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Torsten Tritscher,
Zsófia Jurányi,
Maria Martin,
Roberto Chirico,
Martin Gysel,
Maarten F Heringa, Peter F DeCarlo,
Berko Sierau,
André S H Prévôt,
Ernest Weingartner,
Urs Baltensperger
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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. · 3.63 Impact Factor
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ABSTRACT: In this study, we apply several recently proposed models to the evolution of secondary organic aerosols (SOA) and organic gases advected from downtown Mexico City at an altitude of ∼3.5 km during three days of aging, in a way that is directly comparable to simulations in regional and global models. We constrain the model with and compare its results to available observations. The model SOA formed from oxidation of volatile organic compounds (V-SOA) when using a non-aging SOA parameterization cannot explain the observed SOA concentrations in aged pollution, despite the increasing importance of the low-NO(x) channel. However, when using an aging SOA parameterization, V-SOA alone is similar to the regional aircraft observations, highlighting the wide diversity in current V-SOA formulations. When the SOA formed from oxidation of semivolatile and intermediate volatility organic vapors (SI-SOA) is computed following Robinson et al. (2007) the model matches the observed SOA mass, but its O/C is ∼2× too low. With the parameterization of Grieshop et al. (2009), the total SOA mass is ∼2× too high, but O/C and volatility are closer to the observations. Heating or dilution cause the evaporation of a substantial fraction of the model SOA; this fraction is reduced by aging although differently for heating vs dilution. Lifting of the airmass to the free-troposphere during dry convection substantially increases SOA by condensation of semivolatile vapors; this effect is reduced by aging.
Environmental Science & Technology 03/2011; 45(8):3496-503. · 4.80 Impact Factor
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ABSTRACT: For the data presented here, two Aerodyne aerosol mass spectrometers
(AMS) (Canagaratna, 2007) were deployed together with additional
instrumentation in the metropolitan area of Zurich in winter 2007-8 and
2008-9. A low mixing layer height and stable air masses due to thermal
inversions (typically occurring during winter time) often lead to an
accumulation of particulate matter (PM) emissions in the region of
Zurich. The quantification of various types of aerosol components is
important for source identification which in turn is the basis of
mitigation activities. A high-resolution time-of-flight AMS was
stationed at an urban courtyard in the center, shielded against direct
traffic emissions. A quadrupole-based AMS was deployed in a mobile van
allowing for on-road measurements and investigations into the spatial
variability of aerosol concentration and composition. Contributions of
different source types to ambient submicron aerosol mass were analyzed
using factor analytical modelling results. Positive matrix factorization
(PMF) was applied to the organic mass spectral matrix (Lanz, 2007) to
determine source profiles and strengths. Results indicate that traffic
emissions are the main contributor to primary submicron aerosol mass
concentrations measured on-road, followed by emissions from domestic
wood burning for heating purposes. Oxygenated organic aerosol (OOA),
most of which is secondary, represents the remaining fraction. At the
urban site, the measured aerosol composition is more strongly influenced
by secondary species. The relative mass contributions of OOA, sulphate,
nitrate, and ammonium contributions are higher than on-road. An
important task in terms of local mitigation activities is the
distinction and quantification of contributions of local emissions
versus regional background to ambient particulate matter. We will
present a new method to estimate local contributions based on mobile
measurements data. Canagaratna, M. R., et al. (2007). Mass Spectrom.
Rev., 26: 185-222. Lanz, V. A., et al. (2007). Atmos. Chem. Phys., 7:
1503-1522
04/2010; 12:13411.
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Urs Baltensperger,
Robert Chirico, Peter F DeCarlo,
Josef Dommen,
Kathrin Gaeggeler,
Maarten F Heringa,
Mingli Li,
André S H Prévôt,
M Rami Alfarra,
Deborah S Gross,
Markus Kalberer
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ABSTRACT: Atmospheric aerosol particles consist of a highly complex mixture of thousands of different compounds. Mass spectrometric techniques are well suited for the analysis of these particles, with each method of analysis having specific advantages and disadvantages. On-line techniques offer high time resolution and thus allow for the investigation of rapidly changing signals. They typically measure either single particles or the average non-refractory submicrometer aerosol. Off-line techniques are often coupled to chromatography or another technique separating for a specific property, which enhances their resolving power. Ultra-high resolution mass spectrometry allows for an unambiguous assignment of the elemental composition throughout the majority of the mass range typically measured in ambient aerosol samples, i.e. up to about m/z 400-600. The quantitative determination of individual compounds, or of classes of compounds, remains an important, but often unresolved, topic. Examples of applications of various mass spectrometric techniques are presented, both from laboratory and field studies.
