Evolution under dark conditions of particles from old and modern diesel vehicles, in a new environmental chamber characterized with fresh exhaust emissions

Abstract

Abstract. Atmospheric particles have several impacts on health and environment, especially in urban areas. Part of those particles is not fresh, and has undergone atmospheric chemical and physical processes. Due to not representative experimental conditions, and experimental artifacts such as particle wall losses in chambers, there are uncertainties on the effects of physical processes (condensation, nucleation and coagulation) and how they act on particles from modern vehicles. This study develops a new method to correct wall losses, accounting for size dependence and experiment-to-experiment variations, and applies it to the evolution of fresh diesel exhaust particles to characterize the physical processes acting on them. The correction method is based on the black carbon decay and a size-dependent coefficient to correct particle distributions. Exhaust from 6 diesel passenger cars, Euro 3 to Euro 6, driven on a chassis dynamometer with Artemis Urban cold start and Artemis Motorway cycles, was injected in an 8 m3 chamber with Teflon walls. The physical evolution of particles was characterized during 6 to 10 hours. Condensation occurs even without photochemical reactions, due to the presence of intermediate volatility organic compounds and semi-volatile organic compounds which were quantified at emission, and induces a particle mass increase up to 17 %.h−1, mainly for the older vehicles (Euro 3 and Euro 4). Condensation is 4 times faster when the available particle surface if multiplied by 3. If initial particle number concentration is below [8–9] × 104 #.cm−3, it can increase up to 25 %.h−1 due to nucleation or condensation on particles below 14 nm. Above this threshold, particle number concentration decreases due to coagulation, up to −27 %.h−1.