scholarly journals Diffusivity measurements of volatile organics in levitated viscous aerosol particles

2017 ◽  
Author(s):  
Sandra Bastelberger ◽  
Ulrich K. Krieger ◽  
Beiping Luo ◽  
Thomas Peter
Keyword(s):  
Atmospheric Chemistry ◽  
Glassy State ◽  
Field Measurements ◽  
Tetraethylene Glycol ◽  
Resonance Spectroscopy ◽  
Hygroscopic Growth ◽  
Single Particles ◽  
Diffusion Limitations ◽  
Electrodynamic Balance ◽  
Evaporative Loss

Abstract. Field measurements indicating that atmospheric secondary aerosol (SOA) particles can be present in a highly viscous, glassy state have spurred numerous studies addressing low diffusivities of water in glassy aerosols. The focus of these studies is on kinetic limitations of hygroscopic growth and the plasticizing effect of water. In contrast, much less is known about diffusion limitations of organic molecules and oxidants in viscous matrices. These may affect atmospheric chemistry and gas-particle partitioning of complex mixtures with constituents of different volatility. In this study, we quantify the diffusivity of a volatile organic in a viscous matrix. Evaporation of single particles generated from an aqueous solution of sucrose and small amounts of volatile tetraethylene glycol (PEG-4) is investigated in an electrodynamic balance at controlled humidity (RH) and temperature. The evaporative loss of PEG-4 as determined by Mie resonance spectroscopy is used in conjunction with a radially resolved diffusion model to retrieve translational diffusion coefficients of PEG-4. Comparison of the experimentally derived diffusivities with viscosity estimates for the ternary system reveals a breakdown of the Stokes-Einstein relationship, which has often been invoked to infer diffusivity from viscosity. The evaporation of PEG-4 shows pronounced RH and temperature dependencies and is severely depressed for RH ≲ 30 %, corresponding to diffusivities

scholarly journals Diffusivity measurements of volatile organics in levitated viscous aerosol particles

2017 ◽  
Vol 17 (13) ◽  
pp. 8453-8471 ◽  
Author(s):  
Sandra Bastelberger ◽  
Ulrich K. Krieger ◽  
Beiping Luo ◽  
Thomas Peter
Keyword(s):  
Atmospheric Chemistry ◽  
Aerosol Particles ◽  
Glassy State ◽  
Organic Aerosol ◽  
Diffusion Activation Energy ◽  
Tetraethylene Glycol ◽  
Resonance Spectroscopy ◽  
Hygroscopic Growth ◽  
Diffusion Limitations ◽  
Volatile Organic

Abstract. Field measurements indicating that atmospheric secondary organic aerosol (SOA) particles can be present in a highly viscous, glassy state have spurred numerous studies addressing low diffusivities of water in glassy aerosols. The focus of these studies is on kinetic limitations of hygroscopic growth and the plasticizing effect of water. In contrast, much less is known about diffusion limitations of organic molecules and oxidants in viscous matrices. These may affect atmospheric chemistry and gas–particle partitioning of complex mixtures with constituents of different volatility. In this study, we quantify the diffusivity of a volatile organic in a viscous matrix. Evaporation of single particles generated from an aqueous solution of sucrose and small amounts of volatile tetraethylene glycol (PEG-4) is investigated in an electrodynamic balance at controlled relative humidity (RH) and temperature. The evaporative loss of PEG-4 as determined by Mie resonance spectroscopy is used in conjunction with a radially resolved diffusion model to retrieve translational diffusion coefficients of PEG-4. Comparison of the experimentally derived diffusivities with viscosity estimates for the ternary system reveals a breakdown of the Stokes–Einstein relationship, which has often been invoked to infer diffusivity from viscosity. The evaporation of PEG-4 shows pronounced RH and temperature dependencies and is severely depressed for RH ≲ 30 %, corresponding to diffusivities < 10−14 cm2 s−1 at temperatures < 15 °C. The temperature dependence is strong, suggesting a diffusion activation energy of about 300 kJ mol−1. We conclude that atmospheric volatile organic compounds can be subject to severe diffusion limitations in viscous organic aerosol particles. This may enable an important long-range transport mechanism for organic material, including pollutant molecules such as polycyclic aromatic hydrocarbons (PAHs).

scholarly journals A Dual-Droplet Approach for Measuring the Hygroscopicity of Aqueous Aerosol

