Aerosol Particles In Air Research Articles

Elucidating gas-surface interactions relevant to atmospheric particle growth using combined temperature programmed desorption and temperature-dependent uptake.

Understanding growth mechanisms for particles in air is fundamental to developing a predictive capability for their impacts on human health, visibility, and climate. In the case of highly viscous semi-solid or solid particles, the likelihood of impinging gases being taken up to grow the particle will be influenced by the initial uptake coefficient and by the residence time of the adsorbed gas on the surface. Here, a new approach that combines Knudsen cell capabilities for gas uptake measurements with temperature programmed desorption (TPD) for binding energy measurements of gases is described. The application of this unique capability to the uptake of organic gases on silica demonstrates its utility and the combination of thermodynamic and kinetic data that can be obtained. Lower limits to the initial net uptake coefficients at 170 K are (3.0 ± 0.6) × 10-3, (4.9 ± 0.6) × 10-3 and (4.3 ± 0.8) × 10-3 for benzene, 1-chloropentane, and methanol, respectively, and are reported here for the first time. The uptake data demonstrated that the ideal gas lattice model was appropriate, which informed the analysis of the TPD data. From the thermal desorption measurements, desorption energies of 34.6 ± 2.5, 45.8 ± 5.5, and 40.0 ± 5.6 kJ mol-1 (errors are 1σ) are obtained for benzene, 1-chloropentane, and methanol, respectively, and show good agreement with previously reported measurements. A multiphase kinetics model was applied to quantify uptake, desorption, and diffusion through the particle multilayers and hence extract desorption kinetics. Implications for uptake of organics on silica surfaces in the atmosphere and the utility of this system for determining relationships between residence times of organic gases and particle surfaces of varying composition are discussed in the context of developing quantitative predictions for growth of aerosol particles in air.

Aerosol parameterisation in a three-moment microphysical scheme: Numerical simulation of submicron-sized aerosol scavenging

This paper explores the scavenging of submicron aerosol particles (APs) collected by cloud water and rainwater and by cloud ice nucleation on APs. The scavenging coefficients for different collection processes were calculated and then implemented in a three-moment microphysical scheme of a three-dimensional numerical model. The concentration and mixing ratio of the APs in air and in all hydrometeors were calculated explicitly in the model. We performed several numerical experiments to test the influence of individual processes of AP collection and nucleation of cloud ice on AP scavenging, as well as the redistribution of APs among hydrometeors. We estimated AP scavenging based on the change in the total number and mass of APs in air over time or on the basis of the total number or mass of APs deposited on the ground by precipitation. We found that the initial number of APs in air is reduced mostly due to collection by cloud water. In the absence of ice nucleation on APs, their number in air during 90 min of integration is reduced by 49.73%, which is significantly larger than the reduction in their total mass in air, namely 7.74%. The decrease in the total number of APs in air is largely due to collection by Brownian diffusion, and the decrease in total mass is influenced equally by turbulent and Brownian diffusion. In addition to collection, when all ice nucleation processes are active, the total number of APs in air is reduced by 53.97%, and their total mass in air is reduced by 67.47%. Therefore, ice nucleation on APs is much more important for reducing their total mass in air than collection with liquid hydrometeors. The dominant process is depositional nucleation. The total number (total mass) of APs deposited by precipitation on the ground during 3 h divided by the initial total number (total mass) of APs in air (RAPN and RAPM, respectively) are 29.65% and 7.25%, respectively, in the case of collection without ice nucleation, and 27.63% and 14.88%, respectively, in the case of collection with ice nucleation. In the case of collection of APs by cloud water and rainwater, the RAPN decreases from 29.65% to 27.63% by including ice nucleation, and the RAPM increases from 7.25% to 14.88%.

