Cloud condensation nuclei from the activation with ozone of soot particles
sampled from a kerosene diffusion flame
Symphorien Grimonprez, Alessandro Faccinetto, S ebastien Batut, Junteng Wu, Pascale Desgroux, and
Denis Petitprez
Physicochimie des Processus de Combustion et de l’ Atmosph ere, Universite de Lille, Lille, France
ABSTRACT
Due to the exponential increase in aircraft traffic in recent decades, the role of soot particles emitted by aircraft engines on the radiative forcing needs to be addressed, and especially their interaction with clouds has to be better understood and quantified. In this work, we investigate the hygroscopic properties of fresh and aged soot sampled on line in a kerosene flame. The activated fraction (Fa) of size selected soot is measured by means of a variable supersaturation condensation nucleus counter at several heights above the burner (HAB), thereby probing soot particles with different residence times in the flame, i.e., different degrees of maturity. In order to simulate atmospheric aging, the activity of soot as cloud condensation nuclei is measured as a function of ozone exposure. We show that fresh soot is hydrophobic (Fa 0), while Fa increases when soot is exposed to ozone. The measurements depend on the HAB at which soot particles are sampled showing that activation of soot particles is related to their chemical composition. This study brings new results on the link between atmospheric aging of soot and its hygroscopic properties, which is of great interest for understanding the role of soot in the cloud formation.
Extending the Faraday cup aerosol electrometer based calibration method
up to 5 mm
A. J€ arvinen, J. Keskinen, and J. Yli-Ojanper€ a
Aerosol Physics, Faculty of Natural Sciences, Tampere University of Technology, Tampere, Finland
ABSTRACT
A Faraday cup aerosol electrometer based electrical aerosol instrument calibration setup from nanometers up to micrometers has been designed, constructed, and characterized. The set-up utilizes singly charged seed particles, which are grown to the desired size by condensation of diethylhexyl sebacate. The calibration particle size is further selected with a Differential Mobility Analyzer (DMA). For micrometer sizes, a large DMA was designed, constructed, and characterized. The DMA electrical
mobility resolution was found to be 7.95 for 20 L/min sheath and 2 L/min sample flows. The calibration is based on comparing the instrument’ s response against the concentration measured with a reference Faraday cup aerosol electrometer. The set-up produces relatively high concentrations in the micrometer size range (more than 2500 1/cm3 at 5.3 mm). A low bias flow mixing and splitting between the reference and the instrument was constructed from a modified, large-sized mixer and a four-port flow splitter. It was characterized at different flow rates and as a function of the particle size. Using two of the four outlet ports at equal 1.5 L/min flow rates, the particle concentration bias of the flow splitting was found to be less than ±1% in the size range of 3.6 nm–5.3 mm. The developed calibration set-up was used to define the detection efficiency of a condensation particle counter from 3.6 nm to 5.3 mm with an expanded measurement uncertainty (k ¼ 2) of less than 4% over the entire size range and less than 2% for most of the measurement points.
Determination of the aerosol particle size distribution by means of the
diffusion battery: Analytical inversion
A. A. Onischuka,b,c, S. V. Valiulina,c, A. M. Baklanova, P. P. Moiseenkoa,d, and V. G. Mitrochenkoa,d
aVoevodsky Institute of Chemical Kinetics and Combustion, Novosibirsk, Russia; bDepartment of Physics, Novosibirsk State University, Novosibirsk, Russia; cDepartment of Natural, Social and Economic Sciences, Novosibirsk State Pedagogical University, Novosibirsk, Russia; dAerosol Instruments Ltd, Novosibirsk, Russia
ABSTRACT
The algorithm of the analytical inversion of aerosol size distribution is proposed in this work. As the diffusion battery separates particles into several fractions according to their diffusivity, the total spectrum can be represented as the sum of spectra of fractions. Analytical formulas are derived to calculate mean diameters for particles in different fractions using diffusion battery penetrations as input parameters. The spectra of fractions are approximated by lognormal functions. Two analytical solutions for the aerosol size distribution inversion problem are discussed. The sizing accuracy of analytical solutions is investigated, comparing them with the measurements through transmission electron microscopy using the laboratory-generated NaCl aerosol. The agreement is demonstrated to be within 10% accuracy. It is shown that in case of two-mode size distribution, the spectrum components are well resolved for rather distant peaks (modal diameters of 10 and 300 nm) and poorly resolved for nearby modes (50 and 300 nm). To improve the peak resolution, the procedure of spectrum correction is applied demonstrating an excellent peak separation. Finally, the peak resolution is experimentally verified for the laboratory-generated two-mode spectra of tungsten oxide–NaCl aerosol with the modal diameters of 10 and 60 nm, respectively. Both analytical solutions demonstrated good peak resolution.
