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![SO2 to SO3 conversion estimation by combining data from different studies. Noble metals/washcoats considered: Pt/SiO 2 (Xue et al. [25]), Pt2/Al2O3 (Wyatt et al. [27]), Pt/Al2O3 with different compositions (Deeba et al. [28]), Pt/Al 2 O 3 (Horiuchi et al. [29]).](profile/Barouch-Giechaskiel-2/publication/288809600/figure/fig4/AS:446473268666371@1483458930736/SO2-to-SO3-conversion-estimation-by-combining-data-from-different-studies-Noble.png)
SO2 to SO3 conversion estimation by combining data from different studies. Noble metals/washcoats considered: Pt/SiO 2 (Xue et al. [25]), Pt2/Al2O3 (Wyatt et al. [27]), Pt/Al2O3 with different compositions (Deeba et al. [28]), Pt/Al 2 O 3 (Horiuchi et al. [29]).
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This work studies the formation of nucleation mode (NM) particles from a Euro 3 passenger car operating on 280 ppm wt. sulfur fuel, during on-road plume chasing and in the laboratory. The vehicle produced a distinct NM when its speed exceeded 100 km/h in both sampling environments. A higher particle number (up to 8 times) after 4 min at constant sp...
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Context 1
... extent of the conversion depends mainly on the exhaust gas temperature, the type of noble metal used and the loading and composition of the washcoat. The conversion as a function of temperature generally follows the pattern shown in Figure 8. Data are based on the thermodynamic equilibrium of eq. 1 (for 50 ppm SO 2 according to Xue et al. [25] and Henk et al. [26]), laboratory tests [27,28], and a diesel engine measurement [29] for Pt/Al 2 O 3 and Pt/SiO 2 catalysts. ...
Context 2
... the light of the above, the tests presented in Figures 2-4 for vehicle speed below 100 km/h, correspond to a catalyst temperature below 200-250°C (exhaust gas temperature ~160°C) and hence a negligible conversion of SO 2 to SO 3 is expected based on Figure 8. The conversion though increases at higher speeds/higher temperatures. ...
Context 3
... Figure 6, NM started to appear after 20 min at 100 km/h, following a 30 min conditioning at 120 km/h. A simplified calculation taking into account the fuel sulfur content, a sulfur to sulfate conversion of 2% (at ~200 °C - Figure 8) and λ=2.5 results in ~1 mg/min sulfate emission which translates into 20 mg total sulfate production over those 20 min, before NM appears. Similarly, Vogt et al. [7] when chasing the plume of a Euro 3 vehicle operating on 350 ppm sulfur fuel noticed NM formation after 15 min at 100 km/h when a test at 120 km/h had preceded, which translates into similar total sulfate production to the current study. ...
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... The particle mass (PM) formed from the precursor gases via nucleation and condensation as the exhaust gas dilutes and cools upon exiting the tailpipe is not fully considered to be PN measurements; however the regulation for gaseous hydrocarbons limits the amount of precursor gases produced by the vehicle. The amount of secondary particle matter (both in terms of PN and PM) formed from precursor gases can be considerable (Karjalainen et al., 2014b;Keskinen and Rönkkö, 2010;Kittelson, 1998;Giechaskiel et al., 2007). However, the amount of secondary PM has decreased in the 21st century as the fuel does not contain as much sulfur as before. ...
Vehicle chase measurements used for studying real-world emissions apply various methods for calculating emission factors. Currently available methods are typically based on the dilution of emitted carbon dioxide (CO2) and the assumption that other emitted pollutants dilute similarly. A problem with the current methods arises when the studied vehicle is not producing CO2, e.g. during engine-motoring events, such as on downhill sections. This problem is also encountered when studying non-exhaust particulate emissions, e.g. from electric vehicles. In this study, we compare multiple methods previously applied for determining the dilution ratios. Additionally, we present a method applying multivariate adaptive regression splines and a new method called near-wake dilution. We show that emission factors for particulate emissions calculated with both methods are in line with the current methods for vehicles producing CO2. In downhill sections, the new methods were more robust to low CO2 concentrations than some of the current methods. The methods introduced in this study can hence be applied in chase measurements with changing driving conditions and be possibly extended to estimate non-exhaust emissions in the future.
