Investigating hydrogen peroxide in rainwater of a typical midsized city in tropical Brazil using a novel application of a fluorometric method

This work investigates the effect of public policies related to vehicle emissions on the lower tropospheric concentrations of H2O2 in a typical midsized city in tropical Brazil. The concentrations of H2O2, SO42-, and NO3- in rainwater samples were determined from 2014 to 2017 in the municipality of Ribeirao Preto in Sao Paulo State. A fluorometric method, based on the formation of a highly fluorescent product (2',7'-dichlorofluorescein, DCF), was adapted and optimized for the measurement of H2O2 in natural water samples including seawater. The method was highly specific, accurate and sensitive (LOD = 2 nmol L-1). Its main advantage compared to others, was that the fluorophore remained stable for at least 48 h, offering a longer time interval in which to perform the analysis and therefore facilitating fieldwork. Concentrations of H2O2 in rainwater ranged from 5.8 to 96 timol L-1, with VWM of 28.6 +/- 1.4 limo] L-1 (n = 77). Solar radiation appeared to have a greater impact on production than on consumption of H2O2. The annual VWM concentrations of H2O2 in rainwater were negatively correlated with sulfate (at pH < 5) and nitrate, suggesting that national policies designed to reduce vehicle emissions of SO2 and NO resulted in increased atmospheric H2O2 concentrations, impacting the oxidative capacity of the lower troposphere. Biomass burning emissions and photochemical reactions were also found to be important factors affecting the concentration of H2O2 in the atmosphere. This work expands the current records available for the Southern Hemisphere, where there is a considerable paucity of information regarding temporal production and loss of atmospheric H2O2.