Formaldehyde and volatile organic compounds in Hong Kong homes: concentrations and impact factors Introduction Indoor air pollution caused by volatile organic com- pounds (VOCs) is attracting international interest as many indoor materials and utilities contain VOCs (Godish, 2001). VOCs are classified as organic com- pounds that have boiling point between 50 and 260°C (Godish, 2004). There are hundreds of VOCs in the air, which increases the complexion of indoor air pollution. Previous studies show that indoor air is contaminated to various degrees by a wide variety of hydrocarbons and hydrocarbon derivatives including paraffin, olefin, aromatics, carbonyls, polycyclic aromatics, and chlo- rinated hydrocarbons (Guo et al., 2003; Kim et al., 2001; Lai et al., 2004; Lee et al., 2002a; Park and Ikeda, 2004, 2006; Sawant et al., 2004). Among the indoor VOCs, some are toxic i.e., toluene, whereas some at high levels are carcinogenic such as formalde- hyde and benzene (Olsen et al., 1984; Godish, 2001; ATSDR (Agency for Toxic Substances and Disease Registry), 1994, 2007). Many studies demonstrate that vehicular exhaust and industrial emissions are the major sources of ambient VOCs (e.g. Brocco et al., 1997; Guo et al., 2006; Mayrsohn and Crabtree, 1976), while the sources of VOCs are quite numerous within any indoor environ- ment. These sources include combustion by-products, cooking, construction materials, furnishings, paints, Abstract This paper presents formaldehyde and volatile organic compounds (VOC) concentrations, potential sources and impact factors in 100 homes. The 24-h average formaldehyde concentration in 37 homes exceeded the good class of the Hong Kong Indoor Air Quality Objectives (HKIAQO), whereas the total VOCs concentration in all homes was lower than the HKIAQO. Compared to other East Asian cities, indoor formaldehyde and styrene in Hong Kong was the highest, reflecting that the homes in Hong Kong were more affected by house- hold products and materials. The formaldehyde concentration in newly built apartments was significantly higher than that in old buildings, whereas no relationship between the concentration and the building age was found for VOCs. There was no difference for formaldehyde and toluene between smoking and non-smoking homes, suggesting that cigarette smoking was not the major source of these two species. Homes of a couple with a child had higher form- aldehyde and acetic acid concentrations, while homes with more than three people had higher concentrations of 1-butanol, heptane and d-limonene. When shoes were inside the homes, heptane, acetic acid, nonane and styrene concen- trations were statistically higher than that when shoes were out of the homes. Furthermore, higher levels of 1,2,4-trimethylbenzene, styrene, nonane and hep- tane were found in gas-use families rather than in electricity-use homes. H. Guo, N. H. Kwok, H. R. Cheng, S. C. Lee, W. T. Hung, Y. S. Li Research Centre for Urban Environmental Technology and Management, Department of Civil and Structural Engineering, Hong Kong Polytechnic University, Hong Kong Key words: Formaldehyde; Volatile organic compounds; Homes; Building age; Cigarette smoking; Hong Kong. H. Guo Research Centre for Urban Environmental Technology and Management Department of Civil and Structural Engineering Hong Kong Polytechnic University Hong Kong Tel.: 852 3400 3962 Fax: 852 2334 6389 e-mail: ceguohai@polyu.edu.hk Received for review 27 March 2008. Accepted for publication 6 October 2008. Ó Indoor Air (2009) Practical Implications Long-term exposure to formaldehyde and volatile organic compounds (VOC) in indoor environments may cause a number of adverse health effects such as asthma, dizziness, respiratory and lung diseases, and even cancers. Therefore, it is critical to minimize indoor air pollution caused by formaldehyde and VOCs. The findings obtained in this study would significantly enhance our understanding on the levels, emission sources and factors which affect indoor con- centrations of formaldehyde and VOCs. The results can help housing designers, builders, home residents, and housing department of the government to improve indoor air quality (IAQ) by means of appropriate building materials, clean household products and proper life styles. It can also help policy makers reconcile the IAQ objectives and guidelines. Indoor Air 2009; 19: 206–217 www.blackwellpublishing.com/ina Printed in Singapore. All rights reserved Ó 2009 The Authors Journal compilation Ó Blackwell Munksgaard 2009 INDOOR AIR doi:10.1111/j.1600-0668.2008.00580.x 206