Low-energy photoelectron transmission through aerosol overlayers

The transmission of low-energy (<1.8eV) photoelectrons through the shell of core-shell aerosol particles is studied for liquid squalane, squalene, and DEHS shells. The photoelectrons are exclusively formed in the core of the particles by two-photon ionization. The total photoelectron yield recorded as a function of shell thickness (1-80nm) shows a bi-exponential attenuation. For all substances, the damping parameter for shell thicknesses below 15nm lies between 8 and 9nm, and is tentatively assigned to the electron attenuation length at electron kinetic energies of ~0.5-1eV. The significantly larger damping parameters for thick shells (> 20nm) are presumably a consequence of distorted core-shell structures. A first comparison of aerosol and traditional thin film overlayer methods is provided

The Spider DMA: A miniature radial differential mobility analyzer

The Spider differential mobility analyzer (DMA) is a novel, miniaturized radial DMA developed to provide size classification in the 10–500 nm range for applications requiring high portability and time resolution. Its external dimensions are ∼12 cm in diameter by 6 cm in height (excluding tubing); it weighs ∼350 g, and is designed to operate at 0.6–1.5 L/min sheath and 0.3 L/min sample flowrates. It features a new sample inlet geometry that is designed to produce a uniform azimuthal particle distribution at the entrance of the classifier, optimized sample/sheath flow streams introduction in the classifier to minimize particle delays, and extension of the electric field interaction volume for ∼30% enhanced dynamic range. Based on three-dimensional finite element simulations of flows, electric fields, and particle trajectories, we demonstrate that the Spider DMA transfer functions can be predicted with high fidelity using a parameterized fit based on the Stolzenburg semi-analytical model. Experimental characterization of the instrument response with size-selected particles confirmed close agreement with model prediction; mobility size response is linear over three orders of magnitude in mobility span. Electrical ground shielding of the external surfaces of the DMA has been found to be necessary to avoid particle losses associated with field effects as the high voltage operating limit is approached. The mean deviation between the reference size of polystyrene latex spheres and the Spider DMA measurement is less than 2%, corroborating its high sizing precision and potential for high quality size distribution measurements

Characterization of laboratory and real driving emissions of individual Euro 6 light-duty vehicles – Fresh particles and secondary aerosol formation

Emissions from passenger cars are one of major sources that deteriorate urban air quality. This study presents characterization of real-drive emissions from three Euro 6 emission level passenger cars (two gasoline and one diesel) in terms of fresh particles and secondary aerosol formation. The gasoline vehicles were also characterized by chassis dynamometer studies. In the real-drive study, the particle number emissions during regular driving were 1.1–12.7 times greater than observed in the laboratory tests (4.8 times greater on average), which may be caused by more effective nucleation process when diluted by real polluted and humid ambient air. However, the emission factors measured in laboratory were still much higher than the regulatory value of 6 × 10^(11) particles km^(−1). The higher emission factors measured here result probably from the fact that the regulatory limit considers only non-volatile particles larger than 23 nm, whereas here, all particles (also volatile) larger than 3 nm were measured. Secondary aerosol formation potential was the highest after a vehicle cold start when most of the secondary mass was organics. After the cold start, the relative contributions of ammonium, sulfate and nitrate increased. Using a novel approach to study secondary aerosol formation under real-drive conditions with the chase method resulted mostly in emission factors below detection limit, which was not in disagreement with the laboratory findings

