Molecular characteristics of water-soluble dicarboxylic acids, ω-oxocarboxylic acids, pyruvic acid and α-dicarbonyls in the aerosols from the eastern North Pacific

Aerosol samples (n = 14), collected over the eastern North Pacific (ENP, 27–52°N and 150–172°W), were studied for dicarboxylic acids (hereafter diacids, C2-C10), ω-oxoacids, pyruvic acid, and α-dicarbonyls as well as water-soluble organic carbon (WSOC) and total nitrogen (WSTN). We found diacids as the most abundant compound class followed by ω-oxoacids and α-dicarbonyls. Molecular distributions of diacids were characterized by the predominance of oxalic (C2) (58%) acid followed by malonic (C3) (15%) and succinic (C4) (13.5%) acids. However, we found a predominance of C4 over C3 in five samples, where 4-oxobutanoic acid (ωC4) was the most abundant ω-oxoacid species (34.6% of its class). Moreover, a strong correlation (r2 = 0.72) was obtained between ωC4 and C4 in those samples, suggesting that high abundances of C4 are associated with sea-to-air emission of unsaturated fatty acids and their further photochemical processing. Good relationships between C2 and C3 (r2 = 0.88) and C3 and C4 (r2 = 0.79) in the marine aerosols further suggest that C2 is produced via photochemical degradation of C3 and C4 over the ENP. WSOC and WSTN showed higher abundances in the longitudinal transect of 165-172oW, where ω-oxoacids were abundantly detected. This study demonstrates that atmospheric levels of water-soluble organic aerosols in the ENP are largely regulated by the primary productivity followed by sea-to-air emissions of unsaturated fatty acids and isoprene and the subsequent photochemical oxidation.