The published literature on vehicular interior air quality (VIAQ) has already demonstrated that car commuters can be exposed to significantly enhanced levels of inhalable particles (PM10, PM2.5 and PM1: particles in suspension with diameter less than 10, 2.5 and 1 μm respectively) and gases (CO, CO2, NO2, VOCs). Taxi drivers offer a special case in that they are chronically exposed to TRAPs as an occupational hazard, and this transport mode is additionally interesting in that current taxi fleets utilise various fuel options that include both hybrid and electric vehicles, which generate different patterns of pollutant emissions. While most city taxi fleets are still dominated by traditional gasoline- or diesel-powered engines, this is changing rapidly. In 2017 for example already one third of the 10,523 taxis operating in the city of Barcelona used alternative fuels, with the fleet composition being 67% diesel, 26% hybrid, 6% liquefied gas (LPG, mainly propane and butane), 0.4% compressed natural gas (CNG, methane and ethane) and 0.3% electric. Our study of VIAQ inside taxis included all these vehicle types and involved simultaneous collection (tracked by GPS) of air quality data on inhalable particle mass, number, and chemistry, as well as gaseous contaminants (CO, CO2 and VOCs). The data recorded everyday VIAQ conditions breathed by taxi drivers and passengers during 6-hours of a working day (10.00-16.00) and involved the co-operation of taxi drivers who consented to collect the equipment in the morning and carry it in the car with them as they went about their business.