Ozone(O3) concentration and flux(Fo) were measured using the eddy covariance technique over a wheat field in the Northwest-Shandong Plain of China. The O3-induced wheat yield loss was estimated by utilizing O3exposure-response models. The results showed that:(1) During the growing season(7 March to 7 June, 2012), the minimum(16.1 ppb V) and maximum(53.3 ppb V)mean O3 concentrations occurred at approximately 6:30 and 16:00, respectively. The mean and maximum of all measured O3 concentrations were 31.3 and 128.4 ppb V, respectively. The variation of O3 concentration was mainly affected by solar radiation and temperature.(2) The mean diurnal variation of deposition velocity(V d) can be divided into four phases, and the maximum occurred at noon(12:00). Averaged V d during daytime(6:00–18:00) and nighttime(18:00–6:00) were 0.42 and 0.14 cm/sec, respectively. The maximum of measured V d was about1.5 cm/sec. The magnitude of V d was influenced by the wheat growing stage, and its variation was significantly correlated with both global radiation and friction velocity.(3) The maximum mean F o appeared at 14:00, and the maximum measured F o was-33.5 nmol/(m2·sec). Averaged F o during daytime and nighttime were-6.9 and-1.5 nmol/(m2·sec), respectively.(4) Using O3 exposure-response functions obtained from the USA, Europe, and China, the O3-induced wheat yield reduction in the district was estimated as 12.9% on average(5.5%–23.3%). Large uncertainties were related to the statistical methods and environmental conditions involved in deriving the exposure-response functions.
High concentration ground-level ozone(O3)has adverse effects on plant growth and photosynthesis.Compared to the O3concentration-based index,the O3flux-based(especially stomatal O3uptake)index has been considered the better criterion for assessing the impact of ozone on vegetation and ecosystems.This paper reports on a study of O3flux using the eddy covariance technique over a corn field in the Northwestern Shandong Plain of China.Diurnal variation of atmospheric O3concentration,deposition velocity and flux,and their relationships to environmental factors are analyzed.The results show that:(1)During the observation period(9 August–28 September,2011),there was a strong diurnal variation of O3concentration,with low(16.5 nL L?1)and high(60.1 nL L?1)O3mean concentrations observed around 6:30 and 16:00,respectively.Mean O3concentrations during daytime(6:00–18:00)and nighttime(18:00–6:00)were 39.8±23.1 and 20.7±14.1 nL L?1(mean±std),respectively.The maximum observed concentration was 97.5 nL L?1.The concentration was mainly affected by solar radiation and air temperature.(2)Whether daytime or nighttime,ground-level O3flux is always downward.The diurnal course of mean deposition velocity was divided into 4 phases:a low and stable process during nighttime,fast increasing in early morning,relatively large and steady changes around noon,and quickly decreasing in later afternoon.Daytime and nighttime mean deposition velocities were 0.29 and 0.09 cm s?1,respectively.The maximum deposition velocity was 0.81 cm s?1.The magnitude of deposition velocity was influenced by the corn growth period,and its diurnal variation was significantly correlated with global radiation and relative humidity.(3)O3flux was affected by variations of both O3concentration and deposition velocity,with mean O3fluxes-317.7 and?70.2 ng m?2s?1during daytime and nighttime,respectively.There was strong correlation between O3flux and CO2flux or latent heat flux.By comparing the deposition velocities of daytime and nighttime,we infer that stomatal upt
ZHU ZhiLinSUN XiaoMinDONG YunSheZHAO FengHuaFranz X MEIXNER
