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Source attribution of Bornean air masses by back trajectory analysis during the OP3 project

Robinson, Niall and Newton, Hannah and Allan, James and Irwin, Martin and Hamilton, Jacqui and Flynn, Martin and Bower, Keith and Williams, Paul and Mills, Graham and Reeves, Claire and McFiggans, Gordon and Coe, Hugh (2011) Source attribution of Bornean air masses by back trajectory analysis during the OP3 project. Atmospheric Chemistry and Physics, 11 (18). pp. 9605-9630. ISSN 1680-7316

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    Abstract

    Atmospheric composition affects the radiative balance of the Earth through the creation of greenhouse gases and the formation of aerosols. The latter interact with incoming solar radiation, both directly and indirectly through their effects on cloud formation and lifetime. The tropics have a major influence on incoming sunlight however the tropical atmosphere is poorly characterised, especially outside Amazonia. The origins of air masses influencing a measurement site in a protected rainforest in Borneo, South East Asia, were assessed and the likely sources of a range of trace gases and particles were determined. This was conducted by interpreting in situ measurements made at the site in the context of ECMWF backwards air mass trajectories. Two different but complementary methods were employed to interpret the data: comparison of periods classified by cluster analysis of trajectories, and inspection of the dependence of mean measured values on geographical history of trajectories. Sources of aerosol particles, carbon monoxide and halocarbons were assessed. The likely source influences include: terrestrial organic biogenic emissions; long range transport of anthropogenic emissions; biomass burning; sulphurous emissions from marine phytoplankton, with a possible contribution from volcanoes; marine production of inorganic mineral aerosol; and marine production of halocarbons. Aerosol sub- and super-saturated water affinity was found to be dependent on source (and therefore composition), with more hygroscopic aerosol and higher numbers of cloud condensation nuclei measured in air masses of marine origin. The prevailing sector during the majority of measurements was south-easterly, which is from the direction of the coast closest to the site, with a significant influence inland from the south-west. This analysis shows that marine and terrestrial air masses have different dominant chemical sources. Comparison with the AMAZE-08 project in the Amazon basin shows Bornean composition to arise from a different, more complex mixture of sources. In particular sulphate loadings are much greater than in Amazonia which is likely to mainly be the result of the marine influence on the site. This suggests that the significant region of the tropics made up of island networks is not well represented by extrapolation from measurements made in the Amazon. In addition, it is likely that there were no periods where the site was influenced only by the rainforest, with even the most pristine inland periods showing some evidence of non-rainforest aerosol. This is in contrast to Amazonia which experienced periods dominated by rainforest emissions.

    Item Type: Article
    Journal or Publication Title: Atmospheric Chemistry and Physics
    Additional Information: © Author(s) 2011. This work is distributed under the Creative Commons Attribution 3.0 License.
    Subjects: G Geography. Anthropology. Recreation > GE Environmental Sciences
    Departments: Faculty of Science and Technology > Lancaster Environment Centre
    ID Code: 58675
    Deposited By: ep_importer_pure
    Deposited On: 27 Sep 2012 16:50
    Refereed?: Yes
    Published?: Published
    Last Modified: 10 Apr 2014 00:11
    Identification Number:
    URI: http://eprints.lancs.ac.uk/id/eprint/58675

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