... The limits for PN only consider nonvolatile particles, and the particle mass (PM) formed from the precursor gases via nucleation and condensation as the exhaust gas dilutes and cools upon exiting the tailpipe is mostly neglected. The amount of particle matter (both in terms of PN and PM) formed this way can be considerable (Karjalainen et al., 2014b;Keskinen and Rönkkö, 2010;Kittelson, 1998;Giechaskiel et al., 2007). ...
Vehicle chase measurements used for studying real-world emissions apply various methods for calculating emission factors. Currently available methods are typically based on the dilution of emitted carbon dioxide (CO2) and the assumption that other emitted pollutants dilute similarly. A problem with the current methods arises when the studied vehicle is not producing CO2, e.g., during engine motoring events, such as on downhills. This problem is also encountered when studying non-exhaust emissions, e.g., from electric vehicles. In this study, we compare multiple methods previously applied for determining the dilution ratios. Additionally, we present a method applying Multivariate Adaptive Regression Splines and a new method called Near-Wake Dilution. We show that emission factors calculated with both methods are in line with the current methods with vehicles producing CO2. In downhill sections, the new methods were more robust to low CO2 concentrations than some of the current methods. The methods introduced in this study can hence be applied in chase measurements with changing driving conditions and be possibly extended to estimate non-exhaust emissions in the future.
... The PN emission is low at operating points with very high loads. There is also a marked tendency to increase PN emission with speed, probably because the formation of particle material benefits from the shorter residence times in high-speed regimes [40]. Although the factors and processes that determine the formation of particle matter are complex and still a subject of discussion, it has been mainly attributed to the fuel and the lubricant. ...
div class="section abstract"> Pollutant emissions from vehicles depend on both fuel and driving conditions. This work investigates the impact of using a 20% (V/V) biodiesel blend (B20) on the CO<sub>2</sub>, NOx, and particle number emissions of a light-duty diesel vehicle, using GT-Suite® software. Combustion parameters and emissions were experimentally measured in a Cummins ISF 2.8 L diesel engine and used as inputs for the model. Vehicle simulations using ULSD and B20 were performed for the standard WLTC driving cycle as well as driving cycles representative of Andean cities, that include steep road slopes and heavy traffic. Additionally, simulations considered three gear-shifting strategies, one based on dynamic gear selection and two on imposed-speed thresholds for each gear shift.
Results show that using B20 decreases the particle number emissions in 39 – 79% for the tested driving cycles and gear-shifting strategies. Meanwhile, fuel change showed no significant effect on CO<sub>2</sub>, and NOx emissions were slightly increased between 3 and 11% in the studied cases. Higher emission factors for all pollutants were found with the Andean driving cycles when compared to WLTC, increasing up to 204% in the scenario that included road slope. Regarding the gear-shifting strategies, imposed-speed strategy NEDC led to the lowest fuel consumption and PN emissions, and NBR led to the lowest NOx emissions, while the dynamic strategy led to the highest NOx emissions, with a fuel consumption very similar to NBR strategy.
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... The formation of volatile particles depends on the exhaust gas temperature. The general understanding is that they appear when the temperature is appropriate to convert enough SO2 from SO3 at the DOC [39,[41][42][43] and/or to desorb enough sulfates from the aftertreatment devices [44][45][46][47]. As the exhaust gas is cooled down in the diluter, these sulfates form nucleation mode particles, which grow to the measurement range of the instruments, especially in the presence of hydrocarbons. ...
... The formation of volatile particles depends on the exhaust gas temperature. The general understanding is that they appear when the temperature is appropriate to convert enough SO 2 from SO 3 at the DOC [39,[41][42][43] and/or to desorb enough sulfates from the aftertreatment devices [44][45][46][47]. As the exhaust gas is cooled down in the diluter, these sulfates form nucleation mode particles, which grow to the measurement range of the instruments, especially in the presence of hydrocarbons. ...
... The literature has also highlighted the need of stabilization time to the variability of the volatile particles measurements [56]: Many studies have found that it can take more than 1 h to stabilize the concentration of volatile particles [42,57], similar to what was demonstrated in our study. Other studies have also found higher concentration of volatile particles at the dilution tunnel compared to the tailpipe due to the desorption from the tube between the vehicle and the tailpipe [9,58]. ...
