[show abstract][hide abstract] ABSTRACT: The effect of a post-industrial megacity on local and regional air quality was assessed via a month-long field measurement campaign in the Paris metropolitan area during winter 2010. Here we present source apportionment results from three aerosol mass spectrometers and two aethalometers deployed at three measurement stations within the Paris region. Submicron aerosol composition is dominated by the organic fraction (30–36%) and nitrate (28–29%), with lower contributions from sulfate (14–16%), ammonium (12–14%) and black carbon (7–13%).
Organic source apportionment was performed using positive matrix factorization, resulting in a set of organic factors corresponding both to primary emission sources and secondary production. The dominant primary sources are traffic (11–15% of organic mass), biomass burning (13–15%) and cooking (up to 35% during meal hours). Secondary organic aerosol contributes more than 50% to the total organic mass and includes a highly oxidized factor from indeterminate and/or diverse sources and a less oxidized factor related to wood burning emissions. Black carbon was apportioned to traffic and wood burning sources using a model based on wavelength-dependent light absorption of these two combustion sources. The time series of organic and black carbon factors from related sources were strongly correlated. The similarities in aerosol composition, total mass and temporal variation between the three sites suggest that particulate pollution in Paris is dominated by regional factors, and that the emissions from Paris itself have a relatively low impact on its surroundings.
Atmospheric Chemistry and Physics 01/2013; 13:961-981. · 4.88 Impact Factor
[show abstract][hide abstract] ABSTRACT: Biomass burning is one of the largest aerosol sources worldwide. In this study, the hygroscopic properties of fresh and aged wood burning particles were investigated under controlled laboratory conditions in several smog chamber experiments. Beech log wood was burnt in a residential log wood burner and the particles emitted during the different burning phases (starting, flaming, and smoldering) were analyzed. The particles were photochemically aged using the own volatile organic compound emissions from the burnt wood. The hygroscopic properties of the particles at relative humidities below and above 100% were determined and compared.
The freshly emitted soot particles have a fractal-like structure. The structure collapsed in half of the experiments where soot was present for particles View the MathML source under the presence of a high relative humidity, leading to a more compact structure. This restructuring induces an underestimation of the hygroscopicity measured with mobility diameter based methods.
The hygroscopicity parameter “apparent κ ” of fresh wood combustion particles varies between 0 and 0.39. With aging, the hygroscopicity of the particles generally increases. This is due to the uptake of organic matter and inorganic salts, and because the particles become more oxidized.
One smoldering phase experiment was carried out, which, in contrast to the other experiments, showed very high apparent κ values between 0.2 and 0.4 at the beginning of the experiment, depending on the size of the particles. These values were decreasing with time. This suggests a different composition of the particles, with a higher fraction of inorganic components initially.
The results indicate that it is not possible to use only one κ value for different burning phases and aging times of wood combustion particles in climate models.
Journal of Aerosol Science 01/2013; 56:15-29. · 2.69 Impact Factor
[show abstract][hide abstract] ABSTRACT: A measurement campaign (IMBALANCE) was conducted in 2009 and aimed at
characterizing the physical and chemical properties of freshly emitted
and photochemically aged combustion particles emitted from a log wood
burner and diesel vehicles: a EURO3 Opel Astra with a diesel oxidation
catalyst (DOC) but no particle filter and a EURO2 Volkswagen Transporter
TDI Syncro with no emission after-treatment. Ice nucleation experiments
in the deposition and condensation freezing modes were conducted with
the Portable Ice Nucleation Chamber (PINC) at three nominal
temperatures, -30 °C, -35 °C and -40 °C. Freshly emitted
diesel particles showed ice formation only at -40 °C in the
deposition mode at 137% relative humidity with respect to ice
(RHi) and 92% relative humidity with respect to water
(RHw), and photochemical aging did not play a role in
modifying their ice nucleation behavior. Only one diesel experiment
where α-pinene was added, showed an ice nucleation enhancement
after the aging at -35 °C. Wood burning particles also act as ice
nuclei (IN) at -40 °C in the deposition mode at the same conditions
as for diesel particles and photochemical aging did also not alter the
ice formation properties of the wood burning particles. Unlike diesel
particles, wood burning particles form ice via condensation freezing at
-35 °C with no ice nucleation observed at -30 °C for wood
burning particles. Photochemical aging did not affect the ice nucleation
ability of the diesel and wood burning particles at the three different
temperatures investigated but a broader range of temperatures below -30
°C need to be investigated in order to draw an overall conclusion on
the effect of photochemical aging on deposition/condensation ice
nucleation across the entire temperature range relevant to cold clouds.
