| 1. |
- Bartels-Rausch, Thorsten, et al.
(författare)
-
Ice structures, patterns, and processes: A view across the icefields
- 2012
-
Ingår i: Reviews of Modern Physics. ; 84:2, s. 885-944
-
Forskningsöversikt (refereegranskat)abstract
- From the frontiers of research on ice dynamics in its broadest sense, this review surveys the structures of ice, the patterns or morphologies it may assume, and the physical and chemical processes in which it is involved. Open questions in the various fields of ice research in nature are highlighted, ranging from terrestrial and oceanic ice on Earth, to ice in the atmosphere, to ice on other Solar System bodies and in interstellar space.
|
|
| 2. |
- Andersson, Patrik U, 1970, et al.
(författare)
-
Formation of Highly Rovibrationally Excited Ammonia from Dissociative Recombination of NH4
- 2010
-
Ingår i: Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 1:17, s. 2519-2523
-
Tidskriftsartikel (refereegranskat)abstract
- The internal energy distribution of ammonia formed in the dissociative recombination (DR) of NH4+ with electrons has been studied by an imaging technique at the ion storage ring CRYRING. The DR process resulted in the formation of NH3 + H (0.90 ± 0.01), with minor contributions from channels producing NH2 + H2 (0.05 ± 0.01) and NH2 + 2H (0.04 ± 0.02). The formed NH3 molecules were highly internally excited, with a mean rovibrational energy of 3.3 ± 0.4 eV, which corresponds to 70% of the energy released in the neutralization process. The internal energy distribution was semiquantitatively reproduced by ab initio direct dynamics simulations, and the calculations suggested that the NH3 molecules are highly vibrationally excited while rotational excitation is limited. The high internal excitation and the translational energy of NH3 and H will influence their subsequent reactivity, an aspect that should be taken into account when developing detailed models of the interstellar medium and ammonia-containing plasmas.
|
|
| 3. |
- Boman, Johan, 1955, et al.
(författare)
-
ASSESSING THE ENVIRONMENT WITH X-RAY FLUORESCENCE
- 2011
-
Ingår i: Advances in X-ray Analysis. - 0376-0308. ; 54, s. 266-279
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper we will introduce the general benefits of X-Ray Fluorescence spectrometry (XRF) for assessing the condition of the outer environment, especially where ambient aerosol particles are causing environmental disturbances. Examples from recent environmental studies are presented, and energy dispersive XRF is concluded to be a powerful, nondestructive yet easily applicable tool to supply detailed elemental information of particles collected in different applications. The further development and future potential of the method for detailed analysis of aerosol particles are discussed.
|
|
| 4. |
- Elsasser, M., et al.
(författare)
-
Organic molecular markers and signature from wood combustion particles in winter ambient aerosols: aerosol mass spectrometer (AMS) and high time-resolved GC-MS measurements in Augsburg, Germany
- 2012
-
Ingår i: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 12:14, s. 6113-6128
-
Tidskriftsartikel (refereegranskat)abstract
- The impact of wood combustion on ambient aerosols was investigated in Augsburg, Germany during a winter measurement campaign of a six-week period. Special attention was paid to the high time resolution observations of wood combustion with different mass spectrometric methods. Here we present and compare the results from an Aerodyne aerosol mass spectrometer (AMS) and gas chromatographic - mass spectrometric (GC-MS) analysed PM1 filters on an hourly basis. This includes source apportionment of the AMS derived organic matter (OM) using positive matrix factorisation (PMF) and analysis of levoglucosan as wood combustion marker, respectively. During the measurement period nitrate and OM mass are the main contributors to the defined submicron particle mass of AMS and Aethalometer with 28% and 35%, respectively. Wood combustion organic aerosol (WCOA) contributes to OM with 23% on average and 27% in the evening and night time. Conclusively, wood combustion has a strong influence on the organic matter and overall aerosol composition. Levoglucosan accounts for 14% of WCOA mass with a higher percentage in comparison to other studies. The ratio between the mass of levoglucosan and organic carbon amounts to 0.06. This study is unique in that it provides a one-hour time resolution comparison between the wood combustion results of the AMS and the GC-MS analysed filter method at a PM1 particle size range. The comparison of the concentration variation with time of the PMF WCOA factor, levoglucosan estimated by the AMS data and the levoglucosan measured by GC-MS is highly correlated (R-2 = 0.84), and a detailed discussion on the contributors to the wood combustion marker ion at mass-to-charge ratio 60 is given. At the end, both estimations, the WCOA factor and the levoglucosan concentration estimated by AMS data, allow to observe the variation with time of wood combustion emissions (gradient correlation with GC-MS levoglucosan of R-2 = 0.84). In the case of WCOA, it provides the estimated magnitude of wood combustion emission. Quantitative estimation of the levoglucosan concentration from the AMS data is problematic due to its overestimation in comparison to the levoglucosan measured by the GC-MS.
