Leaf senescence

Leaf senescence-- a big source of acetaldehyde and acetone? 

During experiments to observe formation of leaf VOCs during the drying of cut grasses and hay crops (i.e. induced leaf senescence) we have observed large releases of acetaldehyde (grass) and acetone (clover) as shown in the figures below.  Both of these VOCs have significant impact on atmospheric chemistry.  Acetaldehyde is very reactive in the lower atmosphere, and is a precursor of PAN (peroxyacetyl nitrate), a major air pollutant.  Acetone is very stable in the lower atmosphere, diffuses to the upper troposphere, where it undergoes photolysis, contributing to the oxidative balance of the troposphere-stratosphere boundary.  If natural leaf senescence of crops and the Earth's deciduous forests leads to similar releases of acetaldehyde, acetone and other VOCs, we may have identified yet another important example of biosphere control of the oxidative power of the atmosphere.  Current and planned experiments will address the mechanisms of formation of carbonyl compounds in leaves, and field measurements of the release of these compounds during natural senescence.

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