Featured Application: The particle number emissions of two Diesel vehicles, weighted with one Diesel particulate filter (DPF) active regeneration, were around 2 × 10^11 #/km for solid particles but 20-300 × 10^11 #/km for volatile particles. Abstract: The solid particle number emissions of Diesel vehicles are very low due to the particulate filters as exhaust aftertreatment devices. However, periodically, the trapped particles are oxidized (i.e., active regeneration) in order to keep the backpressure at low levels. The solid particle number emissions during regenerations are only partly covered by the regulations. Many studies have examined the emissions during regenerations, but their contribution to the overall emissions has not been addressed adequately. Furthermore, the number concentration of volatile particles, which is not included in the regulations, can be many of orders of magnitude higher. In this study, the particulate emissions of two light-duty Euro 6 vehicles were measured simultaneously at the tailpipe and the dilution tunnel. The results showed that the weighted (i.e., considering the emissions during regeneration) solid particle number emissions remained well below the applicable limit of 6 × 10^11 #/km (solid particles > 23 nm). This was true even when considering solid sub-23 nm particles. However , the weighted volatile particle number emissions were many orders of magnitude higher, reaching up to 3 × 10^13 #/km. The results also confirmed the equivalency of the solid particle number results between tailpipe and dilution tunnel locations. This was not the case for the volatile particles which were strongly affected by desorption phenomena. The high number of volatiles during re-generations even interfered with the 10 nm solid particle number measurements at the dilution tunnel , even though a catalytic stripper equipped instrument was also used in the dilution tunnel.
... Sometimes, larger coarse mode particles appear originating from the crankcase ventilation, wear, or soot re-entrainment [103,178]. Regarding the precursor gases, oxidation catalysts reduced hydrocarbons, but in many cases increased the SO 2 to SO 3 conversion and NH 3 [179,180]. NO x reduction aftertreatment decreased NO x [181]. ...
... Sulfuric acid is the key nucleating compound as measurements [189] and models show [190][191][192][193]. With low sulfur fuels, lubricants play an important role [189,194] and aftertreatment devices enhance the SO 2 to SO 3 conversion [179]. Relatively high SO 2 concentrations can be measured at diesel vehicles compared to gasoline and gas engines due to the higher oxidative environment in the exhaust [58]. ...
... Hydrocarbons are then necessary for the subsequent growth of such sulfate core particles [158,195,196]. A nucleation mode can be typically seen with high sulfur fuel (300 ppm) and/or lubricant [189,197], high speeds (exhaust gas temperatures) [179,198], and during regenerations [199,200] (see also discussion in [14]). Without aftertreatment devices, hydrocarbons (alkanes, PAHs) may also form a separate nucleation mode [187]. ...
Road transport significantly contributes to air pollution in cities. Emission regulations have led to significantly reduced emissions in modern vehicles. Particle emissions are controlled by a particulate matter (PM) mass and a solid particle number (SPN) limit. There are concerns that the SPN limit does not effectively control all relevant particulate species and there are instances of semi-volatile particle emissions that are order of magnitudes higher than the SPN emission levels. This overview discusses whether a new metric (total particles, i.e., solids and volatiles) should be introduced for the effective regulation of vehicle emissions. Initially, it summarizes recent findings on the contribution of road transport to particle number concentration levels in cities. Then, both solid and total particle emission levels from modern vehicles are presented and the adverse health effects of solid and volatile particles are briefly discussed. Finally, the open issues regarding an appropriate methodology (sampling and instrumentation) in order to achieve representative and reproducible results are summarized. The main finding of this overview is that, even though total particle sampling and quantification is feasible, details for its realization in a regulatory context are lacking. It is important to define the methodology details (sampling and dilution, measurement instrumentation, relevant sizes, etc.) and conduct inter-laboratory exercises to determine the reproducibility of a proposed method. It is also necessary to monitor the vehicle emissions according to the new method to understand current and possible future levels. With better understanding of the instances of formation of nucleation mode particles it will be possible to identify its culprits (e.g., fuel, lubricant, combustion, or aftertreatment operation). Then the appropriate solutions can be enforced and the right decisions can be taken on the need for new regulatory initiatives, for example the addition of total particles in the tailpipe, decrease of specific organic precursors, better control of inorganic precursors (e.g., NH3, SOx), or revision of fuel and lubricant specifications.
