Low molecular weight oxygenated organic compounds dissolved in rainwater from Ribeirão Preto

Author(s)

Fernanda Furlan Giubbina

• Document type: Doctoral Thesis
• Press: Ribeirão Preto.
• Institution: Universidade de São Paulo (USP). Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto (PCARP/BC)
• Defense date: 2017-05-12

Examining board members

Maria Lucia Arruda de Moura Campos; Adalgiza Fornaro; Anne Hélène Fostier; Marco Tadeu Grassi; Anderson Rodrigo Moraes de Oliveira

• Advisor: Maria Lucia Arruda de Moura Campos; Bruno Spinosa de Martinis

Abstract

Although there has been a dramatic increase on the use of ethanol fuel in Brazil and in several other countries, there is a great lack of data related to the abundance of ethanol and associated organic species in the atmosphere. The temporal study of the behavior of ethanol in rainwater in Brazil is pioneer, and may serve as a basis to better understand the changes that occur in the atmosphere due to the increasing use of this fuel. This work presents a new headspace GC-FID method to simultaneously determine acetaldehyde (AA), acetone (AC), methanol (MeOH) and ethanol (EtOH) at environmentally relevant concentrations in the atmosphere and in a variety of natural waters. The method is simpler than those presented in the literature, robust and relatively low-cost. The method presented good recovery, precision and good agreement with a HPLC method for determination of acetaldehyde, methanol, and ethanol, which endorsed the accuracy of the proposed method. The ethanol concentration was determined in rainwater samples from Ribeirão Preto from 2012 to 2016 (n = 186). The volume-weighted mean (VWM) was 5.28 ± 0.49 mol L-1, which is close to the expected concentration at the equilibrium between the gas and aqueous phases. The ethanol value is about 28 times higher than the average found in the city of Wilmington (USA), reflecting the high use of ethanol fuel in Brazil. The annual mean concentrations of ethanol in rainwater samples over 4 years of monitoring varied little, and also did not show significant differences according to the season, agricultural activities, or the direction of the air masses. For the rainwater samples collected from February to December 2016 the VWM concentration of the other analyzed species were: 0.84 ± 0.12 mol L-1 AA (n = 62); 0.70 ± 0.08 mol L-1 AC (n = 59), 10.9 ± 1.19 mol L-1MeOH (n = 62), 15.8 ± 1.64 mol L-1formic acid (n = 67); and 9.76 ± 0.95 mol L-1 acetic acid (n = 67). The identified organic carbon average mass in the samples represented about 20% of the total dissolved organic carbon (DOC) in rainwater. The estimated flux of organic carbon by wet deposition was 5.1 g C m-2 year-1, being 1.0 g C m-2 year-1 identified in this work. In addition to the vehicular emission, an important source of DOC to the atmosphere is the biomass burning, which still occurs frequently in the state. The statistical tools used here, considering the organic species identified together with other major inorganic species, did not allow to clearly separate the predominant emission sources in the region. This may occur because the year-round vehicular emission is predominant in relation to the possible biogenic and by biomass burning emissions. Exposure of rainwater samples to irradiation with artificial sunlight showed that there was loss of EtOH and formation of AA, but the processes neither occurred in stoichiometric proportion, nor at the same rate. In the case of MeOH and formaldehyde, the formation and loss of these species occurred erratically. The absence of a clear trend in the photochemical transformations of alcohols reflects the complexity of the matrix and the reactions involved in the atmosphere. (AU)

• FAPESP's process: 13/13482-3 - Behavior of organic and inorganic species dissolved in the rainwater of Ribeirão Preto: a city in a sugarcane producing region that is rapidly changing
• Grantee: Fernanda Furlan Giubbina Bernardi
• Support Opportunities: Scholarships in Brazil - Doctorate