Global chemical transport model study of ozone response to changes in chemical kinetics and biogenic volatile organic compounds emissions due to increasing temperatures: Sensitivities to isoprene nitrate chemistry and grid resolution

Global modeling studies show a wide variability in the response of the O-3 budget to climate change as projected by applying Intergovernmental Panel on Climate Change scenarios in climate models. We employ sensitivity studies to elucidate the major uncertainties in the response of tropospheric O-3 to perturbations in biogenic volatile organic compounds (BVOC) emissions and reaction rate coefficients due to changes in temperature. The change in global O-3 burden due to an increase in BVOC emissions associated with a +5 K depends critically on the assumed treatment for the fraction of NOx recycled (0-100%) from isoprene nitrate (+9 to +34 Tg), in contrast to the chemical reaction rate coefficients response (-8 to -9 Tg). The model O-3 burden shows sensitivity (40 Tg) to the NOx recycling efficiencies (0-100%) similar to the burden's sensitivity to the grid resolution (4 degrees x 5 degrees -1 degrees x 1 degrees). The correlation of O-3 with total alkyl nitrates (Sigma ANs) in the surface air at a California forest site shows sensitivity to the NOx recycling (40-100%) similar to the correlation's sensitivity to the horizontal resolution (4 degrees x 5 degrees -1 degrees x 1 degrees). The results of the sensitivity simulations imply that the slope of O-3 to Sigma ANs might be used to constrain the yield of isoprene nitrate and NOx recycling fraction, but better agreement could be achieved by using a higher-resolution model with even higher NOx recycling from isoprene nitrate. Our results suggest that the reduction of NOx recycling from isoprene nitrate be set apart from that due to the effect of the grid resolution in the chemical transport model.