The Content of High-Molecular Polycyclic Aromatic Hydrocarbons in Urban Air During FIFA World Cup 2018

Polycyclic aromatic hydrocarbons including benzo(a)pyrene have been determined on aerosol particles in air sampled in several cities of the European part of Russia hosting FIFA World Cup 2018. The average monthly concentrations of benzo(a)pyrene (BaP) in none of the samples in June–July 2018 exceeded the maximum permitted concentration. The maximum average monthly concentration of BaP during the observation period has been found in Kazan (station no 8, July–0.83 ng/m3). The average concentration of BaP in the considered cities decreased along the series: Kazan (0.45 ng/m3), Kaliningrad (0.38 ng/m3), Moscow (0.35 ng/m3), Saransk (0.32 ng/m3), Nizhny Novgorod (0.31 ng/m3), Samara (0.31 ng/m3), Rostov-on-Don (0.26 ng/m3), St. Petersburg (0.22 ng/m3), Volgograd (0.16 ng/m3), Sochi (0.01 ng/m3).

Digital holography of optically-trapped aerosol particles

Many processes taking place in atmospheric aerosol particles are accompanied by changes in the particles’ morphology (size and shape), with potentially significant impact on weather and climate. However, the characterization of dynamic information on particle morphology and position over multiple time scales from microseconds to days under atmospherically relevant conditions has proven very challenging. Here we introduce holographic imaging of unsupported aerosol particles in air that are spatially confined by optical traps. Optical trapping in air allows contact-free observation of aerosol particles under relevant conditions and provides access to extended observation times, while the digital in-line holographic microscope provides six-dimensional spatial maps of particle positions and orientations with maximum spatial resolution in the sub-micron range and a temporal resolution of 240 μs. We demonstrate the broad applicability of our approach for a few examples and discuss its prospects for future aerosol studies, including the study of complex, multi-step phase transitions.

Opto-aerodynamic focusing of aerosol particles

ABSTRACTWe describe a new method for focusing and concentrating a stream of moving micron-sized aerosol particles in air. The focusing and concentrating process is carried out by the combined drag force and optical force that is generated by a double-layer co-axial nozzle and a focused doughnut-shaped hollow laser beam, respectively. This method should supply a new tool for aerosol science and related research.Copyright © 2018 American Association for Aerosol Research

Measurement of back-scattering patterns from single laser trapped aerosol particles in air

We demonstrate a method for measuring elastic back-scattering patterns from single laser trapped micron-sized particles, spanning the scattering angle range of θ=167.7°-180° and φ=0°-360° in spherical coordinates. We calibrated the apparatus by capturing light-scattering patterns of 10 μm diameter borosilicate glass microspheres and comparing their scattered intensities with Lorenz-Mie theory. Back-scattering patterns are also presented from a single trapped Johnson grass spore, two attached Johnson grass spores, and a cluster of Johnson grass spores. The method has potential use in characterizing airborne aerosol particles, and may be used to provide back-scattering data for lidar applications.

Optical and microphysical parameters of arid dust aerosol

The parameters of heavily dusty air in an aerosol chamber under the conditions of an arid zone are studied. The transmission, optical density, Angstrom parameter, aerosol absorption coefficient, and visibility range are calculated. The temporal and spectral dependences of the optical parameters are analyzed. The regularities of the particle-size distribution function in strongly inhomogeneous dust aerosol are studied for coarsely (with a diameter more than 1 μm) and finely dispersed (with a diameter of less than 1 μm) fractions. The sizes and concentrations of the aerosol particles in air were determined using a photoelectric aerosol counter together with a 15-channel analyzer. We present the absorption spectra of coarsely and finely dispersed dust aerosol collected under different meteorological conditions. The possible mechanisms of variations in the aerosol disperse composition are analyzed.

