Simultaneous measurements of on-road/in-vehicle nanoparticles and NOx while driving: Actual situations, passenger exposure and secondary formations

Abstract Simultaneous measurements of on-road and in-vehicle NO and NO 2 levels, particle number concentrations (PNCs), and particles size distributions were performed while driving using a test vehicle equipped with real-time sensors. The results obtained on regional roads showed that heavy-duty vehicles in traffic seem to have a major impact on on-road air quality. Measurements on highways that included a 10 km tunnel and a 2 km uphill section of road indicated that sub-50 nm particles have different features from the other species because of their higher volatility. The other species showed quite high on-road concentrations in the tunnel. In-vehicle conditions were made similar to the on-road ones by setting the air conditioning (AC) mode to the fresh air mode. The in-vehicle NO 2 concentration in the tunnel was over 0.50 ppmV, which is almost five times higher than the 1-hour ambient air quality standard proposed by the World Health Organization (WHO). In sections other than the tunnel, the in-vehicle NO 2 concentration was almost the same as the 1-hour WHO standard. Higher on-road NO 2 /NOx ratios than those of exhaust gases and different behavior of sub-50 nm particles from other species suggested that NO 2 and sub-50 nm particles were mainly due to secondary products formed by atmospheric reactions.