Atmospheric Chemistry and Physics 01/2013; 13(2):761-772. · 4.88 Impact Factor
[show abstract][hide abstract] ABSTRACT: Secondary organic aerosol (SOA), a predominant fraction of particulate
organic mass (OA), remains poorly constrained. Its formation involves
several unknown precursors, formation and evolution pathways and
multiple natural and anthropogenic sources. Here a combined gas-particle
phase source apportionment is applied to wintertime and summertime data
collected in the megacity of Paris in order to investigate SOA origin
during both seasons. This was possible by combining the information
provided by an aerosol mass spectrometer (AMS) and a proton transfer
reaction mass spectrometer (PTR-MS). A better constrained apportionment
of primary OA (POA) sources is also achieved using this methodology,
making use of gas-phase tracers. These tracers allowed distinguishing
between biogenic and continental/anthropogenic sources of SOA. We found
that continental SOA was dominant during both seasons (24-50% of total
OA), while contributions from photochemistry-driven SOA (9% of total OA)
and marine emissions (13% of total OA) were also observed during
summertime. A semi-volatile nighttime component was also identified (up
to 18% of total OA during wintertime). This approach was successfully
applied here and implemented in a new source apportionment toolkit.
Atmospheric Chemistry and Physics 01/2013; 13(16):8411-8426. · 4.88 Impact Factor
[show abstract][hide abstract] ABSTRACT: Primary emissions from a log wood burner and a pellet boiler were characterized by online measurements of the organic aerosol (OA) using a high-resolution time-of-flight aerosol mass spectrometer (HR-TOF-AMS) and of black carbon (BC). The OA and BC concentrations measured during the burning cycle of the log wood burner, batch wise fueled with wood logs, were highly variable and generally dominated by BC. The emissions of the pellet burner had, besides inorganic material, a high fraction of OA and a minor contribution of BC. However, during artificially induced poor burning BC was the dominating species with ∼80% of the measured mass. The elemental O:C ratio of the OA was generally found in the range of 0.2-0.5 during the startup phase or after reloading of the log wood burner. During the burnout or smoldering phase, O:C ratios increased up to 1.6-1.7, which is similar to the ratios found for the pellet boiler during stable burning conditions and higher than the O:C ratios observed for highly aged ambient OA. The organic emissions of both burners have a very similar H:C ratio at a given O:C ratio and therefore fall on the same line in the Van Krevelen diagram.
[show abstract][hide abstract] ABSTRACT: Two-stroke mopeds are a popular and convenient mean of transport in particular in the highly populated cities. These vehicles can emit potentially toxic gaseous and aerosol pollutants due to their engine technology. The legislative measurements of moped emissions are based on offline methods; however, the online characterization of gas and particulate phases offers great possibilities to understand aerosol formation mechanism and to adapt future emission standards. The purpose of this work was to study the emission behavior of two mopeds complying with different European emission standards (EURO-1 and EURO-2). A sophisticated set of online analyzers was applied to simultaneously monitor the gas phase and particulate phase of exhaust on a real time basis. The gaseous emission was analyzed with a high resolution Fourier transform infrared spectrometer (FTIR; nitrogen species) and a resonance-enhanced multiphoton ionization time-of-flight mass spectrometer (REMPI-ToF-MS; polycyclic aromatic hydrocarbons: PAH), whereas the particulate phase was chemically characterized by a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS; organic, nitrate and chloride aerosol) and a multiangle absorption photometer (MAAP; black carbon). The physical characterization of the aerosol was carried out with a condensation particle counter (CPC; particle number concentration) and a fast mobility particle sizer (FMPS; size distribution in real time). In order to extract underlying correlation between gas and solid emissions, principal component analysis was applied to the comprehensive online dataset. Multivariate analysis highlighted the considerable effect of the exhaust temperature on the particles and heavy PAH emissions. The results showed that the after-treatment used to comply with the latest EURO-2 emission standard may be responsible for the production of more potentially harmful particles compared to the EURO-1 moped emissions.
