Fifth, emission of pollutants in excess of permissible emission levels is addressed by an improvement mandate and emission charges. There are two types of emission charges: the “basic charge” is imposed according to the quantity and concentration of pollutants emitted within permissible emission levels, and the “excess charge” is imposed on emissions in excess of permissible emission levels. The basic charge is currently imposed on sulfur oxides and dust, and the excess charge is imposed on nine types of pollutants, including sulfur oxides, ammonia, and dusts. Nitrogen oxides are not subject to the basic charge, but its inclusion is under review.