European Journal of Mass Spectrometry 01/2010; 16(3):389-95. · 1.21 Impact Factor
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Kenneth S Docherty,
Elizabeth A Stone,
Ingrid M Ulbrich, Peter F DeCarlo,
David C Snyder,
James J Schauer,
Richard E Peltier,
Rodney J Weber,
Shane M Murphy,
John H Seinfeld,
Brett D Grover,
Delbert J Eatough,
Jose L Jimenez
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ABSTRACT: Ambient sampling was conducted in Riverside, California during the 2005 Study of Organic Aerosols in Riverside to characterize the composition and sources of organic aerosol using a variety of state-of-the-art instrumentation and source apportionmenttechniques. The secondary organic aerosol (SOA) mass is estimated by elemental carbon and carbon monoxide tracer methods, water soluble organic carbon content, chemical mass balance of organic molecular markers, and positive matrix factorization of high-resolution aerosol mass spectrometer data. Estimates obtained from each ofthese methods indicate that the organic fraction in ambient aerosol is overwhelmingly secondary in nature during a period of several weeks with moderate ozone concentrations and that SOA is the single largest component of PM1 aerosol in Riverside. Average SOA/OA contributions of 70-90% were observed during midday periods, whereas minimum SOA contributions of approximately 45% were observed during peak morning traffic periods. These results are contraryto previous estimates of SOAthroughout the Los Angeles Basin which reported that, other than during severe photochemical smog episodes, SOA was lower than primary OA. Possible reasons for these differences are discussed.
Environmental Science and Technology 11/2008; 42(20):7655-62. · 5.23 Impact Factor
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Allison C Aiken, Peter F Decarlo,
Jesse H Kroll,
Douglas R Worsnop,
J Alex Huffman,
Kenneth S Docherty,
Ingrid M Ulbrich,
Claudia Mohr,
Joel R Kimmel,
Donna Sueper, [......],
Paul J Ziemann,
Manjula R Canagaratna,
Timothy B Onasch,
M Rami Alfarra,
Andre S H Prevot,
Josef Dommen,
Jonathan Duplissy,
Axel Metzger,
Urs Baltensperger,
Jose L Jimenez
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ABSTRACT: A recently developed method to rapidly quantify the elemental composition of bulk organic aerosols (OA) using a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) is improved and applied to ambient measurements. Atomic oxygen-to-carbon (O/C) ratios characterize the oxidation state of OA, and O/C from ambient urban OA ranges from 0.2 to 0.8 with a diurnal cycle that decreases with primary emissions and increases because of photochemical processing and secondary OA (SOA) production. Regional O/C approaches approximately 0.9. The hydrogen-to-carbon (H/C, 1.4--1.9) urban diurnal profile increases with primary OA (POA) as does the nitrogen-to-carbon (N/C, approximately 0.02). Ambient organic-mass-to-organic-carbon ratios (OM/OC) are directly quantified and correlate well with O/C (R2 = 0.997) for ambient OA because of low N/C. Ambient O/C and OM/OC have values consistent with those recently reported from other techniques. Positive matrix factorization applied to ambient OA identifies factors with distinct O/C and OM/OC trends. The highest O/C and OM/OC (1.0 and 2.5, respectively) are observed for aged ambient oxygenated OA, significantly exceeding values for traditional chamber SOA,while laboratory-produced primary biomass burning OA (BBOA) is similar to ambient BBOA, O/C of 0.3--0.4. Hydrocarbon-like OA (HOA), a surrogate for urban combustion POA, has the lowest O/C (0.06--0.10), similar to vehicle exhaust. An approximation for predicting O/C from unit mass resolution data is also presented.
