Physico-Chemical Characterization of Fine and Ultrafine Particles Emitted during Diesel Particulate Filter Active Regeneration of Euro5 Diesel Vehicles

Abstract

Diesel particulate filters (DPFs) are commonly employed in modern passenger cars to comply with current particulate matter (PM) emission standards. DPFs requires periodic regeneration to remove the accumulated matter. During the process, high-concentration particles, in both nucleation and accumulation modes, are emitted. Here, we report new information on particle morphology and chemical composition of fine (FPs) and ultrafine particles (UFPs) measured downstream of the DPF during active regeneration of two Euro 5 passenger cars. The first vehicle was equipped with a close-coupled diesel oxidation catalyst (DOC) and noncatalyzed DPF combined with fuel borne catalyst and the second one with DOC and a catalyzed-diesel particle filter (CDPF). Differences in PM emission profiles of the two vehicles were related to different after treatment design, regeneration strategies, and vehicle characteristics and mileage. Particles in the nucleation mode consisted of ammonium bisulfate, sulfate and sulfuric acid, suggesting that the catalyst desulfation is the key process in the formation of UFPs. Larger particles and agglomerates, ranging from 90 to 600 nm, consisted of carbonaceous material (soot and soot aggregates) coated by condensable material including organics, ammonium bisulfate and sulfuric acid. Particle emission in the accumulation mode was due to the reduced filtration efficiency (soot cake oxidation) throughout the regeneration process.

Technical note: Emission factors, chemical composition and morphology of particles emitted from Euro 5 diesel and gasoline light duty vehicles during transient cycles

“…The mass spectra were characterized by the ion fragments CnH + 2n+1 (m/z = 29, 43, 57, 71, 85…) typical of saturated alkyl compounds (n-alkanes and branched alkanes), CnH + 2n−1 (m/z = 27, 41, 55, 69, 83, 97…) typical of unsaturated aliphatic compounds (cycloalkanes, alkenes), and CnH + 2n−3 (m/z = 67, 81, 95, 109…) typical of bicycloalkanes and alkynes (McLafferty and Turecek, 1993). These spectra are consistent with the signatures found in both gasoline and diesel exhaust emissions (e.g., Canagaratna et al, 2004;Mohr et al, 2009;Chirico et al, 2011;Platt et al, 2013;Collier et al, 2015;Dallmann et al, 2014;R'Mili et al, 2018), and arise from both unburned fuel, lubricating oil, and their partially oxidized products (Maricq, 2007).…”

“…The emission of sulfate containing particles from the two CDPF vehicles was explained by the presence of the catalyst on the DPF walls. It has been proposed that during acceleration or hot engine combustion periods sulfur can be released and converted into SO3 by the catalyst, forming successively sulfuric acid and/or bisulfate/sulfate ammonium ultrafine particles (e.g., Bikas and Zervas, 2007;Bergmann et al, 2009;Arnold et al, 2012;R'Mili et al, 2018).…”

“…At the same time, modern vehicles produce also CO2 and BC which impact the climate (Lelieveld et al, 2019). Vehicle emissions received a lot of attention in the last years and diverse approaches have been used for their quantification, including tunnel studies (Grieshop et al, 2006;Lawrence et al, 2013;Smit et al, 2017), remote sensing or roadside measurements (Jimenez et al, 2000;Peitzmeier et al, 2017;Ropkins et al, 2017), on road (chase) measurements (Canagaratna et al, 2004;Morawska et al, 2007;Hudda et al, 2013;Karjalainen et al, 2014), on board measurements (Huo et al, 2012;Chikhi et al, 2014) and chassis dynamometer facilities (e.g., Andersson et al, 2014;Collier et al, 2015;Karjalainen et al, 2014;Saliba et al, 2017;Jaworski et al, 2018;R'Mili et al, 2018).…”

Ultrafine particles: unique physicochemical properties relevant to health and disease

“…Since 1993, European transportation regulations have concentrated on reducing PM mass, CO 2 , and NO X emissions 49 . In addition to these regulations, minimizing sulfur in diesel or gasoline fuel has resulted in reduced PM emissions in all engines 50 .…”

“…Regeneration, or oxidizing the deposited particles, is intermittently needed to avoid excessive back pressure on the engine. Through the regeneration process, the soot cake is oxidized into gas, and smaller UFPs are released into the ambient air 49 . Passive regeneration takes place when the temperature within the DPF is between 275 and 360°C.…”