Aerosol Particle Size Research Articles

Accuracy Required in Measurements of Refractive Index and Hygroscopic Response to Reduce Uncertainties in Estimates of Aerosol Radiative Forcing Efficiency

AbstractThe magnitude of aerosol radiative forcing resulting from the scattering and absorption of radiation is still uncertain. Sources of uncertainty include the physical and optical properties of aerosol, reflected in uncertainties in real and imaginary refractive indices (n and k) and relative humidity (RH). The effect of RH on the geometrical size of aerosol particles is often reported as a hygroscopic kappa parameter (κ). The objective of this study is to explore the sensitivity of radiative forcing efficiency (RFE) to changes in particle properties in order to better define the accuracy with which optical and hygroscopic measurements must be made to reduce uncertainties in RFE. Parameterizations of precise values of n and k are considered as functions of RH for ammonium sulfate (AS) and brown carbon (BrC). The range of the RFE estimated for typical uncertainties of n and κ for AS of 0.1 μm dry radius is less than ±7% and is not affected by an increase of RH. For typical sizes of AS in the atmosphere (0.35 μm dry radius), the range of the RFE increases to ±20% at 90% RH and ±15% at 99% RH. Absorbing small BrC particles (0.1 μm dry radius) cause cooling at the top of the atmosphere, and as RH and κ increase, the RFE is more negative compared to the usual assumptions of dry unhygroscopic BrC. For larger BrC particles (0.35 μm dry radius), the change in RFE for RHs ~100% compared to dry conditions can take values around −100%.

Evaluation of satellite aerosol retrievals with in situ aircraft and ground measurements: Contribution of relative humidity

The contribution of relative humidity (RH) on Moderate Resolution Imaging Spectroradiometer (MODIS) aerosol optical depth (AOD) was investigated based on in-situ aircraft and ground observations of aerosol and RH from 2007 to 2010 in Beijing, China. The profiles of dry aerosol particle number and size distributions with diameter ranging from 0.1 to 3.0 μm as well as RH were observed during aircraft measurement. The calculated AOD based on aircraft observed dry aerosol particles is lower than MODIS AOD under high RH, but consistent with MODIS AOD after accounting for the aerosol hygroscopic growth effect. A comparison of ground PM2.5 and MODIS AOD further shows that the ratio of PM2.5 concentration to AOD decreases with RH. These results collectively suggest that a strong aerosol hygroscopic growth effect on AOD. The averaged contribution of RH (hygroscopic growth) on AOD are estimated as 37% and 22% respectively based on in-situ aircraft and ground measurements, and hence aerosol concentration would be overestimated if the aerosol hygroscopic growth effect is neglected. As a result, it should be cautious with the applications of AOD in studying the complex relationships between aerosol and its climatic effects.

Physical characterization of the aerosol of an electronic cigarette: impact of refill liquids

Electronic cigarettes are used to evaporate a mixture of solvents, nicotine and flavors. Liquid particles can be generated under these conditions due to evaporation/condensation. The objective of this work is to measure the physical characteristics of the aerosol emission of an e-cigarette using different refill liquids. The aerosol particle number and size are determined with a Scanning Mobility Particle Sizer. Seven liquids are used: propylene glycol (PG), glycerol (VG), a mixture 1:1 of PG/VG, the mixture with 2% or 5% of a commercial flavor, the mixture with 1.2% of nicotine and the mixture with 1.2% of nicotine and 2% of flavor. Particle concentrations of the aerosol emitted from the electronic cigarette are 300–3000 times higher than that of the ambient air. Propylene glycol emits several times more than glycerol. The addition of a flavor or nicotine has little effect on the emission of the total number emitted. The count median diameter of the electronic cigarette particles is 200–400 nm, depending on the liquid used. Count median diameter of emitted particles is affected by the liquid used.

