Epidemiological studies have shown that inhalation of ambient particulate matter is associated with increased cardiovascular diseases, respiratory diseases, cancer and premature death. However, the particle components and underlying mechanisms that contribute to particle toxicity are poorly understood. Inhaled particles may contribute to health effects by producing an excess reactive oxygen species (ROS) in physiological systems. ROS are a class of reactive oxygen-bearing compounds that include the hydroxyl radical (OH), hydrogen peroxide and superoxide. Of all ROS, the OH radical may be the most damaging, capable of capable of oxidizing DNA, proteins and lipids. Particle components that contribute to OH generation under physiological conditions are not well known. Our research develops methods for investigating mechanisms of ROS generation and identifying toxic particle components. Through a combination of laboratory experiments, thermodynamic and chemical kinetic modeling, we explore the following: (1) Measurement of OH radicals with the “terephthalate probe” (2) Reaction mechanisms of OH radical generation from biomass burning components in lung fluid (3) Quantifying malondialdehyde in particulate matter samples.