Effectiveness of emissions standards on automotive evaporative emissions in Europe under normal and extreme temperature conditions

Abstract

Non-methane volatile organic compounds (NMVOCs) are primary precursors for the formation of ozone and secondary organic aerosol which contribute to increased public health risks. Throughout Europe, passenger vehicles contribute significantly to NMVOC emissions due to automotive evaporative emissions controls that are less stringent than those in the United States, Canada, China, and Brazil. Evaporative NMVOC emissions increase significantly, and associated air quality impacts are exacerbated, during periods of high temperature such as heatwaves, which continue to increase in frequency, duration, and intensity. Adoption of strict evaporative emission standards and controls such as onboard refueling vapor recovery systems (ORVR) can significantly reduce evaporative emissions during such events; however, emissions inventories used to inform policy decisions are developed using average temperature profiles which fail to capture the impact of heatwave events on evaporative emissions. This study evaluates the effectiveness of the previous generation (Euro5), current (Euro6d), and proposed (Euro7) emission control standards on evaporative emissions at high temporal and spatial resolution in western and central Europe during July 2019, a month in which a significant heatwave swept through the region. Using temperatures obtained from the Weather Research and Forecasting (WRF) model with observation data and an improved method for estimating evaporative emissions, it is estimated that per-vehicle evaporative NMVOC emissions within the study domain and period are reduced by 25.0% under current Euro6d standards and controls relative to Euro5 standards, and that proposed Euro7 controls, including ORVR, would provide an additional 35.3% emissions reduction relative to Euro6d. During heatwave periods, Euro7 controls demonstrate improved attenuation of temperature-driven emissions increases relative to Euro6d controls, with associated emissions within the study period and domain increasing by 23.4% on average under Euro7 controls versus 29.4% under Euro6d controls. While this study does not quantify the effect of heatwaves and emissions controls on total annual emissions, the results for the study period of July 2019, combined with the low implementation cost of proposed Euro7 evaporative controls and projected continued dominance of petrol vehicles in the European fleet through the middle of this century, suggest that significant NMVOC emissions reductions and associated air quality and health impacts are achievable through the adoption of these more stringent standards and control systems.