| 1. |
- Bilde, M., et al.
(author)
-
Saturation Vapor Pressures and Transition Enthalpies of Low-Volatility Organic Molecules of Atmospheric Relevance: From Dicarboxylic Acids to Complex Mixtures
- 2015
-
In: Chemical Reviews. - : American Chemical Society (ACS). - 0009-2665 .- 1520-6890. ; 115:10, s. 4115-4156
-
Research review (peer-reviewed)abstract
- There are a number of techniques that can be used that differ in terms of whether they fundamentally probe the equilibrium and the temperature range over which they can be applied. The series of homologous, straight-chain dicarboxylic acids have received much attention over the past decade given their atmospheric relevance, commercial availability, and low saturation vapor pressures, thus making them ideal test compounds. Uncertainties in the solid-state saturation vapor pressures obtained from individual methodologies are typically on the order of 50-100%, but the differences between saturation vapor pressures obtained with different methods are approximately 1-4 orders of magnitude, with the spread tending to increase as the saturation vapor pressure decreases. Some of the dicarboxylic acids can exist with multiple solid-state structures that have distinct saturation vapor pressures. Furthermore, the samples on which measurements are performed may actually exist as amorphous subcooled liquids rather than solid crystalline compounds, again with consequences for the measured saturation vapor pressures, since the subcooled liquid phase will have a higher saturation vapor pressure than the crystalline solid phase. Compounds with equilibrium vapor pressures in this range will exhibit the greatest sensitivities in terms of their gas to particle partitioning to uncertainties in their saturation vapor pressures, with consequent impacts on the ability of explicit and semiexplicit chemical models to simulate secondary organic aerosol formation.
|
|
| 2. |
- Nordin, E. Z., et al.
(author)
-
Secondary organic aerosol formation from idling gasoline passenger vehicle emissions investigated in a smog chamber
- 2013
-
In: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 13:12, s. 6101-6116
-
Journal article (peer-reviewed)abstract
- Gasoline vehicles have recently been pointed out as potentially the main source of anthropogenic secondary organic aerosol (SOA) in megacities. However, there is a lack of laboratory studies to systematically investigate SOA formation in real-world exhaust. In this study, SOA formation from pure aromatic precursors, idling and cold start gasoline exhaust from three passenger vehicles (EURO2-EURO4) were investigated with photo-oxidation experiments in a 6 m(3) smog chamber. The experiments were carried out down to atmospherically relevant organic aerosol mass concentrations. The characterization instruments included a high-resolution aerosol mass spectrometer and a proton transfer mass spectrometer. It was found that gasoline exhaust readily forms SOA with a signature aerosol mass spectrum similar to the oxidized organic aerosol that commonly dominates the organic aerosol mass spectra downwind of urban areas. After a cumulative OH exposure of similar to 5 x 10(6) cm(-3) h, the formed SOA was 1-2 orders of magnitude higher than the primary OA emissions. The SOA mass spectrum from a relevant mixture of traditional light aromatic precursors gave f(43) (mass fraction at m/z = 43), approximately two times higher than to the gasoline SOA. However O:C and H:C ratios were similar for the two cases. Classical C-6-C-9 light aromatic precursors were responsible for up to 60% of the formed SOA, which is significantly higher than for diesel exhaust. Important candidates for additional precursors are higher-order aromatic compounds such as C-10 and C-11 light aromatics, naphthalene and methyl-naphthalenes. We conclude that approaches using only light aromatic precursors give an incomplete picture of the magnitude of SOA formation and the SOA composition from gasoline exhaust.
|
|
| 3. |
|
|
| 4. |
- Wittbom, C., et al.
