Hygroscopicity Of Aerosol Particles Research Articles

Chip-Based Dark-filed Microscopy for Sensing the Dynamical Changes of Single Aerosol Nanoparticles

The hygroscopicity of aerosol nanoparticles with the high number concentration in atmosphere significantly affects atmospheric chemistry and visibility, global climate, and human health. Therefore, it is critical to analyze the hygroscopicity of aerosol particles in an atmospheric ambient, where the aerosol's chemical compositions and physical states determine its capability of water uptake. In this work, with the advantages of non-destructive detection, highly sensitivity, and wide-field imaging, a planar photonic chip-based dark-field microscope is developed for real-time imaging and sensing the hygroscopic growth dynamics of single aerosol nanoparticles (diameter around 100 nm) in a label-free manner. The experimental results of single-component and multi-components are well consistent with the calculation results based on extended aerosol inorganic model. This photonic-chip based dark-field microscope can be extended to investigate the physicochemical reactions of various aerosols in real atmospheric environment.

Hygroscopicity of aerosol particles composed of surfactant SDS and its internal mixture with ammonium sulfate at relative humidities up to 99.9%

For atmospheric aerosol particles, the ubiquitous surfactants can significantly influence their hygroscopicity. However, the hygroscopicity of nanoscale particles containing surfactants are not well understood under subsaturated conditions, especially at high relative humidity (RH = 90–100%), due to the limitation of traditional instruments and the diversity of surfactants. Here, the hygroscopicity of nanoscale particles composed of a strong surfactant sodium dodecyl sulfate (SDS) and its mixture with ammonium sulfate (AS) was measured using the high humidity tandem differential mobility analyzer (HHTDMA) at RH up to about 99.9%. Three different models based on Köhler theory but different representations of surfactant characteristics were employed to reproduce the measurement outcomes. Results show that SDS particles start gradual hygroscopic growth after RH reaching 97.5%. For SDS-AS mixed particles with 25% w/w SDS, prompt deliquescence and gradual deliquescence are observed for smaller (20 and 40 nm) and larger particles (100 and 200 nm), respectively. For particles with ≥50% w/w SDS, the onset deliquescence is difficult to found. In general, the model that comprehensively accounts for the surfactant properties including bulk-to-surface partitioning, surface tension reduction, micellization and the effect of RH on hygroscopicity parameter, ĸ (for SDS-AS particles) provides the best predictions for the experimental hygroscopicity of SDS and SDS-AS particles at subsaturation conditions. Besides, factors affecting the accuracy of theoretical model are discussed in detail. The ĸ derived from subsaturated measurement is strongly dependent on RH and dry diameter.

Identifying the hygroscopic properties of fine aerosol particles from diverse sources in urban atmosphere and the applicability in prediction of cloud nuclei

Aerosols hygroscopicity is generally differentiating for particles among various sources, leading to complex effects on visibility impairment and cloud formation. However, the hygroscopicity of aerosol particles from diverse sources is not yet fully understood. Here, combining field observations at an urban site in Beijing and a positive matrix factorization model, we identified aerosols hygroscopicity of six different sources, nucleation, traffic, cooking, aging primary, residential heating, and regional secondary, which corresponds to hygroscopic growth factors (Gfs) of 1.23, 1.15, 1.17, 1.44, 1.48, and 1.47, respectively at relative humidity of 90%. On polluted days, Gf values of particles for the accumulation-mode particles were higher than that under clean conditions. This is largely due to the hygroscopic sources represented by aged and secondary processes showed the dominant role in aerosol population. While on clean days, the Gfs of 40-nm particles showed larger values, that is closely associated with the photochemical-nucleation-sourced particles. By further applying the Gfs together with aerosol spectrum to predict cloud nuclei concentration (CCN), we find the predicted and observed CCN number concentration are well correlated at typical supersaturation in cloud. The study further reveals the dominant roles of secondary processes, contributing up to 90% of the total cloud nuclei. Primary particles from traffic/cooking activities contributed only ∼5%, although they account for 30–40% of the total particle number concentrations in urban Beijing during the studied period. The results indicate the source apportionment of Gfs can well interpret the variation in hygroscopicity of aerosols under different atmospheric conditions and evaluate their effects on cloud formation.

