Emissions of monoterpenes from new Scots pine foliage: dependency on season, stand age and location and importance for models

Abstract. Models to predict the emissions of biogenic volatile organic compounds (BVOCs) from terrestrial vegetation largely use standardised emission potentials derived from shoot enclosure measurements of mature foliage and usually assume that the contribution of BVOCs from new conifer needles is minor to negligible. Extensive observations have, however, recently demonstrated that the potential of new Scots pine needles to emit several different BVOCs can be up to about 500 times higher than that of the corresponding mature foliage. Thus, we build on these discoveries and investigate the impact of previously neglecting enhanced emissions from new Scots pine foliage on estimates of monoterpene emissions and new atmospheric aerosol particle formation and their subsequent growth. We show that the importance of considering the enhanced monoterpene emission potential of new Scots pine foliage decreases as a function of season, tree age and latitude, and that new foliage is responsible for the majority of the whole tree's foliage emissions of monoterpenes during spring time, independently of tree age and location. Our results suggest that annual monoterpene emission estimates from Finland would increase with up to ~ 25 % if the emissions from new Scots pine foliage were explicitly considered, with the majority being emitted during spring time where also new particle formation has been observed to occur most frequently. We estimate that our findings can lead to increases in predictions of the formation rates of 2 nm particles during spring time by ~ 75–275 % in northern Finland and by ~ 125–865 % in southern Finland. Likewise, simulated growth rates of 2–3 nm particles would increase by ~ 65–175 % in northern Finland and by ~ 110–520 % in southern Finland if the enhanced emissions of monoterpenes from new Scots pine foliage were explicitly considered. Our findings imply that we need to introduce a more comprehensive treatment of the emissions of BVOCs from new coniferous foliage in biogenic emission models.