Probing the Source of Hydrogen Peroxide Associated with Coarse Mode Aerosol Particles in Southern California

Coarse mode aerosols were collected at three sites in the Los Angeles area, two in Riverside, CA, one upwind and the other downwind of a major freeway, and also on the campus of the University of California, Los Angeles (UCLA). Coarse mode aerosol mass, H2O2, and H2O2 normalized to aerosol mass averaged 46 +/- 22 mu g/m(3), 17 +/- 8 ng/m(3), and 0.48 +/- 0.32 ng/mu g at the upwind Riverside site and 97 +/- 27 mu g/m(3), 34 +/- 14 ng/m(3), and 0.37 +/- 0.18 ng/mu g at the downwind Riverside site, respectively. H2O2, which appears to be generated by the particles (Arellanes, C.; Paulson, S. E.; Fine, P. M.; Sioutas, C. Environ. Sci. Technol. 2006, 40, 4859-4866), was uncorrelated with particle mass, but was strongly correlated with soluble iron, zinc, and copper (r = 0.47-0.67, p = 0.00-0.01). H2O2 levels were not affected by the addition of dithiothreitol, a marker for quinone redox activity. H2O2 levels were sensitive to the pH of the particle extraction solutions, increasing as the pH was decreased. The initial rate of H2O2 generation by coarse mode aerosols was 7.8 (+/- 5.7) x 10(-8) M similar to initial rates of hydroxyl radical generation from dissolved Fe2+, Cu2+, and Zn2+ solutions. The results support the notion that the majority of coarse mode H2O2 generation is mediated by a small set of transition metals.