Molecular dynamics study on the surface tension of succinic acid-water nano-aerosol droplets

The surface tension plays a significant role in the hygroscopicity of aerosol particles on a nanoscale. However, it cannot be obtained by using the existing measurement techniques. In this study, we simulate the hygroscopic growth of one single succinic acid (SA) particle by using the molecular dynamic (MD) method. Based on the MD simulation results, the surface tension of the stable SA-water droplet is calculated by using a numerical model. Furthermore, the influencing mechanisms of temperature, diameter and concentration of SA on the surface tension of the nanoscale droplet are investigated. The results show that with the temperature increasing from 260 K to 320 K, the surface tension of the droplet decreases, which is mainly caused by the weakening of the intermolecular forces inside the droplet. Besides, the sensitivity of the surface tension to the temperature increases with the increasing SA concentration, which can be explained by the effect of the temperature and the SA concentration on the radial distribution of SA molecules. With the increase of the particle diameter, the surface tension of droplet first increases and then tends to be constant. The normal components of the Irving-Kirkwood pressure tensors are calculated to explain the effect of diameter and SA on the surface tension. In addition, when the SA concentration is increased, the particle diameter range which has an obvious effect on the surface tension is reduced. Moreover, the surface tension of the nanodroplet is negatively correlated with the SA concentration, and the correlation fits into the logarithmic function form, especially for droplet with a diameter smaller than 6.12 nm. The Szyszkowski equation is employed to fit the relationship between SA concentration and the surface tension of droplet. These findings can provide parameter support for improving the theoretical model of particle hygroscopicity and related kinetic processes. This study emphasizes further research on the surface tension of nano-droplets with more complex components.

Numerical simulation of the microphysics and liquid chemical processes occur in fog using size resolving bin scheme

This research aims to understand the role of the initial hygroscopicity of aerosol particles, scavenging mechanisms and of aqueous chemistry in the evolution of the aerosol size distribution. A box model with a size resolving moving bin scheme is used to simulate the fog events over Budapest (Hungary) and Delhi (India). The results from the study are as follows: (i) Aerosol particles can be washed out from the atmosphere more efficiently by Brownian and phoretic scavenging than by activation processes. The efficiency of scavenging mechanisms depends on the size distribution of the dry aerosol particles and the size dependence of the hygroscopicity of the aerosol particles. The efficiency of the phoretic scavenging is also impacted by the duration of the dissipation phase of the fog. (ii) The liquid-phase chemistry, which occurs inside the droplets due to their long residence times in the atmosphere, significantly impacts the size distribution of the regenerated particles. (iii) The liquid-phase chemistry also impacts the hygroscopicity of the regenerated aerosol particles. The enhancement of the concentrations of NH4+, NO3− and S(VI) ions inside the droplets result in a substantial increase of the hygroscopicity of the water-soluble particles. This higher hygroscopicity may impact the fog dissipation by increasing the solution effect and helps to uphold successive fog events under favorable environmental condition.

Surfactant effect on the hygroscopicity of aerosol particles at relative humidity ranging from 80% to 99.5%: Internally mixed adipic acid-ammonium sulfate particles

Surfactant, which is ubiquitous in the atmosphere, has an important effect on the hygroscopicty of nanoscale atmospheric aerosol particles. However, the knowledge on the high relative humidity (RH) section (90–100%) is insufficient due to the limitation of traditional measuring instruments. In this study, the hygroscopicity of aerosol particles consisted of adipic acid (AA) and ammonium sulfate (AS) at RH = 80–99.5% was studied using the experimental and the theoretical method. The growth factor (GF) values at different RH were measured by the high humidity tandem differential mobility analyzer (HHTDMA). With some assumptions, a new model (Model 3 (UNIFAC)) accounting for the reduction of surface tension, the effect of the bulk-surface partitioning of AA and the non-ideal of solution on the particle hygroscopicity was established to describe the experimental results. An overall better performance is shown after comparing with six traditional models. Moreover, the partitioning of AA and the non-ideal of solution were investigated in details by comparing the outcomes of corresponding models. The comparisons between Model 2 (UNIFAC) and Model 3 (UNIFAC) and between Model 3 (Ideal) and Model 3 (UNIFAC) indicate that both the partitioning of AA and the non-ideal properties of solution in particles result in the decrease of GF. In addition, the change of water activity affected by these two dynamic processes acts as a more important factor than surface tension in the decrease of GF. Moreover, RH, the mass ratio and the initial diameter have significant impact on the AA partitioning, the non-ideal properties of solution and their influences on the hygroscopicity of particles.