Molecular understanding of the suppression of new-particle formation by isoprene

Nucleation of atmospheric vapours produces more than half of global cloud condensation nuclei and so has an important influence on climate. Recent studies show that monoterpene (C10H16) oxidation yields highly oxygenated products that can nucleate with or without sulfuric acid. Monoterpenes are emitted mainly by trees, frequently together with isoprene (C5H8), which has the highest global emission of all organic vapours. Previous studies have shown that isoprene suppresses new-particle formation from monoterpenes, but the cause of this suppression is under debate. Here, in experiments performed under atmospheric conditions in the CERN CLOUD chamber, we show that isoprene reduces the yield of highly oxygenated dimers with 19 or 20 carbon atoms - which drive particle nucleation and early growth - while increasing the production of dimers with 14 or 15 carbon atoms. The dimers (termed C-20 and C-15, respectively) are produced by termination reactions between pairs of peroxy radicals (RO2 center dot) arising from monoterpenes or isoprene. Compared with pure monoterpene conditions, isoprene reduces nucleation rates at 1.7 nm (depending on the isoprene = monoterpene ratio) and approximately halves particle growth rates between 1.3 and 3.2 nm. However, above 3.2 nm, C-15 dimers contribute to secondary organic aerosol, and the growth rates are unaffected by isoprene. We further show that increased hydroxyl radical (OH center dot) reduces particle formation in our chemical system rather than enhances it as previously proposed, since it increases isoprene-derived RO2 center dot radicals that reduce C-20 formation. RO2 center dot termination emerges as the critical step that determines the highly oxygenated organic molecule (HOM) distribution and the corresponding nucleation capability. Species that reduce the C-20 yield, such as NO, HO2 and as we show isoprene, can thus effectively reduce biogenic nucleation and early growth. Therefore the formation rate of organic aerosol in a particular region of the atmosphere under study will vary according to the precise ambient conditions.Peer reviewe

Role of iodine oxoacids in atmospheric aerosol nucleation

Iodic acid (HIO₃) is known to form aerosol particles in coastal marine regions, but predicted nucleation and growth rates are lacking. Using the CERN CLOUD (Cosmics Leaving Outdoor Droplets) chamber, we find that the nucleation rates of HIO₃ particles are rapid, even exceeding sulfuric acid–ammonia rates under similar conditions. We also find that ion-induced nucleation involves IO₃⁻ and the sequential addition of HIO₃ and that it proceeds at the kinetic limit below +10°C. In contrast, neutral nucleation involves the repeated sequential addition of iodous acid (HIO₂) followed by HIO₃, showing that HIO₂ plays a key stabilizing role. Freshly formed particles are composed almost entirely of HIO₃, which drives rapid particle growth at the kinetic limit. Our measurements indicate that iodine oxoacid particle formation can compete with sulfuric acid in pristine regions of the atmosphere

Προηγμένες μέθοδοι δειγματοληψίας και ανίχνευσης για τη μέτρηση σωματιδιακών εκπομπών καυσαερίων

