Hygroscopic Properties Of Particles Research Articles

Calculation of aerosol particle hygroscopic properties from OPC derived PM2.5 data

Calculation of aerosol particle hygroscopic properties from OPC derived PM2.5 data

Physical properties and lung deposition of particles emitted from five major indoor sources

The physical properties of indoor particles were measured with an Scanning Mobility Particle Sizer (SMPS) system (14.6–850 nm), an Aerodynamic Particle Sizer (APS, 0.54–18 μm) and an Hygroscopic Tandem Differential Mobility Analyzer (H-TDMA) in an apartment located in an urban background site in Prague (Czech Republic) from 15 August to 8 September, 2014. The total particle maximum number concentration was 9.38 × 104, 1.46 × 105, 2.89 × 104, 2.25 × 105 and 1.57 × 106 particles cm−3 for particles released from vacuum cleaning, soap/W5 cleaning spray, smoking, incense burning and cooking (frying) activities, respectively. Particles emitted from cleaning activities showed unimodal number size distributions, with the majority of particles (>98.2 %) in the ultrafine size range (Dp <100 nm) and modes at a diameter of 19.8 nm for vacuum cleaning and 30.6 nm for soap/W5 cleaning. Smoking and incense burning predominantly generated particles in the accumulation mode with a count median diameter around 90–150 nm while cooking emissions showed a bimodal structure with a main mode at 47.8 nm. Particles from vacuum cleaning, incense burning, smoking and cooking emissions were found to be “nearly hydrophobic” with an average growth factor (Gf) around 1.01–1.10, while particles emitted from desk cleaning using organic compounds were found to be “less-hygroscopic” (Gf ∼1.12–1.16). Based on an adjusted MPPD model with a consideration of the hygroscopic properties of particles, the total lung deposition fractions of these particles by number when they penetrate into the human lung were 0.73 ± 0.02, 0.62 ± 0.03, 0.37 ± 0.03, 0.32 ± 0.03 and 0.49 ± 0.02 for vacuum cleaning, desk cleaning, smoking, incense burning and cooking, respectively.

Particle hygroscopicity and its link to chemical composition in the urban atmosphere of Beijing, China, during summertime

Abstract. Simultaneous measurements of particle number size distribution, particle hygroscopic properties, and size-resolved chemical composition were made during the summer of 2014 in Beijing, China. During the measurement period, the mean hygroscopicity parameters (κs) of 50, 100, 150, 200, and 250 nm particles were respectively 0.16 &amp;amp;pm; 0.07, 0.19 &amp;amp;pm; 0.06, 0.22 &amp;amp;pm; 0.06, 0.26 &amp;amp;pm; 0.07, and 0.28 &amp;amp;pm; 0.10, showing an increasing trend with increasing particle size. Such size dependency of particle hygroscopicity was similar to that of the inorganic mass fraction in PM1. The hydrophilic mode (hygroscopic growth factor, HGF &gt; 1.2) was more prominent in growth factor probability density distributions and its dominance of hydrophilic mode became more pronounced with increasing particle size. When PM2.5 mass concentration was greater than 50 μg m−3, the fractions of the hydrophilic mode for 150, 250, and 350 nm particles increased towards 1 as PM2.5 mass concentration increased. This indicates that aged particles dominated during severe pollution periods in the atmosphere of Beijing. Particle hygroscopic growth can be well predicted using high-time-resolution size-resolved chemical composition derived from aerosol mass spectrometer (AMS) measurements using the Zdanovskii–Stokes–Robinson (ZSR) mixing rule. The organic hygroscopicity parameter (κorg) showed a positive correlation with the oxygen to carbon ratio. During the new particle formation event associated with strongly active photochemistry, the hygroscopic growth factor or κ of newly formed particles is greater than for particles with the same sizes not during new particle formation (NPF) periods. A quick transformation from external mixture to internal mixture for pre-existing particles (for example, 250 nm particles) was observed. Such transformations may modify the state of the mixture of pre-existing particles and thus modify properties such as the light absorption coefficient and cloud condensation nuclei activation.

