Persistent Uptake of H2O2 onto Ambient PM2.5 via Dark-Fenton Chemistry.

Abstract

Particulate matter (PM) and gaseous hydrogen peroxide (H2O2) interact ubiquitously to influence atmospheric oxidizing capacity. However, quantitative information on H2O2 loss and its fate on urban aerosols remain unclear. This study investigated the kinetics of heterogeneous reactions of H2O2 on PM2.5 and explored how these processes are affected by various experimental conditions (i.e., relative humidity, temperature, and H2O2 concentration). We observed a persistent uptake of H2O2 by PM2.5 (with the uptake coefficients (γ) of 10-4-10-3) exacerbated by aerosol liquid water and temperature, confirming the critical role of water-assisted chemical decomposition during the uptake process. A positive correlation between the γ values and the ratio of dissolved iron concentration to H2O2 concentration suggests that Fenton catalytic decomposition may be an important pathway for H2O2 conversion on PM2.5 under dark conditions. Furthermore, on the basis of kinetic data gained, the parameterization of H2O2 uptake on PM2.5 was developed and was applied into a box model. The good agreement between simulated and measured H2O2 uncovered the significant role that heterogeneous uptake plays in the sink of H2O2 in the atmosphere. These findings suggest that the composition-dependent particle reactivity toward H2O2 should be considered in atmospheric models for elucidating the environmental and health effects of H2O2 uptake by ambient aerosols.