Nucleation Particles in Diesel Exhaust:  Composition Inferred from In Situ Mass Spectrometric Analysis

Abstract

Mass spectrometric measurements of size and composition of diesel exhaust particles have been performed under various conditions: chassis dynamometer tests, field measurements near a German motorway, and individual car chasing. Nucleation particles consisting of volatile sulfate and organic material could be detected both at the chassis dynamometer test facility and during individual car chasing. We found evidence that if nucleation occurs, sulfuric acid/water is the nucleating agent. Low-volatile organics species condense only on the preexisting sulfuric acid/water clusters. Nucleation was found to depend strongly on various parameters such as exhaust dilution conditions, fuel sulfur content, and engine load. The latter determines the fraction of the fuel sulfur that is converted to sulfuric acid. The organic compounds (volatile and low-volatile) condense only on preexisting particles, such as both sulfuric acid nucleation particles and larger accumulation mode soot particles. On the latter, sulfuric acid also condenses, if the conditions for nucleation are not given. The overall ratio of sulfate to organic (volatile and low-volatile) is also strongly dependent on the engine load. It was found that the production of nucleation particles even at high engine load can be suppressed by using low-sulfur fuel.

Can Real-World Diesel Exhaust Particle Size Distribution be Reproduced in the Laboratory? A Critical Review Jorma Keskinen

“…59 The combined effect of fuel and lubricant oil sulfur contents on the exhaust size distributions of heavy-duty vehicles has been reported by Kittelson et al 37,53 All of the observations above indicate that the formation of nucleation mode particles is a sulfur-driven process. The AMS studies and volatility studies conducted on-road 66 and the modeling studies performed with onroad data 60 support this concept. As discussed above, the process is sensitive to the ambient conditions (i.e., the ambient air temperature and humidity).…”

“…During on-road and wind tunnel measurements with cars, the nucleation mode has been observed at high speed or at high-load conditions, but generally only when the fuel sulfur content (FSC) has been high and the vehicle has been equipped with an oxidation catalyst 27,54,57,58,61,63,66 . For low FSC (Ͻ50 parts per million [ppm]) or without an oxidizing exhaust aftertreatment, the nucleation mode has generally not been observed.…”

“…For low FSC (Ͻ50 parts per million [ppm]) or without an oxidizing exhaust aftertreatment, the nucleation mode has generally not been observed. 56,58,62,63,66 The exception is high load at highspeed conditions: Uhrner et al 60 and Wehner et al 61 reported nucleation mode particle formation for low FSC (7 ppm) at vehicle speeds exceeding 140 km/hr. In their studies the test vehicle was equipped with an oxidation catalyst.…”

Influence of Waste Cooking Oil Biodiesel on the Particulate Emissions and Particle Volatility of a DI Diesel Engine

“…With more particles being formed, they tend to coagulate to form larger particles. Furthermore, during the dilution and cooling of the exhaust gas, the volatile substances could condense on the surface of the existing particles to form larger ones (Bagley et al, 1998;Schneider et al, 2005). This effect is more significant at high engine load when the exhaust gas temperature is higher (Ning et al, 2004).…”

The Construction and Application of a Multipoint Sampling System for Vehicle Exhaust Plumes

“…Additionally, these studied commonly used instruments such as condensation particle counters (CPCs), electrical low-pressure impactors (ELPIs), and engine exhaust particle sizers (EEPSs), but the components of the particulate matter in the plumes cannot be measured by these instruments. However, Schneider et al (2005) studied the size and components of particulate matter in vehicle exhaust.…”