Production of OH radicals by ultraviolet photolysis of H_2O in an air and surface purifier

摘要

Hydroxyl (OH) radical air purifiers are used for cleaning both air and surfaces of contaminants; these may be gaseous such as volatile organic compounds (VOCs), noxious or hazardous gases, or biological pathogens in aerosol form or on surfaces. We have made the first measurement of the concentration of hydroxyls, [OH], produced by a commercially available air purifier, here an Odorox~® BOSS~(TM) model, which forms OH via gas phase ultraviolet photolysis, at 185 nm, of ambient water vapor. The measurement is made by monitoring the loss of n-heptane in an environmental chamber; this hydrocarbon concentration is measured via gas chromatography/mass spectrometry. When the purifier, placed within the chamber, is turned on, this concentration is reduced owing to reaction with the OH radicals produced. Using the measured hydrocarbon loss rate and the known OH + n-heptane reaction rate coefficient furnishes the [OH] produced by the purifier, an effective steady state value of (3.25 ± 0.80) × 10~6 radicals per cm~3 in the 120 m~3 chamber. The properties of the air purifier, in particular the ultraviolet lamp output, the air throughput in the device, and an estimation of the water vapor concentration, were used to predict the amount of OH produced by the device, with no fitted parameters. Using a reasonable estimate of the OH loss rate within the chamber predicts [OH] = 2.8 × 10~6 radicals per cm~3, in excellent agreement. Thus we understand well the processes occurring in the gas phase during operation of this hydroxyl radical purifier, and can use these quantitative results to design appropriate remediation strategies for various situations. Furthermore, this purifier is known from studies in independent laboratories to be excellent at neutralizing microorganisms (bacterial, viral, mold), airborne or on surfaces remote from the device itself. Reduction of viable populations by factors of 10~4 or more, compared to controls, has been seen. Thus, there exist some chemically active species outside the region of reaction of the OH with VOCs, which itself occurs only inside or near to the photolysis device. We consider qualitatively mechanisms of alkane oxidation to speculate on the species that may be responsible for this activity.