Recent advancements in observations, sources, and environmental effects of atmospheric hydrogen peroxide (H₂O₂)

Atmospheric hydrogen peroxide (H₂O₂) is an important oxidant in the troposphere that impacts atmospheric oxidation capacity and plays key roles in S(IV) oxidation. In the past decade, researchers have proposed new H₂O₂ formation mechanisms as well as its significant environmental effects, based on field measurements, laboratory experiments, and modeling. However, these unconventional chemical processes related to atmospheric H₂O₂ have not been systematically reviewed, previous reviews on atmospheric H₂O₂ were published in the early 2000s. Herein, we review the recent atmospheric H₂O₂ studies throughout the world, mainly focusing on the observations, sources, and environmental effects of atmospheric H₂O₂. First, we summarize the temporal and vertical distributions of atmospheric H₂O₂ across urban, rural, mountainous, forested, and oceanic regions, as well as the upper atmosphere. Next, we discuss recent advancements in understanding potential sources of atmospheric H₂O₂ and its multiphase formation mechanisms. Finally, the increasing environmental effects of atmospheric H₂O₂, including its role in diagnosis of O₃-NO_x-VOCs sensitivity and significance in sulfate formation, are outlined. This review will help gain a comprehensive understanding of atmospheric H₂O₂ evolution and call for more future studies on atmospheric H₂O₂ to better deal with the current complex air pollution challenges.