Aspects of hydrogen peroxide role as an oxidant in the atmosphere in the context of current public policies to vehicular emissions

Author(s)

Caroline Scaramboni

• Document type: Master's Dissertation
• Press: Ribeirão Preto.
• Institution: Universidade de São Paulo (USP). Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto (PCARP/BC)
• Defense date: 2018-04-06

Examining board members

Maria Lucia Arruda de Moura Campos; Adalgiza Fornaro; Thiago Nogueira; Antonio Gustavo Sampaio de Oliveira Filho

• Advisor: Maria Lucia Arruda de Moura Campos

Abstract

The main objective of this work was to provide insights to better understand how the public policies focused on vehicular emissions, including the use of ethanol fuel, can affect the chemical composition of the atmosphere. Hydrogen peroxide (H2O2) is one of the most important oxidants in the troposphere and it can participate in reactions with a variety of organic and inorganic compounds. In this work, determination of H2O2, ethanol, acetaldehyde and other organic and inorganic species was carried out in the gas phase, rainwater and surface water. The fluorimetric method based on the formation of the 2, 7-dichlorofluorescein fluorophore was applied for the first time to determine H2O2 in natural water samples (LOD = 2 nmol L-1 and LOQ = 7 nmol L-1). While other methods require the immediate analysis of the sample, in this case, the fluorophore remains stable for about 48 h, facilitating the analyzes and fieldwork. H2O2 concentrations in rainwater of Ribeirão Preto collected between 2014 and 2017 ranged from 5.8 to 96 mol L-1, with a volume-weighted mean (VWM) of 28.9 ± 1.3 mol L-1 (n = 88). The solar radiation was observed to be a more important parameter in the formation of H2O2 than in its consumption. While the VWM concentrations of sulfate (pH <5) and nitrate in rainwater declined by approximately 35% in 2017 compared to 2014, H2O2 concentrations virtually doubled over the same period. The negative correlation between these species shows that national policies aimed at reducing vehicle emissions may modify the oxidizing capacity of the atmosphere. Gas phase H2O2, ethanol and acetaldehyde concentrations in Ribeirão Preto (RP) and São Paulo (SP) were determined using, for the first time in Brazil, the method of condensate collection. Ethanol concentrations in the atmosphere of RP (15.0 ± 6.6 ppbv, n = 19) and SP (22.0 ± 9.4 ppbv, n = 10) were relatively close, although the SP vehicle fleet is ~ 16 times higher. These ethanol concentrations are about 21 times higher than those reported in the United States due to the high use of ethanol fuel in Brazil. The mean concentrations of H2O2 and acetaldehyde in the atmosphere were, respectively, 2.10 ± 1.46 and 16.3 ± 6.0 ppbv in RP; and 1.29 ± 0.62 and 14.4 ± 5.4 ppbv in SP. Daytime variation showed that while H2O2 concentration increased with solar radiation, ethanol concentration decreased at a rate close to the one of acetaldehyde production. These results indicate that H2O2 may be an important oxidant of ethanol to acetaldehyde in the gas phase, the latter being highly toxic to humans. Fluxes in the air-water interface at the studied sites in RP and SP show that the water body worked as an H2O2 sink. On the other hand, ethanol fluxes were variable, i.e., sometimes invasive and sometimes evasive, with evidence of an important photochemical production of this species in the aquatic environment. (AU)

• FAPESP's process: 16/07534-9 - Aspects of the role of hydrogen peroxide as an oxidant of ethanol in the atmosphere and surface waters
• Grantee: Caroline Scaramboni
• Support Opportunities: Scholarships in Brazil - Master