2021 ◽  
Author(s):  
Jack M. Choczynski ◽  
Ravleen Kaur Kohli ◽  
Craig S. Sheldon ◽  
Chelsea L. Price ◽  
James F. Davies
Keyword(s):  
Chemical Reactivity ◽  
Aerosol Particles ◽  
High Viscosity ◽  
Tetraethylene Glycol ◽  
Hygroscopic Growth ◽  
Electrodynamic Balance ◽  
Sample Droplet ◽  
Better Than

Abstract. Accurate characterization of the water activity and hygroscopicity of aqueous aerosol material allows us to predict the chemical and physical state of aerosol particles exposed to humid conditions in the environment. The hygroscopicity of aerosol determines the size, phase morphology, viscosity, chemical reactivity, and optical properties of constituent particles, and directly impacts their ability to form clouds in the atmosphere. In this work, we describe measurements of hygroscopicity using a linear quadrupole electrodynamic balance (LQ-EDB). We levitate two droplets, one droplet that acts as a relative humidity (RH) probe and one sample droplet, and expose them to controlled environmental conditions. We describe the development of a RH measurement using probe droplets of aqueous NaCl or LiCl, allowing for precise in-situ measurements of RH in the LQ-EDB chamber. We demonstrate that the RH may be determined with an accuracy of 0.5 % at 50 % RH and better than 0.1 % at 90 % RH using NaCl, and show that LiCl is effective at characterizing the RH from ~10 % RH up to ~90 %. We simultaneously measure the response of sample droplets containing aqueous material (including ammonium sulfate, citric acid, 1,2,6-hexanetriol, and tetraethylene glycol) and report hygroscopic growth via their radial growth factors. We use established thermodynamic models to validate the accuracy of the RH probe and to compare with the measured hygroscopicity of the samples. This approach shows significant advantages over other methods for accurately characterizing the hygroscopicity of samples with a range of characteristics, such as high viscosity and vapor pressure.

scholarly journals Investigation of water adsorption and hygroscopicity of atmospherically relevant particles using a commercial vapor sorption analyzer

2017 ◽  
Vol 10 (10) ◽  
pp. 3821-3832 ◽  
Author(s):  
Wenjun Gu ◽  
Yongjie Li ◽  
Jianxi Zhu ◽  
Xiaohong Jia ◽  
Qinhao Lin ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
Radiative Forcing ◽  
Water Adsorption ◽  
Theoretical Data ◽  
Atmospheric Particles ◽  
Relative Mass ◽  
Nonspherical Particles ◽  
Vapor Sorption ◽  
Hygroscopic Growth ◽  
Dry Conditions

Abstract. Water adsorption and hygroscopicity are among the most important physicochemical properties of aerosol particles, largely determining their impacts on atmospheric chemistry, radiative forcing, and climate. Measurements of water adsorption and hygroscopicity of nonspherical particles under subsaturated conditions are nontrivial because many widely used techniques require the assumption of particle sphericity. In this work we describe a method to directly quantify water adsorption and mass hygroscopic growth of atmospheric particles for temperature in the range of 5–30 °C, using a commercial vapor sorption analyzer. A detailed description of instrumental configuration and experimental procedures, including relative humidity (RH) calibration, is provided first. It is then demonstrated that for (NH4)2SO4 and NaCl, deliquescence relative humidities and mass hygroscopic growth factors measured using this method show good agreements with experimental and/or theoretical data from literature. To illustrate its ability to measure water uptake by particles with low hygroscopicity, we used this instrument to investigate water adsorption by CaSO4 ⋅ 2H2O as a function of RH at 25 °C. The mass hygroscopic growth factor of CaSO4 ⋅ 2H2O at 95 % RH, relative to that under dry conditions (RH  < 1 %), was determined to be (0.450±0.004) % (1σ). In addition, it is shown that this instrument can reliably measure a relative mass change of 0.025 %. Overall, we have demonstrated that this commercial instrument provides a simple, sensitive, and robust method to investigate water adsorption and hygroscopicity of atmospheric particles.

scholarly journals Importance of Meteorology and Chemistry in Determining Air Pollutant Levels During COVID-19 Lockdown in Indian Cities

