Abstract. Air pollution is particularly severe in developing megacities, such as
Beijing, where vehicles equipped with modern gasoline-direct-injection (GDI)
engines are becoming one of major sources of the pollution. This study
presents the characteristics of individual particles emitted by a GDI
vehicle and their ageing in a smog chamber under the Beijing urban
environment, as part of the Atmospheric Pollution & Human Health (APHH)
research programme. Using transmission electron microscopy, we identified
the particles emitted from a commercial GDI-engine vehicle running under
various conditions, namely cold-start, hot-start, hot stabilized running,
idle, and acceleration states. Our results showed that most of the particles
were organic, soot, and Ca-rich ones, with small quantities of S-rich and
metal-containing particles. In terms of particle size, the particles
exhibited a bimodal distribution in number vs size, with one mode at 800–900 nm and the other at 140–240 nm. The numbers of organic particles emitted
under hot-start and hot stabilized states were higher than those emitted
under other conditions. The number of soot particles was higher under cold-start and acceleration states. Under the idle state, the proportion of
Ca-rich particles was highest, although their absolute number was low. In
addition to quantifying the types of particles emitted by the engine, we
studied the ageing of the particles during 3.5 h of photochemical
oxidation in an environmental chamber under the Beijing urban environment.
Ageing transformed soot particles into core–shell structures, coated by
secondary organic species, while the content of sulfur in Ca-rich and
organic particles increased. Overall, the majority of particles from
GDI-engine vehicles were organic and soot particles with submicron or
nanometric size. The particles were highly reactive; they reacted in the
atmosphere and changed their morphology and composition within hours via
catalysed acidification that involved gaseous pollutants at high pollution
levels in Beijing.Highlights.
GDI-engine vehicles emitted a large amount of both primary and secondary
organic aerosol (SOA). Higher numbers of organic particles were emitted under hot stabilized running and hot-start states. Sulfate and secondary organic aerosol formed on the surface of primary
particles after ageing. Particles aged rapidly by catalysed acidification under high pollution
levels in Beijing.
Morphology and size of the particles emitted from a gasoline-direct-injection-engine vehicle and their ageing in an environmental chamber
