Application of the UAM-V and use of indicator species to assess control strategies for ozone reduction in the Lower Fraser Valley of British Columbia

Modelled and measured indicator species ratios of O-3/NOz, O-3/NOy, H2O2/HN O3, HCHO/NOy for the Lower Fraser Valley were compared with VOC-NOx-O-3 sen sitivity threshold values reported in previous studies. Modelled region - s pecific indicator ratio thresholds derived from 50% NOx and 50% VOC reducti on scenarios are provided. They show strongest agreement with the H2O2/HNO3 ratio values found elsewhere. A clear transition region for the LFV from V OC to NOx sensitivity could not be identified, but there is evidence that O -3 concentrations in the western valley, dominated by metropolitan Vancouve r, are VOC sensitive, and the more rural eastern valley O-3 concentrations exhibit greater NOx sensitivity. The UAM-V Process Analysis utility was use d to identify physical and chemical mechanisms which contributed to O-3 for mation and destruction and indicate the key importance of entrainment from elevated layers generated by the highly complex meteorological conditions i n determining near surface O-3 concentrations.