Impacts of current ozone pollution on wheat yield in China as estimated with observed ozone, meteorology and day of flowering

Wheat yield loss due to ambient ozone (O-3) and the associated economic losses in China were evaluated for years 2015 and 2016 using for the first time measured O-3 concentration ([O-3]) and meteorological data as well as phenological observations. Relative yield losses (RYL) were estimated using response functions based on both O-3 exposure and flux metrics: AOT40 (the accumulated hourly [O-3] over a threshold of 40 ppb) and POD12 (Phytotoxic Ozone Dose over a threshold of 12 nmol O-3 m(-2)s(-1)). Both metrics showed consistent spatial patterns being highest in the North China Plain, the largest wheat-producing area in China, followed by some provinces in Yangtze River region. The higher stomatal conductance in areas with high [O-3] in year 2015 contributed to higher POD12 values than in 2016. The RYLs for the whole China estimated with AOT40 were 17.1% and 18.1% for years 2015 and 2016, respectively, whereas those with POD12 were lower, 10.6% and 10.2%, respectively. Wheat production losses as translated to annual economic losses were 10 304 and 10 745 million USD (AOT40) or 5912 and 5554 million USD (POD12), for 2015 and 2016, respectively. The O-3 impact estimated with monitoring data suggests its overestimation by some of the previous studies based on model estimates of surface [O-3]. The overestimation could be attributed to the uncertainties in estimating meteorological variables and [O-3], particularly the omission of the correction for the vertical gradient of [O-3] near crop canopy in some studies.Previous simulation studies have overestimated the yield loss of winter wheat by ozone.