|
|
| 5. |
- Gaita, Samuel Mwaniki, 1976, et al.
(författare)
-
Source apportionment and seasonal variation of PM2.5 in a Sub-Sahara African city : Nairobi, Kenya
- 2014
-
Ingår i: Atmospheric Chemistry And Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 14:18, s. 9977-9991
-
Tidskriftsartikel (refereegranskat)abstract
- Sources of airborne particulate matter and their seasonal variation in urban areas in Sub-Saharan Africa are poorly understood due to lack of long-term measurement data. In view of this, filter samples of airborne particulate matter (particle diameter ≤2.5 μm, PM2.5) were collected between May 2008 and April 2010 at two sites (urban background site and suburban site) within the Nairobi metropolitan area. A total of 780 samples were collected and analyzed for particulate mass, black carbon (BC) and 13 trace elements.The average PM2.5 concentration at the urban background site was 21±9.5 μg m−3, whereas the concentration at the suburban site was 13±7.3 μg m−3. The daily PM2.5 concentrations exceeded 25 μg m−3 (the World Health Organization 24 h guideline value) on 29% of the days at the urban background site and 7% of the days at the suburban site. At both sites, BC, Fe, S and Cl accounted for approximately 80% of all detected elements. Positive matrix factorization analysis identified five source factors that contribute to PM2.5 in Nairobi, namely traffic, mineral dust, industry, combustion and a mixed factor (composed of biomass burning, secondary aerosol and aged sea salt).Mineral dust and traffic factors were related to approximately 74% of PM2.5. The identified source factors exhibited seasonal variation, apart from the traffic factor, which was prominently consistent throughout the sampling period. Weekly variations were observed in all factors, with weekdays having higher concentrations than weekends. The results provide information that can be exploited for policy formulation and mitigation strategies to control air pollution in Sub-Saharan African cities.
|
|
| 6. |
- Kong, Xiangrui, et al.
(författare)
-
Environmental molecular beam studies of ice surface processes
- 2011
-
Ingår i: Physics and Chemistry of Ice 2010 (The 12th International Conference on the Physics and Chemistry of Ice, Sapporo, Japan, September 5-10, 2010, Eds. Y. Furukawa, G. Sazaki, T. Uchida, N. Watanabe, Hokkaido University Press, Sapporo, Japan, 2011). - 9784832903616 ; , s. 79-88
-
Konferensbidrag (refereegranskat)abstract
- The development and application of a new molecular beam setup for studies of gas-ice interactions at pressures in the 0.001 mbar range is described. Direct simulation Monte Carlo calculations have been applied to optimize the experimental design with respect to gas transmission through the high pressure zone outside the ice surface and pressure along the surface plane. In a first application of the new setup elastic helium scattering and light scattering have been used to study the formation of water, methanol and water-methanol ice on a graphite surface in the temperature range from 180 to 215 K. Water does not wet the graphite surface under these conditions, in agreement with earlier results obtained below 180 K, while methanol readily forms a thin layer on the surface. Methanol enhances water ice nucleation and influences the properties of the ice formed, but does not have a major impact on ice growth or evaporation once a thick water-containing ice layer has formed. The potential for further development of the molecular beam technique are discussed.
|
|
| 7. |
- Kong, Xiangrui, et al.
