Interannual variability in ozone removal by a temperate deciduous forest

The ozone (O-3) dry depositional sink and its contribution to observed variability in tropospheric O-3 are both poorly understood. Distinguishing O-3 uptake through plant stomata versus other pathways is relevant for quantifying the O-3 influence on carbon and water cycles. We use a decade of O-3, carbon, and energy eddy covariance (EC) fluxes at Harvard Forest to investigate interannual variability (IAV) in O-3 deposition velocities ( vd,O3). In each month, monthly mean vd,O3 for the highest year is twice that for the lowest. Two independent stomatal conductance estimates, based on either water vapor EC or gross primary productivity, vary little from year to year relative to canopy conductance. We conclude that nonstomatal deposition controls the substantial observed IAV in summertime vd,O3 during the 1990s over this deciduous forest. The absence of obvious relationships between meteorology and vd,O3 implies a need for additional long-term, high-quality measurements and further investigation of nonstomatal mechanisms.