Scope of the present thesis was to explore and evaluate advanced sampling and detection methods for the measurement of exhaust particles, and with these to investigate the technologies and operation conditions that affect exhaust particle emissions of modern vehicles. The sampling method evaluated is the "Catalytic Stripper", which is employed for the removal of volatile particles from exhaust aerosol. This method provides additional features over the conventional volatile removal systems for the measurement of solid particle number emissions according to the EU regulation. The study includes a thorough characterization of the device in the laboratory and evaluates its performance against reference instruments in exhaust PM applications. The Pegasor Particle Sensor (PPS) along with the "dual PPS" measurement concept comprise the particle detection methods explored in this study. The PPS, an aerosol instrument based on diffusion charging, was calibrated for exhaust particle number and mass emissions measurements, and evaluated in vehicle exhaust applications. Moreover, a new measurement concept, the dual-PPS, was developed for improved measurement accuracy, offering real-time mean particle size estimation. The above sampling and detection methods were then utilized to explore the effects of various parameters on exhaust PM emissions, including exhaust aftertreatment devices, engine type, ambient temperature, drive prole, and fuel save technologies.Σκοπός της παρούσας διατριβής ήταν η μελέτη και αξιολόγηση προηγμένων μεθόδων δειγματοληψίας και ανίχνευσης για τη μέτρηση σωματιδιακών εκπομπών καυσαερίων από σύγχρονα οχήματα, και η εφαρμογή τους στη διερεύνηση των τεχνολογιών και παραμέτρων οι οποίες τις επηρεάζουν. Η μέθοδος δειγματοληψίας που αξιολογείται είναι ο Καταλυτικός Διαχωριστής, ένας καταλύτης μικρής κλίμακας με δυνατότητες οξείδωσης υδρογονανθράκων και αποθήκευσης θειικών συστατικών. Τα συγκεκριμένα χαρακτηριστικά δίνουν τη δυνατότητα εφαρμογής της συσκευής ως μεθόδου απομάκρυνσης πτητικών σωματιδίων, εναλλακτικής αυτής που ορίζει ο ισχύων ευρωπαϊκός κανονισμός για τη μέτρηση αριθμού στερεών σωματιδίων από κινητήρες και οχήματα. Η παρούσα μελέτη περιλαμβάνει τον λεπτομερή χαρακτηρισμό του καταλυτικού διαχωριστή στο εργαστήριο και αξιολόγηση της απόδοσής του σε τυπικές εφαρμογές μέτρησης. Οι μέθοδος ανίχνευσης σωματιδίων που μελετήθηκε είναι ο αισθητήρας «Pegasor Particle Sensor (PPS)». Η αρχή λειτουργίας του βασίζεται στην ηλεκτρική φόρτιση των σωματιδίων μέσω διάχυσης ιόντων. Ο αισθητήρας βαθμονομήθηκε και έπειτα αξιολογήθηκε σε εφαρμογές μέτρησης σωματιδιακών εκπομπών οχημάτων. Επιπρόσθετα, αναπτύχθηκε μια πρωτότυπη μέθοδος ανίχνευσης σωματιδίων, στην οποία δόθηκε η ενδεικτική ονομασία «dual PPS». Η μέθοδος αυτή δίνει τη δυνατότητα εκτίμησης του μέσου μεγέθους σωματιδίων, βάσει του οποίου μπορεί να γίνει ακριβέστερος υπολογισμός των σωματιδιακών συγκεντρώσεων. Μέσω της εφαρμογής των ανωτέρω μεθόδων δειγματοληψίας και μέτρησης, πραγματοποιήθηκε διερεύνηση των παραμέτρων οι οποίες επηρεάζουν τις σωματιδιακές εκπομπές μηχανοκίνητων οχημάτων. Σε αυτές περιλαμβάνονται οι συσκευές αντιρρύπανσης, ο τύπος κινητήρα, η θερμοκρασία περιβάλλοντος, το προφίλ οδήγησης, και οι τεχνολογίες εξοικονόμησης καυσίμου

Προηγμένες μέθοδοι δειγματοληψίας και ανίχνευσης για την μέτρηση σωματιδιακών εκπομπών καυσαερίων