(författare)
-
Ice Formation via Deposition Mode Nucleation on Bare and Alcohol-Covered Graphite Surfaces
- 2012
-
Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 116:16, s. 8964-8974
-
Tidskriftsartikel (refereegranskat)abstract
- Deposition of water on aerosol particles contributes to ice cloud formation in the atmosphere with implications for the water cycle and climate on Earth. The heterogeneous ice nucleation process is influenced by physicochemical properties of the substrate, but the mechanisms remain incompletely understood. Here, we report on ice formation on bare and alcohol-covered graphite at temperatures from 175 to 213 K, probed by elastic helium and light scattering. Water has a low wettability on bare and butanol-covered graphite resulting in the growth of rough ice surfaces. In contrast, preadsorbed methanol provides hydrophilic surface sites and results in the formation of smooth crystalline ice; an effect that is pronounced also for submonolayer methanol coverages. The alcohols primarily reside at the ice surface and at the ice–graphite interface with a minor fraction being incorporated into the growing ice structures. Methanol has no observable effect on gas/solid water vapor exchange, whereas butanol acts as a transport barrier for water resulting in a reduction in ice evaporation rate at 185 K. Implications for the description of deposition mode freezing are discussed.
|
|
| 8. |
- Kong, Xiangrui, et al.
(författare)
-
Water Accommodation and Desorption Kinetics on Ice
- 2014
-
Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 118:22, s. 3973-3979
-
Tidskriftsartikel (refereegranskat)abstract
- The interaction of water vapor with ice remains incompletely understood despite its importance in environmental processes. A particular concern is the probability for water accommodation on the ice surface, for which results from earlier studies vary by more than 2 orders of magnitude. Here, we apply an environmental molecular beam method to directly determine water accommodation and desorption kinetics on ice. Short D2O gas pulses collide with H2O ice between 170 and 200 K, and a fraction of the adsorbed molecules desorbs within tens of milliseconds by first order kinetics. The bulk accommodation coefficient decreases nonlinearly with increasing temperature and reaches 0.41 +/- 0.18 at 200 K. The kinetics are well described by a model wherein water molecules adsorb in a surface state from which they either desorb or become incorporated into the bulk ice structure. The weakly bound surface state affects water accommodation on the ice surface with important implications for atmospheric cloud processes.
|
|
| 9. |
- Kong, Xiangrui, et al.
(författare)
-
Water Accommodation on Ice and Organic Surfaces: Insights from Environmental Molecular Beam Experiments
- 2014
-
Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 118:47, s. 13378-13386
-
Tidskriftsartikel (refereegranskat)abstract
- Water uptake on aerosol and cloud particles in the atmosphere modifies their chemistry and microphysics with important implications for climate on Earth. Here, we apply an environmental molecular beam (EMB) method to characterize water accommodation on ice and organic surfaces. The adsorption of surface-active compounds including short-chain alcohols, nitric acid, and acetic acid significantly affects accommodation of D2O on ice. n-Hexanol and n-butanol adlayers reduce water uptake by facilitating rapid desorption and function as inefficient barriers for accommodation as well as desorption of water, while the effect of adsorbed methanol is small. Water accommodation is close to unity on nitric-acid- and acetic-acid-covered ice, and accommodation is significantly more efficient than that on the bare ice surface. Water uptake is inefficient on solid alcohols and acetic acid but strongly enhanced on liquid phases including a quasi-liquid layer on solid n-butanol. The EMB method provides unique information on accommodation and rapid kinetics on volatile surfaces, and these studies suggest that adsorbed organic and acidic compounds need to be taken into account when describing water at environmental interfaces.
|
|
| 10. |
- Kovacevik, Borka, 1972, et al.
