Dry deposition processes of volatile organic compounds (VOCDep)

A large range of different volatile organic chemical compounds (VOCs) are released to the atmosphere from vegetation and human activities such as fossil fuel burning and the use of consumer care products. Together with nitrogen oxides, VOCs are one of the two key ingredients for the formation of tropospheric ground-level ozone pollution, causing impacts on human health, biodiversity decline and crop losses. Similarly, through a series of chemical reactions in the atmosphere, many VOCs end up forming the organic fraction of particulate matter (PM) with major impacts on human health around the globe. VOC emissions are needed in models to predict air quality and its impacts and climate change. These models are used to assess measures to reduce emissions to safeguard the health of humans and the environment. For these model predictions to be reliable, the models need to accurately represent VOC emissions, chemical transformation, but also the deposition to vegetation. Whilst considerable effort has gone into the first two aspects, very little is known about the deposition of the various VOC compounds, with deposition rates usually estimated from the behaviour of other (inorganic) compounds with no validation through actual measurements.

This project will make use of recent improvements in VOC measurement technology to perform the first comprehensive study of the rate and processes that control the deposition of a wide range of different VOC compounds of environmental concern. This will be achieved through three different, complementary experimental approaches: (a) the study of VOC uptake to vegetation in the laboratory using gas exchange chambers, (b) the study of VOC uptake to natural and artificial liquid water films and (c) two measurement campaigns of VOC exchange with vegetation, focussing on urban parkland and forest. The results from these measurements and existing datasets from project partners will be used to derive improved model descriptions of the deposition process for incorporation into the numerical models. We will then use two atmospheric chemistry and transport models, a simpler model that can be operated at high spatial resolution and is used to support European and UK policy, and a model with a more detailed description of the chemistry of isoprene, the compound that dominates plant emissions globally to assess the impacts of the new deposition rates on model performance with emphasis on ozone formation, PM formation and the particular role of isoprene in PM formation.