Abstract
In Europe, tropospheric ozone pollution appears as a major air quality issue, and ozone concentrations remain potentially harmful to vegetation. In this study we compared the trends of two ozone metrics widely used for forests protection in Europe, the AOT40 (Accumulated Ozone over Threshold of 40 ppb) which only depends on surface air ozone concentrations, and the Phytotoxic Ozone Dose which is the accumulated ozone uptake through stomata over the growing season, and above a threshold Y of uptake (PODY). By using a chemistry transport model, we found that European-averaged ground-level ozone concentrations (− 2%) and AOT40 metric (− 26.5%) significantly declined from 2000 to 2014, due to successful control strategies to reduce the emission of ozone precursors in Europe since the early 1990s. In contrast, the stomatal ozone uptake by forests increased from 17.5 to 26.6 mmol O3 m−2 despite the reduction in ozone concentrations, leading to an increase of potential ozone damage on plants in Europe. In a climate change context, a biologically-sound stomatal flux-based standard (PODY) as new European legislative standard is needed.
Highlights
Tropospheric ozone (O3) is a secondary short-lived climate pollutant (Shindell et al 2012), formed by the photochemical oxidation of NOx in the presence of carbon monoxide (CO), methane (CH4) and volatile organic compounds (VOCs) (Chameides et al 1988)
POD0 values, the minimum value (14.0 mmol O3 m−2) was found in 2006 in Northern Europe while the maximum values, 29.7 and 32.1 mmol O3 m−2 were observed in Atlantic and Mediterranean Europe, respectively (Fig. 4)
Our results showed a general decrease of O3 concentrations and exposure-based index, namely AOT40, all over Europe and a general increase of flux-based metrics (POD0 and POD1) over the time-period 2000–2014
Summary
Tropospheric ozone (O3) is a secondary short-lived climate pollutant (Shindell et al 2012), formed by the photochemical oxidation of NOx in the presence of carbon monoxide (CO), methane (CH4) and volatile organic compounds (VOCs) (Chameides et al 1988). It is the third most important greenhouse gas in terms of radiative forcing (Mickley et al 2001). In Europe, a target value of 9,000 ppb h,
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