The current Standard specifies the maximum allowable concentrations of SO2 and fluoride in the atmosphere for the protection of crops with important economic values such as vegetables, fruit trees, mulberry tree, tea trees and forage grass. It classifies agricultural crops as sensitive crops, intermediately sensitive crops and tolerance crops in accordance with their sensitivity and presents descriptions of each kind of crops.

Maximum allowable concentration of pollutants in atmosphere for protection crops (GB 9137-88)