Nanoparticle formation in the exhaust of vehicles running on ultra-low sulfur fuel H. Du and F. Yu Atmospheric Sciences Research Center, State University of New York at Albany, Albany, NY 12203, USA
Abstract. The concern of adverse health impacts from exposure to
vehicle-emitted nanoparticles has been escalating over the past few years.
In order to meet more stringent EPA emission standards for particle mass
emissions, advanced exhaust after-treatment systems such as continuously
regenerating diesel particle filters (CRDPFs) have to be employed on
vehicles and fuel with ultra-low sulfur is to be used. Although CRDPFs were
found to be effective in reducing particle mass emissions, they were
revealed to increase the potential of volatile nanoparticle formation.
Significant nanoparticle concentrations have also been detected for vehicles
running on ultra-low sulfur fuel but without CRDPFs. The main focus of this
paper is the formation and evolution of nanoparticles in an exhaust plume
under ultra-low sulfur conditions. Such a study is necessary to project
future nanoparticle emissions as fuel compositions and after-treatment
systems change. We have carried out a comprehensive quantitative assessment
of the effects of enhanced sulfur conversion efficiency, sulfur
storage/release, and presence of non-volatile cores on nanoparticle
formation using a detailed composition resolved aerosol microphysical model
with a recently improved H2SO4-H2O homogeneous nucleation
(BHN) module. Two well-controlled case studies show good agreement between
model predictions and measurements in terms of particle size distribution
and temperature dependence of particle formation rate, which leads us to
conclude that BHN is the main source of nanoparticles for vehicles equipped
with CRDPFs. We found that the employment of CRDPFs may lead to the higher
number concentration of nanoparticles (but smaller size) in the exhaust of
vehicles running on ultra-low sulfur fuel compared to those emitted from
vehicles running on high sulfur fuel. We have also shown that the sulfate
storage and release effect can lead to significant enhancement in
nanoparticle production under favorable conditions. For vehicles running on
ultra-low sulfur fuel but without CRDPFs, the BHN is negligible; however,
the condensation of low volatile organic compounds on nanometer-sized
non-volatile cores may explain the observed nucleation mode particles.
Citation: Du, H. and Yu, F.: Nanoparticle formation in the exhaust of vehicles running on ultra-low sulfur fuel, Atmos. Chem. Phys., 8, 4729-4739, doi:10.5194/acp-8-4729-2008, 2008.