Scope of the present thesis was to explore and evaluate advanced sampling and detection methods for the measurement of exhaust particles, and with these to investigate the technologies and operation conditions that affect exhaust particle emissions of modern vehicles. The sampling method evaluated is the "Catalytic Stripper", which is employed for the removal of volatile particles from exhaust aerosol. This method provides additional features over the conventional volatile removal systems for the measurement of solid particle number emissions according to the EU regulation. The study includes a thorough characterization of the device in the laboratory and evaluates its performance against reference instruments in exhaust PM applications. The Pegasor Particle Sensor (PPS) along with the "dual PPS" measurement concept comprise the particle detection methods explored in this study. The PPS, an aerosol instrument based on diffusion charging, was calibrated for exhaust particle number and mass emissions measurements, and evaluated in vehicle exhaust applications. Moreover, a new measurement concept, the dual-PPS, was developed for improved measurement accuracy, offering real-time mean particle size estimation. The above sampling and detection methods were then utilized to explore the effects of various parameters on exhaust PM emissions, including exhaust after treatment devices, engine type, ambient temperature, drive prole, and fuel save technologies.Σκοπός της παρούσας διατριβής ήταν η μελέτη και αξιολόγηση προηγμένων μεθόδων δειγματοληψίας και ανίχνευσης για τη μέτρηση σωματιδιακών εκπομπών καυσαερίων από σύγχρονα οχήματα, και η εφαρμογή τους στη διερεύνηση των τεχνολογιών και παραμέτρων οι οποίες τις επηρεάζουν. Η μέθοδος δειγματοληψίας που αξιολογείται είναι ο Καταλυτικός Διαχωριστής, ένας καταλύτης μικρής κλίμακας με δυνατότητες οξείδωσης υδρογονανθράκων και αποθήκευσης θειικών συστατικών. Τα συγκεκριμένα χαρακτηριστικά δίνουν τη δυνατότητα εφαρμογής της συσκευής ως μεθόδου απομάκρυνσης πτητικών σωματιδίων, εναλλακτικής αυτής που ορίζει ο ισχύων ευρωπαϊκός κανονισμός για τη μέτρηση αριθμού στερεών σωματιδίων από κινητήρες και οχήματα. Η παρούσα μελέτη περιλαμβάνει τον λεπτομερή χαρακτηρισμό του καταλυτικού διαχωριστή στο εργαστήριο και αξιολόγηση της απόδοσής του σε τυπικές εφαρμογές μέτρησης. Οι μέθοδος ανίχνευσης σωματιδίων που μελετήθηκε είναι ο αισθητήρας «Pegasor Particle Sensor (PPS)». Η αρχή λειτουργίας του βασίζεται στην ηλεκτρική φόρτιση των σωματιδίων μέσω διάχυσης ιόντων. Ο αισθητήρας βαθμονομήθηκε και έπειτα αξιολογήθηκε σε εφαρμογές μέτρησης σωματιδιακών εκπομπών οχημάτων. Επιπρόσθετα, αναπτύχθηκε μια πρωτότυπη μέθοδος ανίχνευσης σωματιδίων, στην οποία δόθηκε η ενδεικτική ονομασία «dual PPS». Η μέθοδος αυτή δίνει τη δυνατότητα εκτίμησης του μέσου μεγέθους σωματιδίων, βάσει του οποίου μπορεί να γίνει ακριβέστερος υπολογισμός των σωματιδιακών συγκεντρώσεων. Μέσω της εφαρμογής των ανωτέρω μεθόδων δειγματοληψίας και μέτρησης, πραγματοποιήθηκε διερεύνηση των παραμέτρων οι οποίες επηρεάζουν τις σωματιδιακές εκπομπές μηχανοκίνητων οχημάτων. Σε αυτές περιλαμβάνονται οι συσκευές αντιρρύπανσης, ο τύπος κινητήρα, η θερμοκρασία περιβάλλοντος, το προφίλ οδήγησης, και οι τεχνολογίες εξοικονόμησης καυσίμου

Impact of Selective Catalytic Reduction on Exhaust Particle Formation over Excess Ammonia Events

While the NH3 – SCR technology has become the dominant method for the abatement of NOx emitted by diesel trucks and passenger vehicles, the impact of urea injection on particle emissions has not yet been thoroughly studied. In this paper we examine a typical NH3 – SCR configuration operating under a simulated malfunctioning condition and we study its impact on both solid and total particle number and size distribution. The tests were conducted on a light-duty diesel engine operating at both low and high load points. Its aftertreatment consisted of a commercial Fe-Zeolite SCR catalyst in series with alternatively a catalytic and an uncoated diesel particle filter. Hydrocarbon post-injection was conducted in some tests to investigate the combined effect of ammonia injection during active DPF regeneration. On average the post-DPF solid >23nm and total <23nm particle number emissions were increased 129% (range 80-193%) and 67% (range 26-136%), respectively, with 100 ppm ammonia slip. This was explicitly related with the NH3 excess concentration, while the count median diameter of the particle distribution remained unaffected. Based on NH3 – SCR kinetics, the particles formed should consist of ammonium sulfates or nitrates. No interaction with the unburned HCs emitted during active DPF regeneration in terms of particle formation was observed.JRC.F.8-Sustainable Transpor