Hydrogen peroxide, methyl hydroperoxide, and formaldehyde in air impacted by biomass burning
The first objective of this study was to improve measurement methods for hydrogen peroxide, methyl hydroperoxide, and other organic hydroperoxide species in the atmosphere. This instrumentation was then used to collect and analyze air impacted by biomass burning emissions, air which was found to be enriched with these compounds and formaldehyde. The second and third objectives of this study were to examine whether hydroperoxide and formaldehyde were directly produced from fires and to investigate the effect of enhanced hydroperoxide and formaldehyde on atmospheric oxidant cycles.^ A HPLC (High Performance Liquid Chromatography) method was developed for airborne measurements of hydrogen peroxide and four organic hydroperoxide species: methyl hydroperoxide, ethyl hydroperoxide, hydroxymethyl hydroperoxide, and peroxyacetic acid. A fifth organic species, 1-hydroxyethyl hydroperoxide, could not be quantified due to its instability during analysis. This method was used for ground measurements at Harvard Forest in the summer of 1992 and at the URI Bay Campus in the summer of 1993 and 1995 and in airborne measurements on board the NASA DC-8 aircraft during PEM-West (A & B) (Pacific Exploratory Mission - West, Phase A and B) in September-October 1991 (A) and January-March 1994 (B) and during TRACE-A (Transport and Atmospheric Chemistry near the Equator - Atlantic) in September-October 1992. The results obtained from these experiments showed that this method can provide reliable measurements of hydroperoxide species with sample resolution of a few minutes.^ In TRACE-A, the concentrations of H$\sb2$O$\sb2,$ CH$\sb3$OOH, and CH$\sb2$O observed in and near biomass burning plumes over Brazil and southern Africa were highly elevated, at least a factor of two higher than those of undisturbed background conditions. Other organic hydroperoxides such as CH$\sb2$(OH)OOH and CH$\sb3$CH(OH)OOH were detected in fire plumes. Based upon the TRACE-A experiment, the highest concentrations of H$\sb2$O$\sb2$ and CH$\sb3$OOH observed During PEM-West (A) are now thought to have been impacted by an aged fire plume from southeast Asia. From these results, it was proposed that hydroperoxide and formaldehyde can be directly produced from biomass burning. This hypothesis was examined with data obtained from TRACE-A through the comparison of hydroperoxide and formaldehyde measurements with model estimates and by comparison to other species known to be produced by biomass fires. Simple fire experiments were also conducted to demonstrate that these species were emitted by fires. The comparison study strongly suggested that biomass burning can be a direct source of these species and the fire experiments showed explicitly that these species can be directly produced from fires.^ As hydroperoxide and formaldehyde are closely coupled to odd-hydrogen and odd-oxygen cycles in the troposphere, the enhancement of these species in air by biomass burning would have significance in the chemistry of atmospheric oxidants. Thus, the effect of enhanced hydroperoxide and formaldehyde on atmospheric oxidants was examined with data from TRACE-A. The results showed that hydroperoxide and formaldehyde played a key role in increasing odd-hydrogen radical production in biomass burning impacted air. Odd-hydrogen radical production from the direct source of these species was estimated to be near 30% of the total radical production. These species are also believed to participate in promoting odd-oxygen production near the source of biomass burning. Therefore, where biomass burning takes place, hydroperoxide and formaldehyde are anticipated to increase the oxidizing capacity of the atmosphere by directly increasing odd-hydrogen radical production and indirectly boosting odd-oxygen production through their emission from biomass burning. ^
Physical Geography|Physics, Atmospheric Science|Engineering, Environmental
"Hydrogen peroxide, methyl hydroperoxide, and formaldehyde in air impacted by biomass burning"
Dissertations and Master's Theses (Campus Access).