Influence of Collecting Substrates on the Characterization of Hygroscopic Properties of Inorganic Aerosol Particles

The influence of six collecting substrates with different physical properties on the hygroscopicity measurement of inorganic aerosol particle surrogates and the potential applications of these substrates were examined experimentally. Laboratory-generated single salt particles, such as NaCl, KCl, and (NH4)2SO4, 1-5 μm in size, were deposited on transmission electron microscopy grids (TEM grids), parafilm-M, Al foil, Ag foil, silicon wafer, and cover glass. The particle hygroscopic properties were examined by optical microscopy. Contact angle measurements showed that parafilm-M is hydrophobic, and cover glass, silicon wafer, Al foil, and Ag foil substrates are hydrophilic. The observed deliquescence relative humidity (DRH) values for NaCl, KCl, and (NH4)2SO4 on the TEM grids and parafilm-M substrates agreed well with the literature values, whereas the DRHs obtained on the hydrophilic substrates were consistently ∼1-2% lower, compared to those on the hydrophobic substrates. The water layer adsorbed on the salt crystals prior to deliquescence increases the Gibb's free energy of the salt crystal-substrate system compared to the free energy of the salt droplet-substrate system, which in turn reduces the DRHs. The hydrophilic nature of the substrate does not affect the measured efflorescence RH (ERH) values. However, the Cl(-) or SO4(2-) ions in aqueous salt droplets seem to have reacted with Ag foil to form AgCl or Ag2SO4, respectively, which in turn acts as seeds for the heterogeneous nucleation of the original salts, leading to higher ERHs. The TEM grids were found to be most suitable for the hygroscopic measurements of individual inorganic aerosol particles by optical microscopy and when multiple analytical techniques, such as scanning electron microscopy-energy dispersive X-ray spectroscopy, TEM-EDX, and/or Raman microspectrometry, are applied to the same individual particles.

Ambient black carbon particle hygroscopic properties controlled by mixing state and composition

Abstract. The wet removal of black carbon aerosol (BC) in the atmosphere is a crucial factor in determining its atmospheric lifetime and thereby the vertical and horizontal distributions, dispersion on local and regional scales, and the direct, semi-direct and indirect radiative forcing effects. The in-cloud scavenging and wet deposition rate of freshly emitted hydrophobic BC will be increased on acquisition of more-hydrophilic components by coagulation or coating processes. The lifetime of BC is still subject to considerable uncertainty for most of the model inputs, which is largely due to the insufficient constraints on the BC hydrophobic-to-hydrophilic conversion process from observational field data. This study was conducted at a site along UK North Norfolk coastline, where the BC particles were transported from different regions within Western Europe. A hygroscopicity tandem differential mobility analyser (HTDMA) was coupled with a single particle soot photometer (SP2) to measure the hygroscopic properties of BC particles and associated mixing state in real time. In addition, a Soot Particle AMS (SP-AMS) measured the chemical compositions of additional material associated with BC particles. The ensemble of BC particles persistently contained a less-hygroscopic mode at a growth factor (gf) of around 1.05 at 90% RH (dry diameter 163 nm). Importantly, a more-hygroscopic mode of BC particles was observed throughout the experiment, the gf of these BC particles extended up to ~1.4–1.6 with the minimum between this and the less hygroscopic mode at a gf ~1.25, or equivalent effective hygroscopicity parameter κ ~0.1. The gf of BC particles (gfBC) was highly influenced by the composition of associated soluble material: increases of gfBC were associated with secondary inorganic components, and these increases were more pronounced when ammonium nitrate was in the BC particles; however the presence of secondary organic matter suppressed the gfBC below that of pure inorganics. The Zdanovskii-Stokes-Robinson (ZSR) mixing rule captures the hygroscopicity contributions from different compositions within ±30% compared to the measured results, however is subject to uncertainty due to the complex morphology of BC component and potential artefacts associated with semivolatile particles measured with the HTDMA. This study provides detailed insights on BC hygroscopicity associated with its mixing state, and the results will importantly constrain the microphysical mixing schemes of BC as used by a variety of high level models. In particular, this provides direct evidence to highlight the need to consider ammonium nitrate ageing of BC particles because this will result in particles becoming hydrophilic on much shorter timescales than for sulphate formation, which is often the only mechanism considered.

