Maximum stomatal conductance also dropped at all sites over that time period. The shape of the diurnal trend in stomatal conductance indicated that during late summer water stress, stomata opened briefly only in the morning. Stomata are the pathway of ozone into foliage. Ozone concentration, however, increased over the season. The Sequoia site is shown here as an example, but this decoupling of ozone flux from concentration is the same at all sites.
Environmental moisture controls stomatal conductance, and thus ozone flux, in a predictable manner.
Although water potential is difficult to measure, the continuous measurement of soil moisture is easy to automate. Eddy Covariance . Ozone concentration and deposition at the canopy scale were decoupled seasonally, resulting in substantial ozone deposition in winter even when ozone concentration was relatively low. Most studies on ozone deposition have focused on the summer months because that is when ozone concentration is typically the highest. Our work shows that two thirds of annual ozone deposition occurred during non-summer months.