Exploring the Atmosphere of Neoproterozoic Earth: The Effect of O2 on Haze Formation and Composition

Abstract Previous studies of haze formation in the atmosphere of the early Earth have focused on N2/CO2/CH4 atmospheres. Here, we experimentally investigate the effect of O2 on the formation and composition of aerosols to improve our understanding of haze formation on the Neoproterozoic Earth. We obtained in situ size, particle density, and composition measurements of aerosol particles produced from N2/CO2/CH4/O2 gas mixtures subjected to FUV radiation (115–400 nm) for a range of initial CO2/CH4/O2 mixing ratios (O2 ranging from 2 ppm to 0.2%). At the lowest O2 concentration (2 ppm), the addition increased particle production for all but one gas mixture. At higher oxygen concentrations (20 ppm and greater), particles are still produced, but the addition of O2 decreases the production rate. Both the particle size and number density decrease with increasing O2, indicating that O2 affects particle nucleation and growth. The particle density increases with increasing O2. The addition of CO2 and O2 not only increases the amount of oxygen in the aerosol, but it also increases the degree of nitrogen incorporation. In particular, the addition of O2 results in the formation of nitrate-bearing molecules. The fact that the presence of oxygen-bearing molecules increases the efficiency of nitrogen fixation has implications for the role of haze as a source of molecules required for the origin and evolution of life. The composition changes also likely affect the absorption and scattering behavior of these particles but optical property measurements are required to fully understand the implications for the effect on the planetary radiative energy balance and climate.

Effect of Particle Morphology on Cloud Condensation Nuclei Activity

Cloud condensation nuclei (CCN) activation is sensitive to the size, composition, and morphology of aerosol particles of <200 nm. By controlling the particle morphology of internally mixed samples (i.e., homogeneous versus phase separated), we have probed the effect of morphology on CCN activity using model organic aerosol systems, where ammonium sulfate was mixed with either pimelic acid or succinic acid in a 50:50 mixture by weight. Surprisingly, for systems of the same composition but distinct morphology, we observe a noticeable impact on CCN activity. Specifically, a phase-separated morphology results in activation diameters close to that of ammonium sulfate, while a homogeneous morphology yields an activation diameter in between the pure inorganic and organic components. Our results suggest that morphology-resolved CCN data may be an important parameter to consider in cloud microphysics models to improve predictions of CCN activity of complex organic aerosols. For laboratory CCN studies, it is import...

Aerosol particle size distribution in the stratosphere retrieved from SCIAMACHY limb measurements

Abstract. Information about aerosols in the Earth's atmosphere is of a great importance in the scientific community. While tropospheric aerosol influences the radiative balance of the troposphere and affects human health, stratospheric aerosol plays an important role in atmospheric chemistry and climate change. In particular, information about the amount and distribution of stratospheric aerosols is required to initialize climate models, as well as validate aerosol microphysics models and investigate geoengineering. In addition, good knowledge of stratospheric aerosol loading is needed to increase the retrieval accuracy of key trace gases (e.g. ozone or water vapour) when interpreting remote sensing measurements of the scattered solar light. The most commonly used characteristics to describe stratospheric aerosols are the aerosol extinction coefficient and Ångström coefficient. However, the use of particle size distribution parameters along with the aerosol number density is a more optimal approach. In this paper we present a new retrieval algorithm to obtain the particle size distribution of stratospheric aerosol from space-borne observations of the scattered solar light in the limb-viewing geometry. While the mode radius and width of the aerosol particle size distribution are retrieved, the aerosol particle number density profile remains unchanged. The latter is justified by a lower sensitivity of the limb-scattering measurements to changes in this parameter. To our knowledge this is the first data set providing two parameters of the particle size distribution of stratospheric aerosol from space-borne measurements of scattered solar light. Typically, the mode radius and w can be retrieved with an uncertainty of less than 20 %. The algorithm was successfully applied to the tropical region (20° N–20° S) for 10 years (2002–2012) of SCIAMACHY observations in limb-viewing geometry, establishing a unique data set. Analysis of this new climatology for the particle size distribution parameters showed clear increases in the mode radius after the tropical volcanic eruptions, whereas no distinct behaviour of the absolute distribution width could be identified. A tape recorder, which describes the time lag as the perturbation propagates to higher altitudes, was identified for both parameters after the volcanic eruptions. A quasi-biannual oscillation (QBO) pattern at upper altitudes (28–32 km) is prominent in the anomalies of the analysed parameters. A comparison of the aerosol effective radii derived from SCIAMACHY and SAGE II data was performed. The average difference is found to be around 30 % at the lower altitudes, decreasing with increasing height to almost zero around 30 km. The data sample available for the comparison is, however, relatively small.

