Passive Sampling For Indoor Volatile Organic Compounds (VOCs) And Their Associated Exposure Risks

Rapid industrial and economic development in China over the past two decadeshas resulted in an increase in urban air pollution, which affects hundreds of millions ofpeople. Volatile organic compounds (VOCs) are recognized as one of the principalpollutants. Health risk assessment of exposure to VOCs for a general population helpslocal and state governments make actions necessary to protect public health. However,to date, population inhalation exposure to VOCs with urbanization in China has notbeen characterized sufficiently; less is known about the health risks of exposure toVOCs, because of the paucity of air quality measurements. Passive sampling is suitablefor large-scale, remote and long-term VOC measurements. Nevertheless, performanceof current passive samplers needs to be improved and traditional methods can’t guidethe structure design and the adsorbent selection simultaneously. In this thesis, theaddressed problems are well studied, and the main academic contributions are asfollows:(1) A modified mass transfer model of passive samplers for uptaking VOCs wasproposed to predict the performance of passive samplers under different conditions. Themodel can be used to reveal the temperature and wind speed dependence of passivesampling rates (SRs) of VOCs and analyze the sensitivity of SRs to key parameters. Theinverse problem design method for optimizing passive samplers was further developed.Using the method, the best combination of diffusion coefficient DSand partitioncoefficient KSAof adsorbent can be easily determined for a passive sampler with givenstructruce, and the best structruce can also be easily achieved for a passive sampler withgiven adsorbent.(2) A new radial diffusive sampler (THPDS) for indoor benzene, toluene andxylenes measurement was developed. The overall uncertainties of THPDS samplers at95%confidence level are21.5%,23.3%and16.9%for benzene, toluene and xylenes,respectively, which satisfy the requirements of the Chinese national standard, NIOSHprotocol and EN482. Using this new sampler, the concentrations of benzene, tolueneand xylenes in43homes with recent renovations in Guangzhou were mearsured. Theaverage concentrations of benzene, toluene, m/p-xylene and o-xylene were18.5μg/m3, 173.2μg/m3,58.1μg/m3and40.8μg/m3respectively. In brief, THPDS sampler providesan adequate and cost-effective alternative for indoor air BTX measurements in China.(3) The study summarized recent VOC measurements conducted within the last15years in urban China. The summary statistics of16pollutants with frequent occurrencein different microenvironments were derived. A Monte Carlo simulation framework wasused to calculate the population personal exposure to VOCs and assess the associatedcancer risk. Average total lifetime cancer risks attributable to VOC exposure are2.27×104and2.93×104for urban working females and males in China, exceeding theacceptable benchmark (106). Formaldehyde,1,4-dichlorobenzene, benzene and1,3-butadiene are the major risk contributors yielding the highest median cancer riskestimates,>1×105. About70%of the risk is due to exposures occurring in homes. Forbenzene, ethylbenzene and carbon tetrachloride, outdoor sources contribute most to therisk; while for all other compounds indoor sources dominate. The variations in VOCconcentrations, cancer potency factors (CPFs) and inhalation rates affect the uncertaintyof risk. The risks are overestimated if variation is not accounted for. Results provideinsight not only into the high-risk compounds in urban China but also into the exposureand associated risk for these compounds, which will allow for more effective means ofpollution abatement and exposure reduction.