Air quality in major Chinese cities met national standards 53.1 percent of the time from January, slightly better than the same period in 2013.

The Environmental Protection Ministry released air quality reports for 74 cities on Friday for the first quarter of the year.

About half of the cities failed to meet the national air quality standards for more than 45 days during the three-month period. PM2.5, also known as fine particles with a diameter less than 2.5 microns, was the top pollutant in the country.

The passing rate for the most polluted Beijing-Tianjin-Hebei cluster was only 30.6 percent, much lower than the national average. But compared with figures for the same region from last year, the number of severely polluted days was reduced by 62 days.

Six cities from Hebei province made to the list of the 10 most heavily polluted cities in the first quarter of 2013. For the same period in 2014, seven cities made the list.

The average passing rate for 25 cities in the Yangtze River Delta was 58.2 percent, slightly higher than the national average. Cities in the Pearl River Delta scored the highest passing rate at 76 percent, with no severe polluting days.

The 10 cities with the worst air quality from January to March were Xingtai, Shijiazhuang, Baoding, Tangshan, Handan, Hengshui, all from Hebei province, Jinan from Shandong province, Xi’an from Shaanxi province, Langfang, also from Hebei province, and Chengdu from Sichuan province.