Fast oxidation of aerosol in a laminar flow tube

Ilmakehä on hapettava ympäristö. Hapetusreaktioiden seurauksena ilmakehään emittoituneet kaasut voivat osittain siirtyä hiukkasfaasiin, jolloin muodostuu sekundääristä hiukkasmassaa. Tämän diplomityön tarkoituksena oli tarkastella läpivirtauskammioiden toimintaa sekundäärisen hiukkasmassan muodostumisen tutkimisessa. Läpivirtauskammiot mahdollistavat ilmakehän useita päiviä kestävän hapetuksen simuloinnin lyhyessä ajassa. Kirjallisuusselvityksen perusteella läpivirtauskammiossa muodostunut sekundäärinen hiukkasmassa vastaa monilta ominaisuuksiltaan ilmakehässä muodostunutta sekundääristä hiukkasmassaa, vaikka kammion olosuhteet eroavatkin huomattavasti ilmakehän olosuhteista. Työn pääpaino oli TTY:n aerosolilaboratorion oman läpivirtauskammion TSARin ominaisuuksien karakterisointi. Mittausten perusteella virtaus TSARissa on lähes laminaarinen ja hiukkashäviöt ovat pieniä. Lisäksi TSARin hapetinaltistusta voidaan kontrolloida, ja maksimissaan saavutetaan altistus, joka vastaa noin viikon hapettumista ilmakehässä. Virtauksen laminaarisuuden ja nopean vasteajan takia TSARilla on mahdollista mitata sekundäärisen hiukkasmassan muodostumista myös nopeasti muuttuvissa päästölähteissä. Muilla läpivirtauskammioilla ei ole tehty tällaisia mittauksia, ja useimmilla se ei ole mahdollistakaan niiden epälaminaarisen virtauksen takia.Atmosphere is an oxidative environment. Some gases emitted to the atmosphere go through oxidation reactions and the reaction products may transfer to the particle phase. The mass transferred from gas to particle phase is called secondary aerosol mass. The aim of this thesis was to study flow tubes in secondary aerosol research. Flow tubes can be used to simulate oxidation that takes several days in the atmosphere so that the simulation takes only few minutes. The literature survey made in this work shows that the secondary aerosol formed in a flow tube resembles in many ways the secondary aerosol formed in the atmosphere, even though the conditions in flow tubes are remarkably different to the conditions in the atmosphere. The main part of this thesis was to characterize a flow tube called TSAR which is developed at the aerosol laboratory of TUT. Based on the measurements, the flow in TSAR is nearly laminar and particle losses are small. In addition, the oxidant exposure in TSAR can be controlled and the maximum exposure is equivalent to the oxidation that takes place in the atmosphere in approximately one week. Because of the laminarity of the flow and fast response time, TSAR can be used to measure the formation of secondary aerosol also in rapidly changing emission sources. This kind of measurement has not been done with other flow tubes, and for most of them it is not even possible because of their nonlaminar flow

Chemical and physical characterization of oil shale combustion emissions in Estonia

In this study, oil shale combustion emission measurements were conducted in a 60 kW(th) Circulating Fluidized Bed combustion test facility located in a laboratory-type environment. A comprehensive set of instruments including a nitrate-ion-based Chemical Ionization Atmospheric Pressure interface Time-of-Flight Mass Spectrometer, a Soot-Particle Aerosol Mass Spectrometer, and a Potential Aerosol Mass (PAM) chamber was utilized to investigate the chemical composition and concentrations of primary and secondary emissions in oil shale combustion. In addition, the size distribution of particles (2.5-414 nm) as well as concentration and composition of gaseous precursors were characterized. Altogether 12 different experiments were conducted. Primary emissions were studied in seven experiments and aged emissions using PAM chamber in five experiments. Combustion temperatures and solid fuel circulation rates varied between different experiments, and it was found that the burning conditions had a large impact on gaseous and particulate emissions. The majority of the combustion particles were below 10 nm in size during good burning whereas in poor burning conditions the emitted particles were larger and size distributions with 2-3 particle modes were detected. The main submicron particle chemical component was particulate organic matter (POM), followed by sulfate, chloride, nitrate, and ammonium. The secondary particulate matter formed in the PAM chamber was mostly POM and the concentration of POM was many orders of magnitude higher in aged aerosol compared to primary emissions. A significant amount of aromatic volatile organic compounds (VOCs) was measured as well. VOCs have the potential to go through gas-to-particle conversion during the oxidation process, explaining the observed high concentrations of aged POM. During good combustion, when VOC emissions were lower, over 80% of SO2 was oxidized either to gaseous H2SO4 (37%) or particulate sulfate (46%) in the PAM chamber, which mimic the atmospheric processes taken place in the ambient air after few days of emission.Peer reviewe

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

Exhaust particle number and composition for diesel and gasoline passenger cars under transient driving conditions : Real-world emissions down to 1.5 nm

