A photochemical trajectory model together with a Master Chemical Mechanism and a highly speciated emission inventory for organic compounds have been used to describe the formation of ozone in north west Europe and to identify the most prolific ozone-forming organic compounds. Observations are reviewed to assess the impact of emission controls on their urban volatile organic compound (VOC) concentration trends with time. The observed trends are then used to deduce the likely trends in episodic peak ozone concentrations and to compare them with observed trends in peak ozone concentrations. It is concluded that it is likely that motor vehicle emission controls have brought about a substantial reduction in episodic peak ozone concentrations in north west Europe during the 1990s. (C) 2003 Elsevier Science Ltd. All rights reserved.