Aerosol Science 37 (2006) 1467 – 1483 www.elsevier.com/locate/jaerosci Effect of physical and biological parameters on enumeration of bioaerosols by portable microbial impactors Maosheng Yao, Gediminas Mainelis ∗ Department of Environmental Sciences, Rutgers, The State University of New Jersey, 14 College Farm Road, New Brunswick, NJ 08901-8551, USA Received 5 April 2006; received in revised form 5 June 2006; accepted 5 June 2006 Abstract A clear understanding of microbial sampler’s ability to recover culturable bioaerosols is essential for better exposure estimate and design of future advanced samplers. This research investigated the physical and biological parameters affecting overall performance of portable microbial samplers when collecting different bioaerosol species. Seven portable samplers with impaction velocity from 1 to 15 m/s and jet-to-plate distance from 1.7 to 6 mm were used. Three bacterial and fungal species were aerosolized and collected by the samplers under controlled humidity, 40–45%. The ability of portable impactors to recover culturable bioaerosols was compared to that of an Andersen-type impactor and a Button Aerosol Sampler equipped with gelatin filter and their relative overall performance was determined. Experimental data indicated that performance of portable microbial samplers varied from model to model, and depended on investigated bioaerosol species. When sampling bacterial species, the relative overall performance of the impactors was highly correlated with their collection efficiency (adjusted R 2 = 0.74.0.94) and inclusion of samplers’ jet velocity and jet-to-plate distance into multiple liner regression did not affect the adjusted R 2 values. In contrast, when sampling fungi, use of the collection efficiency in the linear regression as the sole predictor of the impactors’ relative overall performance yielded adjusted R 2 values ranging from 0.61 to 0.73; inclusion of jet velocity and jet-to-plate distance into multiple liner regression increased the adjusted R 2 values to the range of 0.75–0.89. The data demonstrate that in addition to collection efficiency, jet velocity and jet-to-plate distance also play an important role in the enumeration of bioaerosols by microbial impactors. The results from this investigation could be helpful in selecting and designing microbial samplers for assessing bioaerosol load in various environments.  2006 Elsevier Ltd. All rights reserved. Keywords: Bioaerosol; Sampling efficiency; Impactors; Bioaerosol viability 1. Introduction Exposure to airborne biological agents present in various environments, e.g., office buildings, residential homes, and industrial settings, has been shown to be associated with a number of negative health effects ( Alwis, Mandryk, & Hocking, 1999; Douwes, Thorne, Pearce, & Heederik, 2003; Fung & Hughson, 2003; Husman, 1996; Robbins, Swenson, Nealley, Gots, & Kelman, 2000). Presence of bioaerosols in such environments and the related health risks are usually ∗ Corresponding author. Tel.: +1 732 932 7166; fax: +1 732 932 8644. E-mail address: mainelis@envsci.rutgers.edu (G. Mainelis). 0021-8502/$ - see front matter  2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.jaerosci.2006.06.005