Hygroscopic properties of fresh and aged wood burning particles

Biomass burning is one of the largest aerosol sources worldwide. In this study, the hygroscopic properties of fresh and aged wood burning particles were investigated under controlled laboratory conditions in several smog chamber experiments. Beech log wood was burnt in a residential log wood burner and the particles emitted during the different burning phases (starting, flaming, and smoldering) were analyzed. The particles were photochemically aged using the own volatile organic compound emissions from the burnt wood. The hygroscopic properties of the particles at relative humidities below and above 100% were determined and compared.The freshly emitted soot particles have a fractal-like structure. The structure collapsed in half of the experiments where soot was present for particles ≥100nm under the presence of a high relative humidity, leading to a more compact structure. This restructuring induces an underestimation of the hygroscopicity measured with mobility diameter based methods.The hygroscopicity parameter “apparent κ” of fresh wood combustion particles varies between 0 and 0.39. With aging, the hygroscopicity of the particles generally increases. This is due to the uptake of organic matter and inorganic salts, and because the particles become more oxidized.One smoldering phase experiment was carried out, which, in contrast to the other experiments, showed very high apparent κ values between 0.2 and 0.4 at the beginning of the experiment, depending on the size of the particles. These values were decreasing with time. This suggests a different composition of the particles, with a higher fraction of inorganic components initially.The results indicate that it is not possible to use only one κ value for different burning phases and aging times of wood combustion particles in climate models.

Hygroscopic and Chemical Properties of Aerosols Collected near a Copper Smelter: Implications for Public and Environmental Health

Particulate matter emissions near active copper smelters and mine tailings in the southwestern United States pose a potential threat to nearby environments owing to toxic species that can be inhaled and deposited in various regions of the body depending on the composition and size of the particles, which are linked by particle hygroscopic properties. This study reports the first simultaneous measurements of size-resolved chemical and hygroscopic properties of particles next to an active copper smelter and mine tailings by the towns of Hayden and Winkelman in southern Arizona. Size-resolved particulate matter samples were examined with inductively coupled plasma mass spectrometry, ion chromatography, and a humidified tandem differential mobility analyzer. Aerosol particles collected at the measurement site are enriched in metals and metalloids (e.g., arsenic, lead, and cadmium) and water-uptake measurements of aqueous extracts of collected samples indicate that the particle diameter range of particles most enriched with these species (0.18-0.55 μm) overlaps with the most hygroscopic mode at a relative humidity of 90% (0.10-0.32 μm). These measurements have implications for public health, microphysical effects of aerosols, and regional impacts owing to the transport and deposition of contaminated aerosol particles.

Hygroscopic properties of atmospheric aerosol particles over the Eastern Mediterranean: implications for regional direct radiative forcing under clean and polluted conditions

Abstract. This work examines the effect of direct radiative forcing of aerosols in the eastern Mediterranean troposphere as a function of air mass composition, particle size distribution and hygroscopicity, and relative humidity (RH). During intensive field measurements on the island of Crete, Greece, the hygroscopic properties of atmospheric particles were determined using a Hygroscopicity Tandem Differential Mobility Analyzer (H-TDMA) and a Hygroscopicity Differential Mobility Analyzer-Aerodynamic Particle Sizer (H-DMA-APS). Similar to former studies, the H-TDMA identified three hygroscopic sub-fractions of particles in the sub-μm range: a more hygroscopic group, a less hygroscopic group and a nearly hydrophobic particle group. The average hygroscopic particle growth factors at 90 % RH were a significant function of particle mobility diameter (Dp): 1.42 (± 0.05) at 30 nm compared to 1.63 (± 0.07) at 250 nm. The H-DMA-APS identified up to three hygroscopic sub-fractions at mobility diameters of 1.0 and 1.2 μm. The data recorded between 12 August and 20 October 2005 were classified into four distinct synoptic-scale air mass types distinguishing between different regions of origin (western Mediterranean vs. the Aegean Sea) as well as the degree of continental pollution (marine vs. continentally influenced). The hygroscopic properties of particles with diameter Dp≥150 nm showed the most pronounced dependency on air mass origin, with growth factors in marine air masses exceeding those in continentally influenced air masses. Particle size distributions and hygroscopic growth factors were used to calculate aerosol light scattering coefficients at ambient RH using a Mie model. A main result was the pronounced enhancement of particle scattering over the eastern Mediterranean due to hygroscopic growth, both in the marine and continentally influenced air masses. When RH reached its summer daytime values around 70–80 %, up to 50–70 % of the calculated visibility reduction was due to the hygroscopic growth of the particles by water compared to the effect of the dry particles alone. The estimated aerosol direct radiative forcings for both, marine and continentally influenced air masses were negative indicating a net cooling of the atmosphere due to the aerosol. The radiative forcing ΔFr was nevertheless governed by the total aerosol concentration most of the time: ΔFr was typically more negative for continentally influenced aerosols (ca. −4 W m−2) compared to rather clean marine aerosols (ca. −1.5 W m−2). When RH occasionally reached 90 % in marine air masses, ΔFr even reached values down to −7 W m−2. Our results emphasize, on the basis of explicit particle hygroscopicity measurements, the relevance of ambient RH for the radiative forcing of regional atmospheres.