Novel cylindrical, air-coupled acoustic levitation/concentration devices

A new class of devices for levitation and/or concentration of aerosols and small liquid/solid samples (up to several millimeters in diameter) in air has been developed. The novelty of these devices is their simplicity in design. These are inexpensive, low-power, and, in their simplest embodiment, do not require accurate alignment of a resonant cavity. Best of all, these can be off-the-shelf items. The devices are constructed from a hollow, cylindrical piezoelectric tube. The main design criteria requires a resonant mode of the tube to match a resonant mode of the interior air-filled cavity. Once matched, it is shown that drops of water in excess of 1 mm in diameter may be levitated inside the cylinder cavity against the force of gravity for less than 1 Watt of input electrical power. Efficient concentration/agglomeration of aerosol particles in air is also demonstrated.

The drag coefficient for particles in aerosols flowing through a horizontal conduit

The drag coefficient, CD, was experimentally determined during sedimentation of aerosol particles in air flowing horizontally in a conduit of rectangular cross section, and its relation to the Reynolds numbers for the particle, Rep, and the conduit, Rec, was found. The method used to obtain the frictional force on the particles is based on observation of the trajectories of the particles being deposited on the bottom wall of the conduit. The diameter (dp) and point of deposition of the particles were determined by examining small glass slides distributed along the floor of the apparatus at given positions. The diameter of particles adhering to these laminae can be observed by microscope, but a factor must then be applied to convert these values to the diameters in suspension (dp), since the particles are liquid and undergo flattening as they collect on the glass. Results were compared with the aerodynamic diameter of the particle, obtained independently, and the discrepancies that appeared will need to be investigated further. The velocity profiles of the air inside the apparatus were also recorded. A correlation of the form CD = f(Rep, Rec) is proposed.

A method for aerosol particle removal by applying condensation phenomena

This paper describes an experimental study on a method of removing aerosol particles from air by condensing heated and humidified air. In the experiment, air, including aerosol particles, is circulated by a fan in a closed clean room system consisting of a closed vessel, a humidifier, two condensers, and an after-heater. The concentration of aerosol particles at the inlet of the closed vessel, the relative humidity, and the temperature in the system are measured for several humidification and condensation conditions. We find that the removal rate of aerosol particles in air increases when the mass flow rate of the condensate increases, by means of enlarging the temperature difference between the heating water in the humidifier and the cooling water in the condensers. We also show that this method is more effective when the temperature level in the humidifier is increased. The aerosol particle removal mechanism of this method is considered to be related to the generation of mist using aerosol particles as nuclei, inertia trapping, and the suction effect of condensation. © 1998 Scripta Technica. Heat Trans Jpn Res, 26(6): 398–409, 1997

Number size distribution of insolubleatmospheric aerosol particles in fog/cloud-water

AbstractThe design and the efficiency — curve of a newly developed fog/cloud-water sampler (rotating arm collector)is discussed. Fog/cloud-water samples were taken during Oct./Nov. 1990 on the mountain ‘Kleiner Feldberg’/Taunus, FRG. The number size distribution of the insoluble atmospheric aerosol particles in water is determined in the size range 0.025μm < r p < 10.0μm . The size distribution of activated aerosol particles in air is derived from this distribution. Comparison of the spectrum of the activated aerosol particles with the total distribution of aerosol particles in air (measured during the same campaign, but in the size range 0.008μm < r p < 0.45μm ) indicates, that in the size range r p > 0.06μm the major part of atmospheric aerosol particles becomes activated during fog/clouds. The variations of the size distribution in fog/cloud-water during an event is low.

The homogeneous nucleation rates of H 2SO 4-H 2O aerosol particles in air

The homogeneous nucleation rates for H 2SO 4H 2O solution droplets at 25, 0 and −55°C are calculated and plotted as a function of H 2SO 4 concentration and H 2O concentration. The plotted contours are very useful for quick estimates of the nucleation rates of H 2SO 4H 2O aerosols in smog chambers, polluted atmospheres and the stratosphere under different environmental conditions. The effect of the uncertainty in the saturated vapor pressure of H 2SO 4 on the nucleation rate is also discussed.