Airborne observations of IEPOX-derived isoprene SOA in the Amazon during SAMBBA
Author:
Allan J. D.ORCID, Morgan W. T., Darbyshire E.ORCID, Flynn M. J., Williams P. I., Oram D. E., Artaxo P.ORCID, Brito J.ORCID, Lee J. D.ORCID, Coe H.
Abstract
Abstract. 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 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 5 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 is 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 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.
Funder
Natural Environment Research Council
Publisher
Copernicus GmbH
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