Concentrations, isotopic compositions, and sources of size-resolved, particulate organic carbon and oxalate in near-surface marine air at Bermuda during spring

Abstract

During spring 1998, concentrations and stable isotopic compositions of organic carbon and oxalate were measured in size-segregated aerosols at Bermuda to characterize sources and chemical processing. Marine-derived organic carbon in super-μm-radius aerosol was enriched by an average of 724 ± 91 times relative to surface seawater. Carbon isotopic compositions indicated that, on average, marine-derived carbon accounted for approximately 38% of carbon in both the super- and sub-μm size fractions. Oxalate was present and significantly correlated with marine derived carbon in all size fractions. Most oxalate in super-μm radius aerosol (>1 μm) originated from in situ production involving marine-derived organic precursors, whereas oxalate in smaller size fractions originated primarily from condensation of oxalic acid vapor produced from the oxidation of gaseous marine precursors. The average dry-deposition fluxes of marine organic carbon, continental organic carbon, and oxalate was 3.6, 7.3, and 0.15 μmol C m-2 day-1, respectively. Super-μm aerosol dominated the dry-deposition fluxes of marine (93%) and continental (96%) particulate carbon and oxalate (93%).