(författare)
-
Elemental composition of fine particulate matter (PM2.5) in Skopje, FYR of Macedonia
- 2011
-
Ingår i: X-Ray Spectrometry. - : Wiley. - 0049-8246 .- 1097-4539. ; 40:4, s. 280-288
-
Tidskriftsartikel (refereegranskat)abstract
- Aerosol samples were collected at an urban background site in Skopje, Former Yugoslavic Republic of Macedonia, during four measurement campaigns from December 2006 to October 2007. An impactor was used to collect particulate matter (PM2.5) aerosol particles and the samples were analyzed for the concentrations of particulate mass, black carbon (BC), and 17 elements. The 12-h average PM2.5 concentrations varied in the range 10-140 mu g m(-3) with the highest concentrations measured during wintertime pollution episodes and during the summer period. Pair-wise correlations and crustal enrichment were studied and the data set was analyzed by factor analysis and positive matrix factorization. Major aerosol components were identified as mineral dust (main observed tracers Si, K, Ca, Ti, Fe, Sr, and Rb), combustion (BC, S, K, V, and Ni), traffic-related aerosol (Pb and Zn), and secondary sulfate combined with mineral dust. Combustion sources dominated during wintertime and were likely due to heavy oil combustion, biomass burning, and other industrial activities within the city area. Mineral dust was observed throughout the year, but the concentrations peaked during the unusually hot and dry summer of 2007. It is concluded that Skopje suffers from serious air pollution due to central and residential heating, the transport sector, and industrial activities within the city, and contributions from mineral dust increase the PM2.5 concentrations under dry periods. Topography and meteorological conditions aggravate the problems and make the air quality comparable with the conditions in other highly polluted cities in Southern Europe and worldwide.
|
|
| 11. |
- Papagiannakopoulos, Panos, et al.
(författare)
-
Surface Transformations and Water Uptake on Liquid and Solid Butanol near the Melting Temperature
- 2013
-
Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 117:13, s. 6678-6685
-
Tidskriftsartikel (refereegranskat)abstract
- Water interactions with organic surfaces are of central importance in biological systems and many Earth system processes. Here we describe experimental studies of water collisions and uptake kinetics on liquid and solid butanol from 160 to 200 K. Hyperthermal D2O molecules (0.32 eV) undergo efficient trapping on both solid and liquid butanol, and only a minor fraction scatters inelastically after an 80% loss of kinetic energy to surface modes. Trapped molecules either desorb within a few ms, or are taken up by the butanol phase during longer times. The water uptake and surface residence time increase with temperature above 180 K indicating melting of the butanol surface 4.5 K below the bulk melting temperature. Water uptake changes gradually across the melting point and trapped molecules are rapidly lost by diffusion into the liquid above 190 K. This indicates that liquid butanol maintains a surface phase with limited water permeability up to 5.5 K above the melting point. These surface observations are indicative of an incremental change from solid to liquid butanol over a range of 10 K straddling the bulk melting temperature, in contrast to the behavior of bulk butanol and previously studied materials.
|
|
| 12. |
- Papagiannakopoulos, Panos, et al.
(författare)
-
Water Interactions with Acetic Acid Layers on Ice and Graphite
- 2014
-
Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 118:47, s. 13333-13340
-
Tidskriftsartikel (refereegranskat)abstract
- Adsorbed organic compounds modify the properties of environmental interfaces with potential implications for many Earth system processes. Here, we describe experimental studies of water interactions with acetic acid (AcOH) layers on ice and graphite surfaces at temperatures from 186 to 200 K. Hyperthermal D2O water molecules are efficiently trapped on all of the investigated surfaces, with only a minor fraction that scatters inelastically after an 80% loss of kinetic energy to surface modes. Trapped molecules desorb rapidly from both mu m-thick solid AcOH and AcOH monolayers on graphite, indicating that water has limited opportunities to form hydrogen bonds with these surfaces. In contrast, trapped water molecules bind efficiently to AcOH-covered ice and remain on the surface on the observational time scale of the experiments (60 ms). Thus, adsorbed AcOH is observed to have a significant impact on waterice surface properties and to enhance the water accommodation coefficient compared to bare ice surfaces. The mechanism for increased water uptake and the implications for atmospheric cloud processes are discussed.
|
|
| 13. |
- Romero Lejonthun, Liza, 1973, et al.
