1Center for Atmospheric Particle Studies, Carnegie Mellon University, Pittsburgh, PA 15213, USA
2Engineering and Public Policy, Carnegie Mellon University, Pittsburgh, PA 15213, USA
3Heavy-Duty Diesel Testing Laboratory, California Air Resources Board, Los Angeles, CA 90012, USA
4Mobile Source Operations, California Air Resources Board, El Monte, CA 91731, USA
5Monitoring and Laboratory, California Air Resources Board, El Monte, CA 91731, USA
6Planning and Technical Support, California Air Resources Board, El Monte, CA 91731, USA
7Research Division, California Air Resources Board, Sacramento, CA 95814, USA
8Research and Advanced Engineering, Ford Motor Company, Dearborn, MI 48120, USA
*now at: National Oceanic and Atmospheric Administration Earth System Research Laboratory, Chemical Sciences Division, 325 Broadway, Boulder, CO 80305, USA
**now at: Cooperative Institute for Research in Environmental Sciences, University of Colorado, 216 UCB, Boulder, CO 80309, USA
Received: 19 Jul 2013 – Published in Atmos. Chem. Phys. Discuss.: 16 Sep 2013
Abstract. Environmental chamber ("smog chamber") experiments were conducted to investigate secondary organic aerosol (SOA) production from dilute emissions from two medium-duty diesel vehicles (MDDVs) and three heavy-duty diesel vehicles (HDDVs) under urban-like conditions. Some of the vehicles were equipped with emission control aftertreatment devices, including diesel particulate filters (DPFs), selective catalytic reduction (SCR) and diesel oxidation catalysts (DOCs). Experiments were also performed with different fuels (100% biodiesel and low-, medium- or high-aromatic ultralow sulfur diesel) and driving cycles (Unified Cycle,~Urban Dynamometer Driving Schedule, and creep + idle). During normal operation, vehicles with a catalyzed DPF emitted very little primary particulate matter (PM). Furthermore, photooxidation of dilute emissions from these vehicles produced essentially no SOA (below detection limit). However, significant primary PM emissions and SOA production were measured during active DPF regeneration experiments. Nevertheless, under reasonable assumptions about DPF regeneration frequency, the contribution of regeneration emissions to the total vehicle emissions is negligible, reducing PM trapping efficiency by less than 2%. Therefore, catalyzed DPFs appear to be very effective in reducing both primary PM emissions and SOA production from diesel vehicles. For both MDDVs and HDDVs without aftertreatment substantial SOA formed in the smog chamber – with the emissions from some vehicles generating twice as much SOA as primary organic aerosol after 3 h of oxidation at typical urban VOC / NOx ratios (3 : 1). Comprehensive organic gas speciation was performed on these emissions, but less than half of the measured SOA could be explained by traditional (speciated) SOA precursors. The remainder presumably originates from the large fraction (~30%) of the nonmethane organic gas emissions that could not be speciated using traditional one-dimensional gas chromatography. The unspeciated organics – likely comprising less volatile species such as intermediate volatility organic compounds – appear to be important SOA precursors; we estimate that the effective SOA yield (defined as the ratio of SOA mass to reacted precursor mass) was 9 ± 6% if both speciated SOA precursors and unspeciated organics are included in the analysis. SOA production from creep + idle operation was 3–4 times larger than SOA production from the same vehicle operated over the Urban Dynamometer Driving Schedule (UDDS). Fuel properties had little or no effect on primary PM emissions or SOA formation.
Revised: 24 Feb 2014 – Accepted: 04 Mar 2014 – Published: 13 May 2014
Gordon, T. D., Presto, A. A., Nguyen, N. T., Robertson, W. H., Na, K., Sahay, K. N., Zhang, M., Maddox, C., Rieger, P., Chattopadhyay, S., Maldonado, H., Maricq, M. M., and Robinson, A. L.: Secondary organic aerosol production from diesel vehicle exhaust: impact of aftertreatment, fuel chemistry and driving cycle, Atmos. Chem. Phys., 14, 4643-4659, doi:10.5194/acp-14-4643-2014, 2014.