2021 ◽  
Author(s):  
Leigh Crilley ◽  
Yashar Iranpour ◽  
Cora J. Young
Keyword(s):  
Atmospheric Chemistry ◽  
Field Measurements ◽  
Air Pollutant ◽  
Mitigation Strategies ◽  
Ozone Production ◽  
Linear Relationships ◽  
Regional Sources ◽  
Volatile Organic ◽  
Emission Changes ◽  
Indian Cities

To accurately quantify impact of short-term interventions (such as COVID-19 lockdown) on air pollutant levels, meteorology and atmospheric chemistry need to be considered in addition to emission changes. We demonstrate that regional sources have a significant influence on PM<sub>2.5 </sub>levels in Delhi and Hyderabad due to the small reduction calculated post-lockdown after weather-normalization, indicating that future PM<sub>2.5</sub> mitigation strategies should focus on national-scale, as well as local sources. Furthermore, we demonstrate with field measurements that ozone production in Delhi is likely volatile organic compound (VOC)-limited, in agreement with previous modelling predictions, indicating that ozone mitigation should focus on dominant VOC sources. This work highlights the complexity in developing mitigation strategies for air pollution due to its non-linear relationships with emissions, chemistry and meteorology.

scholarly journals Electrodynamic balance measurements of thermodynamic, kinetic, and optical aerosol properties inaccessible to bulk methods

2015 ◽  
Vol 8 (6) ◽  
pp. 2397-2408 ◽  
Author(s):  
S. S. Steimer ◽  
U. K. Krieger ◽  
Y.-F. Te ◽  
D. M. Lienhard ◽  
A. J. Huisman ◽  
...  
Keyword(s):  
Refractive Index ◽  
Light Scattering ◽  
Room Temperature ◽  
Shikimic Acid ◽  
Resonance Spectroscopy ◽  
Equilibrium Conditions ◽  
Electrodynamic Balance ◽  
Mie Resonance ◽  
Water Diffusivity ◽  
Activity Density

Abstract. Measurements of a single, levitated particle in an electrodynamic balance are an established tool for deriving thermodynamic and material data such as density, refractive index and activities of components of an aqueous solution under supersaturated conditions, where bulk measurements are not possible. The retrieval relies on combining mass-to-charge data and size data from light scattering. Here, we use a combination of low- and high-resolution Mie resonance spectroscopy to obtain radius data, enabling an accurate size determination not only when the particle is in equilibrium, but also when it is out of equilibrium due to kinetic limitation of mass transport. With the data measured under non-equilibrium conditions, it is possible to retrieve the water diffusivity. A challenge is that the radius retrieval by comparing measured light scattering with Mie theory requires the knowledge of refractive index as a function of concentration. Here, we show an iterative retrieval of refractive index and size for compounds for which data cannot be obtained in the bulk either due to lack of sufficient amounts of sample or limited solubility. We demonstrate the measurement strategy and the retrieval of water activity, density, refractive index and water diffusivity for aqueous shikimic acid. Water diffusivity in concentrated shikimic acid decreases by 6 orders of magnitude at 250 K compared to that at room temperature.

scholarly journals Characterization and first results from LACIS-T: a moist-air wind tunnel to study aerosol–cloud–turbulence interactions

2020 ◽  
Vol 13 (4) ◽  
pp. 2015-2033 ◽  
Author(s):  
Dennis Niedermeier ◽  
Jens Voigtländer ◽  
Silvio Schmalfuß ◽  
Daniel Busch ◽  
Jörg Schumacher ◽  
...  
Keyword(s):  
Wind Tunnel ◽  
Spatial Scales ◽  
Experimental Studies ◽  
Field Measurements ◽  
Hygroscopic Growth ◽  
Moist Air ◽  
Aerosol Cloud ◽  
Cloud Microphysical Processes ◽  
First Results ◽  
Microphysical Processes

