Ozone Concentrations and Ozone Flux at the Univerity of Michigan Biological Station PROPHET Tower from 2002-2005

Measurements of ozone, sensible heat, and latent heat fluxes and plant
physiological parameters were made at a northern mixed hardwood forest
located at the University of Michigan Biological Station in northern
Michigan from June 27 to September 28, 2002. These measurements were
used to calculate total ozone flux and partitioning between stomatal
and non-stomatal sinks. Total ozone flux varied diurnally with maximum
values reaching 100 8mol m-2 h-1 at midday and minimums at or near
zero at night. Mean daytime canopy conductance was 0.5 mol m-2 s-1.
During daytime, non-stomatal ozone conductance accounted for as much
as 66% of canopy conductance, with the non-stomatal sink representing
63% of the ozone flux. Stomatal conductance showed expected patterns
of behaviour with respect to photosynthetic photon flux density (PPFD)
and vapour pressure defecit (VPD). Non-stomatal conductance for ozone
increased monotonically with increasing PPFD, increased with
temperature (T) before falling off again at high T, and behaved
similarly for VPD. Day-time non-stomatal ozone sinks are large and
vary with time and environmental drivers, particularly PPFD and T.
This information is crucial to deriving mechanistic models that can
simulate ozone uptake by different vegetation types.