High spatial resolution ozone risk-assessment for Asian forests

Background tropospheric ozone (O3) is increasing particularly over China and India, and becomes a major threat to Asian forests. By using the coupled WRF-Chem model at high spatial resolution (8 km) over Asia in 2015, we showed that both standards AOT40 (European) and W126 (United States) underestimated the O3 risk to deciduous forests and overestimated it to evergreen forests compared to the biologically based metric POD1. Both metrics AOT40 and W126 showed different spatial distribution and exceedance extent with respect to POD1. We found very high potential of O3 impacts on deciduous forest growth in Asia, while potential O3 impacts on evergreen forest types were lower. The most limiting factors were light availability, soil water content and air temperature (65%, 29% and 6%, respectively), making this region of the globe at high O3 risk for deciduous species and at medium O3 risk for evergreen species. For the first time, the O3 risk to Asian forests was quantified at high spatial resolution; and our results suggested: (i) a relevant overestimation of O3 risk to evergreen forests when using AOT40 and W126 relative to the more biologically based POD1 metric; and (ii) a significant underestimation of O3 risk to the boreal deciduous forests when using AOT40 and W126 relative to POD1 because of stomatal aperture permissive condition.