Abstract. The interactions between turbulence and cloud microphysical processes have been investigated primarily through numerical simulation and field measurements over the last 10 years. However, only in the laboratory we can be confident in our knowledge of initial and boundary conditions and are able to measure under statistically stationary and repeatable conditions. In the scope of this paper, we present a unique turbulent moist-air wind tunnel, called the Turbulent Leipzig Aerosol Cloud Interaction Simulator (LACIS-T) which has been developed at TROPOS in order to study cloud physical processes in general and interactions between turbulence and cloud microphysical processes in particular. The investigations take place under well-defined and reproducible turbulent and thermodynamic conditions covering the temperature range of warm, mixed-phase and cold clouds (25∘C>T>-40∘C). The continuous-flow design of the facility allows for the investigation of processes occurring on small temporal (up to a few seconds) and spatial scales (micrometer to meter scale) and with a Lagrangian perspective. The here-presented experimental studies using LACIS-T are accompanied and complemented by computational fluid dynamics (CFD) simulations which help us to design experiments as well as to interpret experimental results. In this paper, we will present the fundamental operating principle of LACIS-T, the numerical model, and results concerning the thermodynamic and flow conditions prevailing inside the wind tunnel, combining both characterization measurements and numerical simulations. Finally, the first results are depicted from deliquescence and hygroscopic growth as well as droplet activation and growth experiments. We observe clear indications of the effect of turbulence on the investigated microphysical processes.

scholarly journals Impact of aerosol hygroscopic growth on retrieving aerosol extinction coefficient profiles from elastic-backscatter lidar signals

2017 ◽  
Author(s):  
Gang Zhao ◽  
Chunsheng Zhao ◽  
Ye Kuang ◽  
Jiangchuan Tao ◽  
Wangshu Tan ◽  
...  
Keyword(s):  
Extinction Coefficient ◽  
Enhancement Factor ◽  
Field Measurements ◽  
Relative Bias ◽  
Aerosol Extinction ◽  
Hygroscopic Growth ◽  
The North ◽  
True Value ◽  
Lidar Measurements ◽  
Aerosol Extinction Coefficient

Abstract. Light detection and ranging (lidar) measurements have been widely used to profile ambient aerosol extinction coefficient (σext). Particle extinction-to-backscatter ratio (lidar ratio, LR), which highly depends on aerosol dry particle number size distribution (PNSD) and aerosol hygroscopicity, is introduced to retrieve the σext profile from elastic-backscatter lidar signals. Conventionally, a constant column integrated LR that is estimated from aerosol optical depth is used by the retrieving algorithms. In this paper, the influences of aerosol PNSD, aerosol hygroscopic growth and relative humidity (RH) profiles on the variation of LR are investigated based on the datasets from field measurements in the North China Plain (NCP). Results show that LR has an enhancement factor of 2.2 when RH reaches 92 %. Simulation results indicate that both the magnitude and vertical structures of the σext profiles by using column-related LR method are significantly biased from the original σext profile. The relative bias, which is mainly influenced by RH and PNSD, can reach up to 40 % when RH at the top of the mixed layer is above 90 %. A new algorithm for retrieving σext profiles and a new scheme of LR enhancement factor by RH in the NCP are proposed in this study. The relative bias between the σext profile retrieved with this new algorithm and the ideal true value is reduced to below 13 %.

Effect of ammonium salts on the photochemical degradation of iron containing organic aerosol

2020 ◽  
Author(s):  
Ulrich Krieger ◽  
Nir Bluvshtein ◽  
Jing Dou
Keyword(s):  
Citric Acid ◽  
Gas Phase ◽  
Degradation Rate ◽  
Uv Light ◽  
Lower Troposphere ◽  
Organic Aerosol ◽  
Photochemical Degradation ◽  
Single Particles ◽  
Electrodynamic Balance ◽  
Humidity Dependence

&lt;p&gt;Formation of organic aerosol by oxidation of gas phase compounds has been intensely studied, and is much better understood than the aerosol ageing transformations during the lifetime of organic aerosol. Aerosol ageing influences how those aerosol particles affect climate and human health and is still not well constrained in current models.&lt;/p&gt;&lt;p&gt;Photochemistry in the condensed phase is an important mechanism responsible for ageing of organic aerosol. In the lower troposphere, where UV light intensity with sufficiently low wavelength to directly photolyze aerosol components is low, indirect photochemistry (catalyzing redox processes of non-absorbing molecules) is especially relevant. Recently we studied transition metal complex photochemistry in single particles levitated in an electrodynamic balance. In particular, we investigated the aqueous iron(III)-citrate/citric acid system and found that irradiation at 473 nm led to rapid and significant degradation of the citric acid. Up to 80% of the initial particle mass was partitioned to the gas phase with the degradation rate depending on kinetic transport limitations of oxygen. These kinetic limitations arise are influenced strongly by the relative humidity dependence of particle viscosity where water acts as a plasticizer.&lt;/p&gt;&lt;p&gt;Here we will report on photochemical degradation experiments adding various salts in different (ammonium sulfate, ammonium bisulfate, etc.) to the reference system iron(III)-citrate/citric acid. Preliminary experiments suggest that pH of the aerosol particle influences the degradation rate in this system significantly.&lt;/p&gt;

scholarly journals Rapid formation of isoprene photo-oxidation products observed in Amazonia

