Molecular marker characterization of the organic composition of submicron aerosols from Mediterranean urban and rural environments under contrasting meteorological conditions

► Larger contributions of primary sources in urban site, leading to higher hydrocarbon levels. ► OA in the urban site is influenced by similar extent to biomass burning as the rural background site. ► Air pollution leads to formation of SOA, resulting in high OOA concentrations in BCN and MSY. ► Good correlations were observed between the off-line and the on-line data for the OA fractions.