How to calculate the number of days of heavy pollution?

Definition of heavy pollution day, determination of concentration and determination of duration.

1. Definition of days of heavy pollution: In a specific period of time, the concentration of pollutants exceeds the standards stipulated by the state or region, and such days are defined as days of heavy pollution.

2. Determination of concentration: The country or region will formulate new pollutant concentration standards, for example, the daily average concentration of PM2.5 exceeds 75 μ g/m3, or the daily average concentration of sulfur dioxide exceeds 50 μ g/m3.

3. Determination of duration: The days with heavy pollution not only require the pollutant concentration to exceed the standard, but also require this high concentration state to last for a certain period of time, 24 hours in a row (spanning natural days).