Hygroscopicity and chemical composition of Antarctic sub-micrometre aerosol particles and observations of new particle formation

Abstract. The Antarctic near-coastal sub-micrometre aerosol particle features in summer were characterised based on measured data on aerosol hygroscopicity, size distributions, volatility and chemical ion and organic carbon mass concentrations. Hysplit model was used to calculate the history of the air masses to predict the particle origin. Additional measurements of meteorological parameters were utilised. The hygroscopic properties of particles mostly resembled those of marine aerosols. The measurements took place at 130 km from the Southern Ocean, which was the most significant factor affecting the particle properties. This is explained by the lack of additional sources on the continent of Antarctica. The Southern Ocean was thus a likely source of the particles and nucleating and condensing vapours. The particles were very hygroscopic (HGF 1.75 at 90 nm) and very volatile. Most of the sub-100 nm particle volume volatilised below 100 °C. Based on chemical data, particle hygroscopic and volatile properties were explained by a large fraction of non-neutralised sulphuric acid together with organic material. The hygroscopic growth factors assessed from chemical data were similar to measured. Hygroscopicity was higher in dry continental air masses compared with the moist marine air masses. This was explained by the aging of the marine organic species and lower methanesulphonic acid volume fraction together with the changes in the inorganic aerosol chemistry as the aerosol had travelled long time over the continental Antarctica. Special focus was directed in detailed examination of the observed new particle formation events. Indications of the preference of negative over positive ions in nucleation could be detected. However, in a detailed case study, the neutral particles dominated the particle formation process. Freshly nucleated particles had the smallest hygroscopic growth factors, which increased subsequent to particle aging.

Hygroscopic properties of submicrometer atmospheric aerosol particles measured with H-TDMA instruments in various environments–a review

The hygroscopic properties play a vital role for the direct and indirect effects of aerosols on climate, as well as the health effects of particulate matter (PM) by modifying the deposition pattern of inhaled particles in the humid human respiratory tract. Hygroscopic Tandem Differential Mobility Analyzer (H-TDMA) instruments have been used in field campaigns in various environments globally over the last 25 yr to determine the water uptake on submicrometre particles at subsaturated conditions. These investigations have yielded valuable and comprehensive information regarding the particle hygroscopic properties of the atmospheric aerosol, including state of mixing. These properties determine the equilibrium particle size at ambient relative humidities and have successfully been used to calculate the activation of particles at water vapour supersaturation. This paper summarizes the existing published H-TDMA results on the sizeresolved submicrometre aerosol particle hygroscopic properties obtained from ground-based measurements at multiple marine, rural, urban and free tropospheric measurement sites. The data is classified into groups of hygroscopic growth indicating the external mixture, and providing clues to the sources and processes controlling the aerosol. An evaluation is given on how different chemical and physical properties affect the hygroscopic growth.

Hygroscopic properties and extinction of aerosol particles at ambient relative humidity in South-Eastern China

During the “Program of Regional Integrated Experiments of Air Quality over Pearl River Delta 2004 (PRIDE-PRD2004)” hygroscopic properties of particles in the diameter range 22 nm to 10 μ m were determined. For that purpose, a Humidifying Differential Mobility Particle Sizer (H-DMPS) and a Micro-Orifice Uniform Deposition Impactor (MOUDI) were operated. The derived size-dependent particle hygroscopic growth factors were interpolated to ambient relative humidity (RH) and used to calculate the particle number size distributions (PNSDs) at ambient conditions. A comparison between the modeled particle extinction coefficients ( σ ext , Mie ) and those observed with a Raman lidar was made. It is shown that the particle extinction coefficient ( σ ext ) at ambient RH can be properly estimated with Mie-model calculations based on the in situ physico-chemical measurements of dry and humidified PNSD and chemical composition.

