports on October 15, and authored by two experts from the Nanjing University of Information Science and Technology, said that among the 190 cities they monitored, only 25 met national air quality standards.
Analysts said they believe that although China has made headway in recent years in protecting the environment, there's a long way to go.
The two authors analyzed the density of PM2.5 - airborne particles smaller than 2.5 microns in diameter and a major air pollutant - collected from the latest air quality monitoring network of China's Ministry of Environmental Protection in 190 major cities from April 2014 to April 2015.
The article said that the population-weighted exposure to PM2.5 is 61 micrograms per cubic meter, three times higher than the global level.
It also concluded that the PM2.5 density is generally higher in northern China than in the south, and that the density is higher in inland than coastal cities.
"There is less rainfall in northern China and emissions from coal-fired heating plants in winter have led to a high density in these areas," Qi Zhiqiang, a research fellow from the Nanjing University-ISC Environmental Health and Safety Academy, told the Global Times.
Qi added that based on another report on 161 cities, only 16 cities met national standards in 2014, mostly located in the Pearl River Delta region.
The article also said the density of PM2.5 generally peaks in winter and drops during summer. Aside from geographical factors, a greater amount of PM2.5 is found in spring in the northwestern, central and western parts of China and autumn in eastern China due to sandstorms and open biomass burning.
A report released by environmental campaign group Greenpeace in July showed that PM2.5 density ranked highest in Beijing, Henan and Hebei provinces, while Yunnan and Hainan provinces as well as the Tibet Autonomous Region enjoy the best air quality.
The density level of PM2.5 particles in a day radically changes after 4 pm, since vehicular traffic increases, according to the article.
The article added that the government needs to determine the specific cause in certain places, as the PM2.5 density varies from place to place and at different times.
Zhang Yuanxun, an expert at the Chinese Academy of Sciences, told the Global Times that it took time to tackle the problem, and has called for stricter law enforcement and harsher punishments.
China has implemented a new environmental protection law, dubbed as the strictest ever law.