A method for estimating the ratio of aerosol mass concentration to the imaginary part of the atmospheric complex refractive index and its application

Based on the principle of light propagation, it is necessary to obtain the ratio (RMN) of atmospheric aerosol mass concentration to the imaginary part of the atmospheric equivalent refractive index for measuring aerosol mass vertical flux. In this paper, the factors affecting the RMN values are analyzed by numerical calculation under an ideal state and by using observational data. Numerical calculations show that the RMN is mainly determined by the aerosol particle size distribution (PSD), hygroscopicity parameters and relative humidity. With the same relative humidity, the smaller the geometric mean diameter (Dg) is, the larger the RMN, and when the aerosol particle hygroscopicity parameter is greater than 0.14, the greater the relative humidity is, the smaller the RMN. Comprehensive experiments were conducted in urban Hefei, and the results of observations at Hefei confirm the numerical results. Data from ten cities across China also confirm the numerical results. The order of geometric mean diameter of aerosol particles at the ten sites can be determined by the order of RMN, and the order of hygroscopicity parameters at the ten sites can be determined by the order of the change rate of RMN with relative humidity. The geometric mean diameters of aerosol particles are different among the ten sites, while the hygroscopicity parameters are similar.

Study on Gravity Sedimentation of Multicomponent Hygroscopic Aerosols in Reactor Severe Accident

In the event of a severe accident, the multicomponent hygroscopic aerosols in the containment will absorb water under the high humidity condition, thereby influencing the gravity sedimentation behavior. In this study, a physical model of the equilibrium particle diameter of the multicomponent hygroscopic aerosol particles was developed through theoretical analysis, and it was also validated by experimental results. The model focuses on the effect of solubility on the hygroscopic process and explains the reason why the multicomponent hygroscopic particles grow along a discontinuity curve. Based on a typical gigawatt-class pressurized water reactor, the effects of relative humidity, dry particle diameter and mass fraction of hygroscopic components on the removal coefficient of the gravity sedimentation were investigated. The results show that the velocity of the gravity sedimentation will significantly increase, only if the aerosol particles grow to a certain degree. Only when the humidity is more than a certain value, the sedimentation process of the pure hygroscopic aerosol particles with a dry particle diameter exceeding 0.1 μm will accelerate due to hygroscopicity, and this humidity limit will decrease as the dry particle diameter increases. With the progress of the accident, the mass fraction of non-hygroscopic components in the aerosol particles gradually decreases, leading the above-mentioned humidity limit increasing and the acceleration of gravity sedimentation due to the hygroscopicity decreasing in the same humidity.

Hygroscopic growth of aerosol particles consisted of oxalic acid and its internal mixture with ammonium sulfate for the relative humidity ranging from 80% to 99.5%

The hygroscopicity of atmospheric aerosol particles plays an important role in their effects on the environment and the public health. Oxalic acid (OA) has been recognized as the dominant dicarboxylic acid in the urban and the remote aerosol particles, so a number of studies have investigated the hygroscopicity of aerosols consisted of pure OA and its mixture with inorganic salt. However, few experimental studies have focused on the hygroscopicity of nanoscale particles at high relative humidity (RH) below saturation of water vapor (i.e., RH = 90–100%) due to the limitation of traditional measuring instruments. In this work, the hygroscopic growth factor (GF) of the aerosol particles composed of pure OA and internally mixed OA-ammonium sulfate (AS) at RH = 80–99.5% were studied using a high humidity tandem differential mobility analyzer (HHTDMA). The experimental results were used to verify the applicability of models including the ideal solution model, the extended aerosol inorganics model (E-AIM) combining with the revised universal quasi-chemical functional group activity coefficients (UNIFAC-Peng) model, the Aerosol Inorganic–Organic Mixtures Functional groups Activity Coefficients (AIOMFAC) model and the Zdanovskii–Stokes–Robinson (ZSR) model. According to the experimental results, the effect of RH, the composition and the initial dry particle diameter (D0) on the hygroscopic growth factor (GF) and the effective hygroscopicity parameter (κ) of particles at RH = 80–99.5% were analyzed in details. It has been found that for pure OA particles with D0 = 80/100 nm, the prediction of the UNIFAC-Peng model and the AIOMFAC model becomes more accurate than the ideal solution model with the increasing of RH, while all models cannot describe the GF of smaller particles at RH = 80–99.5%. For mixed OA-AS aerosol particles, the chemical reaction is an important reason for the discrepancies between the HHTDMA results and the model prediction. For the pure OA aerosol particles at RH ≤ 96% and particles containing AS at RH ≤ 99.5%, the sensitivity of GF to D0 is positively and negatively correlated with RH and D0, respectively. However, for all aerosol types in this study, the sensitivity of GF to RH is positively correlated with both D0 and RH. In addition, the κ based on the measurement is clearly dependent on D0 (at RH = 95–99.5%), RH and the particle composition (at RH = 80–99.5%). The measured hygroscopicity of aerosol particles at high RH might be useful in addressing challenges in solving the discrepancies between the κ measured under subsaturated and supersaturated conditions.

