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 emissions in an alpine city were dominated by biogenic sources, but especially at lower temperatures the anthropogenic influences were non-negligible. Inter-seasonal emission measurements revealed consistency for monoterpenes and sesquiterpenes, but a large difference in isoprene between the summers 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 emissions were about four times higher in 2018 than in 2015. This factor decreased to 2.3 after standardizing isoprene emissions to 30 °C air temperature and photosynthetic active radiation (PAR) of 1000 μmol m-2 s-1. Based on emission model parameterizations, increased leaf temperatures can explained ~50 % of these differences, but standard emission potentials remained higher in 2018, when a heat wave persisted. Potential other reasons for the differences such as emission parameterization, footprint changes, water stress conditions and tree trimming are investigated.
Highlights
Biogenic and anthropogenic volatile organic compounds (BVOCs, AVOCs) in the atmosphere can contribute to surface air pollution both due to their influence on tropospheric ozone formation and due to their potential to act as precursors for secondary organic aerosol formation (Derwent et al, 1996, Fehsenfeld et al, 1992, Fuentes et al, 2000, Goldstein et al, 2009, Laothawornkitkul et al, 2009, Riipinen et al, 2012)
It has been shown that RO2 self-reactions of monoterpenes and sesquiterpenes can rapidly create highly oxidized matter (HOM) and are a key player for new particle formation (NPF) events in forests under low NOx conditions (Simon et al, 2020)
A correlation between isoprene and benzene fluxes in early spring before the start of the vegetation period can be extrapolated to the summer months. This resulted in a maximum of 20-30% influence of anthropogenic sources on isoprene emissions during both 2015 and 2018 summer measurement periods
Summary
Biogenic and anthropogenic volatile organic compounds (BVOCs, AVOCs) in the atmosphere can contribute to surface air pollution both due to their influence on tropospheric ozone formation and due to their potential to act as precursors for secondary organic aerosol formation (Derwent et al, 1996, Fehsenfeld et al, 1992, Fuentes et al, 2000, Goldstein et al, 2009, Laothawornkitkul et al, 2009, Riipinen et al, 2012). BVOCs are playing a important role globally, as their emission strength is estimated to be 10 times larger than AVOCs (Guenther et al, 2012, Piccot et al, 1992). Attributed to isoprene, 15% to monoterpenes and about 0.5% to sesquiterpenes (Guenther et al, 2012). In coniferous forests monoterpene and sesquiterpene emissions often dominate (Johansson and Janson, 1993, Thunis and Cuvelier, 2000, Juráň et al, 2017). It has been shown that RO2 self-reactions of monoterpenes and sesquiterpenes can rapidly create highly oxidized matter (HOM) and are a key player for new particle formation (NPF) events in forests under low NOx conditions (Simon et al., 2020)
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