[show abstract][hide abstract] ABSTRACT: Soot particles can significantly influence the Earth's climate by
absorbing and scattering solar radiation as well as by acting as cloud
condensation nuclei. However, despite their environmental (as well as
economic and political) importance, the way these properties are
affected by atmospheric processing of the combustion exhaust gases is
still a subject of discussion. In this work, individual soot particles
emitted from two different vehicles, a EURO 2 transporter, a EURO 3
passenger car, and a wood stove were investigated on a single-particle
basis. The emitted exhaust, including the particulate and the gas phase,
was processed in a smog chamber with artificial solar radiation. Single
particle specimens of both unprocessed and aged soot were characterized
using near edge X-ray absorption fine structure spectroscopy (NEXAFS)
and scanning electron microscopy. Comparison of NEXAFS spectra from the
unprocessed particles and those resulting from exhaust photooxidation in
the chamber revealed changes in the carbon functional group content. For
the wood stove emissions, these changes were minor, related to the
relatively mild oxidation conditions. For the EURO 2 transporter
emissions, the most apparent change was that of carboxylic carbon from
oxidized organic compounds condensing on the primary soot particles. For
the EURO 3 car emissions oxidation of primary soot particles upon
photochemical aging has likely contributed as well. Overall, the changes
in the NEXAFS fingerprints were in qualitative agreement with data from
an aerosol mass spectrometer. Furthermore, by taking full advantage of
our in situ microreactor concept, we show that the soot particles from
all three combustion sources changed their ability to take up water
under humid conditions upon photochemical aging of the exhaust. Due to
the selectivity and sensitivity of the NEXAFS technique for the water
mass, also small amounts of water taken up into the internal voids of
agglomerated particles could be detected. Because such small amounts of
water uptake do not lead to measurable changes in particle diameter, it
may remain beyond the limits of volume growth measurements, especially
for larger agglomerated particles.
ATMOSPHERIC CHEMISTRY AND PHYSICS 11/2011; 11(22):11777-11791. · 5.51 Impact Factor
[show abstract][hide abstract] ABSTRACT: Soot particles are an important component of atmospheric aerosol and their interaction with water is important for their climate effects. The hygroscopicity of fresh and photochemically aged soot and secondary organic aerosol (SOA) from diesel passenger car emissions was studied under atmospherically relevant conditions in a smog chamber at sub-and supersaturation of water vapor. Fresh soot particles show no significant hygroscopic growth nor cloud condensation nucleus (CCN) activity. Ageing by condensation of SOA formed by photooxidation of the volatile organic carbon (VOC) emission leads to increased water uptake and CCN activity as well as to a compaction of the initially non-spherical soot particles when exposed to high relative humidity (RH). It is important to consider the latter effect for the interpretation of mobility based measurements. The vehicle with oxidation catalyst (EURO3) emits much fewer VOCs than the vehicle without after-treatment (EURO2). Consequently, more SOA is formed for the latter, resulting in more pronounced effects on particle hygroscopicity and CCN activity. Nevertheless, the aged soot particles did not reach the hygroscopicity of pure SOA particles formed from diesel VOC emissions, which are similarly hygroscopic (0.06 < κH − TDMA < 0.12 and 0.09 < κCCN < 0.14) as SOA from other precursor gases investigated in previous studies.
