Airborne observations of IEPOX-derived isoprene SOA in the Amazon during SAMBBA

Isoprene is a potentially highly significant but currently poorly quantified source of secondary organic aerosols (SOA). This is especially important in the tropics, where large rainforests act as significant sources of isoprene. Methylfuran, produced through thermal decomposition during analysis, h...

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Bibliographic Details
Published in:Atmospheric chemistry and physics 2014-10, Vol.14 (20), p.11393-11407
Main Authors: Allan, J. D, Morgan, W. T, Darbyshire, E, Flynn, M. J, Williams, P. I, Oram, D. E, Artaxo, P, Brito, J, Lee, J. D, Coe, H
Format: Article
Language:English
Subjects:
Air pollution
Analysis
Atmospheric and Oceanic Physics
Environmental Sciences
Global Changes
Ocean, Atmosphere
Physics
Rain forests
Sciences of the Universe
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Summary:Isoprene is a potentially highly significant but currently poorly quantified source of secondary organic aerosols (SOA). This is especially important in the tropics, where large rainforests act as significant sources of isoprene. Methylfuran, produced through thermal decomposition during analysis, has recently been suggested as a marker for isoprene SOA formation through the isoprene epoxydiol (IEPOX) route, which mostly occurs under low NOx conditions. This is manifested as a peak at m/z=82 in Aerodyne Aerosol Mass Spectrometer (AMS) data. Here we present a study of this marker measured during five flights over the Amazon rainforest on board the UK Facility for Airborne Atmospheric Measurement (FAAM) BAe-146 research aircraft during the South American Biomass Burning Analysis (SAMBBA) campaign. Cases where this marker is and is not present are contrasted and linked to the presence of acidic seed particles, lower NOx concentrations and higher humidities. There are also data to suggest a role of organic nitrogen in the particulate composition. Furthermore, an inspection of the vertical trends of the marker indicates that concentrations are highest at the top of the boundary layer (possibly due to semivolatile repartitioning) and that upwards through the free troposphere, the mass spectral profile evolves towards that of low volatility oxygenated aerosol. These observations offer insights into the behaviour of IEPOX-derived SOA formation above the Amazon rainforest and the suitability of methylfuran as a marker for this process.
ISSN:1680-7324
1680-7316
1680-7324
DOI:10.5194/acp-14-11393-2014