Solar radiometer sensing of multi-year aerosol features over a tropical urban station: direct-Sun and inversion products

Abstract. The AErosol RObotic NETwork (AERONET) is the most developed ground-based network for aerosol remote sensing and has been playing a significant role not only in monitoring air quality for protecting human health but also in assessing the radiative budget of our planet Earth. In this paper, we report the direct-Sun and inversion products, comprising of spectral variation of aerosol optical depth (AOD), associated Ångström exponent (AE), fine- and coarse-mode aerosol fractions, aerosol size distribution (ASD), refractive index (RI), asymmetry parameter (AP), single scattering albedo (SSA), aerosol radiative forcing (ARF) and columnar concentration of gas constituents such as water vapor (H2O), obtained from a Cimel Sun–sky radiometer, functioning in Pune, India, under the AERONET program since October 2004. These long-term measurements carried out from 2005 to 2015 could serve as an urban aerosol optical long-term average or climatology. The AOD long-term variations at all wavelengths, considered in the study, exhibited an increasing trend, implying year-to-year enhancement in aerosol loading. The mean seasonal variations in AOD from cloud-free days indicated greater values during the monsoon season, revealing dominance of hygroscopic aerosol particles over the station. Contribution by different aerosol types to AOD has also been deduced and discussed, and dominance of a mixed type of aerosols (44.85 %) found, followed by combination of biomass burning and urban industrial aerosols (22.57 %) compared to other types of aerosols during the study period. The long-term datasets, derived aerosol and trace gas products play a significant role in understanding aerosol climate forcing, trends and evaluation of regional air pollution and validation of aerosol transport models over the study region.

In Situ Quantitative Observation of Hygroscopic Growth of Single Nanoparticle Aerosol by Surface Plasmon Resonance Microscopy.

Aerosol particle hygroscopicity is an important factor in visibility reduction, cloud formation, radiation forcing, and the global climate. The high number concentration of nanoparticles (defined as particles with diameters below 100 nm) means that their hygroscopic growth abilities and potential contributions to the climate and environment are significant. Therefore, a rapid and accurate in situ analysis method for single nanoparticle hygroscopic growth in an atmospheric environment is important to characterize the effects of the particle's physical and chemical properties in this process. In this work, surface plasmon resonance microscopy with azimuthal rotation illumination (SPRM-ARI) is used to observe the hygroscopic growth and water content of single nanoparticles in situ. The hygroscopic growth results of a single-component nanoparticle are well matched with the extended aerosol inorganic model (E-AIM) results, and the proposed method remains reliable even when the relative humidity (RH) exceeds 90%. For a bicomponent nanoparticle (with NaCl as the primary content), the presence of a component without deliquescence phase transitions under increasing humidity conditions causes the measured data to differ from both the Zdanovskii-Stokes-Robinson (ZSR) model and E-AIM predictions in the low RH range. However, because of their complete liquefaction, the growth factor (GF) variation of the bicomponent nanoparticle is close to the model predictions in the high RH range. Finally, based on the positive correlation between particle volume and the gray intensity of SPRM-ARI, GF values can be obtained from the cube root of the gray intensity and the actual water content of single nanoparticles can then be derived.