Environmental Research Letters 09/2011; 6(3):034026. · 3.58 Impact Factor
[show abstract][hide abstract] ABSTRACT: A series of photo-oxidation smog chamber experiments were performed to investigate the primary emissions and secondary aerosol formation from two different log wood burners and a residential pellet burner under different burning conditions: starting and flaming phase. Emissions were sampled from the chimney and injected into the smog chamber leading to primary organic aerosol (POA) concentrations comparable to ambient levels. The composition of the aerosol was measured by an Aerodyne high resolution time-of-flight aerosol mass spectrometer (HR-TOF-AMS) and black carbon (BC) instrumentation. The primary emissions were then exposed to xenon light to initiate photo-chemistry and subsequent secondary organic aerosol (SOA) production. After correcting for wall losses, the average increase in organic matter (OM) concentrations by SOA formation for the starting and flaming phase experiments with the two logwood burners was found to be a factor of 4.1 ± 1.4 after five hours of aging. No SOA formation was observed for the stable burning phase of the pellet burner. The startup emissions of the pellet burner showed an increase in OM concentration by a factor of 3.3. Average emission factors of BC + POA + SOA, calculated from CO2 emission, were found to be in the range of 0.04 to 3.9 g kg-1 wood for the stable burning pellet burner and an old log wood burner during startup respectively. SOA contributed significantly to the ion C2H4O2+ at mass to charge ratio m/z 60, a commonly used marker for primary emissions of wood burning. The primary organic emissions from the three different burners showed a wide range in O/C atomic ratio (0.19-0.60) for the starting and flaming conditions, which also increased during aging. Primary wood burning emissions have a rather low relative contribution at m/z 43 (f43) to the total organic mass spectrum. The non-oxidized fragment C3H7+ has a considerable contribution at m/z 43 for the fresh OA with an increasing contribution of the oxygenated ion C2H3O+ during aging. After five hours of aging, the OA has a rather low C2H3O+ signal for a given CO2+ fraction, possibly indicating a higher ratio of acid to non-acid oxygenated compounds in wood burning OA compared to other OOA.
ATMOSPHERIC CHEMISTRY AND PHYSICS 01/2011; 11:8081-8113. · 5.51 Impact Factor
[show abstract][hide abstract] ABSTRACT: Soot particles are an important component of atmospheric aerosol and their interaction with water is important for their climate effects. The hygroscopicity of fresh and photochemically aged soot and secondary organic aerosol (SOA) from diesel passenger car emissions was studied under atmospherically relevant conditions in a smog chamber at sub-and supersaturation of water vapor. Fresh soot particles show no significant hygroscopic growth nor cloud condensation nucleus (CCN) activity. Ageing by condensation of SOA formed by photooxidation of the volatile organic carbon (VOC) emission leads to increased water uptake and CCN activity as well as to a compaction of the initially non-spherical soot particles when exposed to high relative humidity (RH). It is important to consider the latter effect for the interpretation of mobility based measurements. The vehicle with oxidation catalyst (EURO3) emits much fewer VOCs than the vehicle without after-treatment (EURO2). Consequently, more SOA is formed for the latter, resulting in more pronounced effects on particle hygroscopicity and CCN activity. Nevertheless, the aged soot particles did not reach the hygroscopicity of pure SOA particles formed from diesel VOC emissions, which are similarly hygroscopic (0.06 <
Environmental Research Letters 01/2011; 6(3):034026. · 3.58 Impact Factor
[show abstract][hide abstract] ABSTRACT: Soot particles can significantly influence the Earth's climate by absorbing and scattering solar radiation as well as by acting as cloud condensation nuclei. However, despite their environmental (as well as economic and political) importance, the way these properties are affected by atmospheric processing is still a subject of discussion. In this work, soot particles emitted from two different cars, a EURO 2 transporter, a EURO 3 passenger vehicle, and a wood stove were investigated on a single-particle basis. The emitted exhaust, including the particulate and the gas phase, was processed in a smog chamber with artificial solar radiation. Single particle specimens of both unprocessed and aged soot were characterized using x-ray absorption spectroscopy and scanning electron microscopy. Comparison of the spectra from the unprocessed and aged soot particles revealed changes in the carbon functional group content, such as that of carboxylic carbon, which can be ascribed to both the condensation of secondary organic compounds on the soot particles and oxidation of primary soot particles upon photochemical aging. Changes in the morphology and size of the single soot particles were also observed upon aging. Furthermore, we show that the soot particles take up water in humid environments and that their water uptake capacity increases with photochemical aging.
