NERC OP3 PROJECT: Objectives

NERC OP3 Project : Objectives

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Oxidant and Particle Photochemical Processes
above a South-East Asian tropical rain forest : Objectives

The objectives of the OP3-Danum-08 project are (i) to understand how emissions of reactive trace gases from a tropical rain forest mediate the production and processing of oxidants and particles in the troposphere, and (ii) to better understand the impact of these processes on local, regional and global scale atmospheric composition, chemistry and climate.

The key questions to be addressed by the project are:

Q1. What are the rates of transfer and the speciation of organic compounds emitted from this tropical forest region? We will use a range of state of the art measurement systems to quantify and speciate the fluxes of biologically produced reactive compounds from the forest canopy and underlying soils to the boundary layer. These fluxes will be compared with those measured at other forest locations (e.g. Amazonia) and our ability to estimate these fluxes using emission models will be critically evaluated. We will assess the representativeness of the measured fluxes to the wider region using Earth Observation and other methods.

Q2. How are these biogenic reactive compounds chemically processed in the near and intermediate field? OH/HO2/RO2/NO3/halogen measurements, combined with constrained box models, provide a means of understanding the in situ chemistry. We anticipate that some of the chemical processing will be very rapid and the mechanisms complex, but typical of a region contributing substantially to the transfer of VOCs to the free and upper troposphere (FT and UT, respectively). An important tool will be the use of VOC ratios, coupled with chemical-transport models and in situ OH measurements, to understand the timescales of transport and transformation from the source region.

Q3. How do these emissions contribute to the formation of longer-lived intermediate products? While the primary biogenic VOCs probably react rapidly, it is clear that some of the intermediates in the oxidation chain have quite long lifetimes, facilitating transfer to the FT and UT. The roles of these compounds in the chemistry of the UT and in the formation of photochemically active species, such as acetone, known to be present in the UT, is very poorly understood. Measurement of concentrations of oxygenates, coupled with detailed chemical trajectory models and 3-D mesoscale chemistry-transport models, will considerably enhance our understanding.

Q4. To what extent does the regional biogenic emission control the secondary aerosol budget and its hygroscopic and radiative properties? What is the composition of the organic fraction of the submicrometre aerosol and how does this relate to the photochemical processing of the gas phase VOC precursors? These processes are highly uncertain and certainly no detailed data exist from this part of the world at present. Measurements of highly time resolved aerosol composition, coupled with detailed organic analysis for key markers and organic functionality, will provide a detailed knowledge of the aerosol chemistry. This will enable improved understanding of an, as yet poorly understood, important aerosol source that may well control cloud droplet number in an area where large convective cloud activity is prevalent.

Q5. What are the effects of these biogenic emissions on global chemistry and climate? We will assess how biogenic emissions from Borneo impact the global atmosphere and contrast this with the roles of Amazonia and Africa. An important question is how these impacts will change under land-use and climate change scenarios. We will use a state of the art climate model with detailed tropospheric chemistry to assess the effects of changing emissions.

Participation:

Please contact the Principal Investigator n.hewitt@lancaster.ac.uk if you would like to participate in the OP3 project

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