Aerosolization of Zn-DTPA Decorporation Agent Using Jet and Ultrasonic Nebulizers

Chelating agents such as diethylenetriamine pentaacetic acid (DTPA) can be used as a decorporation drug in the zinc (Zn) form to treat internal radioactive contamination after exposure to plutonium or americium in a nuclear accident. Although Zn-DTPA is normally administered intravenously, inhalation of Zn-DTPA in aerosol form is a better route for direct delivery to the lungs. This work investigates the feasibility of synthesizing Zn-DTPA from three common chemicals and aerosolizing it using a jet or ultrasonic nebulizer. The particle size distribution (PSD) of this decorporation agent at different concentrations were tested in vitro using two different methods: inertial impaction and aerodynamic time of flight. The particles were generated using either a jet nebulizer or an ultrasonic nebulizer. Two parameters, namely the mass median aerodynamic diameter and the geometric standard deviation, were assessed to determine the PSD of the generated aerosols. These parameters were obtained for different concentrations of Zn-DTPA using both nebulizers. Zn-DTPA was successfully synthesized for decorporation purposes. Aerosol particles within the inhalable range were successfully generated by both nebulizers from four different concentrations of Zn-DTPA. It was found that the medication concentration did not affect the PSD of Zn-DTPA. The ultrasonic nebulizer was observed to produce a slightly larger aerosol particle size and required slightly longer treatment periods to deliver an effective dose to the lungs when compared with the jet nebulizer. Both nebulizers can be sustainably run to administer the agent for effective decorporation treatment of a large population after any major nuclear accident.

Photo-oxidation products of α-pinene in coarse, fine and ultrafine aerosol: A new high sensitive HPLC-MS/MS method

Oxidation products of α-pinene represent a fraction of organic matter in the environmental aerosol. α-pinene is one of most abundant monoterpenes released in the atmosphere by plants, located typically in boreal, temperate and tropical forests. This primary compound reacts with atmospheric oxidants, such as O3, O2, OH radicals and NOx, through the major tropospheric degradation pathway for many monoterpenes under typical atmospheric condition. Although several studies identified a series of by-products deriving from the α-pinene photo-oxidation in the atmosphere, such as pinic and cis-pinonic acid, the knowledge of the mechanism of this process is partially still lacking. Thus, the investigation of the distribution of these acids in the different size aerosol particles provides additional information on this regard.The aim of this study is twofold. First, we aim to improve the existing analytical methods for the determination of pinic and cis-pinonic acid in aerosol samples, especially in terms of analytical sensitivity and limits of detection (LOD) and quantification (LOQ). We even attempted to increase the knowledge of the α-pinene photo-oxidation processes by analysing, for the first time, the particle-size distribution up to nanoparticle level of pinic and cis-pinonic acid. The analysis of aerosol samples was carried out via high-performance liquid chromatography coupled to a triple quadrupole mass spectrometer. The instrumental LOD values of cis-pinonic and pinic acid are 1.6 and 1.2 ng L−1 while LOQ values are 5.4 and 4.1 ng L−1, respectively. Samples were collected by MOUDI II™ cascade impactor with twelve cut-sizes, from March to May 2016 in the urban area of Mestre-Venice (Italy).The range concentrations in the aerosol samples were from 0.1 to 0.9 ng m−3 for cis-pinonic acid and from 0.1 to 0.8 ng m−3 for pinic acid.

Aerosol Component of the Atmosphere of Saturn: Comparison of the Vertical Structure Characteristics in Latitudinal Belts

The altitude dependences of the aerosol and gas scattering components of the effective optical depth in the latitudinal belts of Saturn’s Northern Hemisphere have been obtained from the reflectance spectra in the methane absorption bands at λ = 727 and 619 nm measured in 2015. Zonal characteristics of the vertical structure of the cloud cover of Saturn have been estimated. In the latitudinal belts, the aerosol, the relative concentration of which monotonically decreases with depth in the atmosphere, was found, and no signs of substantial cloud clusterings and rarefactions were observed. The largest and smallest aerosol amounts were determined at the latitudes of 49° N and 80° N, respectively. The altitude levels where the sizes of aerosol particles or their nature may change were revealed. We failed to determine the atmospheric level where the relative concentration of aerosol particles is largest; however, the character of the obtained dependences suggests that such a level is probably in the higher layers of the atmosphere of the giant planet.

