China's air quality continues to improve in the first half of this year, the country's environmental ministry said on Sunday.

China's biggest 338 cities breathed in cleaner air for the first half this year, recording 76.7 percent of clean air between January and June, a four percentage points increase from the same period in 2015.

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Levels of PM2.5, which are tiny hazardous pollutants, in Beijing also plummeted to nearly 18 percent compared with 2015. However, in the first half of the year, Beijing still suffered from an average PM2.5 concentration of 64 micrograms per cubic meter, which is nearly twice the official state standard of 35 micrograms and over six times more than the World Health Organization's annual average of no more than 10 micrograms, according to EWN.

Although the ministry did not explain the reasons for the air quality improvements, it said that it is following stringent measures to curb polluters and deal with overcapacity, particularly in the heavily polluting steel sector. Furthermore, the country's economic slowdown has also likely played a role.

Earlier this month, the ministry revealed that it penalized several state-owned polluters in May for exceeding emission limits. A subsidiary of PetroChina Co Ltd in Dalian was fined 2.9 million yuan (around $433,000).

Meanwhile, of the 10 most polluted cities, six were from the industrial northern province of Hebei, down from seven in 2015. By the end of 2015, China initiated a two-month probe into the province and discovered that companies were into "fraudulent activities" and were disregarding orders not to expand industrial capacity.

Tagsair quality, clean air, emission