Ozone vegetation damage effects on gross primary productivity in the United States

We apply an off-line process-based vegetation model (the Yale Interactive Terrestrial Biosphere model) to assess the impacts of ozone (O-3) vegetation damage on gross primary productivity (GPP) in the United States during the past decade (1998-2007). The model's GPP simulation is evaluated at 40 sites of the North American Carbon Program (NACP) synthesis. The ecosystem-scale model version reproduces interannual variability and seasonality of GPP at most sites, especially in croplands. Inclusion of the O-3 damage impact decreases biases of simulated GPP at most of the NACP sites. The simulation with the O-3 damage effect reproduces 64% of the observed variance in summer GPP and 42% on the annual average. Based on a regional gridded simulation over the US, summertime average O-3-free GPP is 6.1 g C m(-2) day(-1) (9.5 g C m(-2) day(-1) in the east of 95 degrees W and 3.9 g C m(-2) day(-1) in the west). O-3 damage decreases GPP by 4-8% on average in the eastern US and leads to significant decreases of 11-17% in east coast hot spots. Sensitivity simulations show that a 25% decrease in surface O-3 concentration halves the average GPP damage to only 2-4 %, suggesting the substantial co-benefits to ecosystem health that may be achieved via O-3 air pollution control.