Imaging aerosols with digital holography

The shape and size of aerosol particles influence whether they heat or cool Earth and its atmosphere.

Influence of diluent volume of colistimethate sodium on aerosol characteristics and pharmacokinetics in ventilator-associated pneumonia caused by MDR bacteria.

Nebulized colistimethate sodium (CMS) can be used to treat ventilator-associated pneumonia caused by MDR bacteria. The influence of the diluent volume of CMS on aerosol delivery has never been studied. The main objectives of the study were to compare aerosol particle characteristics and plasma and urine pharmacokinetics between two diluent volumes in patients treated with nebulized CMS. A crossover study was conducted in eight patients receiving nebulized CMS every 8 h. After inclusion, nebulization started with 4 million international units (MIU) of CMS diluted either in 6 mL (experimental dilution) or in 12 mL (recommended dilution) of normal saline in a random order. For each diluent volume, CMS aerosol particle sizes were measured and plasma and urine samples were collected every 2 h. Nebulization time and stability of colistin in normal saline were assessed. The mass median aerodynamic diameters were 1.4 ± 0.2 versus 0.9 ± 0.2 μm (P < 0.001) for 6 and 12 mL diluent volumes, respectively. The plasma area under the concentration-time curve from 0 to 8 h (AUC0-8) of colistinA+B was 6.6 (4.3-17.0) versus 6.7 (3.6-14.0) μg·h/mL (P = 0.461) for each dilution. The total amount of colistin and CMS eliminated in the urine represented, respectively, 17% and 13% of the CMS initially placed in the nebulizer chamber for 6 and 12 mL diluent volumes (P = 0.4). Nebulization time was shorter [66 (58-75) versus 93 (69-136) min, P = 0.042] and colistin stability was better with the 6 mL diluent volume. Nebulization with a higher concentration of CMS in saline (4 MIU in 6 mL) decreases nebulization time and improves colistin stability without changing plasma and urine pharmacokinetics or aerosol particle characteristics for lung deposition.

Resuspension of house dust and allergens during walking and vacuum cleaning

ABSTRACTConventional wisdom has been that hard, resilient surfaces resuspend fewer particles than carpeted surfaces, however, exceptions to this have been demonstrated and uncertainty remains about the factors that lead to this resuspension, notably, the effect of vacuum cleaning on either increasing or reducing resuspension from flooring. The purpose of this study was to determine how resuspension of house dust by aerodynamic size or particle type, including cat allergen and bacterial endotoxin, is affected by flooring, dust loading, embedding dust, and walking/cleaning activities. House dust was blown in and allowed to settle in a walk-in chamber after overnight deposition followed by walking or a vacuum cleaning procedure. Using an aerosol particle sizer and large-volume air samplers at different heights in the chamber, concentrations of airborne particles, resuspension rates, and fractions were computed for four types of flooring conditions during six walking activities. Carpeting resulted in significantly more airborne cat allergen and airborne endotoxin than a laminate floor. Height does have an effect on measured allergen over carpet and this is apparent with concentrations at the infant and adult air samplers. Walking on laminate flooring resuspends less house dust than walking on an equally dusty carpeted floor, where dust is entirely on the surface of the carpet. However, vacuum cleaning a laminate floor resuspended more dust than vacuum cleaning carpets, at large particle sizes of 5 µm and 10 µm. Activities following a deep cleaning of hard resilient or a carpeted surface is likely to leave no differences in resuspended particles between them.

