Hydrochloric Acid can be emitted from many industrial processes, where it is either used in that form, stored with tank ventilation, or generated from the process.
HCl will usually be in fine, sub-micron mist form.
The gas comes from the process or vapours are drawn from the tank into a scrubber by a suction fan.
Pharmaceutical plant – general process vent emissions of HCl
Air Pollution