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Emissions from diesel buses can be lowered by retrofitting

Emissions from diesel buses can be lowered by retrofitting

The study indicated that emissions from EURO VI buses and EEV buses with retrofitted diesel particulate filter and selective catalytic reduction technology are significantly lower than emission from lower emission standard busses.

Exhaust emissions from traffic significantly affect urban air quality. The study conducted by Finnish Meteorological Institute, Tampere University and HSY focused on in-traffic emissions of diesel-fueled city buses. In general, results demonstrate that advanced exhaust aftertreatment systems efficiently reduce emissions of soot particles. However, more variation was observed for nanoparticles.

Exhaust emissions of buses were measured by chasing the buses during their normal scheduled operation with a mobile laboratory. The instruments installed in the mobile laboratory measured the exhaust plume. The measurements included different gas analyzers for CO2 and NOx and particle instruments to characterize exhaust particle concentration and size distributions over large size range as well as black carbon concentration.

The bus types in the measurements were meeting EEV (enhanced environmentally friendly vehicle) and Euro VI emission limits. In addition, the effects of retrofitting of EEV with diesel particulate filter and selective catalytic reduction technology to exhaust emissions were studied.

Based on the measurement results, the average emission factors of particle number (PN), particle mass (PM1), lung deposited surface area (LDSA) and black carbon (BC) were calculated. The average emission factors for particle mass and black carbon were significantly lower for EURO VI and EEV retrofitted with DPF when compared to EEV level bus.

However, for retrofitted EEV buses more variation in the particle number (PN) concentrations were observed compared to EURO VI bus with constantly low particle number emissions. Also, on average, the EEV buses were observed to emit the largest amounts of nanocluster aerosol (NCA), i.e., the particles with size between 1.3 and 3 nm. High nanocluster aerosol emissions were linked also with high particle number emissions.

This study was funded by Business Finland, Helsinki Region Environmental Services Authority (HSY) and Pegasor Oy through the Cityzer -project.

Further information:

Senior researcher Hilkka Timonen, Finnish Meteorological Institute, tel. +358 50 380 2864,

Järvinen, A., Timonen, H., Karjalainen, P., Bloss, M., Simonen, P., Saarikoski, S., Kuuluvainen, H., Kalliokoski, J., Dal Maso, M., Niemi, J. V., Keskinen, J., and Rönkkö, T.: Particle emissions of Euro VI, EEV and retrofitted EEV city buses in real traffic, Environmental pollution, 250, 708-716, 10.1016/j.envpol.2019.04.033, 2019.

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