Total peroxides and sulfate in rainwater in the Mexican eastern Pacific Ocean during the Climatic Experiment in the Americas Warm Water Pools

Abstract

Total peroxides were analyzed in 26 rainwater samples collected on board of the R/V El Puma of the National Autonomous University of México (UNAM) during the Climatic Experiment in the Americas Warm Water Pools (ECAC-1) over the eastern Pacific Ocean between 12 and 14º N, and between 98 and 100º W, from May 23 to 25, 2001. The volume weighted mean concentration of total peroxides was 13.1 ± 1.94 μM. Also, sulfate ion was analyzed. The volume weighted mean concentrations for sulfate and sea-salt sulfate were 0.76 ± 0.59 and 0.04 ± 0.06 mg L^-1, respectively. Excess sulfate (non-sea-salt sulfate) represented 95% of the total sulfate. The total peroxides concentration in rainwater correlated significantly with total sulfate and excess sulfate (0.560 and 0.586 at a p < 0.05, respectively) possibly because most of the excess sulfate and hydrogen peroxide, observed in the Mexican eastern Pacific Ocean, could have been produced from the oxidation of biogenic sulfur compounds. The non-significant correlation between sea-salt sulfate and total peroxides was due to the fact that H₂O₂ does not react with the sulfate already present in sea salt aerosols. Also, the concentration of total peroxides did not correlate with rain intensity probably because a significant fraction of H₂O₂ could have been generated within cloud droplets.