Atmospheric H2O2 measurement: comparison of cold trap method with impinger bubbling method

Area of Science:

• Atmospheric Chemistry
• Environmental Science
• Analytical Chemistry

Background:

• Accurate measurement of atmospheric hydrogen peroxide (H2O2) is vital for understanding atmospheric oxidation processes.
• Previous methods, like air impinger bubbling, may be subject to interferences.
• Ozone (O3) reactions with organic compounds can potentially generate peroxides in aqueous solutions.

Purpose of the Study:

• To develop and validate a reliable cold trap method for collecting atmospheric H2O2.
• To compare the cold trap method with the established air impinger bubbling method.
• To investigate the source of discrepancies observed between the two collection techniques.

Main Methods:

• Atmospheric air was drawn through a glass trap cooled with a dry ice-acetone slush at 2.5 L/min for 2 hours.
• Collection efficiency was assessed, and interferences from O3, SO2, and organic matter were evaluated.
• Results were compared with those obtained using the air impinger bubbling method.

Main Results:

• The cold trap method demonstrated collection efficiency > 99% with negligible interferences.
• Impinger method consistently yielded higher total peroxide (H2O2 + organic peroxide) values (0.06-3.7 ppb) compared to the cold trap method (0.02-1.2 ppb).
• Laboratory experiments indicated that ozone reactions with organic compounds in the impinger solution likely generated additional peroxides.

Conclusions:

• The cold trap method provides a more accurate measure of atmospheric H2O2 by avoiding artifactual peroxide formation.
• The air impinger method overestimates H2O2 due to ozone-induced reactions with atmospheric organics in the aqueous phase.
• Ozone-organic compound reactions in atmospheric water droplets may be a significant pathway for H2O2 generation in clouds and rainwater.