Forests forming particles

The work of LEAF scientists from the Institute for Climate and Atmospheric Science (ICAS) in the School of Earth and Environment featured recently in a study indicating that molecules emitted by trees are helping to form new particles in the atmosphere.

The distribution of particles in the atmosphere controls various properties of clouds and the Earth’s climate; some particles are emitted directly, whilst others are formed in the atmosphere.

"Newly formed particles make a substantial contribution to the total number of particles in the atmosphere, therefore it’s vitally important to understand the processes by which these particles form, and how this could change in the future", explains Dr Catherine Scott, a LEAF scientist and co-author on the study.

For the new study, published in the journal Science, researchers from the CLOUD (Cosmics Leaving OUtdoor Droplets) project conducted experiments in the CERN laboratory near Geneva. "The chamber used by the CLOUD scientists is specially designed to be very clean; this is important because otherwise it is impossible to tell exactly which molecules are forming the particles", added Dr Scott.

The experiments indicated that gases emitted by trees react to give molecules that play a crucial role in the formation of new particles. The gases in question are called monoterpenes, such as alpha-pinene, and are emitted by many species of vegetation, but particularly by pine, spruce and fir trees.

LEAF scientists then used computer simulations of the global atmosphere to test the experimental findings from the CLOUD chamber. Their detailed computer model, GLOMAP, is able to simulate the processes that control the number of particles in the atmosphere, how big the particles are, and how long they remain there. They found that including the new findings in their simulations helped to more accurately predict the number of particles in the atmosphere, and how this changes during the course of the year.

"As well as emitting particles and gases into the atmosphere through processes like combustion, humans are altering natural sources of gases and particles, for example through deforestation. It's vital that we understand how these two sources combine so that we can predict how changing levels of these emissions will affect the atmosphere, and climate, in the future", explained Dr Scott.

Find out more about the ways that plants interact with the atmosphere here.