Effect of particle charge on aerosol dynamics in Teflon environmental chambers
Sophia M. Charan , Weimeng Kong, Richard C. Flagan , and John H. Seinfeld
Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California, USA
ABSTRACT
The contribution of particle charge to the rate of particle wall deposition has been a persistent source of uncertainty for experiments performed in environmental chambers. By tracking the preferential deposition of positively charged particles; by comparing experiments carried out under standard, humid, and highly statically charged conditions; and by performing two-parameter optimizations for the chamber eddy-diffusion coefficient (ke) and the average magnitude of the electric field (E),
the effect of charge on the rate of particle-wall deposition is isolated. A combined experimental and computational method is also developed for determining values for ke and E within a FEP Teflon chamber. To fully account for the effects of charge on particle dynamics in environmental chambers, studies of the effect of air ion concentration on the rate of particle coagulation over a typical 20 h experiment are performed and demonstrated, in general, that particle charge is negligible for characteristic chamber ion concentrations. While the effect of particle charge on aerosol dynamics in an environmental chamber must be addressed for each specific chamber, we demonstrate experimentally that for the Caltech 19 m3 Environmental Chamber, charge effects on the rate of particle-wall deposition are negligible.
Numerical investigation of spatially nonhomogeneous acoustic agglomeration using sectional algorithm
Xiaopeng Shang, Bing Feng Ng , Man Pun Wan, Jinwen Xiong, and Shmitha Arikrishnan
School of Mechanical and Aerospace Engineering, Nanyang Technological University, Singapore
ABSTRACT
In the simulation of acoustic agglomeration, the conventional temporal model assumes spatial homogeneity in aerosol properties and sound field, which is often not the case in real applications. In this article, we investigated the effects of spatial nonhomogeneity of sound field on the acoustic agglomeration process through a one-dimensional spatial sectional model. The spatial sectional model is validated against existing experimental data and results indicate lower requirements on the number of sections and better accuracy. Two typical cases of spatial nonhomogeneous acoustic agglomeration are studied by the established model. The first case involves acoustic agglomeration in a standing wave field with spatial alternation of acoustic kernels from nodes to antinodes. The good agreement between the simulation and experiments demonstrates the predictive capability
of the present spatial sectional model for the standing-conditioned agglomeration. The second case incorporates sound attenuation in the particulate medium into acoustic agglomeration. Results indicate that sound attenuation can influence acoustic agglomeration significantly, particularly at high frequencies, and neglecting the effects of sound attenuation can cause overprediction of agglomeration rates. The present investigation demonstrates that the spatial sectional method is capable of simulating the spatially nonhomogeneous acoustic agglomeration with high computation efficiency and numerical robustness and the coupling with flow dynamics will be the goal of future work.
Effective density of airborne particles in a railway tunnel from field
measurements of mobility and aerodynamic size distributions
Yingying Cha and Ulf Olofsson
Department of Machine Design, KTH Royal Institute of Technology, Stockholm, Sweden
ABSTRACT
The objective of this study is to investigate the particle effective density of aerosol measurements in a railway tunnel environment. Effective density can serve as a parameter when comparing and calibrating different aerosol measurements. It can also be used as a proxy parameter reflecting the source of particles. Effective density was determined using two different methods. Method one defined it by the ratio of mass concentration to apparent volume size distribution. Method two relied
on a comparison of aerodynamic and mobility diameter size distribution measurements. The aerodynamic size range for method one was 0.006– 10 mm, and for method two, it was 10–660 nm. Using the first method, a diurnal average value of about 1.87 g/cm3 was observed for the measurements with tapered element oscillating microbalance (TEOM) in tandem with aerodynamic particle sizer þ scanning mobility particle sizer (SMPS), and 1.2 g/cm3 for the combination of TEOM with electrical low pressure impactor plus (ELPI þ) in the presence of traffic. With method two, the effective density was 1.45 g/cm3 estimated from the size distribution measurements with ELPI þ and fast mobility particle sizer (FMPS), and 1.35 g/cm3 from ELPI þ in tandem with SMPS. With both calculation methods, the effective density varied for conditions with and without traffic, indicating different sources of particles. The proportion of particles with small sizes (10–660 nm) had a significant effect on the value of the effective density when no traffic was operating. The responses of different instruments to the railway particle measurements were also compared.