... Diesel vehicles have high air-fuel ratio and condensation is unlikely. Volatile nucleation mode particles can be seen with high exhaust gas temperature and high sulfur content [68], but at other conditions are less likely. For spark ignition engines nucleation particles at low idle are also not probable [69]. ...
For the type approval of compression ignition (diesel) and gasoline direct injection vehicles, a particle number (PN) limit of 6 × 10 ^11 p/km is applicable. Diesel vehicles in circulation need to pass a periodical technical inspection (PTI) test, typically every two years, after the first four years of circulation. However, often the applicable smoke tests or on-board diagnostic (OBD) fault checks cannot identify malfunctions of the diesel particulate filters (DPFs). There are also serious concerns that a few high emitters are responsible for the majority of the emissions. For these reasons, a new PTI procedure at idle run with PN systems is under investigation. The correlations between type approval cycles and idle emissions are limited, especially for positive (spark) ignition vehicles. In this study the type approval PN emissions of 32 compression ignition and 56 spark ignition vehicles were compared to their idle PN concentrations from laboratory and on-road tests. The results confirmed that the idle test is applicable for diesel vehicles. The scatter for the spark ignition vehicles was much larger. Nevertheless, the proposed limit for diesel vehicles was also shown to be applicable for these vehicles. The technical specifications of the PTI sensors based on these findings were also discussed.
... Other materials such as zinc, nickel, chromium, and copper are used either as stand-alone scavengers or as promoters, to modify trap performance, strengthen desired reactions, and influence the adsorption/desorption temperatures. Figure 5b summarizes SO 2 to SO 3 conversion efficiencies from the literature of commonly used oxidation catalysts (based also on the review in [78]). The space velocity was around 35,000-50,000 h −1 . ...
Vehicle regulations include limits for non-volatile particle number emissions with sizes larger than 23 nm. The measurements are conducted with systems that remove the volatile particles by means of dilution and heating. Recently, the option of measuring from 10 nm was included in the Global Technical Regulation (GTR 15) as an additional option to the current >23 nm methodology. In order to avoid artefacts, i.e., measuring volatile particles that have nucleated downstream of the evaporation tube, a heated oxidation catalyst (i.e., catalytic stripper) is required. This review summarizes the studies with laboratory aerosols that assessed the volatile removal efficiency of evaporation tube and catalytic stripper-based systems using hydrocarbons, sulfuric acid, mixture of them, and ammonium sulfate. Special emphasis was given to distinguish between artefacts that happened in the 10–23 nm range or below. Furthermore, studies with vehicles’ aerosols that reported artefacts were collected to estimate critical concentration levels of volatiles. Maximum expected levels of volatiles for mopeds, motorcycles, light-duty and heavy-duty vehicles were also summarized. Both laboratory and vehicle studies confirmed the superiority of catalytic strippers in avoiding artefacts. Open issues that need attention are the sulfur storage capacity and the standardization of technical requirements for catalytic strippers.
... In this case, the outlet SO 2 concentration was 485 ppm indicating that 3.5% of SO 2 was converted to SO 3 in agreement to the 4% difference that was found. The SO 2 to SO 3 conversion in an oxidation catalyst should initiate at T > 200 C ( Giechaskiel et al. 2007). In our tests, the aerosol flow overcomes this temperature in all operating conditions except for 15 (l/min) without preheating. ...
Solid particle number vehicle exhaust measurements necessitate an aerosol conditioning system that removes efficiently volatile particles, does not create artifacts and minimizes solid nucleation particle losses. Here, we present the development and evaluation of a catalytic stripper based on a unique dual-function monolithic reactor that oxidizes hydrocarbons and stores sulphur material. The catalytic stripper was tested for its tetracontane particle removal efficiency, sulphur adsorption capacity with sulphur dioxide, and particle penetration with solid CAST-generated particles. The optimal operation conditions were examined including different aerosol flows and configurations, i.e. as a stand-alone device and as part of a volatile removal system with a hot and a cold dilution stage upstream and downstream of the catalytic stripper, respectively. The catalytic stripper managed to comply with current legislation requirements for solid particle number measurements down to 23 nm as a stand-alone device and showed great potential as part of a volatile particle removal (VPR) system for measurements at least down to 10 nm. Finally, we compared the performance of two VPR systems that use the developed catalytic stripper (VPR-CS) and an evaporation tube (VPR-ET), respectively. Our results suggest that the VPR-CS exhibits higher volatile removal efficiency without creating artifacts while the particle losses are lower with the VPR-ET. Nevertheless, when measuring solid nucleation particles generated by a diesel engine with the VPR-CS, the measurement uncertainty was very low due to its high particle penetration fractions.
