Development of a compound-specific isotope analysis method for atmospheric formaldehyde and acetaldehyde

Area of Science:

• Environmental Chemistry
• Atmospheric Science
• Analytical Chemistry

Background:

• Atmospheric formaldehyde and acetaldehyde are key volatile organic compounds influencing air quality and climate.
• Understanding their sources and transformations requires precise measurement of their isotopic composition.

Purpose of the Study:

• To develop and validate a novel method for determining compound-specific carbon-13 isotopic compositions (δ¹³C) of atmospheric formaldehyde and acetaldehyde at ppb and sub-ppb levels.
• To assess the isotopic fractionation introduced by the 2,4-dinitrophenylhydrazine (DNPH) derivatization method used for carbonyl collection.

Main Methods:

• Utilized gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS) for isotopic analysis.
• Employed the standard DNPH derivatization technique for collecting atmospheric carbonyls.
• Calculated compound-specific δ¹³C values using stoichiometric mass balance based on the isotopic composition of carbonyl-DNPH derivatives and DNPH.

Main Results:

• The GC/C/IRMS method demonstrated high precision for measuring δ¹³C of formaldehyde and acetaldehyde.
• The DNPH derivatization process showed excellent reproducibility (average error < 0.5‰) and negligible isotopic fractionation for both formaldehyde and acetaldehyde.
• Preliminary atmospheric measurements at urban sites revealed significant differences in the δ¹³C values of formaldehyde and acetaldehyde.

Conclusions:

• The developed method accurately determines the carbon isotopic composition of atmospheric formaldehyde and acetaldehyde without significant fractionation from the derivatization step.
• The distinct isotopic signatures observed suggest the method's potential for tracing the sources (primary emission vs. secondary formation) and sinks of these carbonyls in the atmosphere.