This document analyzes data obtained from international studies which compare natural gas, diesel and hybrid technologies for buses, in order to find out differences in particulate Matter (PM10), Nitrogen Oxides (NOx), non-methane hydrocarbon (NMHC), carbon monoxide (CO), greenhouse gas, and air toxic emissions. The results presented here are for 90 passenger 12m buses. Two types of comparisons were made: i) technology comparison; and ii) fuel comparison. The comparison revealed that buses using ultra low sulfurdiesel (ULSD) with Diesel Particulate Filters (DPF) and buses using Compressed Natural Gas (CNG) with Oxidation Catalysts (OC) have the lowest emissions of PM10 and CO emissions; CNG with OC have less NOx and Greenhouse Gases emissions, while ULSD with DPF had less NMHC emissions. Post-treatment technologies are presented as a low-cost option to reduce emissions. Hybrid diesel buses were found to be the technology that has the lowest emissions for majority of the pollutants.
Abstract