Functional group characterization of indoor, outdoor, and personal PM 2.5 : results from RIOPA Abstract Fourier transform infrared (FTIR) spectra of outdoor, indoor, and personal fine particulate matter (PM 2.5 ) samples were collected during the Relationship of Indoor, Outdoor, and Personal Air (RIOPA) study. FTIR spectroscopy provides functional group information about the entire PM 2.5 sample without any chemical preparation. It is particularly important to char- acterizing the poorly understood organic fraction of PM 2.5 . To our knowledge this is the first time that FTIR spectroscopy has been applied to a PM 2.5 exposure study. The results were used to chemically characterize indoor air and personal exposure. Sulfate was strongest in outdoor samples, which is consistent with the generally accepted understanding that sulfate is of outdoor origin. Absorbances attributed to soil dust were also seen in many outdoor and some indoor and personal samples. Inorganic nitrate absorbances were a common feature of many California and some New Jersey samples. Carbonyl absorbances showed substantial variation in strength, number of peaks, and wave number shift between samples, indicating variability in composition and sources. Absorbances attributed to aliphatic hydrocarbon and amide functional groups were enhanced in many personal and indoor samples, which suggested the influence of indoor sources in these homes. We speculate that meat cooking is one possible source of particulate amides. A. Reff 1 , B. J. Turpin 1,2 , R. J. Porcja 1,2 , R. Giovennetti 1 , W. Cui 1 , C. P. Weisel 2 , J. Zhang 2 , J. Kwon 1,2 , S. Alimokhtari 2 , M. Morandi 3 , T. Stock 3 , S. Maberti 3 , S. Colome 4 , A. Winer 5 , D. Shendell 5 , J. Jones 5 , C. Farrar 5 1 Department of Environmental Sciences, Rutgers University, New Brunswick, NJ, 2 Environmental and Occupational Health Sciences Institute, Piscataway, NJ, 3 School of Public Health, University of Texas, Houston Health Sciences Center, Houston, TX, 4 Integrated Environmental Sciences, Irvine, CA, 5 Environmental Science and Engineering Program, School of Public Health, University of California, Los Angeles, CA, USA Key words: FTIR; Infrared spectroscopy; PM 2.5 ; Organic particulate matter; Aerosol composition; Personal exposure. Barbara J. Turpin Department of Environmental Sciences, Rutgers University, 14 College Farm Road, New Brunswick, NJ 08901, USA Tel.: 732 932 9540 Fax: 732 932 8644 e-mail: turpin@aesop.rutgers.edu Received for review 16 October 2003. Accepted for publication 5 August 2004. Practical Implications To our knowledge this is the first time that FTIR spectroscopy has been used to characterize the composition of indoor and personal PM 2.5 . The presence of sulfate, nitrate, ammonium, soil dust and a number of organic func- tional groups are all detected in one analysis on filter samples without extraction or other sample preparation. Differences between indoor and outdoor spectra are used to identify spectral features due to indoor-generated PM 2.5 . Particularly interesting are the much larger aliphatic absorbances, shifts in carbonyl absorbances, and occasional small amide absorbances found in indoor and personal spectra but rarely in outdoor spectra. These observations are important because organics make up a large portion of PM 2.5 mass and their composition and properties are poorly characterized. The properties and behavior of organic compounds in airborne particles are often predicted based on their functional group composition. This analysis begins the development of a better understanding of the functional group composition of indoor and personal PM 2.5 and how it differs from that of outdoor PM 2.5 . Eventually this will lead to an improved understanding of the properties, behavior and effects of PM 2.5 of indoor and outdoor origin. Indoor Air 2005; 15: 53–61 www.blackwellpublishing.com/ina Printed in Denmark. All rights reserved Copyright Ó Blackwell Munksgaard 2004 INDOOR AIR doi:10.1111/j.1600-0668.2004.00323.x 53