Isoprene emissions in the tropics

Trees emit isoprene as a function of temperature and light to improve plant thermo-tolerance.

Isoprene represents approximately 50 per cent of all non-methane biogenic volatile organic carbon emissions released into the atmosphere, and nearly 75 per cent of the world’s isoprene emissions come from tropical ecosystems. Yet the tropics, and the Australian continent in particular, remains largely unstudied.

The chemical transformation of isoprene in the atmosphere has a profound effect on the concentration and variation of species which contribute to radiative forcing: tropospheric ozone (O3), secondary organic aerosol, and methane (CH4). Thus, the isoprene flux is of central importance to understanding interactions between atmospheric chemistry and climate.

Recent analysis of satellite data show an unexpected seasonal variation of isoprene emissions in the tropics even when light and temperature are normalised. This observation has not been reflected to date in field studies, which tend to be short term and located outside the tropics. Within the region, studies tend to focus on areas with limited species representation, such as palm plantations.

A long-term measurement campaign in the North Queensland Daintree Rainforest is underway. As the data is collected, the results will be scaled up from a local model to a basin-wide and regional scale and modelled using the Model of Emissions of Gases and Aerosols from Nature (MEGAN) at the University of Edinburgh, Scotland. This study will provide valuable insight into the emission patterns of a tropical ecosystem over seasonal time scales and substantially improve global emissions models.

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