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The anthropogenic and biogenic contributions of isoprene, monoterpenes, sesquiterpenes and methanol in an urban area were estimated based on direct eddy covariance flux observations during four campaigns between 2018 and 2021. While these compounds are typically thought to be dominated by biogenic sources on regional and global scales, the role of potentially significant anthropogenic emissions in urban areas has been recently debated. Typical fluxes of isoprene, monoterpenes and sesquiterpenes were on the order of 0.07 ± 0.02, 0.09 and 0.003 nmol m -2 s -1 during spring. During summer, emission fluxes of isoprene, monoterpenes and sesquiterpenes were higher on the order of 0.85 ± 0.09, 0.11 and 0.004 nmol m -2 s -1. It was found that the contribution of the anthropogenic part is strongly seasonally dependent. For isoprene, the anthropogenic fraction can be as high as 64 % in spring but is typically very low < 18 % during the summer season. For monoterpenes, the anthropogenic fraction was estimated to be between 43 % in spring and less than 20 % in summer. With values of 2.8 nmol m -2 s -1 in spring and 3.2 nmol m -2 s -1 in summer, methanol did not exhibit a significant seasonal variation of observed surface fluxes. However, there was a difference in emissions between weekdays and weekends (about 2.3 times higher on weekdays in spring). This suggests that methanol emissions are likely influenced by anthropogenic activities during all seasons. [ABSTRACT FROM AUTHOR]

The anthropogenic and biogenic contributions of isoprene, monoterpenes, sesquiterpenes and methanol in an urban area were estimated based on direct eddy covariance flux observations during four campaigns between 2018 and 2021. While these compounds are typically thought to be dominated by biogenic sources on regional and global scales, the role of potentially significant anthropogenic emissions in urban areas has been recently debated. Typical fluxes of isoprene, monoterpenes and sesquiterpenes were on the order of 0.09 nmol m-2 s-1, 0.09 nmol m-2 s-1 and 0.003 nmol m-2 s-1 during spring. During summer, emission fluxes of isoprene, monoterpenes and sesquiterpenes were higher on the order of 0.85 nmol m-2 s-1, 0.11 nmol m-2 s-1, 0.004 nmol m-2 s-1. It was found that the contribution of the anthropogenic part is strongly seasonally dependent. For isoprene the anthropogenic fraction can be as high as 64 % in spring, but is typically very low < 18 % during the summer season. For monoterpenes the anthropogenic fraction was estimated between 43 % in spring and less than 20 % in summer. With values of 2.8 nmol m-2 s-1 in spring and 3.2 nmol m-2 s-1 in summer, methanol did not exhibit a significant seasonal variation of observed surface fluxes. However, there was a difference in emissions between weekdays and weekends (about 2.3 times higher on weekdays in spring). This suggests that methanol emissions are likely influenced by anthropogenic activities during all seasons. [ABSTRACT FROM AUTHOR]

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 x 10-3 nmol m-2 s-1 in 2015 and 0.11 nmol m-2 s-1 and 3.4 x 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. [ABSTRACT FROM AUTHOR]

Drought events are expected to become more frequent with climate change. To predict the effect of plant emissions on air quality and potential feedback effects on climate, the study of biogenic volatile organic compound emissions under stress is of great importance. Trees can often be subject to a combination of abiotic stresses, for example due to drought or ozone. Even though there is a large body of knowledge on individual stress factors, the effects of combined stressors are not much explored. This study aimed to investigate changes of biogenic volatile organic compound emissions and physiological parameters in Quercus robur L. during moderate to severe drought in combination with ozone stress. Results show that isoprene emissions decreased while monoterpene and sesquiterpene emissions increased during the progression of drought. We exposed plants with daily ozone concentrations of 100 ppb for 1 h for 7 d, which resulted in faster stomatal closure (e.g., a mean value of - 31.3 % at an average stem water potential of - 1 MPa), partially mitigating drought stress effects. Evidence of this was found in enhanced green leaf volatiles in trees without ozone fumigation, indicating cellular damage. In addition we observed an enhancement in (C 8 H 8 O 3)H + emissions likely corresponding to methyl-salicylate in trees with ozone treatment. Individual plant stress factors are not necessarily additive, and atmospheric models should implement stress feedback loops to study regional-scale effects. [ABSTRACT FROM AUTHOR]

Drought events are expected to become more frequent with climate change. To predict the effect of plant emissions on air-quality and potential feedback effects on climate, the study of biogenic volatile organic compound emissions under stress is of great importance. Trees can often be subject to a combination of abiotic stresses, for example due to drought or ozone. Even though there is a large body of knowledge on individual stress factors, the effects of combined stressors are not much explored. This study aimed to investigate changes of biogenic volatile organic compound emissions and physiological parameters in Quercus robur L. during moderate to severe drought in combination with ozone stress. Results show that isoprene emissions decreased while monoterpene and sesquiterpene emissions increased during the progression of drought. Exposing plants additionally to ozone, resulted in faster stomatal closure partially mitigating drought stress effects. Evidence of this was found in enhanced green leaf volatiles in trees without ozone fumigation indicating cellular damage. In addition we observed an enhancement in Methyl Salicylate emissions in trees with ozone treatment. Individual plant stress factors are not necessarily additive and atmospheric models should implement stress feedback loops to study regional scale effects. [ABSTRACT FROM AUTHOR]