Research On Methods In Comprehensive Performance Evaluation Of Photocatalytic Indoor Air Cleaners

In recent years, indoor air quality (IAQ) problems are being paid more and more attention in China. It is widely recognized that IAQ affects human comfort and health, as well as work rate of indoor staff. The most important reason for low IAQ is the large amount of volatile organic compounds (VOCs) in indoor air. Air cleaners using photocatalytic oxidation (PCO) by employing UV irradiation is an innovative approach with high potentials to remove indoor VOCs. However, the categories of PCO cleaners vary and the efficiencies are of high diversity among those categories. On the other hand, PCO cleaners possibly generate by-products, among which, some are harmful to human health in application. Presently, there are problems of lacks of researches on PCO cleaners in practical application with multiple VOCs, as well as universal standards or criteria considering human health. These unsolved problems restrict the advanced use of PCO techniques. The main academic contributions are as follows:First of all, in a test platform with real indoor air environment, A"pull-down"method was employed to test the elimination of several domestic-focused VOCs, including formaldehyde, benzene, toluene,etc., by a PCO cleaner under varies of initial indoor conditions with both single and multiple components. The detecting data from Proton Transfer Reaction Mass Spectrometer (PTR-MS) for those pollutants were calibrated and corrected. Compared with results in literature which employed PCO cleaners to remove single-component pollutant, higher converting rates and more types of by-products were detected while multiple VOCs were eliminated by the PCO cleaner. In the tests, some by-products with small molecular weight, such as butadiene and acrylaldehyde, are among gas by-products, which was not mentioned in literature. Furthermore, the fact was commentated that competitive adsorption with varying degrees is brought by different relative humidity, thus, in the process of removing VOCs by PCO cleaners, there are optimized concentrations of water vapour in terms of efficiency and converting rates of by-products, respectively. Additionally, those optimized concentrations vary among each component of VOCs. Moreover, when relative humidity is in range of 25% to 80%, which was tested in this thesis, the converting rates of by-products are in positive correlations with relative humidity. This conclusion annotated influence from water vapour towards the elimination of VOCs from PCO cleaners.Furthermore, the eliminating efficiencies and generation of by-products of PCO cleaners were studied under varies of initial indoor conditions with different relative humidity and VOCs compounds. Analytic conclusion in by-products from PCO cleaners by the work of Mo's Ph.D thesis was verified. Some suspicious by-products which have not been mentioned in literature were detected with multiple VOCs as initial compounds, which indicated that the generation of by-products from the application of PCO cleaner in real indoor air would be more complicated. The fact was commentated that competitive adsorption with varying degrees is brought by different relative humidity and constitution of VOCs, therefore those effects towards PCO cleaner tests, as well as reasons for that, were studied.Finally, Health-Related Index (HRI) was used in analyzing results from PCO cleaner tests derived by this thesis. Overall performance Evaluation (OPE) was put forward to evaluate the health effects of a PCO cleaner, and this index is determined by PCO cleaning benefitηPCO and HRI. Therefore, the overall characteristics of PCO products were analyzed, and combining the test results and analysis, feasibility of PCO cleaner was illuminated. These researches can benefit and be executive in the labeling and overall evaluation for PCO cleaners.