Volatile organic compounds (VOCs) are deƒned as organic compounds that evaporate readily at room temperature, such as benzene, toluene, ethylbenzene, and xylenes (BTEX) and chlorinated solvents such as trichloroethylene (U.S. Environmental Protection Agency [USEPA], 2011). VOCs are easily absorbed and broadly metabolized in the human body (Agency for Toxic Substances and Diseases Registry [ATSDR], 2004). The U.S. Environmental Protection Agency (USEPA) has speciƒed a number of VOCs as air toxics. In many urban areas of Asia, several anthropogenic sources, such as trafƒc, residential, and industry, release large amounts of VOCs into the atmosphere, which subsequently build up to high ambient levels. In the atmosphere with the presence of sunlight, VOCs participate in photochemical reactions with NOx (nitrogen oxides) to form photochemical smog. High levels of ƒne particles and surface ozone present in the smog are health hazards. Ozone is a strong greenhouse gas and a phytotoxic pollutant that damages plants and affects agriculture and forestry, as highlighted in Chapter 6.