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

Abstract. We apply an off-line process-based vegetation model (the Yale Interactive Terrestrial Biosphere model) to assess the impacts of ozone (O₃) 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 O₃ damage impact decreases biases of simulated GPP at most of the NACP sites. The simulation with the O₃ 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 O₃-free GPP is 6.1 g C m⁻² day⁻¹ (9.5 g C m⁻² day⁻¹ in the east of 95° W and 3.9 g C m⁻² day⁻¹ in the west). O₃ 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 O₃ concentration halves the average GPP damage to only 2–4%, suggesting the substantial co-benefits to ecosystem health that may be achieved via O₃ air pollution control.