Formation of secondary aerosol from emissions of a Euro 6d-compliant gasoline vehicle with a particle filter

Abstract

The most recent European regulation, the Euro 6d emission standard, requires all gasoline direct injection (GDI) vehicles to use both a three-way catalyst (TWC) and a gasoline particle filter (GPF) as exhaust aftertreatment. These aftertreatment methods are aimed at reducing NO_x and primary particle emissions. However, the formation of secondary organic aerosols (SOAs) from the volatile organic compound (VOC) emissions of a Euro 6d compliant GDI vehicle, factory equipped with a GPF is not yet investigated. Therefore, to explore the SOA formation and effects of the GPF, the exhaust of a Euro 6d compliant GDI vehicle was characterized at 4 different steady state speeds, idling (0 km h⁻¹), 50, 80 and 100 km h⁻¹. The exhaust was oxidised in a photochemical emission aging flow tube reactor (PEAR) by reactions with OH radicals equivalent of 2.2 days of atmospheric day time oxidation. It was found that the GPF completely removes primary particles larger than 10 nm, at all investigated vehicle speeds. However, significant SOA was formed after oxidation, with the highest SOA formation potential per kg fuel consumed at 50 km h⁻¹. The main SOA precursors were determined to be toluene, xylene and trimethyl-benzene which were found to account for at least 50% of SOA formed at all driving speeds. Furthermore, high emissions of ammonia (NH₃) could be observed in the exhaust under all driving conditions which resulted in the subsequent formation of ammonium nitrate (NH₄NO₃) after aging. The formation of NH₄NO₃ additionally facilitated the co-condensation of organic gas phase products after OH oxidation enhancing SOA mass even further.