AbstractHeat-periods in summer occurred more frequently in this decade and affected the well-being of citizens in several ways. One effect of heat-periods is a higher photochemical ozone (O3) production rate, which leads to higher O3 concentrations. Strategies to influence urban climate and air pollution more often include urban trees. A side effect of urban trees is the emission of biogenic VOCs (BVOCs), which are participating in urban O3 production. In this study, we investigate the effect of urban tree BVOCs during heat-period conditions on O3 formation using an integrated urban-scale biogenic emissions and chemistry transport model chain. To demonstrate the possibility of investigating the effect of urban trees on O3 production under heat-period conditions, we performed simulations in the densely populated Rhein-Ruhr area (DE) in July 2018. The results show impacts of up to 4% higher averaged maximum daily 8 h mean (MDA8) O3 concentrations due to local isoprene emissions and up to additional 15% higher MDA8 O3 values when decreasing NOx emissions from traffic and increasing urban tree emissions. In general, the relevance of biogenic emissions is expected to increase in future due to higher frequency of heat-period events related to climate change and due to the decreasing trend of anthropogenic emissions in response to current legislation. Therefore, the established model chain can be a valuable tool for urban planning.