This action promulgates national emission standards for hazardous air pollutants (NESHAP) for hydrochloric acid process steel pickling facilities and hydrochloric acid regeneration plants pursuant to section 112 of the Clean Air Act (Act). Major source facilities subject to the rule emit hydrochloric acid (HCl), a hazardous air pollutant (HAP). Chronic exposure to HCl has been reported to cause gastritis, chronic bronchitis, dermatitis, and photosensitization. Acute inhalation exposure to HCl may cause hoarseness, inflammation and ulceration of the respiratory tract, chest pain, and pulmonary edema. Hydrochloric acid regeneration plants also emit chlorine (Cl<INF>2</INF>), which is also a HAP. Acute exposure to high levels of Cl<INF>2</INF> results in chest pain, vomiting, toxic pneumonitis, pulmonary edema, and death. At lower levels, Cl<INF>2</INF> is a potent irritant to the eyes, the upper respiratory tract, and lungs. The final rule provides public health protection by requiring new or existing pickling lines that use hydrochloric acid as the primary pickling solution, hydrochloric acid regeneration plants, and acid storage tanks to meet emission standards reflecting application of the maximum achievable control technology (MACT). Implementation of the rule is expected to reduce HAP emissions by more than 2,200 megagrams per year (Mg/yr) (2,500 tons per year (tpy) from current levels.