Persistent Uptake of H₂O₂ onto Ambient PM_2.5 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.

Measurement report: Vanadium-containing ship exhaust particles detected in and above the marine boundary layer in the remote atmosphere

“…This Fenton or Fenton-like chemistry is suggested to play an important role in H2O2 atmospheric budget and can influence the oxidative capacity of the atmosphere. Iron is the most important transition metal for controlling the OH, HO2, H2O2 budget and is thought to be the main driver of H2O2 uptake in ambient aerosols (Qin et al, 2022). This ROS budget is thought to be controlled by the number concentration of iron-containing particles rather than the total iron mass fraction (Khaled et al, 2022), which highlights the importance of single-particle chemical analysis for determining the oxidative capacity of the atmosphere.…”