Hygroscopic properties of submicrometer atmospheric aerosol particles measured with H-TDMA instruments in various environments—a review

The hygroscopic properties play a vital role for the direct and indirect effects of aerosols on climate, as well as the health effects of particulate matter (PM) by modifying the deposition pattern of inhaled particles in the humid human respiratory tract. Hygroscopic Tandem Differential Mobility Analyzer (H-TDMA) instruments have been used in field campaigns in various environments globally over the last 25 yr to determine the water uptake on submicrometre particles at subsaturated conditions. These investigations have yielded valuable and comprehensive information regarding the particle hygroscopic properties of the atmospheric aerosol, including state of mixing. These properties determine the equilibrium particle size at ambient relative humidities and have successfully been used to calculate the activation of particles at water vapour supersaturation. This paper summarizes the existing published H-TDMA results on the sizeresolved submicrometre aerosol particle hygroscopic properties obtained from ground-based measurements at multiple marine, rural, urban and free tropospheric measurement sites. The data is classified into groups of hygroscopic growth indicating the external mixture, and providing clues to the sources and processes controlling the aerosol. An evaluation is given on how different chemical and physical properties affect the hygroscopic growth.

Soot particles in the free troposphere over Australia

Abstract Aircraft observations were carried out in the middle troposphere at 5–6 km altitude over Australia in the PACE-II (Pacific Atmospheric Chemistry Experiment) campaign in October 1994. Concentrations of particles with radii larger than 4 nm and 0.15 μm were measured with a condensation nucleus (CN) counter and an optical counter, respectively. Individual aerosol particles were collected on electron microscopic grids using a jet impactor and subsequently examined using a transmission electron microscope coupled with an energy-dispersive X-ray (EDX) analyzer. High concentrations of CN (⩾4 nm) and large particles (0.15–0.5 μm radius) were found over the areas in northern Australia between Alice Springs and Darwin. Samples collected in this region had a large fraction of submicrometer soot-containing particles that had both K and S with a median S/(S+K) weight ratio of 0.4. The hygroscopic properties of particles with radii between 0.03 and 0.8 μm were examined with the dialysis (extraction) of water-soluble material. The sample collected in the area with high particle concentrations showed that the abundance of internally mixed soot particles was 88% of particles in the radius range of 0.1–0.35 μm. Approximately 50% of these mixed particles with radii ⩾0.2 μm were covered with semi-transparent material (probably organic material). Present research suggested that these particles were aged biomass burning particles originating from northern Australia and had been modified by chemical reactions and probably by coagulation during long-range transport. These soot particles were found to be present as internally mixed particles, with a soluble fraction that would make them efficient cloud condensation nuclei (CCN).

Diurnal, weekly, and seasonal variation of hygroscopic properties of submicrometer urban aerosol particles

Abstract Hygroscopic properties of aerosol particles at an urban background site in Leipzig, Germany, were measured using a Hygroscopicity-Tandem Differential Mobility Analyzer (H-TDMA) system. Hygroscopic properties of particles with dry diameter of 50 nm (Dd 50 ) and 150 nm (Dd 150 ) were determined at 92% relative humidity (RH) for a period of eight months in the year 2000. For both Dd, the results revealed two major hygroscopic groups (nearly hydrophobic group with an average growth factor of 1.06±0.04 for Dd 50 and 1.09±0.04 for Dd 150 , and more hygroscopic with 1.44±0.08 for Dd 50 and 1.65±0.08 for Dd 150 ) and a less-pronounced third group (less hygroscopic with 1.25±0.08 for Dd 50 and 1.33±0.07 for Dd 150 ). A simple solubility model was applied to these growth factors to estimate soluble volume fractions. Based on these estimated fractions, for all three hygroscopic groups the Dd 50 particles were composed of smaller amounts of soluble material than were the Dd 150 particles; the soluble volume fraction for more hygroscopic particles was only 50% for the Dd 50 particles and 70% for the Dd 150 particles. Calculated number fractions revealed that 31% of Dd 50 particles and 22% of Dd 150 particles showed nearly hydrophobic behavior. For both particle sizes, the number fraction of nearly hydrophobic particles showed a characteristic diurnal variation dependent on the two daily rush-hour periods. Also, the number fraction of nearly hydrophobic particles on weekdays was about 10% higher than that on weekends. In winter (November–February), the number fraction of nearly hydrophobic particles showed two maxima that coincided with the two daily rush-hour periods. In summer (May–August), only one distinct maximum during the morning rush-hour period was observed.

