In-situ Calibration of the Hydroperoxyl Radical Using an Immobilized TiO2Photocatalyst in the Atmosphere
Year: 2008
Type: article
Abstract: The present study is the first report of utilizing $TiO_2$ photocatalyst to analytically calibrate the hydroperoxyl radical ( $HO_2\;^{\cdot}$ ). An in-situ calibration method of $HO_2\;^{\cdot}$ is proposed for air monitoring by using an 2-methyl-6-(pmethoxyphenyl)- 3,7-dihydroimidazo-[1,2-a]pyrazin-3-one (MCLA)-chemiluminescence (CL) technique. In this method, $HO_2\;^{\cdot}$ ( $pK_a$ = 4.80) is produced by the ultraviolet (UV) photolysis of immobilized $TiO_2$ using a constant flow rate of air equilibrated water, in which $HO_2\;^{\cdot}$ is controlled by using various lengths of knotted tubing reactor (KTR). The principle of the proposed calibration is based on the experimentally determined halflife ( $t_{1/2}$ ) of $HO_2\;^{\cdot}$ and its empirically observed pH-dependent rate constant, $k_{obs}$ , at a given pH. The concentration of $HO_2\;^{\cdot}$ / $O_2\;^{\cdot}$ − is increased as pH increases. This pH dependence is due to the different disproportionative reactivities between $HO_2\;^{\cdot}$ / $O_2\;^{\cdot}$ − and $HO_2\;^{\cdot}$ / $O_2\;^{\cdot}$ −. Experimental results indicate the practical feasibility of the approach, producing very promising method.
Author: Kwon, Bum-Gun;
Language: English
Subfield: Atmospheric Science
Field: Earth and Planetary Sciences
Domain: Physical Sciences
Open Access status: bronze
Funder: Ministry of Environment
OpenAlex ID: W758452913