Trends of Aerosol Optical Properties over the Heavy Industrial Zone of Northeastern Asia in the Past Decade (2004–15)

The heavy industrial zone of northeastern Asia is dominated by year-round industrial scattering aerosols that undergo hygroscopic growth in summer. With the rapid economic development over the past decade, aerosol optical depth (AOD) has increased (6.35% yr−1) with an annual-mean AOD of 0.61 ± 0.13. Simultaneously, the aerosol particle size and aerosol scattering have increased, with an annual-mean scattering aerosol optical depth (SAOD) reaching 0.58 ± 0.15. However, considering that the annual AOD/gross domestic product (GDP) per capita decreased, the environmental degradation caused by aerosol emission is expected to reach a turning point based on the environmental Kuznets curve (EKC) hypothesis. In addition, annual-mean radiative forcing at the top, bottom, and interior of the atmospheric column reached −2.35 ± 2.33, −54.16 ± 7.26, and 51.81 ± 7.93 W m−2, respectively. The increase in unit SAOD contributes to the growth in net negative top-of-atmosphere (TOA) forcing and surface (SFC) forcing, and unit absorption aerosol optical depth (AAOD) increases together with atmosphere (ATM) forcing. Moreover, the cooling effect of aerosols on the Earth–atmosphere system showed an increase over the most recent 10 years related to the increase in scattering aerosol from development in the old industrial base. Except for local sources, under the western air masses, the circum–Bohai Sea economic zone was the potential source area of anthropogenic aerosols throughout the year with annual daily mean AOD, single-scattering albedo (SSA), TOA forcing, and SFC forcing values of 0.88, 0.93, −8.08, and −63.05 W m−2, respectively. The Mongolian Plateau was the potential natural dust source area under the northeastern air masses.

Technical challenges in obtaining an optimized powder/DPI combination for inhalation delivery of a bi-component generic drug

Development of bi-component generic orally inhaled product (OIP) delivered from dry powder inhaler (DPI) is challenging due to the necessity to demonstrate the similarity of size distribution of both APIs in inhaled aerosol. The effects of selected technical factors on OIP development are investigated. The Monodose inhalers with different aerodynamic resistance were used to aerosolize generic fluticasone/salmeterol formulations. Flow dynamics in the DPIs was analyzed during realistic use. The effects of lactose grade, capsule types and blending equipment on aerosol particle size were studied with compendial methods. The best dispersion of bi-component powder was obtained in a medium-resistant (∼0.108 hPa0.5 min L−1) Monodose DPI as compared to low- and high-resistant devices. All studied technological factors had influence on the fine particle dose of each API and fluticasone/salmeterol mass ratio. It was demonstrated that the selected Monodose inhaler in combination with the newly developed bi-component drug formulation was able to reproduce the quality of inhalable aerosol obtained from Diskus DPI. Since powder dispersion depends on the energy available in a single breath, an optimized DPI is needed in generic OIP. By adjusting several technological factors it is possible to obtain the reproducible product with the required dose of each aerosolized APIs.

Ash Aerosol and Deposition Formation Mechanisms during Air/Oxy-combustion of Rice Husks in a 100 kW Combustor

Pulverized rice husks are co-fired with natural gas in a 100 kW (rated) down-fired oxy-fuel combustor (OFC) under two conditions: 1) air combustion (denoted as Air); 2) oxy-combustion with 70% O2 and 30% CO2 in the inlet oxidant gas (denoted as OXY70). Studied in this paper are: 1) mechanisms governing the partitioning of inorganic matter within the fly ash aerosol, and 2) how these affect mechanisms of deposition on heat transfer surfaces. In each case, the ash aerosol particle size distributions (PSDs) were determined using electric mobility/light scattering instruments (SMPS/APS) and a Berner Low Pressure Impactors (BLPI), where the latter collected size segregated aerosol for subsequent analysis. The ash deposition rate was measured experimentally using a specially designed probe, and its relationship with aerosols was explored. The properties of the deposits were also investigated using a laser diffraction particle size analyzer for PSDs, and SEM/EDS and XRD for compositions. The data show that, comp...

The characteristics simulation of FMCW laser backscattering signals

A Monte Carlo simulation model of FMCW laser transmission in a smoke interference environment was established in this paper. The aerosol extinction coefficient and scattering coefficient changed dynamically in the simulation according to the smoke concentration variation, aerosol particle distributions and photon spatial positions. The simulation results showed that the smoke backscattering interference produced a number of amplitude peaks in the beat signal spectrum; the SNR of target echo signal to smoke interference was related to the transmitted laser wavelength and the aerosol particle size distribution; a better SNR could be obtained when the laser wavelength was in the range of 560–1660 nm. The characteristics of FMCW laser backscattering signals generated by simulation are consistent with the theoretical analysis. Therefore, this study was greatly helpful for improving the ability of identifying target and anti-interference in the further research.

