Conventional cabin heating in electric buses – the scale of pollution

Electric buses are generally considered as zero-emission vehicles and have thus become common in city transport to reduce pollution. However, electric buses in cold regions often utilise diesel-powered auxiliary heaters for cabin thermal management, which contradicts the zero-emission status. Studies have shown auxiliary heaters can emit significant amounts of gaseous and particulate emissions, although the extend of this issue has not been investigated. This paper introduces a method for estimating the annual emissions stemming from electric bus auxiliary heater use. The emission estimate was derived by combining empirical emission data with bus operation schedules and historical weather data. The findings reveal that a fleet of 1 254 electric buses with auxiliary heaters could annually emit up to 5.3 million kilograms of tailpipe CO2 along with notable quantities of local pollutants. Nevertheless, greenhouse gas emissions from the auxiliary heaters were found to be relatively low compared to diesel engines, with CO2 emissions per unit of work used being approximately 10% to 30% of those produced by Euro VI buses. The local pollutants (CO, NOx and particulates) from auxiliary heaters can be significantly higher. For instance, auxiliary heater CO emissions per unit of work were found to be 1 to 19 times higher than those of diesel engines.