Urban Aerosol Hygroscopicity During Haze Weather

The hygroscopicity of aerosols has an important influence on atmospheric visibility and is one of the main causes of haze pollution. Based on observations of the aerosol hygroscopic growth factor (GF), water soluble inorganic ions, and organic carbon/elemental carbon (OC/EC) data during haze weather from April 17 to May 21, in 2014, the hygroscopic properties of aerosols and corresponding effects on haze in Nanjing were analyzed. The results showed that the distribution of GF was bimodal and varied from 1.12 to 1.64. With the increase of particle size, the average hygroscopic growth factor (GFmean) changed less and the standard deviation of wettability (σ) increased gradually; meanwhile, the degree of external mixing of chemical components increased gradually. The hygroscopicity of aerosol particles in the day was better than that at night, but the mixing degree was weaker than that at night; in non-haze weather, the hygroscopicity of aerosol particles was stronger and the degree of external mixing was higher, while the hygroscopicity and mixing degree of haze particles showed opposite trends. With the increase of haze levels, the hygroscopicity of aerosol particles grew weaker and the degree of external mixing decreased further. Relative humidity can have a significant impact on the chemical components of aerosols and their hygroscopic capacity. Under a low humidity background, the main chemical components of aerosols included NH4+, NO3-, SO42-, OC, and EC, and the content of OC/EC in aerosols during haze days was more abundant; in haze weather with low relative humidity, abundant organic matter was the main reason for the decrease of the moisture absorption capacity of small-scale aerosols. The level of relative humidity in the haze weather was also an important factor affecting the hygroscopic capacity of aerosols. The contents of (NH4)2SO4, OC, and insoluble substances in aerosols were the highest, followed by NH4NO3. The contents of these chemical components showed obvious diurnal variation characteristics, which resulted in significant diurnal variation of the hygroscopicity of the aerosols. κchem calculated by the chemical composition and κmean acquired by observations using H-TDMA showed good consistency, and the correlation coefficient was 0.8903. In haze weather, the correlation between them was further enhanced. Therefore, the major chemical components of aerosols could be used to predict the hygroscopic properties of aerosols.

Measuring hygroscopicity of internally mixed NaNO3 and glutaric acid particles by vacuum FTIR.

Sodium nitrate as an important inorganic component can be chemically formed from the reactions of nitrogen oxides and nitric acid (HNO3) with sea salt in atmosphere. Organic acids contribute a significant fraction of photochemical formed secondary organics that can condense on the preexisting nitrate-containing particles. Atmospheric particles often include a complex mixture of nitrate and secondary organic materials accumulated within the same individual particles. Here we studied the hygroscopicity of aerosol particles composed of sodium nitrate and glutaric acid (GA) by using a pulsed RH controlling system and a rapid scan vacuum FTIR spectrometer (PRHCS-RSVFTIR). The water content in the particles and efflorescence ratios of both NaNO3 and GA at ambient relative humidity (RH) as a function of time were obtained from the rapid-scan infrared spectra with a sub-second time resolution. Our study showed that both NaNO3 and GA crystallized at 44.1% RH during two different RH control processes (stepwise and pulsed processes). It was found that the addition of GA could suppress the efflorescence of NaNO3 during the dehumidifying process. In addition, the mixed NaNO3/GA particles release HNO3 during the dehumidifying and humidifying cycles. These findings are important in further understanding the role of interactions between water-soluble dicarboxylic acids and nitrates on hygroscopicity and environmental effects of atmospheric particles.

The Dependence of Radius on Relative Humidity and Solute Mass at High Relative Humidities Up to and Including 100%

AbstractThis manuscript presents a rigorous examination of the equilibrium radius ratio of hygroscopic aerosol particles that are solution drops of ideal and actual inorganic solutes for a range of solute masses in the relative humidity range 99–100%. Analysis is presented first for ideal solutes over a range of solute masses for different hygroscopicities, providing a theoretical framework for the subsequent analysis of actual solutes. Dimensionless quantities are used to reduce the Köhler equation to one with no free parameters and an approximate solution is presented. Next analysis is presented for three common inorganic solutes of atmospheric importance: sodium chloride, ammonium sulfate, and sulfuric acid, with a range of solute masses considered for each substance. The extent to which nonideality is important for these solutes over the ranges of relative humidities and solute masses considered is examined. A simple but accurate single‐parameter expression is presented for the equilibrium radius ratio as a function of relative humidity that contains the dependences on solute mass and composition for these solutes. The accuracy of this expression is quantified and factors that limit this accuracy are discussed. The expression is accurate to within 5% over most of the range of mass‐equivalent dry radii from 10 to 250 nm and relative humidities from below 99 up to 100%, over which the equilibrium radius ratio varies by more than a factor of 5, and it remains finite at 100% relative humidity. Finally, measurements of hygroscopic growth of aerosol particles in this relative humidity range are discussed.