Atmospheric Chemistry and Physics Discussions. 01/2011; 11:14455-14493.
[show abstract][hide abstract] ABSTRACT: Time and size resolved data of trace elements were obtained from measurements with a rotating drum impactor (RDI) and subsequent X-ray fluorescence spectrometry. Trace elements can act as indicators for the identification of sources of particulate matter <10 μm (PM10) in ambient air. Receptor modeling was performed with positive matrix factorization (PMF) for trace element data from an urban background site in Zürich, Switzerland. Eight different sources were identified for the three examined size ranges (PM1−0.1, PM2.5−1 and PM10−2.5): secondary sulfate, wood combustion, fire works, road traffic, mineral dust, de-icing salt, industrial and local anthropogenic activities. The major component was secondary sulfate for the smallest size range; the road traffic factor was found in all three size ranges. This trace element analysis is complemented with data from an Aerodyne high-resolution time-of-flight aerosol mass spectrometer (AMS), assessing the PM1 fraction of organic aerosols. A separate PMF analysis revealed three factors related to three of the sources found with the RDI: oxygenated organic aerosol (OOA, related to inorganic secondary sulfate), hydrocarbon like organic aerosol (HOA, related to road traffic) and biomass burning organic aerosol (BBOA), explaining 60%, 22% and 17% of total measured organics, respectively. Since different compounds are used for the source classification, a higher percentage of the ambient PM10 mass concentration can be apportioned to sources by the combination of both methods.
ATMOSPHERIC CHEMISTRY AND PHYSICS 01/2011; · 5.51 Impact Factor
[show abstract][hide abstract] ABSTRACT: Organic aerosol (OA) represents a significant and often major fraction of the non-refractory PM1 (particulate matter with an aerodynamic diameter da < 1 mum) mass. Secondary organic aerosol (SOA) is an important contributor to the OA and can be formed from biogenic and anthropogenic precursors. Here we present results from the characterization of SOA produced from the emissions of three different anthropogenic sources. SOA from a log wood burner, a Euro 2 diesel car and a two-stroke Euro 2 scooter were characterized with an Aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-TOF-AMS) and compared to SOA from alpha-pinene. The emissions were sampled from the chimney/tailpipe by a heated inlet system and filtered before injection into a smog chamber. The gas phase emissions were irradiated by xenon arc lamps to initiate photo-chemistry which led to nucleation and subsequent particle growth by SOA production. Duplicate experiments were performed for each SOA type, with the averaged organic mass spectra in the m/z range 12-250 showing Pearson's r values >0.94 for the correlations between the different SOA types after 5 h of aging. High-resolution mass spectra (HR-MS) showed that the dominant peaks in the MS, m/z 43 and 44, are dominated by the oxygenated ions C2H3O+ and CO2+, respectively, similarly to the relatively fresh semi-volatile oxidized OA (SV-OOA) observed in the ambient aerosol. The atomic O : C ratios were found to be in the range of 0.25-0.55 with no major increase during the first 5 h of aging. On average, the diesel SOA showed the lowest O : C ratio followed by SOA from wood burning, alpha-pinene and the scooter emissions. Grouping the fragment ions based on their carbon number revealed that the SOA source with the highest O : C ratio had the largest fraction of small ions. Fragment ions containing up to 3 carbon atoms accounted for 66%, 68%, 72% and 76% of the organic spectrum of the SOA produced by the diesel car, wood burner, alpha-pinene and the scooter, respectively. The HR data of the four sources could be clustered and separated using principal component analysis (PCA). The model showed a significant separation of the four SOA types and clustering of the duplicate experiments on the first two principal components (PCs), which explained 79% of the total variance. Projection of ambient SV-OOA spectra resolved by positive matrix factorization (PMF) showed that this approach could be useful to identify large contributions of the tested SOA sources to SV-OOA. The first results from this study indicate that the SV-OOA in Barcelona is strongly influenced by diesel emissions in winter while in summer at SIRTA at the southwestern edge of Paris SV-OOA is more similar to alpha-pinene SOA. However, contributions to the ambient SV-OOA from SOA sources that are not covered by the model can cause major interference and therefore future expansions of the PCA model with additional SOA sources is recommended.
