Deciphering anthropogenic and biogenic contributions to selected NMVOC emissions in an urban area

Abstract. 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.