Processes controlling the composition of precipitation at a remote southern hemispheric location: Torres del Paine National Park, Chile

Precipitation composition measured at Torres del Paine National Park, Chile (TdP) (51 degrees 10'S, 71 degrees 58'W), between 1984 and 1993 was acidic (volume-weighted-pH of 4.96) with a dilute seawater component. H+ was the dominant non-seasalt (nss) cation; in decreasing order of abundance, nss anions were HCOO-, Cl-, SO4= CH3COO-, and NO3-. Relative to lower latitude, remote locations, concentrations and per- event depositions of nss SO4=, NO3-, and NH4+ at TdP were lower; those of HCOOt (HCOO- + HCOOH) and CH3COOHt (CH3COO- and CH3COOH) were similar; and those of CH3SO3- were higher. Concentrations and deposition fluxes of HCOOt, CH3COOt, nss SO4= CH3SO3-, and NH4+ varied seasonally with summer maxima and winter minima. Carboxylic acids probably originated from both direct terrestrial emissions and oxidation of hydrocarbons emitted by marine and terrestrial biota. Nss SO4= and CH3SO3- originated primarily from oxidation of biogenic (CH3)(2)S emitted from the southern Pacific Ocean. Direct emissions of NH3 from upwind terrestrial and marine ecosystems probably accounted for most observed NH4+.NO3- concentrations and depositions were highest during the latter part of austral winter and spring suggesting abiotic controls. Transport of precursors from lightning, biomass burning, and fossil-fuel combustion at lower latitudes and possibly transport of reactive N from the stratosphere apparently contributed oxidized N to the southern Patagonian troposphere. Although the ionic strength of precipitation at TdP is currently among the world's lowest, future changes are likely because of increases in local and regional population and energy and food production.