... The quantification of total PN concentration is difficult as their formation and concentration depends on many parameters, such as the after-treatment devices (e.g., [92]), the pre-conditioning and history of the vehicle (e.g., [93]), the fuel and the lubricant used (e.g., [94]), the ambient conditions (e.g., [95]), and the amount of soot present, since this promotes the competing process of condensation and adsorption instead of nucleation [96]. The regulated method uses constant volume sampling which means low dilution (around 6:1) at high exhaust flow rates and high dilution at low exhaust flow rates (>30:1). ...
... However, when the exhaust gas temperature increases, a high concentration of nucleation mode particles is measured (see last part of Figure 11). This is attributed to the formation of sulfuric acid particles due to the high conversion of SO 2 to SO 3 at the catalyst of the vehicle (see [82,92,93,97,103]). Note that the SPN concentrations remained at relatively low levels. ...
... However, when the exhaust gas temperature increases, a high concentration of nucleation mode particles is measured (see last part of Figure 11). This is attributed to the formation of sulfuric acid particles due to the high conversion of SO2 to SO3 at the catalyst of the vehicle (see [82,92,93,97,103]). Note that the SPN concentrations remained at relatively low levels. ...
Particulate matter (PM), and in particular ultrafine particles, have a negative impact on human health. The contribution of vehicle PM emissions to air pollution is typically quantified with emission inventories, which need vehicle emission factors as input. Heavy-duty vehicles, although they represent a small percentage of the vehicle population in nearly every major country, contribute the majority of the on-road PM emissions. However, the published data of modern heavy-duty vehicle emissions are scarce, and for the newest Euro VI technologies, almost non-existent. The main objective of this paper is to present Solid Particle Number (SPN) emission factors from Euro VI heavy-duty vehicles using diesel, Compressed Natural Gas (CNG), or Liquefied Natural Gas (LNG). Urban, rural and motorway (highway) emissions were determined on the road at various European cities using SPN Portable Emission Measurement Systems (PEMS). Additional tests on a heavy-duty chassis dynamometer showed that the solid sub-23 nm fraction, which is not covered at the moment in the European regulation, is high, especially for CNG engines. The significant contribution of regeneration events and the effect of ambient temperature and engine cold-start on particle emissions were also discussed.
... In the oxidation catalyst, sulphur dioxide of exhaust gas can be converted to sulphur trioxide under high exhaust temperatures. (Giechaskiel et al., 2007) Thus, the nucleation mode of particles downstream the SCR catalyst may be caused by sulphuric acid originating from reaction between sulphur trioxide and water vapor (Vaaraslahti et al., content of fuel or lubricating oil were not observed to change during the study. ...
The main objective of this study was to find out how the non-road diesel engine running period of 500 hours affects the exhaust particle size distribution. By means of an engine exhaust particle sizer (EEPS), particle number was measured before the endurance test and after 250 and 500 hours of engine operation. The size distributions were determined at full and 75% loads both at rated and at intermediate speeds. The soot, gaseous emissions and the basic engine performance were also determined and lubricating oil was analysed a few times during the running period. A blend of low-sulphur fossil diesel and soybean methyl ester (B20) was used as fuel in the 4-cylinder, turbocharged, intercooled engine which was equipped with a diesel oxidation catalyst (DOC) and a selective catalytic reduction (SCR) system. All emissions were measured downstream the catalysts. During the 500 hours of operation, the particle number increased considerably within an approximate size range of 7 to 30 nm. Between the initial and final measurements, no notable differences were observed in the particle number emissions within a particle size range of 50 to 200 nm. The copper content of lubricating oil also increased significantly during the 500 hours’ experiment. One possible reason for the substantial increase in the nucleation mode particle number was assumed to be copper, which is one of the metallic elements originating from engine wear. The engine efficiency was almost equal, and the differences both in smoke and hydrocarbon emission were negligible throughout the 500 hours’ experiment.
