Molecular distributions and isotopic compositions of organic aerosols over the western North Atlantic: Dicarboxylic acids, related compounds, sugars, and secondary organic aerosol tracers

Stable carbon isotope ratios of aerosol total carbon and individual diacids and oxoacids were determined using an isotope ratio mass spectrometer. The stable carbon isotopic composition of oxalic acid increased from the coast (−17.5‰) to the open ocean (−12.4‰), confirming that photochemical aging of organic aerosols occurred during the atmospheric over the ocean. Stable carbon isotope ratios of bulk aerosol carbon also increased from the coast near Boston (−24.3‰) to the open ocean near Bermuda (−18.2‰), consistent with photochemical aging of organic aerosols.