Interannual variability of terpenoid emissions in an alpine city
L. Kaser, Arianna Peron, M. Graus, Marcus Striednig, Georg Wohlfahrt, Stanislav Juráň, Thomas Karl
Abstract
Abstract. Terpenoid emissions above urban areas are a complex mix of biogenic and anthropogenic emission sources. In line with previous studies we found that summertime terpenoid fluxes in an alpine city were dominated by biogenic sources. Inter-seasonal emission measurements revealed consistency for monoterpenes and sesquiterpenes but a large difference in isoprene between the summers of 2015 and 2018. Standardized emission potentials for monoterpenes and sesquiterpenes were 0.12 nmol m−2 s−1 and 3.0×10-3 nmol m−2 s−1 in 2015 and 0.11 nmol m−2 s−1 and 3.4×10-3 nmol m−2 s−1 in 2018, respectively. Observed isoprene fluxes were almost 3 times higher in 2018 than in 2015. This factor decreased to 2.3 after standardizing isoprene fluxes to 30 ∘C air temperature and photosynthetic active radiation (PAR) to 1000 µmol m−2 s−1. Based on emission model parameterizations, increased leaf temperatures can explain some of these differences, but standardized isoprene emission potentials remained higher in 2018 when a heat wave persisted. These data suggest a higher variability of interannual isoprene fluxes than for other terpenes. Potential reasons for the observed differences such as emission parameterization, footprint changes, water stress conditions, and tree trimming are investigated.