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What drives isoprene in tropical Australia?

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thesis
posted on 29.03.2022, 01:01 authored by Rebecca Leigh Wilson
Isoprene is the dominant biogenic svolatile organic compound (BVOC) emitted from plants across the globe, with a mass of 400-600 Tg emitted annually. Its emission and chemical degradation plays a central role in the atmosphere, contributing to the formation of ground-level ozone and secondary organic aerosol.Tropical ecosystems contribute up to 75% of the global isoprene budget. Seasonal isoprene emission patterns in tropical regions remains unclear, particularly when compared to the mid-latitudes. It was hypothesised that in tropical regions, isoprene would be consistent throughout the year. However, a 12-year record of satellite observations of formaldehyde (HCHO) over the Amazon basin showed that HCHO columns reduced by 20-40% each year during the wet-to-dry transition. This thesis verifies these observations and investigates the hypothesis with a long-term, ground-based measurement study in a rainforest environment, paying particular attention to this transition period. To improve understanding of seasonal isoprene emissions patterns I conducted a measurement and modelling campaign in Far North Queensland to understand the drivers of isoprene emission in tropical Australia. A Fast Isoprene Sensor was installed in the Daintree Rainforest and I measured canopy-level isoprene concentrations over three years. They show that isoprene emissions follow a seasonal cycle, which differs from the Amazon. The measurements are compared against GOME-2B satellite observations and MEGAN and MLC-CHEM models to investigate factors driving emission patterns across several timescales. Findings show that model bias decreases by over 10% when leaf area index varies in response to the growing season and the emission factor is optimised by time and season. This is the first major BVOC study to be conducted in the Daintree, and is the first isoprene study in tropical Australia in over 20 years. The results presented in this thesis represent the first observations of seasonal isoprene emission patterns in Australia and provide an important contrast to other tropical ecosystems.

History

Table of Contents

1. Introduction -- 2. Site description and methodology -- 3. FIS field campaign results -- 4. Modelling with MLC-CHEM and MEGAN -- 5. Opportunities for future work.

Notes

"This thesis is submitted to Macquarie University and The University of Edinburgh for the degree of Doctor of Philosophy" -- title page. Empirical thesis. Bibliography: pages 201-226

Awarding Institution

Macquarie University

Degree Type

Thesis PhD

Degree

PhD, Macquarie University, Faculty of Science and Engineering, Department of Environmental Sciences

Department, Centre or School

Department of Environmental Sciences

Year of Award

2018

Principal Supervisor

Peter Nelson

Additional Supervisor 1

Paul Palmer

Rights

Copyright Rebecca Leigh Wilson 2018. Copyright disclaimer: http://mq.edu.au/library/copyright

Language

English

Extent

1 online resource (xvii, 226 pages) colour illustrations, colour maps

Former Identifiers

mq:70736 http://hdl.handle.net/1959.14/1267228