CCN measurements at the Princess Elisabeth Antarctica research station during three austral summers

Abstract. For three austral summer seasons (2013–2016, each from December to February) aerosol particles arriving at the Belgian Antarctic research station Princess Elisabeth (PE) in Dronning Maud Land in East Antarctica were characterized. This included number concentrations of total aerosol particles (NCN) and cloud condensation nuclei (NCCN), the particle number size distribution (PNSD), the aerosol particle hygroscopicity, and the influence of the air mass origin on NCN and NCCN. In general NCN was found to range from 40 to 6700 cm−3, with a median of 333 cm−3, while NCCN was found to cover a range between less than 10 and 1300 cm−3 for supersaturations (SSs) between 0.1 % and 0.7 %. It is shown that the aerosol is dominated by the Aitken mode, being characterized by a significant amount of small, and therefore likely secondarily formed, aerosol particles, with 94 % and 36 % of the aerosol particles smaller than 90 and ≈35 nm, respectively. Measurements of the basic meteorological parameters as well as the history of the air masses arriving at the measurement station indicate that the station is influenced by both marine air masses originating from the Southern Ocean and coastal areas around Antarctica (marine events – MEs) and continental air masses (continental events – CEs). CEs, which were defined as instances when the air masses spent at least 90 % of the time over the Antarctic continent during the last 10 days prior to arrival at the measurements station, occurred during 61 % of the time during which measurements were done. CEs came along with rather constant NCN and NCCN values, which we denote as Antarctic continental background concentrations. MEs, however, cause large fluctuations in NCN and NCCN, with low concentrations likely caused by scavenging due to precipitation and high concentrations likely originating from new particle formation (NPF) based on marine precursors. The application of HYSPLIT back trajectories in form of the potential source contribution function (PSCF) analysis indicate that the region of the Southern Ocean is a potential source of Aitken mode particles. On the basis of PNSDs, together with NCCN measured at an SS of 0.1 %, median values for the critical diameter for cloud droplet activation and the aerosol particle hygroscopicity parameter κ were determined to be 110 nm and 1, respectively. For particles larger than ≈110 nm the Southern Ocean together with parts of the Antarctic ice shelf regions were found to be potential source regions. While the former may contribute sea spray particles directly, the contribution of the latter may be due to the emission of sea salt aerosol particles, released from snow particles from surface snow layers, e.g., during periods of high wind speed, leading to drifting or blowing snow. The region of the Antarctic inland plateau, however, was not found to feature a significant source region for aerosol particles in general or for cloud condensation nuclei measured at the PE station in the austral summer.

Hygroscopicity of dimethylaminium-, sulfate-, and ammonium-containing nanoparticles

Dimethylamine (DMA) and sulfuric acid (SA) are the important constituents of atmospheric aerosols. To accurately predict the behavior of DMA-containing aerosol systems, exact thermodynamic models are needed. The applicability of these models needs to be tested carefully in different experimental settings to continuously validate and improve their performance. In this work, the Extended Aerosol Inorganics Model (E-AIM) was used to simulate the hygroscopicity of aerosol particles generated from five different aqueous DMA-SA solutions. The applicability of the model was tested in the 10–200 nm size range and from DMA-SA molar ratios ranging from 1:3 to 2:1. The aerosol hygroscopic growth at 0–80% RH was determined with two tandem differential mobility analyzers, and the composition of the generated particles was measured with the Aerosol Mass Spectrometer (AMS), which revealed that the particles contained also ammonium. The model accurately captured the hygroscopicity for particles larger than 80 nm. With particles smaller than 80 nm, the model underestimated the hygroscopicity in all the studied experimental conditions. An increase in hygroscopicity parameter κ with decreasing particle size implied a plausible base evaporation in the experimental setup, which in turn may have affected the modeled hygroscopicity as the composition of the smallest particles may have differed from the AMS measurements. Coupling E-AIM to a dynamic evaporation model, however, could not produce compositions whose modeled hygroscopic behavior would match the measured hygroscopic growth at smaller sizes. Our results, therefore, suggest that DMA thermodynamics are not modeled correctly in E-AIM or there exists uncertainty in the physicochemical parameters.© 2018 American Association for Aerosol Research

