Characterization of carbonaceous aerosols outflow from India and 2 Arabia : Biomass / biofuel burning and fossil fuel combustion

6 [1] A major objective of the Indian Ocean Experiment (INDOEX) involves the 7 characterization of the extent and chemical composition of pollution outflow from the 8 Indian Subcontinent during the winter monsoon. During this season, low-level flow 9 from the continent transports pollutants over the Indian Ocean toward the Intertropical 10 Convergence Zone (ITCZ). Traditional standardized aerosol particle chemical analysis, 11 together with real-time single particle and fast-response gas-phase measurements 12 provided characterization of the sampled aerosol chemical properties. The gasand 13 particle-phase chemical compositions of encountered air parcels changed according to 14 their geographic origin, which was traced by back trajectory analysis. The temporal 15 evolutions of acetonitrile, a long-lived specific tracer for biomass/biofuel burning, 16 number concentration of submicrometer carbon-containing particles with potassium 17 (indicative of combustion sources), and mass concentration of submicrometer non-sea18 salt (nss) potassium are compared. High correlation coefficients (0.84 < r < 0.92) are 19 determined for these comparisons indicating that most likely the majority of the species 20 evolve from the same, related, or proximate sources. Aerosol and trace gas 21 measurements provide evidence that emissions from fossil fuel and biomass/biofuel 22 burning are subject to long-range transport, thereby contributing to anthropogenic 23 pollution even in areas downwind of South Asia. Specifically, high concentrations of 24 submicrometer nss potassium, carbon-containing particles with potassium, and 25 acetonitrile are observed in air masses advected from the Indian subcontinent, 26 indicating a strong impact of biomass/biofuel burning in India during the sampling 27 periods (74 (±9)% biomass/biofuel contribution to submicrometer carbonaceous 28 aerosol). In contrast, lower values for these same species were measured in air masses 29 from the Arabian Peninsula, where dominance of fossil fuel combustion is suggested by 30 results from single-particle analysis and supported by results from gas-phase 31 measurements (63 (±9))% fossil fuel contribution to submicrometer carbonaceous 32 aerosol). Results presented here demonstrate the importance of simultaneous, detailed 33 gasand particle-phase measurements of related species when evaluating possible 34 source contributions to aerosols in different regions of the world.