Atmospheric Chemistry and Physics 01/2011; 11:29055-29091. · 4.88 Impact Factor
[show abstract][hide abstract] ABSTRACT: The European Commission recently established a novel test facility for heavy-duty vehicles to enhance more sustainable transport. The facility enables the study of energy efficiency of various fuels/scenarios as well as the chemical composition of evolved exhaust emissions. Sophisticated instrumentation for real-time analysis of the gas and particulate phases of exhaust has been implemented. Thereby, gas-phase characterization was carried out by a Fourier transform infrared spectrometer (FT-IR; carbonyls, nitrogen-containing species, small hydrocarbons) and a resonance-enhanced multiphoton ionization time-of-flight mass spectrometer (REMPI-TOFMS; monocyclic and polycyclic aromatic hydrocarbons). For analysis of the particulate phase, a high-resolution time-of-flight aerosol mass spectrometer (HR-TOF-AMS; organic matter, chloride, nitrate), a condensation particle counter (CPC; particle number), and a multiangle absorption photometer (MAAP; black carbon) were applied. In this paper, the first application of the new facility in combination with the described instruments is presented, whereby a medium-size truck was investigated by applying different driving cycles. The goal was simultaneous chemical characterization of a great variety of gaseous compounds and particulate matter in exhaust on a real-time basis. The time-resolved data allowed new approaches to view the results; for example, emission factors were normalized to time-resolved consumption of fuel and were related to emission factors evolved during high speeds. Compounds could be identified that followed the fuel consumption, others showed very different behavior. In particular, engine cold start, engine ignition (unburned fuel), and high-speed events resulted in unique emission patterns.
[show abstract][hide abstract] ABSTRACT: In this study we present measurements of gas and aerosol phase composition for a mixed vehicle fleet in the Gubrist tunnel (Switzerland) in June 2008. PM1 composition measurements were made with a High-Resolution Time-of-Flight Aerosol Mass Spectrometer (AMS) and a Multi Angle Absorption Photometer (MAAP). Gas-phase measurements of CO, CO2, NOx and total hydrocarbons (THC) were performed with standard instrumentation. Weekdays had a characteristic diurnal pattern with 2 peaks in concentrations for all traffic related species corresponding to high vehicle density (∼300±30 vehicles per 5min) in the morning rush hour between 06:00 and 09:00 and in the afternoon rush hours from approximately 15:30 to 18:30.The emission factors (EF) of OA were heavily influenced by the OA mass loading. To exclude this partitioning effect, only organic aerosol mass concentrations from 60μgm−3 to 90μgm−3 were considered and for these conditions the EF(OA) value for HDV was 33.7±2.3mgkm−1 for a temperature inside the tunnel of 20–25°C. This value is not directly applicable to ambient conditions because it is derived from OA mass concentrations that are roughly a factor of 10 higher than typical ambient concentrations. An even higher EF(OA)HDV value of 47.4±1.6mgkm−1 was obtained when the linear fit was applied to all data points including OA concentrations up to 120μgm−3.Similar to the increasing EF, the OA/BC ratio in the tunnel was also affected by the organic loading and it increased by a factor of ∼3 over the OA range 10–120μgm−3. This means that also the OA emission factors at ambient concentrations of around 5–10μgm−3 would be 2–3 times lower than the emission factor given above. For OA concentrations lower than 40μgm−3 the OA/BC mass ratio was below 1, while at an OA concentration of 100–120μgm−3 the OA/BC ratio was ∼1.5. The AMS mass spectra (MS) acquired in the tunnel were highly correlated with the primary organic aerosol (POA) MS from a EURO 3 diesel vehicle with a speed similar to the average tunnel speed.
