Persistent Uptake of H 2 O 2 onto Ambient PM 2.5 via Dark-Fenton Chemistry.

Particulate matter (PM) and gaseous hydrogen peroxide (H 2 O 2 ) interact ubiquitously to influence atmospheric oxidizing capacity. However, quantitative information on H 2 O 2 loss and its fate on urban aerosols remain unclear. This study investigated the kinetics of heterogeneous reactions of H 2 O 2 on PM 2.5 and explored how these processes are affected by various experimental conditions (i.e., relative humidity, temperature, and H 2 O 2 concentration). We observed a persistent uptake of H 2 O 2 by PM 2.5 (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 H 2 O 2 concentration suggests that Fenton catalytic decomposition may be an important pathway for H 2 O 2 conversion on PM 2.5 under dark conditions. Furthermore, on the basis of kinetic data gained, the parameterization of H 2 O 2 uptake on PM 2.5 was developed and was applied into a box model. The good agreement between simulated and measured H 2 O 2 uncovered the significant role that heterogeneous uptake plays in the sink of H 2 O 2 in the atmosphere. These findings suggest that the composition-dependent particle reactivity toward H 2 O 2 should be considered in atmospheric models for elucidating the environmental and health effects of H 2 O 2 uptake by ambient aerosols.