Beijing environmental authorities announced on May 9 that good air quality days for the capital from January to April increased to 84 days, and heavy pollution days were reduced to three.

Yao Hui, Deputy Director of the municipal ecology and environment bureau said the average concentration of PM2.5, airborne particles smaller than 2.5 micrometers in diameter that pose serious health risks, was 51 micrograms per cubic meter during the period.

The average concentration of PM2.5 in Beijing was 51 micrograms per cubic meter last year, down 12.1 percent year on year, according to the annual environment report published on May 9.

Beijing started to implement a three-year action plan to win the war against air pollution. It has taken actions to curb pollutants from diesel trucks, dust and volatile organic compounds.

Nearly 5,000 cases related to environmental pollution were investigated last year, with a total of 230 million yuan ($33.7 million) fined for violations of environmental laws.

Environmental departments checked more than 216 million heavy-duty diesel vehicles and punished over 325,000 vehicles that exceeded the emission standards in 2018.