(author)
-
Effect of solubility limitation on hygroscopic growth and cloud drop activation of SOA particles produced from traffic exhausts
- 2018
-
In: Journal of Atmospheric Chemistry. - : Springer Science and Business Media LLC. - 0167-7764 .- 1573-0662. ; 75:4, s. 359-383
-
Journal article (peer-reviewed)abstract
- Hygroscopicity measurements of secondary organic aerosol (SOA) particles often show inconsistent results between the supersaturated and subsaturated regimes, with higher activity as cloud condensation nucleus (CCN) than indicated by hygroscopic growth. In this study, we have investigated the discrepancy between the two regimes in the Lund University (LU) smog chamber. Various anthropogenic SOA were produced from mixtures of different precursors: anthropogenic light aromatic precursors (toluene and m-xylene), exhaust from a diesel passenger vehicle spiked with the light aromatic precursors, and exhaust from two different gasoline-powered passenger vehicles. Three types of seed particles were used: soot aggregates from a diesel vehicle, soot aggregates from a flame soot generator and ammonium sulphate (AS) particles. The hygroscopicity of seed particles with condensed, photochemically produced, anthropogenic SOA was investigated with respect to critical supersaturation (sc) and hygroscopic growth factor (gf) at 90% relative humidity. The hygroscopicity parameter κ was calculated for the two regimes: κsc and κgf, from measurements of sc and gf, respectively. The two κ showed significant discrepancies, with a κgf /κsc ratio closest to one for the gasoline experiments with ammonium sulphate seed and lower for the soot seed experiments. Empirical observations of sc and gf were compared to theoretical predictions, using modified Köhler theory where water solubility limitations were taken into account. The results indicate that the inconsistency between measurements in the subsaturated and supersaturated regimes may be explained by part of the organic material in the particles produced from anthropogenic precursors having a limited solubility in water.
|
|
| 5. |
- Boldemann, C., et al.
(author)
-
Preschool outdoor play environment may combine promotion of children's physical activity and sun protection. Further evidence from Southern Sweden and North Carolina
- 2011
-
In: Science and Sports. - : Elsevier BV. - 0765-1597. ; 26:2, s. 72-82
-
Conference paper (peer-reviewed)abstract
- Objective. - To study the impact of preschool outdoor environments on children's physical activity and solar ultraviolet (UV) exposure at different latitudes and countries. Methods. Outdoor environments of 11 preschools (two in Raleigh NC, USA, Lat.36 degrees N, nine in Malmo, Sweden, Lat.55 degrees N) were scored (OPEC) regarding space, vegetation, hilly terrain and level of integration between open spaces, vegetation and play structures. Free sky (%) was determined by imaging. Physical activity was measured by pedometers and solar UV-exposure by polysulphone dosimeters during 5 days in spring 2009, and individual background data gathered by questionnaires and anthropometric measurements. Global UV radiation was measured and available individual UV radiation (%) computed. Results. - In Malmo, mean step count/minute was 21.2 in preschools with high-scored environment vs. 17.6 in low-scored environments, and UV-exposure lower, 26% vs. 43% of available UV during outdoor stay. In Raleigh, step count/minute was 12.3 and UV-exposure of available UV 27% during outdoor stay. Conclusions. - Step count/minute was lower in Raleigh than in Malmo, but in Malmo children at low-scored environments ran a higher risk of sunburn than in Raleigh. Trees and shrubbery integrated in children's playscape trigger both physical activity and sun-protective behaviour in Sweden, and previous measurements in Stockholm were confirmed. Such outdoor environment should be recommended, but the role of season and climate needs to be further explored. (C) 2011 Elsevier Masson SAS. All rights reserved.
|
|
| 6. |
|
|
| 7. |
- Malik, Azhar, et al.
(author)
-
A Potential Soot Mass Determination Method from Resistivity Measurement of Thermophoretically Deposited Soot
- 2011
-
In: AEROSOL SCIENCE AND TECHNOLOGY. - : Taylor and Francis. - 0278-6826 .- 1521-7388. ; 45:2, s. 284-294
-
Journal article (peer-reviewed)abstract
- Miniaturized detection systems for nanometer-sized airborne particles are in demand, for example in applications for onboard diagnostics downstream particulate filters in modern diesel engines. A soot sensor based on resistivity measurements was developed and characterized. This involved generation of soot particles using a quenched co-flow diffusion flame; depositing the particles onto a sensor substrate using thermophoresis and particle detection using a finger electrode structure, patterned on thermally oxidized silicon substrate. The generated soot particles were characterized using techniques including Scanning Mobility Particle Sizer for mobility size distributions, Differential Mobility Analyzer-Aerosol Particle Mass analyzer for the mass-mobility relationship, and Transmission Electron Microscopy for morphology. The generated particles were similar to particles from diesel engines in concentration, mobility size distribution, and mass fractal dimension. The primary particle size, effective density and organic mass fraction were slightly lower than values reported for diesel engines. The response measured with the sensors was largely dependent on particle mass concentration, but increased with increasing soot aggregate mobility size. Detection down to cumulative mass as small as 20-30 mu g has been demonstrated. The detection limit can be improved by using a more sensitive resistance meter, modified deposition cell, larger flow rates of soot aerosol and modifying the sensor surface.
|
|
| 8. |
|
|
| 9. |
|
|
| 10. |
|
|
