Hydrochloric acid: A regional perspective on concentrations and formation in the atmosphere of Southern California

Abstract

Atmospheric gaseous hydrochloric acid (HCl) concentrations and water-soluble species in the aerosol phase were measured at nine sites in Southern California throughout the year 1986. Annual average HCl concentrations measured by the denuder difference method ranged from 0.39 ppb at an offshore island to 1.25 ppb onshore at Hawthorne, California. An ion balance on the aerosol shows that coarse particle chloride begins as sea salt over the ocean and is depleted relative to aerosol sodium with transport inland. Total chloride and sodium balances show that chloride depletion from the aerosol is matched by a comparable increase in gaseous HCl concentrations, consistent with the proposition that acid gas reactions with sea salt are the principal source of gaseous HCl in the Southern California atmosphere. Fine aerosol chloride exceeds fine particle sodium on a number of occasions, particularly at one inland site known for extraordinarily high NH_3 levels. There is evidence that coarse aerosol chloride from sea salt is being processed by atmospheric reactions through HCl to form fine aerosol, possibly NH_4Cl.

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