Underestimated Ammonia Emissions from Road Vehicles.

In this study, we use comprehensive vehicle emission remote sensing measurements of over 230,000 passenger cars to estimate total UK ammonia (NH) emissions. Estimates are made using "top-down" and "bottom-up" methods that demonstrate good agreement to within 1.1% for total fuel consumed or CO emitted. A central component of this study is the comprehensive nature of the bottom-up emission estimates that combine highly detailed remote sensing emission data with over 4000 km of 1 Hz real driving data. Total annual UK NH emissions from gasoline passenger cars are estimated to be 7.8 ± 0.3 kt from the bottom-up estimate compared with 3.0 ± 1.7 kt reported by the UK national inventory. An important conclusion from the analysis is that both methodologies confirm that gasoline passenger car NH emissions are underestimated by a factor of about 2.6 compared with the 2018 UK National Atmospheric Emissions Inventory. Furthermore, we find that inventory estimates of urban emissions of NH for passenger cars are underestimated by a factor of 17.