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Thomas Wainman,^1,* Junfeng Zhang,¹ Charles J. Weschler,² and Paul J. Lioy¹

¹Environmental and Occupational Health Sciences Institute, UMDNJ-Robert Wood Johnson Medical School and Rutgers University, Piscataway, New Jersey, USA
²Telcordia Technologies, Red Bank, New Jersey, USA

Abstract

Little information currently exists regarding the occurrence of secondary organic aerosol formation in indoor air. Smog chamber studies have demonstrated that high aerosol yields result from the reaction of ozone with terpenes, both of which commonly occur in indoor air. However, smog chambers are typically static systems, whereas indoor environments are dynamic. We conducted a series of experiments to investigate the potential for secondary aerosol in indoor air as a result of the reaction of ozone with d-limonene, a compound commonly used in air fresheners. A dynamic chamber design was used in which a smaller chamber was nested inside a larger one, with air exchange occurring between the two. The inner chamber was used to represent a model indoor environment and was operated at an air exchange rate below 1 exchange/hr, while the outer chamber was operated at a high air exchange rate of approximately 45 exchanges/hr. Limonene was introduced into the inner chamber either by the evaporation of reagent-grade d-limonene or by inserting a lemon-scented, solid air freshener. A series of ozone injections were made into the inner chamber during the course of each experiment, and an optical particle counter was used to measure the particle concentration. Measurable particle formation and growth occurred almost exclusively in the 0.1-0.2 µm and 0.2-0.3 µm size fractions in all of the experiments. Particle formation in the 0.1-0.2 µm size range occurred as soon as ozone was introduced, but the formation of particles in the 0.2-0.3 µm size range did not occur until at least the second ozone injection occurred. The results of this study show a clear potential for significant particle concentrations to be produced in indoor environments as a result of secondary particle formation via the ozone-limonene reaction. Because people spend the majority of their time indoors, secondary particles formed in indoor environments may make a significant contribution to overall particle exposure. This study provides data for assessing the impact of outdoor ozone on indoor particles. This is important to determine the efficacy of the mass-based particulate matter standards in protecting public health because the indoor secondary particles can vary coincidently with the variations of outdoor fine particles in summer. Key words: indoor air chemistry, limonene, ozone, particulate matter, secondary organic aerosol. Environ Health Perspect 108:1139-1145 (2000) . [Online 6 November 2000]

http://ehpnet1.niehs.nih.gov/docs/2000/108p1139-1145wainman/ abstract.html

Address correspondence to J. Zhang, Environmental and Occupational Health Sciences Institute, UMDNJ-Robert Wood Johnson Medical School and Rutgers University, 170 Frelinghuysen Rd., Piscataway, NJ 08854-8020 USA. Telephone: (732) 445-0158. Fax: (732) 445-0116. E-mail: jjzhang@eohsi.rutgers.edu

*Current address Oak Ridge National Laboratory, Oak Ridge, TN.

We thank M. Robson, executive director of EOHSI, for his friendship, advice, and support, which made this research possible.

The financial support for this research was provided by the Environmental and Occupational Health Sciences Institute (EOHSI) . J. Zhang and P.J. Lioy are supported in part by a NIEHS center grant ES05022-10 to EOHSI.

Received 2 June 2000 ; accepted 31 July 2000.