Photochemical Aging of Atmospheric Fine Particles as a Potential Source for Gas-Phase Hydrogen Peroxide

Abstract

Atmospheric hydrogen peroxide (H2O2), as an important oxidant, plays a key role in atmospheric sulfate formation, affecting the global radiation budget and causing acid rain deposition. The disproportionation reactions of hydroperoxyl radicals (HO2) in both gas and aqueous phases have long been considered as dominant sources for atmospheric H2O2. However, these known sources cannot explain the significant formation of H2O2 in polluted areas under the conditions of high NO levels and low ambient relative humidity (RH). Here, we show that under relatively dry conditions during daytime, atmospheric fine particles directly produce abundant gas-phase H2O2. The formation of H2O2 is verified to be by a reaction between the particle surface −OH group and HO2 radicals formed by photooxidation of chromophoric dissolved organic matters (CDOMs), which is slightly influenced by the presence of high NO levels but remarkably accelerated by water vapor and O2. In contrast to aqueous-phase chemistry, transition metal ions (TMIs) are found to significantly suppress H2O2 formation from the atmospheric fine particles. The H2O2 formed from relatively dry particles can be directly involved in in situ SO2 oxidation, leading to sulfate formation. As CDOMs are ubiquitous in atmospheric fine particles, their daytime photochemistry is expected to play important roles in formation of H2O2 and sulfate worldwide.

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

“…This could be explained by the unknown sources of gaseous H 2 O 2 during haze events that have not been considered in this model. Recent studies have found that photooxidation processes involving organics can release H 2 O 2 , , accounting for the “missing” sources of gas-phase H 2 O 2 . Furthermore, the net photoreaction effects on the H 2 O 2 budget should also be considered in future models.…”

Photochemistry of Imidazole-2-carbaldehyde in Droplets as a Potential Source of H2O2 and Its Oxidation of SO2

“…20,21 The photochemical aging of atmospheric fine particles can directly produce abundant gas-phase H 2 O 2 by a reaction between the particle surface −OH groups and HO 2 • radicals formed by photooxidation of chromophoric dissolved organic matter (CDOM). 22 Moreover, brown carbon (BrC) induced HO 2…”

“…Previous studies found that ammonium sulfate seeds containing glyoxal exposed to UV light and organic precursors (e.g., limonene, isoprene, α-pinene, β-pinene, and toluene) exhibited a photoinduced SOA growth . Further studies have shown that this may be attributed to the formed photosensitizers, which can initiate radical chemistry and contribute to additional aerosol aging. , The photochemical aging of atmospheric fine particles can directly produce abundant gas-phase H 2 O 2 by a reaction between the particle surface −OH groups and HO 2 • radicals formed by photooxidation of chromophoric dissolved organic matter (CDOM) . Moreover, brown carbon (BrC) induced HO 2 • and organic radicals with an upper limit of 20 and 200 M/day .…”

Accelerated Photolysis of H2O2 at the Air–Water Interface of a Microdroplet

“…Hydroxyl radicals (·OH) are highly reactive species that are found throughout nature and are involved in a wide range of important chemical reactions. , In the atmosphere, ·OH is responsible for driving the rapid conversion of gaseous pollutants, such as volatile organic compounds (VOCs) and nitrogen oxides (NO x ), into secondary organic aerosols (SOAs) and nitrate. These chemical reactions are crucial in the formation and growth of fine particles during haze events, which can have severe environmental and health impacts. − Additionally, ·OH plays an essential role in the oxidation of sulfur dioxide (SO 2 ) into sulfate and the deposition of acid rain, which can harm aquatic and terrestrial ecosystems. , In aquatic systems, ·OH is a crucial player in accelerating the cyclings of elements, such as the oxidation and mineralization of organic carbon. , ·OH is also involved in the transformation of pollutants, such as pesticides, pharmaceuticals, and other organic contaminants. , Understanding the role of ·OH in these processes is vital for predicting and mitigating the impacts of environmental pollution on human and ecosystem health.…”

“…3−5 Additionally, •OH plays an essential role in the oxidation of sulfur dioxide (SO 2 ) into sulfate and the deposition of acid rain, which can harm aquatic and terrestrial ecosystems. 6,7 In aquatic systems, •OH is a crucial player in accelerating the cyclings of elements, such as the oxidation and mineralization of organic carbon. 8,9 •OH is also involved in the transformation of pollutants, such as pesticides, pharmaceuticals, and other organic contaminants.…”