2009 ◽  
Vol 9 (20) ◽  
pp. 7753-7767 ◽  
Author(s):  
T. Karl ◽  
A. Guenther ◽  
A. Turnipseed ◽  
G. Tyndall ◽  
P. Artaxo ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
Global Climate ◽  
Field Measurements ◽  
Oxidative Capacity ◽  
Oxidation Products ◽  
Lower Atmosphere ◽  
Peroxy Radicals ◽  
Aerosol Formation ◽  
Photo Oxidation ◽  
Voc Oxidation

Abstract. Isoprene represents the single most important reactive hydrocarbon for atmospheric chemistry in the tropical atmosphere. It plays a central role in global and regional atmospheric chemistry and possible climate feedbacks. Photo-oxidation of primary hydrocarbons (e.g. isoprene) leads to the formation of oxygenated VOCs (OVOCs). The evolution of these intermediates affects the oxidative capacity of the atmosphere (by reacting with OH) and can contribute to secondary aerosol formation, a poorly understood process. An accurate and quantitative understanding of VOC oxidation processes is needed for model simulations of regional air quality and global climate. Based on field measurements conducted during the Amazonian Aerosol Characterization Experiment (AMAZE-08) we show that the production of certain OVOCs (e.g. hydroxyacetone) from isoprene photo-oxidation in the lower atmosphere is significantly underpredicted by standard chemistry schemes. Recently reported fast secondary production could explain 50% of the observed discrepancy with the remaining part possibly produced via a novel primary production channel, which has been proposed theoretically. The observations of OVOCs are also used to test a recently proposed HOx recycling mechanism via degradation of isoprene peroxy radicals. If generalized our observations suggest that prompt photochemical formation of OVOCs and other uncertainties in VOC oxidation schemes could result in uncertainties of modelled OH reactivity, potentially explaining a fraction of the missing OH sink over forests which has previously been largely attributed to a missing source of primary biogenic VOCs.

scholarly journals Impact of aerosol hygroscopic growth on retrieving aerosol extinction coefficient profiles from elastic-backscatter lidar signals

2017 ◽  
Vol 17 (19) ◽  
pp. 12133-12143 ◽  
Author(s):  
Gang Zhao ◽  
Chunsheng Zhao ◽  
Ye Kuang ◽  
Jiangchuan Tao ◽  
Wangshu Tan ◽  
...  
Keyword(s):  
Extinction Coefficient ◽  
Enhancement Factor ◽  
Field Measurements ◽  
Relative Bias ◽  
Aerosol Extinction ◽  
Hygroscopic Growth ◽  
The North ◽  
True Value ◽  
Lidar Measurements ◽  
Aerosol Extinction Coefficient

Abstract. Light detection and ranging (lidar) measurements have been widely used to profile the ambient aerosol extinction coefficient (σext). The particle extinction-to-backscatter ratio (lidar ratio, LR), which strongly depends on the aerosol dry particle number size distribution (PNSD) and aerosol hygroscopicity, is introduced to retrieve the σext profile from elastic-backscatter lidar signals. Conventionally, a constant column-integrated LR that is estimated from aerosol optical depth is used by the retrieving algorithms. In this paper, the influences of aerosol PNSD, aerosol hygroscopic growth and relative humidity (RH) profiles on the variation in LR are investigated based on the datasets from field measurements in the North China Plain (NCP). Results show that LR has an enhancement factor of 2.2 when RH reaches 92 %. Simulation results indicate that both the magnitude and vertical structures of the σext profiles by using the column-related LR method are significantly biased from the original σext profile. The relative bias, which is mainly influenced by RH and PNSD, can reach up to 40 % when RH at the top of the mixed layer is above 90 %. A new algorithm for retrieving σext profiles and a new scheme of LR enhancement factor by RH in the NCP are proposed in this study. The relative bias between the σext profile retrieved with this new algorithm and the ideal true value is reduced to below 13 %.

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