Fly ash is produced when pulverised fuels are burnt. Like other types of dust, fly ash may affect vegetation by both physical and chemical processes. Physically, particles may cover the leaf surface and reduce the amount of light available for photosynthesis, or may occlude stomata. Occlusion may lead to increased resistance to gas exchange, or may prevent full stomatal closure, leading to water stress. Increased transpiration is a common response to dust exposure. Deposition rates to tall vegetation are greater than to short vegetation.
Indirect effects of fly ash may be beneficial - an increase in radial growth of Scots pine was attributed to oil shale fly ash deposition in a study in Estonia (Parn, 2002).
Chemically, fly ash may be acidic or neutral, and may have associated with it quantities of carbon (soot) and other organic matter. The smaller particles of fly ash may be transported for hundreds of km in cloud, and be deposited as wet deposition. The subject has been reviewed by Farmer (1993).
Often, deposition rates are not measured, and exposure is judged by amounts retained on leaves. However, removal of particles from plant surfaces by rain varies very greatly among plant species, from those that are 'self-cleaning' (the lotus effect) to those that accumulate large quantities (Neinhuis & Barthlott, 1997). Most industrial processes are regulated to prevent emission of fly ash particles.
|Critical Load/ Level|
No estimate available