Hydrogen Peroxide Associated with Ambient Fine-Mode, Diesel, and Biodiesel Aerosol Particles in Southern California

To investigate the sources of H2O2 generation in fine-mode aerosols, a series of measurements on laboratory-generated particles, source materials, and ambient particles collected in the Los Angeles area were performed. Ambient fine-mode H2O2 levels were associated with transition metals, and were increased by the addition of dithiothreitol, a marker for quinone redox activity. H2O2 levels were sensitive to the pH of the particle extraction solutions, peaking in the pH range of 2.5-5.5. The initial rate of H2O2 generation by fine-mode ambient aerosols averaged 5.9 (+/- 2.8) x 10(-9) M min(-1), in the range of the initial rates of H2O2 generation by active quinones and hydroxyl radical generation by transition metals. H2O2 levels were persistent, remaining nearly constant for about a week in ambient fine-mode particles. Laboratory experiments show that secondary organic aerosols and diesel and biodiesel exhaust particles generate as much or more H2O2 than ambient particles. These data indicate roles for metals such as iron, zinc, and copper, with additional sources, likely quinones and other unidentified organics, in the H2O2 generation by fine-mode aerosols.