Sources, sinks and chemical processing of volatile organic compounds within a South-East Asian rainforest canopy
2 Lancaster University
3 University of East Anglia
4 University of Manchester
O 4.1 in Forest biogeochemistry of reactive trace gases
07.10.2009, 09:40-10:05, Kutschenhaus
We report the physical measurements and modelling findings from comprehensive in-canopy measurements conducted during July 2008 as part of the ACES/OP3 campaign at Danum Valley (Sabah, Borneo, Malaysia). Time-series profile data of biogenic Volatile Organic Compounds (VOCs) concentration, photo-active radiation (PAR), NOx, O3, temperature, aerosol size distributions, leaf area index and turbulence statistics have been collected in order to provide a comprehensive description of chemistry and transport within the rainforest canopy. Significant concentrations of isoprene and monoterpene are observed during daylight hours. However, across the eight days of measurements, there is considerable day-to-day variation in the concentration and dispersion of compounds. These differences are partly explained by variations of in-canopy turbulence and measured PAR. Measured in-canopy turbulence is low (the friction velocity, as measured at the top tree platform is generally less than ~ 0.4m/s), and PAR is influenced by fast changing cloud cover. An Inverse Lagrangian Transport source/sink analysis demonstrates that the bulk of the isoprene and monoterpene is emitted from the uppermost levels of the trees. The measurements also show that the longer-lived degradation products of these VOCs are transported further down into the canopy. In addition, larger concentrations of methanol observed close to the ground suggest that this compound is partly emitted from leaf litter and other debris.
The ultimate intent is to use the collected data in a 1D size segregated aerosol chemistry and transport model. Whilst the in-canopy measurements will help to constrain and validate the chemical interactions and transport of matter inside the canopy the model will make predictions of the escape efficiency and upward flux into the lower troposphere. These predictions can be compared with above canopy measurements that were also taken as part of the OP3 campaign. Preliminary output from this model will also be presented.
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