(författare)
-
Interactions of N2O5 and Related Nitrogen Oxides with Ice Surfaces: Desorption Kinetics and Collision Dynamics
- 2014
-
Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 118:47, s. 13427-13434
-
Tidskriftsartikel (refereegranskat)abstract
- The detailed interactions of nitrogen oxides with ice are of fundamental interest and relevance for chemistry in cold regions of the atmosphere. Here, the interactions of NO, NO2, N2O4, and N2O5 with ice surfaces at temperatures between 93 and 180 K are investigated with molecular beam techniques. Surface collisions are observed to result in efficient transfer of kinetic energy and trapping of molecules on the ice surfaces. NO and NO2 rapidly desorb from pure ice with upper bounds for the surface binding energies of 0.16 +/- 0.02 and 0.26 +/- 0.03 eV, respectively. Above 150 K, N2O4 desorption follows first-order kinetics and is well described by the Arrhenius parameters E-a = 0.39 +/- 0.04 eV and A = 10((15.41.2)) s(1), while a stable N2O4 adlayer is formed at lower temperatures. A fraction of incoming N2O5 reacts to form HNO3 on the ice surface. The N2O5 desorption rates are substantially lower on pure water ice (Arrhenius parameters: Ea = 0.36 +/- 0.02 eV; A = 10(15.3 +/- 0.7) s(-1)) than on HNO3-covered ice (Ea = 0.24 +/- 0.02 eV; A = 10(11.5 +/- 0.7) s(-1)). The N2O5 desorption kinetics also sensitively depend on the sub-monolayer coverage of HNO3, with a minimum in N2O5 desorption rate at a low but finite coverage of HNO3. The studies show that none of the systems with resolvable desorption kinetics undergo ordinary desorption from ice, and instead desorption likely involves two or more surface states, with additional complexity added by coadsorbed molecules.
|
|
| 14. |
- Shannigrahi, Ardhendu Sekhar, 1965, et al.
(författare)
-
n-Alkanoic monocarboxylic acid concentrations in urban and rural aerosols : Seasonal dependence and major sources
- 2014
-
Ingår i: Atmospheric research. - : Elsevier BV. - 0169-8095 .- 1873-2895. ; 143, s. 228-237
-
Tidskriftsartikel (refereegranskat)abstract
- We report new data on the abundance and distribution of n-monocarboxylic acids (n-MCAs) in fine- and coarse-mode aerosols in rural and urban areas of Sweden, and determine their possible sources. Overall, C6–C16n-MCAs accounted for ~ 0.5–1.2% of the total PM10 (particulate matter ≤ 10 μm) mass. In general, the C12–C16 fraction was the most abundant (> 75%), with the exception of wintertime samples from a rural site, where C6–C11 acids accounted for 65% of the total C6–C16n-MCA mass. Positive matrix factorization analysis revealed four major sources of n-MCAs: traffic emissions, wood combustion, microbial activity, and a fourth factor that was dominated by semi-volatile n-MCAs.Traffic emissions were important in the urban environment in both seasons and at the rural site during winters, and were a major source of C9–C11 acids. Wood combustion was a significant source at urban sites during the winter and also to some extent at the rural site in both seasons. This is consistent with the use of wood for domestic heating but may also be related to meat cooking. Thus, during the winter, traffic, wood combustion and microbial activity were all important sources in the urban environment, while traffic was the dominant source at the rural site. During the summer, there was considerable day-to-day variation in n-MCA concentrations but microbial activity was the dominant source. The semi-volatile low molecular weight C6–C8 acids accounted for a small (~ 5–10%) fraction of the total mass of n-MCAs. This factor is unlikely to be linked to a single source and its influence instead reflects the partitioning of these compounds between the gas and particle phases. This would explain their greater contribution during the winter.
|
|
| 15. |
- Thomson, Erik S, et al.
(författare)
-
Collision Dynamics and Solvation of Water Molecules in a Liquid Methanol Film
- 2011
-
Ingår i: Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 2:17, s. 2174-2178
-
Tidskriftsartikel (refereegranskat)abstract
- Environmental molecular beam experiments are used to examine water interactions with liquid methanol films at temperatures from 170 to 190 K. We find that water molecules with 0.32 eV incident kinetic energy are efficiently trapped by the liquid methanol. The scattering process is characterized by an efficient loss of energy to surface modes with a minor component of the incident beam that is inelastically scattered. Thermal desorption of water molecules has a well characterized Arrhenius form with an activation energy of 0.47 ± 0.11 eV and pre-exponential factor of 4.6 × 10^(15±3) s^(–1). We also observe a temperature-dependent incorporation of incident water into the methanol layer. The implication for fundamental studies and environmental applications is that even an alcohol as simple as methanol can exhibit complex and temperature-dependent surfactant behavior.
|
|
| 16. |
- Thomson, Erik S, et al.