Effects of thermal airflow and mucus-layer interaction on hygroscopic
droplet deposition in a simple mouth– throat model
Xiaole Chena, Clement Kleinstreuerb, Wenqi Zhonga, Yu Fengc, and Xianguang Zhoud
aKey Laboratory of Energy Thermal Conversion and Control of Ministry of Education, Southeast University, Nanjing, Jiangsu Province, China; bDepartment of Mechanical and Aerospace Engineering, North Carolina State University, Raleigh, North Carolina, USA; cSchool of Chemical Engineering, Oklahoma State University, Stillwater, Oklahoma, USA; dSchool of Medicine, Southeast University, Nanjing, Jiangsu Province, China
ABSTRACT
Hygroscopic growth of inhaled aerosols plays an important role in determining particle trajectories and hence local deposition sites. Accurate predictions of airway temperature and humidity as well as droplet–vapor interaction are critical for the calculation of hygroscopic growth. Employing a simple mouth–throat (MT) model as a computer simulation test bed, the effects of interactive heat transfer between air–droplet flow and mucus-tissue-layer have been analyzed. For a steady inhalation flow
rate of 15 L/min, air temperature and relative humidity distributions affecting droplet growth, deposition efficiency (DE), and deposition pattern have been compared for different thermal airway-wall conditions. The effects considered include: (i) the latent heat of mucus-layer evaporation and convection heat transfer; (ii) convection heat transfer only; and (iii) mucus-tissue layer with constant temperature. As the most important outcome, the validated modeling results show that thermal airflow and mucus-layer interaction can significantly reduce hygroscopic growth and thereby decrease the DE of multicomponent droplets up to 10%. The modeling framework presented can be readily expanded to other systems.
Single-step synthesis of N-doped TiO2 by flame aerosol method
and the effect of synthesis parameters
Panagiotis G. Smirniotis, Thirupathi Boningari, and Siva Nagi Reddy Inturi
Chemical Engineering Program, College of Engineering and Applied Science, University of Cincinnati, Cincinnati, Ohio, USA
ABSTRACT
We have established a novel route for the synthesis of N-doped TiO2 by adopting flame aerosol (FSP) technique and investigated the effect of water content on the physicochemical properties of the as-synthesized nanoparticles. The key characteristics of the developed method are to modify the precursor solution in order to incorporate nitrogen atoms into the TiO2 lattice without altering the FSP set-up. The reduction of the flame enthalpy resulting in N-incorporation into the TiO2 and the N-doping can be greatly enhanced further by the addition of secondary N-source (urea). Our XRD results reveal a shift of the (101) plane anatase diffraction peak to lower angles in our N-doped TiO2 compared to undoped TiO2, which suggest the distortion and strain in the crystal lattice prompted by the incorporation of the nitrogen atoms. The growth or expansion of crystal lattice can be attributed to
the larger atomic radius of respective nitrogen atoms (r ¼ 1.7 Å) compared to oxygen (r ¼ 1.40 Å). Our XPS and EDX spectroscopy results elucidate that the nitrogen was effectively doped into the crystal lattice of TiO2 in our as-synthesized N-TiO2 catalysts predominantly in the form of interstitial nitrogen (Ti O N). The nitrogen atoms incorporation into the crystal lattice of titania modifies the electronic band structure of TiO2, resulting in a new mid-gap energy state N 2p band formed above O 2p valence band. This occurrence narrows the band gap of TiO2 (from 3.12 to 2.51 eV) in our N-doped TiO2 and shifts the optical
absorption to the visible region.
Generation of high concentrations of respirable solid-phase aerosols from
viscous fluids
Xin Heng and Donovan B. Yeates
KAER Biotherapeutics, Escondido, CA, USA
ABSTRACT
High outputs of respirable solid-phase aerosols were generated from viscous solutions or suspensions of low- and high-molecular weight polyvinylpyrrolidone (PVP) solutions, 10% (w/v) albumin and, gamma globulin solutions as well as 10.3% (w/v) surfactant suspensions. A central fluid flow was aerosolized by coaxial converging compressed air. The water was evaporated from the droplets using warm dilution air and infrared radiation. The resulting aerosol particles were concentrated using a virtual impactor. The aerosols were generated at fluid flow rates between 1 and 3 ml/min and delivered at a flow rate of 44 l/min as
2.6–3.6 lm MMAD aerosols with geometric standard deviations between 1.5 and 2. Increases in viscosity over the range of 4–39 cSt caused a modest increase in MMAD. Increases in aerosol exit orifice diameter were associated with a decrease in aerosol diameter. Increases in compressed air pressure caused a decrease in aerosol diameter. Increases in fluid flow rate resulted in modest increases in MMAD together with proportional increases in output mass. Aerosolizing 10% 8 kDa PVP at 3 ml/min resulted in the delivery of 193 mg/min of PVP at 64% efficiency enabling 1.2 g to be collected in 7 min. Aerosolizing 10.3% surfactant suspensions at 3 ml/min resulted in the delivery of up to 163 mg/min with 59% efficiency. The surface tension of the surfactant was not changed by these processes. SEM showed dimpled particles of PVP, albumin, and gamma globulin indicating that their aerodynamic diameter was less than their morphometric diameter.