Recent recommendations given by WHO include systematic measurements of ambient particle number concentration and black carbon (BC) concentrations. In India and several other highly polluted areas, the air quality problems are severe and the need for air quality related information is urgent. This study focuses on particle number emissions and BC emissions of passenger cars that are technologically relevant from an Indian perspective. Particle number and BC were investigated under real-world conditions for driving cycles typical for Indian urban environments. Two mobile laboratories and advanced aerosol and trace gas instrumentation were utilized. Our study shows that passenger cars without exhaust particle filtration can emit in real-world conditions large number of particles, and especially at deceleration a significant fraction of particle number can be even in 1.5–10 nm particle sizes. The mass concentration of exhaust plume particles was dominated by BC that was emitted especially at acceleration conditions. However, exhaust particles contained also organic compounds, indicating the roles of engine oil and fuel in exhaust particle formation. In general, our study was motivated by serious Indian air quality problems, by the recognized lack of emission information related to Indian traffic, and by the recent WHO air quality guidance; our results emphasize the importance of monitoring particle number concentrations and BC also in Indian urban areas and especially in traffic environments where people can be significantly exposed to fresh exhaust emissions.Peer reviewe

Effects of driving conditions on secondary aerosol formation from a GDI vehicle using an oxidation flow reactor

A comprehensive study on the effects of photochemical aging on exhaust emissions from a vehicle equipped with a gasoline direct injection engine when operated over seven different driving cycles was assessed using an oxidation flow reactor. Both primary emissions and secondary aerosol production were measured over the Federal Test Procedure (FTP), LA92, New European Driving Cycle (NEDC), US06, and the Highway Fuel Economy Test (HWFET), as well as over two real-world cycles developed by the California Department of Transportation (Caltrans) mimicking typical highway driving conditions. We showed that the emissions of primary particles were largely depended on cold-start conditions and acceleration events. Secondary organic aerosol (SOA) formation also exhibited strong dependence on the cold-start cycles and correlated well with SOA precursor emissions (i.e., non-methane hydrocarbons, NMHC) during both cold-start and hot-start cycles (correlation coefficients 0.95–0.99), with overall emissions of ∼68–94 mg SOA per g NMHC. SOA formation significantly dropped during the hot-running phases of the cycles, with simultaneous increases in nitrate and ammonium formation as a result of the higher nitrogen oxide (NOx) and ammonia emissions. Our findings suggest that more SOA will be produced during congested, slow speed, and braking events in highways.acceptedVersionPeer reviewe

Particle growth with photochemical age from new particle formation to haze in the winter of Beijing, China

Secondary aerosol formation in the aging process of primary emission is the main reason for haze pollution in eastern China. Pollution evolution with photochemical age was studied for the first time at a comprehensive field observation station during winter in Beijing. The photochemical age was used as an estimate of the time scale attributed to the aging process and was estimated from the ratio of toluene to benzene in this study. A low photochemical age indicates a fresh emission. The photochemical age of air masses during new particle formation (NPF) days was lower than that on haze days. In general, the strongest NPF events, along with a peak of the formation rate of 1.5 nm(J(1.5)) and 3 nmparticles (J(3)), were observed when the photochemical age was between 12 and 24 h while rarely took place with photochemical ages less than 12 h. When photochemical age was larger than 48 h, haze occurred and NPF was suppressed. The sources and sinks of nanoparticles had distinct relation with the photochemical age. Our results show that the condensation sink (CS) showed a valley with photochemical ages ranging from 12 to 24 h, while H2SO4 concentration showed no obvious trend with the photochemical age. The high concentrations of precursor vapours within an air mass lead to persistent nucleation with photochemical age ranging from 12 to 48 h in winter. Coincidently, the fast increase of PM2.5 mass was also observed during this range of photochemical age. Noteworthy, CS increased with the photochemical age on NPF days only, which is the likely reason for the observation that the PM2.5 mass increased faster with photochemical age on NPF days compared with other days. The evolution of particles with the photochemical age provides new insights into understanding how particles originating from NPF transform to haze pollution. (C) 2020 Elsevier B.V. All rights reserved.Peer reviewe

HELIOS/SICRIT/mass spectrometry for analysis of aerosols in engine exhaust

Current legislations typically characterize systems of aerosols, such as from vehicle exhaust, primarily by number concentration and size distributions. While potential health threats have a dependence on the particle size, the chemical composition of particles, including the volatile and semi-volatile components adsorbed onto nonvolatile particle cores present at roadside and urban settings, is important in understanding the impact of exhaust particles on health. To date, the only tools suitable for an online in-depth chemical aerosol characterization are aerosol mass spectrometers, which are typically composed of complex and cost intensive instrumentation. We present a new analytical system, which combines a novel inexpensive infrared-radiation-based evaporation system (HELIOS) with a commercially available highly efficient atmospheric ionization source (SICRIT) connected to a rather low-price ion-trap mass spectrometer. Our inexpensive, robust and mobile aerosol characterization HELIOS/SICRIT/Mass Spectrometry system enables highly sensitive chemical analysis of particle-associated volatile substances. We validate the HELIOS/SICRIT/Mass Spectrometry system in laboratory experiments with coated particles generated under controlled conditions, and show that the system is capable of identification of combustion-generated polycyclic aromatic hydrocarbons and relative quantification of individual chemical species adsorbed on particle surfaces. We then employ our system to analyze real-world vehicle engine exhaust aerosol and show through time-resolved measurements with high time resolution (<10 s) that the chemical composition of the particles changes during different parts of an engine test cycle.acceptedVersionPeer reviewe

