We have attempted to measure gaseous H₂O₂ in air using an aqueous trapping method. With continuous bubbling, H₂O₂ levels in the traps reached a plateau, indicating that a state of dynamic equilibrium involving H₂O₂ destruction was established. We attribute this behavior to the interaction of ozone and its decomposition products (OH, O₃ ⁻) with H₂O₂ in aqueous solution. This hypothesis was investigated by replacing the air stream with a mixture of N₂, O₂ and O₃. The results of this experiment show that H O was both produced and destroyed in the traps. These results have led us to question the validity of techniques which employ aqueous traps to measure H₂O₂in air.

Measurements of H₂O₂ in rainwater collected in Miami, Florida, and the Bahama Islands area indicate the presence of H₂O₂concentration levels ranging from (1–7)×10⁻⁵ M. No systematic trends in H₂O₂ concentration were observed during an individual storm, in marked contrast to the behavior of other anions (e.g., [NO₃ ⁻], [SO₄ ⁼], and [Cl⁻]). The data suggest that a substantial fraction of the H₂O₂found in precipitation is generated by aqueous-phase reactions within the cloudwater rather than via rainout and washout of gaseous H₂O₂.

Elevated levels of non-sea-salt sulfate and SO₂ in samples collected off the west coast of South America indicate that there is a major source of atmospheric sulfur in the region of southern Peru and northern Chile. During a 1983 cruise, observed concentrations of non-sea-salt sulfur, SO₂, selenium, arsenic, and antimony were comparable to levels reported for moderately polluted urban air. In contrast, methanesulfonic acid levels were typical of coastal marine air. Clearly, the elevated atmospheric sulfur levels in this region cannot be ascribed to oceanic organosulfur emissions. The major inputs are tentatively attributed to the smelting of sulfide ores which is a major industry in this region. The transport of smelter derived aerosols to this region may have a number of consequences for the atmospheric and oceanic chemistry of the Peruvian upwelling area.

Methane sulfonic acid (MSA) is an oxidation product of the reaction of OH radical with dimethyl sulfide and, hence, should be an important constituent of marine air. MSA concentrations in marine aerosols ranged from 0.009 to 0.075 μg/m³ in samples from the Pacific and Indian oceans and Miami, Florida. In the samples from remote areas (Pacific and Indian oceans), MSA levels averaged 6.7% (S = 1.9) of the non-sea-salt (nss) SO₄ ⁼. In the Miami area, ratios were occasionally lower because of the impact of local sulfur emissions (probably pollutant SO₂). MSA concentrations in seven rainwater samples collected at Miami, Florida, ranged from 0.001 to 0.034 ppm. Cascade impactor samples from Miami, Florida, and the Gulf of Mexico indicate that MSA occurs primarily in the smaller particles, as does nss SO₄ ⁼ values. In the two samples analyzed, MSA is concentrated on slightly coarser particles than nss SO₄ ⁼. The size distributions of both MSA and nss SO₄ ⁼ differ markedly from that of sea salt Na⁺, suggesting that at least the first step in the oxidation of organosulfur compounds is a gas phase reaction. The observed concentrations of MSA in marine air are the result of formation from gas phase reaction of dimethyl sulfide (and other volatile organosulfur compounds) with OH radical and destruction by aqueous phase reaction with OH radical in aerosols. Preliminary experiments indicate that MSA oxidation probably yields SO₄ ⁼ under atmospheric conditions. Therefore, MSA destruction is a potentially important pathway for the formation of nss SO₄ ⁼ in the marine atmosphere. The magnitude of the fluxes involved in the organosulfur cycle cannot be calculated from the MSA data because of the uncertainty in the free radical chemistry of aerosols.

Atmospheric concentrations of aerosol methanesulfonic acid (MSA) and non-sea-salt (nss) sulfate were measured in samples collected during one year periods at Fanning and American Samoa Islands in the Pacific Ocean. Mean concentrations were 0.045 (s=0.011) ug/m⊃3 MSA and 0.67 (s=0.13) ug/m⊃3 nss sulfate at Fanning, and 0.026 (s=0.012) ug/m⊃3 MSA and 0.41 (0.19) ug/m⊃3 nss sulfate at American Samoa. MSA and nss sulfate were significantly correlated at both stations (r=0.76), with a mean MSA/nss sulfate ratio of 0.065. The higher mean levels of MSA and nss sulfate at Fanning compared to American Samoa apparently reflect differences in the biological productivity of the surface ocean in the two regions.