40 CFR §63.1158

(a) Pickling lines—(1) Continuous pickling lines. No owner or operator of a new or reconstructed affected continuous pickling line at a steel pickling facility shall cause or allow to be discharged into the atmosphere from the affected pickling line:

(i) Any gases that contain HCl in a concentration in excess of 6 ppmv; or (ii) HCl at a mass emission rate that corresponds to a collection efficiency of less than 99 percent. (2) Batch pickling lines. No owner or operator of a new or reconstructed affected batch pickling line at a steel pickling facility shall cause or allow to be discharged into the atmosphere from the affected pickling line: (i) Any gases that contain HCl in a concentration in excess of 18 ppmv; or (ii) HCl at a mass emission rate that corresponds to a collection efficiency of less than 97 percent. (b) Hydrochloric acid regeneration plants. (1) No owner or operator of a new or reconstructed affected plant shall cause or allow to be discharged into the atmosphere from the affected plant any gases that contain HCl in a concentration greater than 12 ppmv. (2) In addition to the requirement of paragraph (b)(1) of this section, no owner or operator of a new or reconstructed affected plant shall cause or allow to be discharged into the atmosphere from the affected plant any gases that contain Cl2 in a concentration in excess of 6 ppmv.