[en] Ozone (O_3) is both a greenhouse gas and a secondary air pollutant causing adverse impacts on forests ecosystems at different scales, from cellular to ecosystem level. Specifically, the phytotoxic nature of O_3 can impair CO_2 assimilation that, in turn affects forest productivity. This study aims to evaluate the effects of tropospheric O_3 on Gross Primary Production (GPP) at 37 European forest sites during the time period 2000–2010. Due to the lack of carbon assimilation data at O_3 monitoring stations (and vice-versa) this study makes a first attempt to combine high resolution MODIS Gross Primary Production (GPP) estimates and O_3 measurement data. Partial Correlations, Anomalies Analysis and the Random Forests Analysis (RFA) were used to quantify the effects of tropospheric O_3 concentration and its uptake on GPP and to evaluate the most important factors affecting inter-annual GPP changes. Our results showed, along a North-West/South-East European transect, a negative impact of O_3 on GPP ranging from 0.4% to 30%, although a key role of meteorological parameters respect to pollutant variables in affecting GPP was found. In particular, meteorological parameters, namely air temperature (T), soil water content (SWC) and relative humidity (RH) are the most important predictors at 81% of test sites. Moreover, it is interesting to highlight a key role of SWC in the Mediterranean areas (Spanish, Italian and French test sites) confirming that, soil moisture and soil water availability affect vegetation growth and photosynthesis especially in arid or semi-arid ecosystems such as the Mediterranean climate regions. Considering the pivotal role of GPP in the global carbon balance and the O_3 ability to reduce primary productivity of the forests, this study can help in assessing the O_3 impacts on ecosystem services, including wood production and carbon sequestration. - Highlights: • Assessment of the surface O_3 effects on Gross Primary Production (GPP) • GPP is negatively related to O_3 concentration and positively to O_3 fluxes • Temperature and relative humidity were the most important factors controlling GPP. • Key role of the Soil Water Content in the Mediterranean regions.