|Title:||Effect of NH₃on indoor reactive oxygen species formation from ozone/D-limonene reactions|
|Subject:||Ammonia -- Environmental aspects.|
Air -- Pollution
Hong Kong Polytechnic University -- Dissertations
|Department:||Faculty of Construction and Environment|
|Pages:||x, 67 leaves : ill. (some col.) ; 30 cm.|
|Abstract:||D-limonene is one of the dominant terpenoids in indoor environment, which can be emitted from cleaning products and air fresheners. D-limonene is prone to oxidation resulting in the formation of secondary pollutants including hydrogen peroxide and organic peroxides and carbonyl compounds which can pose health risks on residents. In this study, the effect of ammonia (NH3) on the formation of indoor hydrogen peroxide (H₂O₂) and organic hydroperoxides (ROOH) from ozone/d-limonene reactions was investigated in a large environmental chamber (3.2m × 3.2m × 2.5m). The experimental results demonstrated that reactions between ozone and d-limonene at typical indoor concentrations produced hydroperoxides. H₂O₂ and organic hydroperoxides were measured with an Aerolaser AL-2021 analyzer based on the enzyme-catalyzed fluorescence technique. Peroxides were detected by their liquid-phase reaction with p-hydroxyphenylacetic acid catalyzed by horseradish peroxidase. This reaction produces a fluorescent dimmer that can be excited at 326 nm (Cd-lamp) and detected at between 400 and 420 nm. Two parallel channels were used to distinguish between H₂O₂ and organic hydroperoxides. One channel detects all hydroperoxides, and the other measures the organic hydroperoxides by breaking down the H₂O₂ by catalase before detection. In this way, H₂O₂ is determined through the subtraction method. Carbonyl compounds were sampled into silica cartridges impregnated with a Desert Research Institute (DRI) standard carbonyl sampler at a flow rate of 1 L min-1 for 1 h. A total of 14 carbonyls can be monitored through the cartridge samples by HPLC (high-pressure liquid chromatography system; Series 2000, PerkinElmer, Norwalk , CT). Total hydroperoxides concentration was 1.2-1.5 ppb after ozone and d-limonene injection. This experiment also demonstrated that the presence of NH₃ could reduce the production of hydrogen peroxide and organic hydroperoxides. The total hydroperoxides concentration was 0.9-1.2 ppb with NH₃ existence, which was 20% lower than that without NH₃. The maximum concentrations of hydrogen peroxide without and with NH₃ were 1.382 ppbv and 1.086 ppbv, respectively. With the injection of ozone and d-limonene, the increase of H₂O₂ and ROOH concentration was basically linear (with correlation coefficient greater than 0.982). The increasing rate of H₂O₂ was 0.025 ppbv/min without NH₃. While this value was 0.019 ppbv/min in the presence of NH₃ which was 24% lower than that without NH₃. The production rate of H₂O₂ was 0.128 ppbv/ppbv d-limonene with NH₃, which was 24.3% lower than that without NH3. The ROOH increasing rate in the presence of NH₃ was 33.3% lower than that without NH₃. After ozone/d-limonene introduction, the acetaldehyde and formaldehyde concentration increased 1105%, 257%, and 508%, respectively. MEK was also detected. Experiment results show that ozone/d-limonene reactions produce hydroperoxides and carbonyl compounds which both have cancer risks. Hence, effective measures need to be applied to minimize indoor d-limonene concentration for reducing health risk to human.|
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