ABSTRACT
Atmospheric strong acids consist principally of nitric and sulfuric acids derived from the oxidation of sulfur dioxide and nitrogen oxides which in turn were emitted from stationary and (for NOx) mobile combustion sources (1). Some evidence suggests that hydrochloric acid may also be present in the atmosphere (2) derived from primary, coal-fired utility emissions or evolved due to interactions between sea salt and acidic sulfate aerosols. These species are neutralized principally by atmospheric gaseous ammonia (the latter mostly originated from surface biogenic and anthropogenic sources) and soil-derived particulate matter to produce the observed composition of sulfate and nitrate aerosols and the levels of nitric acid found in the atmosphere (3,4). Despite the acknowledged general validity of the above summary statements, many questions remain to be fully addressed: What is the relative strong acid content of atmospheric aerosols, especially its spatial and temporal variability? Is aerosol strong acid content associated only with aerosol sulfate and nitrate? Are ammonia and nitric acid in equilibrium with atmospheric aerosols? Are atmospheric gaseous strong acids (HNO3, HCl, etc.) present in amounts comparable with aerosol species? Do weak acids contribute significantly to the acidity of atmospheric samples? What are the relationships of gaseous and aerosol strong acids to the composition of clouds and precipitation?
