Summary: | Formaldehyde (HCHO) plays an important role in ozone chemistry in the troposphere. Its photolysis can be a significant radical source as well as an important sink of atmospherically important free radicals. Here, the impact of HCHO on ozone (O3) chemistry in the lower troposphere was investigated. A continuous flow injection analysis formaldehyde measurement system, which utilizes the Hantzsch reaction and fluorescence detection, was assembled and evaluated during a formaldehyde intercomparison. This method was used to conduct ambient measurements of formaldehyde at several sites during five separate field measurement campaigns. The formaldehyde budget was evaluated for a site located in a Northern Michigan deciduous forest, sampling ∼10 m above the forest canopy. Isoprene oxidation was found to be the most important formaldehyde source at this site, with comparable rates of removal via photolysis, dry deposition, and reaction with the hydroxyl radical (OH). Formaldehyde was an important radical source, particularly in the morning, before ozone photolysis becomes efficient. The impact of formaldehyde on the marine Arctic troposphere was studied during polar sunrise in 1998 (PSE98) and 2000 (Alert 2000). During PSE98, it was found that the snowpack interstitial air contains elevated formaldehyde relative to the ambient air aloft, possibly as a result of photochemical production, suggesting a flux into the atmosphere. During both SNOW99 and Summit 99, we found some evidence for both photochemical formaldehyde production and release through physical processes through measurements of ambient air and snowpack interstitial air. In the final study, Alert 2000, we investigated formaldehyde in the snowpack interstitial air in a series of experiments designed to investigate the roles of physical and photochemical mechanisms in the snowpack release/production of formaldehyde.
|