Impact of power level and refill liquid composition on the aerosol output and particle size distribution generated by a new-generation e-cigarette device

The new high-power Electronic Nicotine Delivery System (ENDS) can generate aerosols with higher nicotine concentrations than older ENDS. Aerosol particle sizes affect deposition patterns and then p...

Exposure assessments for a cross-sectional epidemiologic study of US carbon nanotube and nanofiber workers

Recent animal studies have suggested the potential for wide-ranging health effects resulting from exposure to carbon nanotubes and nanofibers (CNT/F). To date, no studies in the US have directly examined the relationship between occupational exposure and potential human health effects. Our goal was to measure CNT/F exposures among US workers with representative job types, from non-exposed to highly exposed, for an epidemiologic study relating exposure to early biologic effects. 108 participants were enrolled from 12 facilities across the US. Personal, full-shift exposures were assessed based on the mass of elemental carbon (EC) at the respirable and inhalable aerosol particle size fractions, along with quantitatively characterizing CNT/F and estimating particle size via transmission electron microscopy (TEM). Additionally, sputum and dermal samples were collected and analyzed to determine internal exposures and exposures to the hands/wrists. The mean exposure to EC was 1.00 μg/m3 at the respirable size fraction and 6.22 μg/m3 at the inhalable fraction. Analysis by TEM found a mean exposure of 0.1275 CNT/F structures/cm3, generally to agglomerated materials between 2 and 10 μm. Internal exposures to CNT/F via sputum analysis were confirmed in 18% of participants while ∼70% had positive dermal exposures. We demonstrated the occurrence of a broad range of exposures to CNT/F within 12 facilities across the US. Analysis of collected sputum indicated internal exposures are currently occurring within the workplace. This is an important first step in determining if exposures in the workforce have any acute or lasting health effects.

Stratospheric aerosol particle size distribution based on multi-color polarization measurements of the twilight sky

Polarization measurements of the twilight background with Wide-Angle Polarization Camera (WAPC) are used to detect the depolarization effect caused by stratospheric aerosol near 20km altitude. Based on a number of observations in central Russia in spring and summer 2016, we found the parameters of lognormal size distribution of aerosol particles. This confirmed the previously published results of the colorimetric method as applied to the same twilights. The mean particle radius (about 0.1µm) and size distribution are also in agreement with the recent data of in situ and space-based remote sensing of stratospheric aerosol. The methods considered here provide two independent techniques of the stratospheric aerosol study based on the twilight sky analysis.

Long-term observations of the background aerosol at Cabauw, The Netherlands

Long-term measurements of PM2.5 mass concentrations and aerosol particle size distributions from 2008 to 2015, as well as hygroscopicity measurements conducted over one year (2008–2009) at Cabauw, The Netherlands, are compiled here in order to provide a comprehensive dataset for understanding the trends and annual variabilities of the atmospheric aerosol in the region. PM2.5 concentrations have a mean value of 14.4μgm-3 with standard deviation 2.1μgm-3, and exhibit an overall decreasing trend of −0.74μgm-3year-1. The highest values are observed in winter and spring and are associated with a shallower boundary layer and lower precipitation, respectively, compared to the rest of the seasons. Number concentrations of particles smaller than 500nm have a mean of 9.2×103particles cm-3 and standard deviation 4.9×103particles cm-3, exhibiting an increasing trend between 2008 and 2011 and a decreasing trend from 2013 to 2015. The particle number concentrations exhibit highest values in spring and summer (despite the increased precipitation) due to the high occurrence of nucleation-mode particles, which most likely are formed elsewhere and are transported to the observation station. Particle hygroscopicity measurements show that, independently of the air mass origin, the particles are mostly externally mixed with the more hydrophobic mode having a mean hygroscopic parameter κ of 0.1 while for the more hydrophilic mode κ is 0.35. The hygroscopicity of the smaller particles investigated in this work (i.e., particles having diameters of 35nm) appears to increase during the course of the nucleation events, reflecting a change in the chemical composition of the particles.