[show abstract][hide abstract] ABSTRACT: Photochemical aging experiments were performed for emissions of diesel vehicles and wood burners, and alpha-pinene at the smogchamber at the Paul Scherrer Institute in Switzerland. The measurements include black carbon measurements ,organic mass measurements with the Aerodyne high-resolution Aerosol mass spectrometer and off-line GC-MS measurements. We will discuss the evolving of the particle aging in these systems in terms of oxygen to carbon ratio and other elemental composition analysis like the Van Krevelen plot.
[show abstract][hide abstract] ABSTRACT: Combustion emissions are a complex mixture of black carbon (BC), organics, and other compounds in the gas and particle phase. In global climate modeling BC is categorized in hydrophobic and hydrophilic, but the fraction of particles in each category is quite difficult to quantify. A particle is called hydrophobic, if it is non-wettable and therefore cannot act as cloud condensation nuclei (CCN). Hydrophilic particles are hygroscopic, if they can take up water at elevated RH. The hygroscopicity and the CCN activation of diesel exhaust particles were measured during experiments at the PSI smog chamber with a Hygroscopicity Tandem Differential Mobility Analyzer (H-TDMA) at 95% relative humidity (RH), which measures diameter growth factors (GF), the ratio of the wet (d(RH)) and the dry diameter (d0), and with a Cloud Condensation Nuclei Counter (CCNC) at RH > 100%. Diesel exhaust from different passenger cars was introduced via heated injection system into the chamber. Fresh soot (BC and primary organic aerosol (POA)) is known to form nm-size fractal aggregates. These primary soot particles were coated with secondary organic aerosol (SOA) mass after lights were turned on. The figure conceptually illustrates the observed findings. Fresh soot particles are hydrophobic as they do not activate as cloud droplets even at high supersaturations like non-hygroscopic but wettable particles do. SOA coating appears on the soot aggregates after photochemical aging was started. Slightly aged particles were found to be CCN-active and thus they are hydrophilic. However, the GF of the H-TDMA was 1, indicating the hygroscopicity of these particles. Our measurements show that photochemical aging with SOA formation can change a hydrophobic (non-wettable) soot particle into a hydrophilic (or even hygroscopic) particle. Schematic of the water interaction and water uptake by soot particles during the aging process (black aggregate = BC + POA). The SOA coating (green) is increasing with aging time, thus coated particles are able to interact with water (blue).
[show abstract][hide abstract] ABSTRACT: European regulation for Euro 5/6 light duty emissions introduced the measurement of non-volatile particles with diameter > 23 nm. The volatile phase is removed by using a heated dilution stage (150 °C) and a heated tube (at 300–400 °C). We investigated experimentally the removal efficiency for volatile species of the specific protocol by conducting measurements with two Euro 3 diesel light duty vehicles, a Euro 2 moped, and a Euro III heavy duty vehicle with the system's heaters on and off. The particle number distributions were measured with a Scanning Mobility Particle Sizer (SMPS) and a Fast Mobility Particle Sizer (FMPS). An Aerosol Mass Spectrometer (AMS) was used to identify the non-refractory chemical composition of the particles. A Multi-Angle Absorption Photometer (MAAP) was used to measure the black carbon concentration. The results showed that the condensed material in the accumulation mode (defined here as particles in the diameter range of ∼ 50–500 nm) was removed with an efficiency of 50–90%. The (volatile) nucleation mode was also completely evaporated or was decreased to sizes < 23 nm; thus these particles wouldn't be counted from the particle counter, indicating the robustness of the protocol.
Science of The Total Environment 10/2010; · 3.26 Impact Factor