The Effects of the Catalytic Converter and Fuel Sulfur Level on Motor Vehicle Particulate Matter Emissions:  Light Duty Diesel Vehicles

Abstract

Wind tunnel measurements and direct tailpipe particulate matter (PM) sampling are utilized to examine how the combination of oxidation catalyst and fuel sulfur content affects the nature and quantity of PM emissions from the exhaust of a light duty diesel truck. When low sulfur fuel (4 ppm) is used, or when high sulfur (350 ppm)fuel is employed without an active catalyst present, a single log-normal distribution of exhaust particles is observed with a number mean diameter in the range of 70-83 nm. In the absence of the oxidation catalyst, the high sulfur level has at most a modest effect on particle emissions (<50%) and a minor effect on particle size (<5%). In combination with the active oxidation catalyst tested, high sulfur fuel can lead to a second, nanoparticle, mode, which appears at approximately 20 nm during high speed operation (70 mph), but is not present at low speed (40 mph). A thermodenuder significantly reduces the nanoparticle mode when set to temperatures above approximately 200 degrees C, suggesting that these particles are semivolatile in nature. Because they are observed only when the catalyst is present and the sulfur level is high, this mode likely originates from the nucleation of sulfates formed over the catalyst, although the composition may also include hydrocarbons.

Winter and summer time size distributions and densities of traffic-related aerosol particles at a busy highway in Helsinki

“…Sakurai et al (2003b) estimated a density of 0.8 g/cm 3 for these compounds. In addition, the nucleation mode formation is connected to the sulphate formation, especially when oxidation catalyst is used (Lepperhof, 2001;Maricq et al, 2002;Vaaraslahti et al, 2004). According to studies of Vogt et al(2003); Gieshaskiel et al (2005) the sulphuric acidwater nucleation seems to have an important role in the nucleation mode formation.…”

Traffic is a major source of atmospheric nanocluster aerosol

“…The observed NCA concentrations varied significantly depending on the traffic rate and wind direction. The emission factors of NCA for traffic were 2.4·10 15 (kg fuel ) −1 in a roadside environment, 2.6·10 15 (kg fuel ) −1 in a street canyon, and 2.9·10 15 (kg fuel ) −1 in an on-road study throughout Europe. Interestingly, these emissions were not associated with all vehicles.…”

“…Interestingly, these emissions were not associated with all vehicles. In engine laboratory experiments, the emission factor of exhaust NCA varied from a relatively low value of 1.6·10 12 (kg fuel ) −1 to a high value of 4.3·10 15 (kg fuel ) −1 . These NCA emissions directly affect particle concentrations and human exposure to nanosized aerosol in urban areas, and potentially may act as nanosized condensation nuclei for the condensation of atmospheric low-volatile organic compounds.…”

Effects of a diesel oxidation catalyst on gaseous pollutants and fine particles from an engine operating on diesel and biodiesel

“…A significant decrease in the OC/ EC ratio by the DOC was observed at 25% load, 2690 r $min -1 , due to the high OC fraction in engine out particles at this low load. It is reported that the primary effect of the DOC on PM is the reduction in the OC fraction (or SOF) [4,7,8,16]. Vaaraslahti et al investigated the effect of a conventional DOC and a particle oxidation catalyst on the diesel particles [16].…”

“…Research has shown that DOC could affect PM emissions in three ways: soot oxidation, soluble organic fraction (SOF) removal, and sulfate formation [6,7]. PM mass emissions may be increased by a DOC through significant sulfate formation when the fuel sulfur content is high [6].…”