Α dosimetry model of hygroscopic particle growth in the human respiratory tract

The objective of the current study was to determine the growth and deposition of hygroscopic aerosol particles in the human respiratory tract. A hygroscopic particle growth methodology was incorporated into an existing particle dosimetry model (Exposure Dose Model 2, ExDoM2) using the κ-Kohler theory, the International Commission on Radiological Protection (ICRP) formulation for hygroscopic growth and mathematical formulations for taking into account the residence time, the influence of hygroscopicity on the particle’s density, and hygroscopic growth at 99.5% relative humidity. In order to validate ExDoM2, the results of the model were compared with experimental total deposition data for NaCl particles. The incorporation of the hygroscopic growth resulted in predictions closer to the experimental data than to model results without the use of a hygroscopic model formulation. The hygroscopicity plays a more significant role in the lower regions (tracheobronchial (TB) and alveolar-interstitial (AI) regions) of the respiratory tract. In particular, the hygroscopicity of NaCl particles decreases the deposition in the AI region for particles in the size range 0.03 μm ≤ aerodynamic diameter (dae) ≤ 0.2 μm while for the size range 0.3 μm ≤ dae ≤ 3 μm, the hygroscopicity increases the deposition in the AI region. In addition, it is observed that the deposition of (NH4)2SO4 and NH4NO3 particles with dae ≥ 0.30 μm is higher when the hygroscopic properties of the particles are taken into consideration. However, the particle deposition in the range 0.02 μm ≤ dae ≤ 0.25 μm is decreased due to hygroscopicity.

Rebounding hygroscopic inorganic aerosol particles: Liquids, gels, and hydrates

ABSTRACTParticle rebound was studied for ten atmospherically relevant inorganics. Experiments were conducted with submicron particles in aerosol form to a relative humidity (RH) of <5% followed by progressive exposure to RH up to 95% for 2 s. At low RH, particles of MgCl2, NaCl, NH4Cl, KCl, (NH4)2SO4, and Na2SO4 crystallized. As RH increased, these particles completed the transition from rebounding to adhering close to their deliquescence RH (DRH). The onset of decreased rebound, however, was below the DRH. Rebound curves for particles of MgCl2, NH4NO3, MgSO4, and NaNO3 had different features than explained by water adsorption and deliquescence. Particles of MgCl2 had rebound curves characterized by two domains, corresponding to its two hydrates. At low RH, particles of MgSO4 and NaNO3 did not crystallize but rebound occurred, suggesting a glassy or high-viscosity though noncrystalline state. Gel formation for MgSO4 can increase viscosity, affecting rebound behavior. Particles of NH4NO3 adhered even to <5...

VH-TDMA: A description and verification of an instrument to measure aerosol particle hygroscopicity and volatility

ABSTRACTThe aim of this study was to provide a description and characterize the performance of a volatility hygroscopicity tandem differential mobility analyzer (VH-TDMA) by calibration measurements. In our investigations, we used the two calibration standards most often used by the TDMA community: ammonium sulfate ((NH4)2SO4) and sodium chloride (NaCl) particles. The hygroscopic growth factors, volatility factors, and the hygroscopic growth factors of the nonvolatile particle core were measured in different relative humidity and thermal denuder temperature conditions. The measured hygroscopic growth and deliquescence relative humidities for ammonium sulfate and sodium chloride particles are in line with theory and results from previous measurements, as are the measurements for volatility and hygroscopicity of the particle core. We summarize the measurement campaigns, where the VH-TDMA has been deployed, and show the instrument is capable of measuring high quality data of atmospheric particle properties i...

A broad supersaturation scanning (BS2) approach for rapid measurement of aerosol particle hygroscopicity and cloud condensation nuclei activity

Abstract. The activation and hygroscopicity of cloud condensation nuclei (CCN) are key to the understanding of aerosol–cloud interactions and their impact on climate. They can be measured by scanning the particle size and supersaturation in CCN measurements. The scanning of supersaturation is often time-consuming and limits the temporal resolution and performance of CCN measurements. Here we present a new approach, termed the broad supersaturation scanning (BS2) method, in which a range of supersaturation is simultaneously scanned, reducing the time interval between different supersaturation scans. The practical applicability of the BS2 approach is demonstrated with nano-CCN measurements of laboratory-generated aerosol particles. Model simulations show that the BS2 approach may also be applicable for measuring CCN activation of ambient mixed particles. Due to its fast response and technical simplicity, the BS2 approach may be well suited for aircraft and long-term measurements. Since hygroscopicity is closely related to the fraction of organics/inorganics in aerosol particles, a BS2-CCN counter can also serve as a complementary sensor for fast detection/estimation of aerosol chemical compositions.