Constraining the Formation and Fate of Hydroperoxides in the Remote Atmosphere
<p> Atmospheric hydroperoxides form as second generation products in the atmospheric oxidation of many volatile organic compounds (VOCs) during reactions of these VOCs with OH and HO<sub>2</sub> (i.e. HO<sub>x</sub>), where HO<sub>x</sub> are among the atmos...
| Summary: | <p> Atmospheric hydroperoxides form as second generation products in the atmospheric oxidation of many volatile organic compounds (VOCs) during reactions of these VOCs with OH and HO<sub>2</sub> (i.e. HO<sub>x</sub>), where HO<sub>x</sub> are among the atmosphere's main oxidants and thus drivers of the majority of atmospheric chemistry. Once formed, the lifetime and ultimate fate of hydroperoxides are set by a variety of potential chemical and physical pathways that have different impacts on the atmosphere's oxidizing capacity, including either recycling HO<sub>x</sub> or removing HO<sub>x</sub>. This dissertation explores the role of hydroperoxides with several different structures through field and laboratory studies using CF<sub>3</sub>O<sup>-</sup> chemical ionization mass spectrometry (CIMS) to understand the role of these hydroperoxides in the oxidation chemistry of the remote atmosphere.</p>
<p>Hydrogen peroxide (H<sub>2</sub>O<sub>2</sub>) and methyl hydroperoxide (MHP, CH<sub>3</sub>OOH) are two of the most abundant hydroperoxides found in oceanic environments. Both hydroperoxides were measured using time of flight and tandem quadrupole CIMS aboard the NASA DC-8 aircraft during the Atmospheric Tomography Mission, enabling a seasonal investigation into their global distribution with near pole-to-pole coverage across the Pacific and Atlantic Oceans and ranging in altitude from the marine boundary layer to the upper troposphere and lower stratosphere. Hydroxymethyl hydroperoxide (HMHP, HOCH<sub>2</sub>OOH) and isoprene hydroxy hydroperoxides (ISOPOOH, HOC<sub>5</sub>H<sub>8</sub>OOH) are organic hydroperoxides derived from the oxidation of isoprene, one of the dominant biogenic VOCs in forested environments. The loss of HMHP from the atmosphere via reaction with OH is investigated in the laboratory using time of flight CIMS and laser induced fluorescence along with theoretical chemical modeling methods. To better distinguish the varying roles of structurally complex hydroperoxides, a novel field-deployable gas chromatograph integrated with a high resolution time of flight CIMS is developed that sensitively detects hydroperoxides along with a number of other oxidation products. This instrument is deployed at a rural forested site in northern Michigan during the PROPHET field campaign to probe the relative contribution of different ISOPOOH isomers to the oxidation pathways of isoprene.</p> |
|---|