Fast oxidation of aerosol in a laminar flow tube

Ilmakehä on hapettava ympäristö. Hapetusreaktioiden seurauksena ilmakehään emittoituneet kaasut voivat osittain siirtyä hiukkasfaasiin, jolloin muodostuu sekundääristä hiukkasmassaa. Tämän diplomityön tarkoituksena oli tarkastella läpivirtauskammioiden toimintaa sekundäärisen hiukkasmassan muodostumisen tutkimisessa. Läpivirtauskammiot mahdollistavat ilmakehän useita päiviä kestävän hapetuksen simuloinnin lyhyessä ajassa. Kirjallisuusselvityksen perusteella läpivirtauskammiossa muodostunut sekundäärinen hiukkasmassa vastaa monilta ominaisuuksiltaan ilmakehässä muodostunutta sekundääristä hiukkasmassaa, vaikka kammion olosuhteet eroavatkin huomattavasti ilmakehän olosuhteista. Työn pääpaino oli TTY:n aerosolilaboratorion oman läpivirtauskammion TSARin ominaisuuksien karakterisointi. Mittausten perusteella virtaus TSARissa on lähes laminaarinen ja hiukkashäviöt ovat pieniä. Lisäksi TSARin hapetinaltistusta voidaan kontrolloida, ja maksimissaan saavutetaan altistus, joka vastaa noin viikon hapettumista ilmakehässä. Virtauksen laminaarisuuden ja nopean vasteajan takia TSARilla on mahdollista mitata sekundäärisen hiukkasmassan muodostumista myös nopeasti muuttuvissa päästölähteissä. Muilla läpivirtauskammioilla ei ole tehty tällaisia mittauksia, ja useimmilla se ei ole mahdollistakaan niiden epälaminaarisen virtauksen takia.Atmosphere is an oxidative environment. Some gases emitted to the atmosphere go through oxidation reactions and the reaction products may transfer to the particle phase. The mass transferred from gas to particle phase is called secondary aerosol mass. The aim of this thesis was to study flow tubes in secondary aerosol research. Flow tubes can be used to simulate oxidation that takes several days in the atmosphere so that the simulation takes only few minutes. The literature survey made in this work shows that the secondary aerosol formed in a flow tube resembles in many ways the secondary aerosol formed in the atmosphere, even though the conditions in flow tubes are remarkably different to the conditions in the atmosphere. The main part of this thesis was to characterize a flow tube called TSAR which is developed at the aerosol laboratory of TUT. Based on the measurements, the flow in TSAR is nearly laminar and particle losses are small. In addition, the oxidant exposure in TSAR can be controlled and the maximum exposure is equivalent to the oxidation that takes place in the atmosphere in approximately one week. Because of the laminarity of the flow and fast response time, TSAR can be used to measure the formation of secondary aerosol also in rapidly changing emission sources. This kind of measurement has not been done with other flow tubes, and for most of them it is not even possible because of their nonlaminar flow

Potential of renewable fuel to reduce diesel exhaust particle emissions

The use of fossil fuels in traffic is a significant source of air pollutants and greenhouse gases in rapidly growing and densely populated cities. Diesel exhaust emissions including particle number concentration and size distribution along with the particles’ chemical composition and NOx were investigated from a Euro 4 passenger car with a comprehensive set of high time-resolution instruments. The emissions were compared with three fuel standards – European diesel (EN590), Indian diesel (BS IV) and Finnish renewable diesel (Neste MY) – over the New European Driving Cycle (NEDC) and the Worldwide harmonized Light vehicles Test Cycle (WLTC). Fuel properties and driving conditions strongly affected exhaust emissions. The exhaust particulate mass emissions for all fuels consisted of BC (81–88%) with some contribution from organics (11–18%) and sulfate (0–3%). As aromatic-free fuel, the MY diesel produced around 20% lower black carbon (BC) emissions compared to the EN590 and 29–40% lower compared to the BS IV. High volatile nanoparticle concentrations at high WLTC speed conditions were observed with the BS IV and EN590 diesel, but not with the sulfur-free MY diesel. These nanoparticles were linked to sulfur-driven nucleation of new particles in cooling dilution of the exhaust. For all the fuels non-volatile nanoparticles in sub-10 nm particle sizes were observed during engine braking, and they were most likely formed from lubricant-oil-originated compounds. With all the fuels, the measured particulate and NOx emissions were significantly higher during the WLTC cycle compared to the NEDC cycle. This study demonstrated that renewable diesel fuels enable mitigations of particulate and climate-warming BC emissions of traffic, and will simultaneously help tackle urban air quality problems.Peer reviewe