Field measurements of hygroscopic properties and state of mixing of nucleation mode particles

Abstract. An Ultrafine Tandem Differential Mobility Analyser (UF-TDMA) has been used in several field campaigns over the last few years. The investigations were focused on the origin and properties of nucleation event aerosols, which are observed frequently in various environments. This paper gives a summary of the results of 10 nm and 20 nm particle hygroscopic properties from different measurement sites: an urban site, an urban background site and a forest site in Finland and a coastal site in western Ireland. The data can be classified in four hygroscopic growth classes: hydrofobic, less-hygroscopic, more-hygroscopic and sea-salt. Similar classification has been earlier presented for Aitken and accumulation mode particles. In urban air, the summertime 10 nm particles showed varying less-hygroscopic growth behaviour, while winter time 10 nm and 20 nm particles were externally mixed with two different hygroscopic growth modes. The forest measurements revealed diurnal behaviour of hygroscopic growth, with high growth factors at day time and lower during night. The urban background particles had growth behaviour similar to the urban and forest measurement sites depending on the origin of the observed particles. The coastal measurements were strongly affected by air mass history. Both 10 nm and 20 nm particles were hygroscopic in marine background air. The 10 nm particles produced during clean nucleation burst periods were hydrofobic. Diurnal variation and higher growth factors of 10 nm particles were observed in air affected by other source regions. External mixing was occasionally observed at all the sites, but incidents with more than two growth modes were extremely rare.

The effects of particle chemical character and atmospheric processes on particle hygroscopic properties

Hygroscopic properties of atmospheric aerosol particles were studied by constructing a simple model that relates the particle hygroscopic growth factor to the amount of soluble matter bound in the particulate phase, to matter that is exchangeable with the gas phase, and to matter that reduces particle water absorption. The model was applied to explain the general results obtained from many TDMA measurements, such as the existence of two distinctive particle types, the “less” and the “more”-hygroscopic particles, in the atmospheric aerosol. It was demonstrated that the “less”-hygroscopic particles are likely to contain a major insoluble part. “More”-hygroscopic particles, being frequently almost totally water soluble, must have either (i) a significant fraction of soluble material absorbing water less efficiently than typical atmospheric inorganic salts, or (ii) substances that actively reduce the amount of water that particles are able to absorb. Of atmospheric processes, coagulation and interphase chemical reactions gradually turn hydrophobic particles into less-hygroscopic ones, whereas water-absorbing properties of less-hygroscopic particles are likely to be modified mainly by the condensational gas-to-particle transport. The process responsible for turning less-hygroscopic particles into more-hygroscopic ones in the atmosphere, and for maintaining the separation between the two hygroscopicity classes, is probably the processing of the air through nonprecipitating clouds.

Elemental composition of fog interstitial particle size fractions and hydrophobic fractions related to fog droplet nucleation scavenging

The cloud nucleation scavenging process was studied during a joint campaign of the EUROTRAC sub-project Ground-based Cloud Experiment. It was found that the particle size has a strong influence on the partitioning of particles between the cloud droplet and the interstitial aerosol reservoirs. A new aerosol sampling unit, the relative humidity processing system, was employed for the extraction of particles with a low growth-ability with respect to increased relative humidity. The system supplied tracer elements on the particle growth-ability. These elements could be used to identify a factor related to particle hygroscopic properties, which was in effect as a selector of cloud condensation nuclei. DOI: 10.1034/j.1600-0889.1992.t01-1-00012.x

Elemental composition of fog interstitial particle size fractions and hydrophobic fractions related to fog droplet nucleation scavenging

The cloud nucleation scavenging process was studied during a joint campaign of the EUROTRAC sub-project Ground-based Cloud Experiment. It was found that the particle size has a strong influence on the partitioning of particles between the cloud droplet and the interstitial aerosol reservoirs. A new aerosol sampling unit, the relative humidity processing system, was employed for the extraction of particles with a low growth-ability with respect to increased relative humidity. The system supplied tracer elements on the particle growth-ability. These elements could be used to identify a factor related to particle hygroscopic properties, which was in effect as a selector of cloud condensation nuclei. DOI: 10.1034/j.1600-0889.1992.t01-1-00012.x