The Ministry of Environmental Protection has drafted definitions for the conditions that qualify a day as having haze pollution.

The primary indicator of haze pollution is PM2.5, particles with a diameter of less than 2.5 microns, which can penetrate the lungs.

A haze pollution day occurs when the average concentration of PM2.5 is above 75 micrograms per cubic meter and visibility is less than 5 km for more than six consecutive hours due to an increasing concentration of fine particulate matter in the air.