Effects of Gaseous Sulphuric Acid on Diesel Exhaust Nanoparticle Formation and Characteristics (original) (raw)
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Volatile Nanoparticle Formation and Growth within a Diluting Diesel Car Exhaust
Journal of the Air & Waste Management Association, 2011
A major source of particle number emissions is road traffic. However, scientific knowledge concerning secondary particle formation and growth of ultrafine particles within vehicle exhaust plumes is still very limited. Volatile nanoparticle formation and subsequent growth conditions were analyzed here to gain a better understanding of "real-world" dilution conditions. Coupled computational fluid dynamics and aerosol microphysics models together with measured size distributions within the exhaust plume of a diesel car were used. The impact of soot particles on nucleation, acting as a condensational sink, and the possible role of low-volatile organic components in growth were assessed. A prescribed reduction of soot particle emissions by 2 orders of magnitude (to capture the effect of a diesel particle filter) resulted in concentrations of nucleation-mode particles within the exhaust plume that were approximately 1 order of magnitude larger. Simulations for simplified sulfuric acid-water vapor gas-oil containing nucleation-mode particles show that the largest particle growth is located in a recirculation zone in the wake of the car. Growth of particles within the vehicle exhaust plume up to detectable size depends crucially on the relationship between the mass rate of gaseous precursor emissions and rapid dilution. Chassis dynamometer measurements indicate that emissions of possible hydrocarbon precursors are significantly enhanced under high engine load conditions and high engine speed. On the basis of results obtained for a diesel passenger car, the contributions from light diesel vehicles to the observed abundance of measured nucleation-mode particles near busy roads might be attributable to the impact of two different time scales: (1) a short one within the plume, marked by sufficient precursor emissions and rapid dilution; and (2) a second and comparatively long time scale resulting from the mix of different precursor sources and the impact of atmospheric chemistry. IMPLICATIONS Volatile nucleation-mode particles still dominate curbside size distributions. In contrast to nonvolatile vehicle particle number emission factors, the formation of volatile curbside particle number concentrations depends on processes that cannot be reproduced on vehicle test benches in a reasonably economic way. Greater understanding of formation processes and subsequent growth, chemical composition, and the impact of volatile precursor mix is needed to properly evaluate health effects. An integrated approach is necessary when assessing emissions from different sources and measures.
Investigation of ultrafine particle formation during diesel exhaust dilution
Environmental science & technology, 1999
Measurements of the size distribution of particles emitted from a modern heavy duty diesel engine using fuel with a sulfur content of between 0.03 and 0.05% by mass have been made under constant engine operating conditions, but with variations in the humidity of dilution air and dilution ratio prior to particle size measurement. The results show clearly that the measured size distribution is crucially dependent upon the conditions of dilution, hence creating real difficulties for comparison of data between different investigators. Conditions of high dilution ratio and high relative humidity both tend to favor the production of nanoparticles, especially within the range below 50 nm diameter. Application of homogeneous nucleation theory shows that nanoparticle production during dilution is qualitatively consistent with the production of sulfuric acid, but the predicted nucleation rates are lower than those measured, in common with studies of nucleation in the atmosphere. Chemical analysis of size-fractionated particles shows enhancement of sulfate concentrations in humid dilution conditions and at high dilution ratios consistent with the above mechanism. The possible role of semivolatile organic compounds in these processes has not been investigated.
Composition of Semi-volatile Particles from Diesel Exhaust
SAE Technical Paper Series, 2005
Vehicle exhaust particles from diesel passenger vehicles were studied in terms of volatility and chemical composition. Condensation of semi-volatile compounds leads to particle growth during exhaust dilution and cooling. The particle growth was observed to be particle surface related. At higher vehicle speed and load some of the semi-volatile material forms nucleation particles that are dominating the particle number concentration. The nucleation mode is completely volatile at 180°C and consists mainly of sulfate. The amount of organic material is smaller. The organics/sulfate ratio is larger for the soot mode indicating an earlier condensation process of organics before they are incorporated in the nucleation process. Under typical atmospheric dilution conditions most of the semi-volatile material is present in the soot mode. The semi-volatile material evaporates at temperature between 130°C and 180°C. Thermal treatment using a thermodenuder enables complete evaporation of the nucleation particles, however not all material from the soot particles is removed.
Influence of Diesel Fuel Sulfur on Nanoparticle Emissions from City Buses
Environmental Science & Technology, 2006
Particle emissions from twelve buses, operating alternately on low sulfur (LS; 500 ppm) and ultralow sulfur (ULS; 50 ppm) diesel fuel, were monitored. The buses were 1-19 years old and had no after-treatment devices fitted. Measurements were carried out at four steady-state operational modes on a chassis dynamometer using a mini dilution tunnel (PM mass measurement) and a Dekati ejector diluter as a secondary diluter (SMPS particle number). The mean particle number emission rate (s -1 ) of the buses, in the size range 8-400 nm, using ULS diesel was 31% to 59% lower than the rate using LS diesel in all four modes. The fractional reduction was highest in the newest buses and decreased with mileage up to about 500 000 km, after which no further decrease was apparent. However, the mean total suspended particle (TSP) mass emission rate did not show a systematic difference between the two fuel types. When the fuel was changed from LS to ULS diesel, the reduction in particle number was mainly in the nanoparticle size range. Over all operational modes, 58% of the particles were smaller than 50 nm with LS fuel as opposed to just 45% with ULS fuel, suggesting that sulfur in diesel fuel was playing a major role in the formation of nanoparticles. The greatest influence of the fuel sulfur content was observed at the highest engine load, where 74% of the particles were smaller than 50 nm with LS diesel compared to 43% with ULS diesel.
Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering, 2017
High-sulphur and medium-sulphur diesel fuels are still used in several countries. Although diesel particulate filter technology for on-road diesel engines has existed since 1989, the availability of high-sulphur and medium-sulphur diesel fuels in the market causes delays in the use of catalysed filter technologies. However, the situation in places such as Tehran is considered unhealthy because of particles and black carbon, and full distribution of ultra-low-sulphur diesel is awaited eagerly. The purpose of this study is to investigate the effect of the sulphur content in fuels on the gaseous and solid exhaust emissions of a 220 kW Euro II engine equipped with a sintered metal active–passive filter, focusing on the regeneration phenomenon. The results show that the efficiency for filtering the maximum number of particles was 99.9% and that the average was above 99% for steady-state operating conditions for both high-sulphur diesel (7700 ppm) and medium-sulphur diesel (229 ppm). The ...
Investigation of Diesel Nanoparticle Nucleation Mechanisms
Aerosol Science and Technology, 2008
Most of the nanoparticle number emissions from diesel engines are found in the nucleation mode (D p <∼ 30 nm). These nanoparticles are mainly formed by nucleation as diesel engine exhaust gas cools and dilutes in the atmosphere. Diesel nanoparticles have raised concerns because of their suspected human health effects. There are two main theories describing diesel nanoparticle nucleation: homogeneous nucleation, most likely binary of sulfuric acid and water, and ion-induced nucleation. In this study we assess the likelihood of the ionic mechanism.
Sulfur Driven Nucleation Mode Formation in Diesel Exhaust under Transient Driving Conditions
Environmental Science & Technology, 2014
Sulfur driven diesel exhaust nucleation particle formation processes were studied in an aerosol 16 laboratory, on engine dynamometers, and on the road. All test engines were equipped with a 17 combination of a diesel oxidation catalyst (DOC) and a partial diesel particulate filter (pDPF). At steady 18 operating conditions the formation of semi-volatile nucleation particles directly depended on SO 2 19 conversion in the catalyst. The nucleation particle emission was most significant after a rapid increase in 20 engine load and exhaust gas temperature. Results indicate that the nucleation particle formation at 21 transient driving conditions does not require compounds such as hydrocarbons or sulfated hydrocarbons, 22 but on the other hand, it cannot be explained only by the nucleation of sulfuric acid. A real-world 23 exhaust study with a heavy duty diesel truck showed that the nucleation particle formation occurs even 24 with ultra-low sulfur diesel fuel, even at downhill driving conditions, and that nucleation particles can 25 contribute 60% of total particle number emissions. In general, due to sulfur storage and release within 26 the exhaust aftertreatment systems and transients in driving, emissions of nucleation particles can even 27 be the dominant part of modern diesel vehicle exhaust particulate number emissions. 28
Atmospheric Chemistry and Physics Discussions, 2015
A high concentration of volatile nucleation mode particles (NUP) formed in the atmosphere when the exhaust cools and dilutes has hazardous health effects and it impairs the visibility in urban areas. Nucleation mechanisms in diesel exhaust are only poorly understood. We performed model studies using two sectional aerosol dynamics process models AEROFOR and MAFOR on the formation of particles in the exhaust of a diesel engine, equipped with an oxidative after-treatment system and running with low fuel sulfur content (FSC) fuel, under laboratory sampling conditions where the dilution system mimics real-world conditions. Different nucleation mechanisms were tested. Based on the measured gaseous sulfuric acid (GSA) and non-volatile core and soot particle number concentrations of the raw exhaust, the model simulations showed that the best agreement between model predictions and measurements in terms of particle number size distribution was obtained by barrier-free heteromolecular homogeneous nucleation between the GSA and a semivolatile organic vapour combined with the homogeneous nucleation of GSA alone. Major growth of the particles was predicted to occur due to the similar organic vapour at concentrations of (1−2)×10 12 cm −3. The pre-existing core and soot mode concentrations had an opposite trend on the NUP formation, and the maximum NUP formation was predicted if a diesel particle filter (DPF) was used. On the other hand, the model predicted that the NUP formation ceased if the GSA concentration in the raw exhaust was less than 10 10 cm −3 , which was the case when biofuel was used.
Environmental …, 2001
Diesel engines are known to emit high number concentrations of nanoparticles (diameter < 50 nm), but the physical and chemical mechanisms by which they form are not understood. Information on chemical composition is lacking because the small size, low mass concentration, and potential for contamination of samples obtained by standard techniques make nanoparticles difficult to analyze. A nanodifferential mobility analyzer was used to size-select nanoparticles (mass median diameter ∼25-60 nm) from diesel engine exhaust for subsequent chemical analysis by thermal desorption particle beam mass spectrometry. Mass spectra were used to identify and quantify nanoparticle components, and compound molecular weights and vapor pressures were estimated from calibrated desorption temperatures. Branched alkanes and alkyl-substituted cycloalkanes from unburned fuel and/or lubricating oil appear to contribute most of the diesel nanoparticle mass. The volatility of the organic fraction of the aerosol increases as the engine load decreases and as particle size increases. Sulfuric acid was also detected at estimated concentrations of a few percent of the total nanoparticle mass. The results are consistent with a mechanism of nanoparticle formation involving nucleation of sulfuric acid and water, followed by particle growth by condensation of organic species.
Environmental Science & Technology, 2005
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 lowvolatile) 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 lowvolatile) 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 lowsulfur fuel.