What is the relationship between excessive PM2.5 in the air and fine weather?

PM2.5 refers to the total amount of particulate matter with a diameter less than 2.5 units in the air, which is not directly related to sunny days and cloudy days, but it is definitely smaller after rain, and it is generally smaller in sunny days, but if straw is burned, it will definitely be bigger when fireworks are set off. But if it is foggy, the value will be higher, and the current measurement method is not very mature (world unified method). It is best to wear a mask in foggy days. If it is not a susceptible group, the weather is generally fine.