Underestimated Ammonia Emissions from Road Vehicles.

Naomi J Farren,Rebecca A Rose,David C Carslaw,Jack Davison,Rebecca L Wagner

doi:10.1021/acs.est.0c05839

Abstract

In this study, we use comprehensive vehicle emission remote sensing measurements of over 230,000 passenger cars to estimate total UK ammonia (NH3) emissions. Estimates are made using "top-down" and "bottom-up" methods that demonstrate good agreement to within 1.1% for total fuel consumed or CO2 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 NH3 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 NH3 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 NH3 for passenger cars are underestimated by a factor of 17.

Highlights

Ammonia (NH3) emissions contribute significantly to the formation of fine particulate matter (PM2.5) in the atmosphere and nitrogen deposition in ecosystems
We find that inventory estimates of urban emissions of NH3 for passenger cars are underestimated by a factor of 17
Two spectroscopic remote sensing (RS) instruments were used to measure vehicle emissions: the Fuel Efficiency Automobile Test (FEAT) instrument developed by the University of Denver and the Opus AccuScan RSD 5000

Summary

■ INTRODUCTION

Ammonia (NH3) emissions contribute significantly to the formation of fine particulate matter (PM2.5) in the atmosphere and nitrogen deposition in ecosystems. Recent research suggests that emissions of vehicular NH3 and NOx can lead to transient, inhomogeneous conditions in urban environments, whereby the gas-to-particle ammonium nitrate system is out of equilibrium and gas-phase supersaturations are sustained This process can drive the rapid growth of new particles, enabling newly formed particles to survive scavenging losses in highly polluted environments.[5] The enhanced pathway to particle formation is supported by a 15N isotope study, which showed that fossil fuel combustion-related activities dominated atmospheric NH3 sources during severe haze episodes in urban Beijing, China.[6]. There are two main sources of NH3 emissions from road vehicles catalyst-equipped gasoline vehicles and light- and heavy-duty diesel vehicles that rely on selective catalytic reduction (SCR) In both cases, NH3 is not released directly from the internal combustion engine; instead, it is formed as an unintended consequence of the technologies introduced to reduce NOx emissions. We provide new UK total NH3 estimates and consider the wider atmospheric impacts of these estimates

■ MATERIALS AND METHODS

■ ACKNOWLEDGMENTS

■ REFERENCES