Investigating the role of organic compounds in intercontinental ozone transport: Reactivity scales and Global Warming Potentials (GWPs)

A global Lagrangian three-dimensional chemistry-transport model has been used to study intercontinental ozone transport from North American sources of organic compounds to receptors in Europe (Mace Head, Ireland) and in Eurasia (Mount Waligaun). Pulses of seventeen volatile organic compounds (VOCs) were emitted across North America, producing short-term ozone responses at the receptors over the first month which decayed rapidly, followed by a longer-term response which decayed more slowly. The short-term ozone responses were highly VOC-dependent and were characterised as VOC-driven. The long-term ozone responses were caused by the VOC chemistry depleting the hydroxyl (OH) radical steady state, slowing down methane oxidation, building up the methane burden and increasing methane-driven ozone production. Indices were designed and employed to quantify the short-term ozone responses, the intercontinental ozone creation potential (IOCP), and the long-term responses, the OH depletion index (OHDI). The radiative forcing consequences of the ozone and methane responses to the seventeen VOC emission pulses were estimated over a one-hundred-year time horizon and the global warming potentials (GWPs) were calculated for each VOC species. The main features of VOC chemistry were delineated and used to explain the relative magnitudes of the IOCPs, OHDIs and GWPs.