Fireworks worsened pollution in many Chinese cities during Lunar New Year celebrations, the environment ministry said.

“Heavy air pollution” was recorded at 68 of the 161 cities monitored, while 16 experienced “severe air pollution,” on the evening of Jan. 30 as fireworks were set off across the country, the Ministry of Environment Protection said in a statement yesterday.

The concentration of fireworks was the main reason for the bad air quality across the country, an unnamed official with the environment ministry was quoted as saying in the statement.

Posters this year in Beijing warned residents about the effects on air pollution of fireworks that are traditionally set off in the streets to commemorate the Lunar New Year. The Beijing Municipal Environmental Monitoring Center said on its official Weibo account yesterday that fireworks might lead to further deterioration in air quality.

“You may as well watch spring festival shows on TV at home,” it said. “And keep the firecrackers on hand until the fifth day of the first Lunar month.”

The concentration of PM2.5 pollutants — particles smaller than 2.5 microns in diameter that pose the biggest health risk — was 17 at 4 p.m. on Jan. 30 in Beijing, according to the U.S. Embassy’s air monitor. By 1 a.m. the next day the level had reached 469, data released on its Twitter feed show.