Aerosol Science 39 (2008) 168 – 174 www.elsevier.com/locate/jaerosci Development and evaluation of a particle-bound reactive oxygen species generator Prasanna Venkatachari, Philip K. Hopke ∗ Center for Air Resources Engineering and Science, Clarkson University, Potsdam, NY 13676, USA Received 10 August 2007; received in revised form 24 October 2007; accepted 2 November 2007 Abstract Identifying the most important sources and variability of source impact for particulate matter is essential to assessing their health impacts. A central hypothetical mechanism of how particles affect human health involves the generation of reactive oxygen radicals at target sites in situ. These could be generated via activation of cells by cell–particle interactions and by oxidative species present in particulate matter. However, prior studies have shown that there are reactive oxygen species (ROS) associated with ambient respirable particles. In order to assess the health effects of particle-bound oxidative species, a generator was developed to produce ROS-bearing model particles and deliver known, reproducible, and stable exposures to these model particles that could be used in toxicological studies. The generator was found to be capable of providing a stable throughput of these particles with an average ROS generation capability of 6.5 nmol of equivalent H 2 O 2 /m 3 of (aerosol + ozone) flow sampled. The development, characterization, and evaluation of the ROS-bearing particle generator is described.  2007 Elsevier Ltd. All rights reserved. Keywords: Reactive oxygen species; ROS; Particulate matter; Toxicity 1. Introduction Over the last decade, fine particulate matter (PM 2.5 ) have been linked to a range of respiratory and cardiovascular health problems because of their long lifetimes in the ambient air and respiratory deposition characteristics (ICRP, 1994; Seinfeld, 2004). Numerous epidemiological studies conducted over this period have shown that PM 2.5 is correlated with severe health effects, including enhanced mortality (Bernstein et al., 2004 and references therein). Moreover, tox- icological investigations have demonstrated substantial pulmonary toxicity of model and real environmental particles, and have postulated particle size, surface area, and composition as potential parameters and components relevant to the observed health effects (Donaldson & Tran, 2002). However, the mechanisms and processes that cause the observed adverse health effects have not yet been resolved. A number of mechanisms have been proposed to explain the adverse health effects of PM. Recent studies have reported a major role for the generation of reactive oxygen species (ROS) and pulmonary and systemic oxidative stress in the initiation and progression of dysfunction associated with PM exposure (Gurgueira, Lawrence, Coull, Murthy, & Gonzalez-Flecha, 2002; Nel, Diaz-Sanchez, Ng, Hiura, & Saxon, 1998). ROS has been defined to include families of oxygen-centered or related free radicals, ions, and molecules. The free radical family includes hydroxyl, hydroperoxyl ∗ Corresponding author. Tel.: +1 315 268 3861; fax: +1 315 268 4410. E-mail address: hopkepk@clarkson.edu (P.K. Hopke). 0021-8502/$ - see front matter  2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.jaerosci.2007.11.003