Environmental Science and Technology 07/2008; 42(12):4478-85. · 5.23 Impact Factor
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ABSTRACT: We present a new elemental analysis (EA) technique for organic species (CHNO) that allows fast on-line analysis (10 s) and reduces the required sample size to approximately 1 ng, approximately 6 orders of magnitude less than standard techniques. The composition of the analyzed samples is approximated by the average elemental composition of the ions from high-resolution electron ionization (EI) mass spectra. EA of organic species can be performed on organic/inorganic mixtures. Elemental ratios for the total organic mass, such as oxygen/carbon (O/C), hydrogen/carbon (H/C), and nitrogen/carbon (N/C), in addition to the organic mass to organic carbon ratio (OM/OC), can be determined. As deviations between the molecular and the ionic composition can appear due to chemical influences on the ion fragmentation processes, the method was evaluated and calibrated using spectra from 20 compounds from the NIST database and from 35 laboratory standards sampled with the high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS). The analysis of AMS (NIST) spectra indicates that quantification of O/C is possible with an error (average absolute value of the relative error) of 30% (17%) for individual species. Precision is much better than accuracy at +/-5% in the absence of air for AMS data. AMS OM/OC has an average error of 5%. Additional calibration is recommended for types of species very different from those analyzed here. EA was applied to organic mixtures and ambient aerosols (sampled at 20 s from aircraft). The technique is also applicable to other EI-HRMS measurements such as direct injection MS.
Analytical Chemistry 12/2007; 79(21):8350-8. · 5.86 Impact Factor
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Peter F DeCarlo,
Joel R Kimmel,
Achim Trimborn,
Megan J Northway,
John T Jayne,
Allison C Aiken,
Marc Gonin,
Katrin Fuhrer,
Thomas Horvath,
Kenneth S Docherty,
Doug R Worsnop,
Jose L Jimenez
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ABSTRACT: The development of a new high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) is reported. The high-resolution capabilities of this instrument allow the direct separation of most ions from inorganic and organic species at the same nominal m/z, the quantification of several types of organic fragments (CxHy, CxHyOz, CxHyNp, CxHyOzNp), and the direct identification of organic nitrogen and organosulfur content. This real-time instrument is field-deployable, and its high time resolution (0.5 Hz has been demonstrated) makes it well-suited for studies in which time resolution is critical, such as aircraft studies. The instrument has two ion optical modes: a single-reflection configuration offers higher sensitivity and lower resolving power (up to approximately 2100 at m/z 200), and a two-reflectron configuration yields higher resolving power (up to approximately 4300 at m/z 200) with lower sensitivity. The instrument also allows the determination of the size distributions of all ions. One-minute detection limits for submicrometer aerosol are <0.04 microg m(-3) for all species in the high-sensitivity mode and <0.4 microg m(-3) in the high-resolution mode. Examples of ambient aerosol data are presented from the SOAR-1 study in Riverside, CA, in which the spectra of ambient organic species are dominated by CxHy and CxHyOz fragments, and different organic and inorganic fragments at the same nominal m/z show different size distributions. Data are also presented from the MIRAGE C-130 aircraft study near Mexico City, showing high correlation with independent measurements of surrogate aerosol mass concentration.
Analytical Chemistry 01/2007; 78(24):8281-9. · 5.86 Impact Factor
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ABSTRACT: Different on-line submicron particle sizing techniques report different "equivalent diameters." For example, differential mobil-ity analyzers (DMAs) report electrical mobility diameter (d m), while a number of recently developed instruments (such as the Aero-dyne aerosol mass spectrometer, or AMS) measure vacuum aero-dynamic diameter (d va). Particle density and physical morphology (shape) have important effects on diameter measurements. Here a framework is presented for combining the information content of different equivalent diameter measurements into a single co-herent mathematical description of the particles. We first present a review of the mathematical formulations used in the literature and their relationships. We then show that combining d m and d va measurements for the same particle population allows the placing of constraints on particle density, dynamic shape factor (χ), and fraction of internal void space. The amount of information that can be deduced from the combination of d m and d va measurements for various particle types is shown. With additional measurements and/or some assumptions, all relevant parameters can be deter-mined. Specifically, particle mass can be determined from d m and d va measurements if the particle density is known and an assump-tion about χ is made. Even if χ and density are not known, particle mass can be estimated within about a factor of 2 from d m and d va measurements alone. The mass of a fractal particle can also be esti-mated under certain conditions. The meaning of various definitions Received 2 July 2004; accepted 29 October 2004. We thank Prof. Rick Flagan of Caltech for guiding our first steps in this area of research a few years ago. We are also grateful to Dan Imre and the AMS users' community for helpful discussions.
Aerosol Science and Technology 06/2004; 38:1185-1205. · 2.67 Impact Factor
