Potential of diesel emissions reduction strategies in Xi’an, China

Diesel vehicles contributed 70 % of the NOx and more than 90 % of the PM in the 2014 on-road emissions inventory in China. Attention is therefore being focused on diesel vehicles because of their significantly higher NOx and PM emission rates and vehicle miles traveled, relative to gasoline-powered cars. Xi’an city has taken many measures to reduce diesel exhaust emissions. In this present study, the main objectives were to identify potential of emission-reduction strategies—fuel-standard improvements, elimination of “yellow-brand” vehicles, increased use of alternative fuels (CNG, LNG), and installation of DPFs in older vehicles—and to quantify the relative effectiveness of each of these potential strategies. A revised MOVES model was used to estimate PM and NOx emission inventories for selected scenarios at the county scale, for Xi’an city. The results show that, for NOx reduction, the best strategy would be fuel-standard improvements (Scenario 1), followed by (in order of effectiveness) the increased use of alternative fuels (Scenario 3), elimination of “yellow-brand” diesel vehicles (Scenario 2), and retrofitting older vehicles by installing DPFs (Scenario 4), whereas for PM10 or PM2.5, the effectiveness sequence of control strategies was found to be Scenario 1, Scenario 3, Scenario 2, and Scenario 4. It was also found that medium-weight and heavy trucks have a larger potential for NOx and PM reductions than do other vehicle types. These results are of paramount importance, not only for Xi’an but also for other cities that are considering adopting possible strategies to mitigate air pollution from vehicles.