Reactive aldehyde chemistry explains the missing source of hydroxyl radicals

Area of Science:

• Atmospheric chemistry
• Environmental science
• Climate science

Background:

• Hydroxyl radicals (OH) are key to the atmosphere's self-cleansing capacity, influencing air quality and climate.
• Current chemical mechanisms underestimate OH levels in low nitrogen oxide and high volatile organic compound environments.
• Isoprene autoxidation has been identified as a contributor to missing OH sources, but its role is insufficient to explain all discrepancies.

Purpose of the Study:

• To identify and quantify a significant missing source of hydroxyl radicals (OH) in the troposphere.
• To investigate the role of reactive aldehyde chemistry, specifically carbonyl organic peroxy radicals, in OH regeneration.
• To assess the impact of this chemistry on atmospheric self-cleansing capacity under various emission scenarios.

Main Methods:

• Utilized quantum chemical calculations to investigate reaction pathways.
• Analyzed the autoxidation of carbonyl organic peroxy radicals (R(CO)O2) derived from higher aldehydes.
• Examined the H-migration and subsequent photolysis of intermediate species.

Main Results:

• Carbonyl organic peroxy radicals undergo rapid H-migration to form unsaturated hydroperoxyl-carbonyls.
• These intermediates generate OH through fast photolysis, representing a major OH regeneration pathway.
• This aldehyde chemistry explains a substantial portion of the previously unaccounted-for OH sources.

Conclusions:

• Reactive aldehyde chemistry is a critical, previously underestimated OH regeneration mechanism.
• This pathway is more significant than isoprene autoxidation in specific atmospheric regimes.
• The findings have implications for understanding air quality and climate regulation, especially in future low nitrogen oxide societies and under carbon neutrality scenarios.