Biogenic volatile organic compound (VOC) emission estimates from an urban tree canopy

Biogenic emissions of the. volatile organic compounds isoprene and monoterpenes (BVOCs) can contribute to tropospheric ozone and secondary particle formation and have indirect effects on climate change. While there are few studies of BVOC emissions from European towns and cities, several studies in North America indicate that the urban tree canopy may be a significant source of BVOC compounds, contributing to ozone and particle formation in the urban air-shed. Here, BVOC emissions from the U.K. West Midlands (UKWM) metropolitan area were estimated and compared with anthropogenic VOC emission estimates, and with BVOC emission estimates for other urban and U.K. regions. Monoterpene and isoprene emission potential estimates, for the UKWM urban land-use classes spanned as much as two orders of magnitude, from 17-104 g.km(-2).h(-1) and from 42-1570 g km(-2).h(-1), respectively. Isoprene emission potential estimates for the UKWM urban land classes (42-530 g.km(-2.)h(-1)) were of the same order of magnitude as isoprene emission measurements for U.K. gorse heathland in early summer (43 g.km(-2).h(-1)), and up to approximately one order of magnitude lower than those measured from U.K. Sitka spruce forests in summer (658-6760 g.km(-2).h(-1)). In the UKWM, the land class average of SigmaBVOC emission estimates (similar to75-165 kg.km(-2).yr(-1)) were approximately two orders of magnitude lower than anthropogenic VOC emission estimates for the same area (70 000 kg.km(-2).yr(-1)). Biogenic isoprene emission estimates from at least two of the UKWM urban land-use classes were equivalent to, or greater than, estimates of anthropogenic isoprene emissions. The extrapolation methodologies are critically discussed in the context of their uncertainties, and in the context of their generic potential.