A volatile question

Text by Lauri Laanisto

Anthony King, science journalist from Dublin, has written a feature piece about volatile organic compounds in The Royal Society of Chemistry´s webportal Chemistry World. Among other researchers, also Ülo Niinemets and our workgroup´s activities feature in this article (link to full text). Here are the mentioned passages:

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Järvselja forest (pic from here)

In southern Estonia, plant scientist Ulo Niinemets, at the Estonia University of Life Sciences, carries out lab studies and collaborates with field scientists in the Jarvselja experimental forest, a mix of spruce and birch. He believes that volatile emissions are far more dynamic than assumed. Some plants regularly emit certain VOCs, but others ramp up in response to stress. Norway spruce sends out waves of limonene when infested by spruce spider mite, for instance.

‘Every plant can emit volatiles under certain stress conditions. This is why we have vastly underestimated the emission potential of vegetation,’ says Niinemets, who heads up a European Research Council project on this topic. While oak is a strong emitter of VOCs, once herbivores arrive it changes its blend, dampening down on isoprene and ramping up sesqueterpenes such as pleasant smelling caryophyllene. This is a larger, more complex compound than isoprene and is even more likely to adhere to particles and lead to SOAs.

Niinemets says we need quantitative data on plants and how it is impacting aerosol formation. We know that some species are stronger emitters of certain VOCs. Maple, hazel, holly and English oak are low isoprene emitters; willow, poplar and birch are all high emitters. ‘You might make a decision about which trees to plant in response to that information,’ says Hewitt, since isoprene emitters in urban areas generate ozone smog if NOx is coming from cars. He has reported that some trees, such as black gum, English oak and poplar, are detrimental in terms of urban air quality.

There seems to be a long road ahead before the data going into climate models on VOCs and aerosols is near complete. This is the message from field and lab scientists. Across the Baltic, Jaana Back found that individual stands of Scots pine trees emit different blends of VOCs. ‘It is an inherited property and cannot be changed over a tree’s lifetime,’ explains Back, a professor of forest–atmosphere interactions at the University of Helsinki, Finland.

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