(författare)
-
Collision dynamics and uptake of water on alcohol-covered ice
- 2013
-
Ingår i: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 13:4, s. 2223-2233
-
Tidskriftsartikel (refereegranskat)abstract
- Molecular scattering experiments are used to investigate water interactions with methanol and n-butanol covered ice between 155 K and 200 K. The inelastically scattered and desorbed products of an incident molecular beam are measured and analyzed to illuminate molecular scale processes. The residence time and uptake coefficients of water impinging on alcohol-covered ice are calculated. The surfactant molecules are observed to affect water transport to and from the ice surface in a manner that is related to the number of carbon atoms they contain. Butanol films on ice are observed to reduce water uptake by 20 %, whereas methanol monolayers pose no significant barrier to water transport. Water colliding with methanol covered ice rapidly permeates the alcohol layer, but on butanol water molecules have mean surface lifetimes of less than or similar to 0.6 ms, enabling some molecules to thermally desorb before reaching the water ice underlying the butanol. These observations are put into the context of cloud and atmospheric scale processes, where such surfactant layers may affect a range of aerosol processes, and thus have implications for cloud evolution, the global water cycle, and long term climate.
|
|
| 17. |
- Tuoriniemi, Jani, 1982, et al.
(författare)
-
Intermethod comparison of the particle size distributions of colloidal silica nanoparticles
- 2014
-
Ingår i: Science and Technology of Advanced Materials. - : Informa UK Limited. - 1468-6996 .- 1878-5514. ; 15:3
-
Tidskriftsartikel (refereegranskat)abstract
- There can be a large variation in the measured diameter of nanoparticles depending on which method is used. In this work, we have strived to accurately determine the mean particle diameter of 3040 nm colloidal silica particles by using six different techniques. A quantitative agreement between the particle size distributions was obtained by scanning electron microscopy (SEM), and electrospray-scanning mobility particle sizer (ES SMPS). However, transmission electron microscopy gave a distribution shifted to smaller sizes. After confirming that the magnification calibration was consistent, this was attributed to sample preparation artifacts. The hydrodynamic diameter, d(h), was determined by dynamic light scattering (DLS) both in batch mode, and hyphenated with sedimentation field flow fractionation. Surprisingly the dh were smaller than the SEM, and ES SMPS diameters. A plausible explanation for the smaller sizes found with DLS is that a permeable gel layer forms on the particle surface. Results from nanoparticle tracking analysis were strongly biased towards larger diameters, most likely because the silica particles provide low refractive index contrast. Calculations confirmed that the sensitivity is, depending on the shape of the laser beam, strongly size dependent for particles with diameters close to the visualization limit.
|
|
| 18. |
- Uddling, Johan, 1972, et al.
(författare)
-
To what extent do molecular collisions arising from water vapour efflux impede stomatal O3 influx?
- 2012
-
Ingår i: Environmental Pollution. - : Elsevier BV. - 0269-7491. ; 170, s. 39-42
-
Tidskriftsartikel (refereegranskat)abstract
- Pre-requisite for reliable O 3 risk assessment for plants is determination of stomatal O 3 uptake. One unaddressed uncertainty in this context relates to transpiration-induced molecular collisions impeding stomatal O 3 influx. This study quantifies, through physical modelling, the error made when estimating stomatal O 3 flux without accounting for molecular collisions arising from transpiratory mass flow of gas out of the leaf. The analysis demonstrates that the error increases with increasing leaf-to-air water vapour mole fraction difference (Δw), being zero in water vapour saturated air and 4.2% overestimation at Δw of 0.05. Overestimation is approximately twice as large in empirical studies quantifying stomatal O 3 flux from measured leaf or canopy water flux, if neglecting both water vapour-dry air collisions (causing overestimation of leaf conductance) and collisions involving O 3. Correction for transpiration-induced molecular collisions is thus relevant for both empirical research and for large-scale modelling of stomatal O 3 flux across strong spatial Δw gradients. Negligence of molecular collisions arising from transpiration causes overestimation of stomatal ozone flux that increase with leaf-to-air mole fraction difference of water vapour.
|
|
