An analysis of Tianjin's air pollutants has identified dust as the main component of the city's smog.

Tianjin, about 100 kilometers southeast of Beijing, is the second city after the capital to release an analysis of its fine particulate matter, or PM2.5.

The analysis, released over the weekend, comes after the national environmental authority asked that China's five major cities and 30 other municipalities and capitals, excluding Lhasa, present their analyses before the end of 2014.

"By analyzing the pollutants, we can take different measures, specifically in different areas, to curb smog," said Feng Yinchang, a professor at the College of Environmental Science and Engineering who oversees the research.

According to Tianjin's analysis, dust amounted to about 30 percent of the city's air pollutants. The burning of coal accounted for 27 percent, motor vehicle exhaust 20 percent, and industrial production 17 percent.

This varies dramatically from Beijing's results, where motor vehicle exhausts, at 31.1 percent, contributed heavily to the city's smog. The burning of coal contributed to 22.4 percent of PM2.5, followed by industrial production (18.1 percent) and dust (14.3 percent).

Feng said industrial production is likely the main pollutant in Shijiazhuang, capital of Hebei province, which hasn't released its analysis.

Feng, who called for cross-regional cooperation, said air pollution in one area often affects another.

"About 28 to 36 percent of the PM2.5 in Beijing is the result of migrating pollutants," he said. "In Tianjin, the percentage is from 22 to 34."

Smog has affected large parts of China since 2013, threatening people's health. The situation in North China is especially serious.

The average density of PM2.5 in Beijing last year was 89.5 micrograms per cubic meter, far beyond the pollution control cap target of 60. Beijing has reduced traffic, phased out old motor vehicles and banned coal use to improve its air quality.