Advanced chemical analysis and comparative evaluation of emissions from urban buses under real driving conditions

Urban diesel buses remain significant sources of atmospheric pollutants due to their intensive operation in densely populated areas. This study presents a detailed comparison of tailpipe emissions from a Euro V bus, equipped with exhaust gas recirculation and a diesel oxidation catalyst, and a Euro VI bus, fitted with a particulate filter and selective catalytic reduction. Vehicles were tested over the ISC-M3 cycle and a representative urban route in Lyon, France. Regulated gases and solid particle numbers were measured in real time using portable emissions measurement systems (PEMS) and Fourier transform infrared spectroscopy (FTIR), while the water soluble organic aerosol fraction of the condensates was collected at the tailpipe and analyzed offline by ultra-high performance liquid chromatography coupled with Orbitrap mass spectrometry (UHPLC-Orbitrap-MS), using both positive and negative electrospray ionization modes. Under ISC conditions, compared to the Euro V version, the Euro VI bus reduced NO_x emissions from 5.340 to 0.795 g kWh^-1, CO from 1.040 to 0.205 g kWh^-1, THC from 0.100 to 0.035 g kWh^-1, NH₃ from 0.291 to 0.014 g kWh^-1, and particle number from 6.19 × 10¹² to 5.02 × 10¹¹ # kWh^-1, with similar trends in urban operation. Despite these reductions, both buses emitted complex mixtures of intermediate- and semi-volatile organic compounds, including nitrogen and sulfur containing species with high potential for secondary organic aerosol formation, underscoring the need for emission controls targeting unregulated pollutants.