The oxidation products of unsaturated fatty acids in the atmosphere are of great interest because of their harmful health effects and the effects they have on daily climate conditions. When unsaturated fatty acids are oxidized, they create reactive diacids and ω-oxo-acids that are key components for nucleation and growth of aerosols. Dicarboxylic acids and ω-oxo-acids have been reported to occur in the atmosphere: in particular, nonanedioic acid and 9-oxo-nonanoic acid which are oxidative products of oleic acid. The presence of fatty acid breakdown products in rainwater DOC extracts was studied through GC-MS analysis of extracts of rainwater.

The series of dicarboxylic acid and ω-oxo-acid standards were synthesized and analyzed by nuclear magnetic resonance (NMR) and gas chromatography and mass spectrometry (GC-MS) as their methyl esters. The synthesis of nonanedioic acid dimethyl ester and 9-oxo-nonanoic acid methyl ester is described. C₆-C₁₀ dicarboxylic methyl ester standards were synthesized as standards for comparison to the rainwater DOC.

A natural rainwater DOC extract was reacted with BF3/MeOH to convert free acids to their methyl esters. The GC-MS results showed that none of the C₆-C₁₀ dicarboxylic acid dimethyl esters, or 9-oxo-nonanoic acid were present in the sample. However, a saturated fatty acid, palmitic acid, was detected and calculated to be present in rainwater at ~0.2 μM concentrations.