Cloud Condensation Nucleation Research Articles

Hygroscopicity and cloud condensation nucleation activities of hydroxyalkylsulfonates

Hydroxyalkylsulfonates may contribute significantly to atmospheric particles; however, their hygroscopic properties and cloud condensation nuclei (CCN) activities remain unknown. In this study, three complementary techniques were utilized to examine the hygroscopicity of sodium hydroxymethanesulfonate (NaHMS), sodium 2-hydroxyethylsulfonate (NaHES), and ammonium 2-hydroxyethylsulfonate (NH4HES) under subsaturated and supersaturated environments. The mass changes in the three hydroxyalkylsulfonates at different relative humidities at 25 °C were examined by a vapor sorption analyzer, and the mass growth factors were measured to be 3.25 ± 0.01 for NaHMS, 3.32 ± 0.02 for NaHES, and 3.34 ± 0.04 for NH4HES at 90% RH. Their hygroscopic growth was investigated by a humidity tandem differential mobility analyzer, and hygroscopic growth factors were 1.78 ± 0.02 for NaHMS, 1.71 ± 0.02 for NaHES, and 1.68 ± 0.03 for NH4HES at 90% RH. Furthermore, the CCN activities of NaHMS, NaHES, and NH4HES were explored, and their single hygroscopicity parameters (κccn) were measured to be 0.649 ± 0.097 for NaHMS, 0.559 ± 0.069 for NaHES, and 0.434 ± 0.073 for NH4HES. In addition, the hygroscopic growth and CCN activities of binary mixtures of ammonium sulfate with one of the three hydroxyalkylsulfonates were also examined.

Interactions of organosulfates with water vapor under sub- and supersaturated conditions

Abstract. Organosulfates (OSs) are important constituents of secondary organic aerosols, but their hygroscopic properties and cloud condensation nucleation (CCN) activities have not been well understood. In this work we employed three complementary techniques to characterize interactions of several OSs with water vapor under sub- and supersaturated conditions. A vapor sorption analyzer was used to measure mass changes in OS samples with relative humidity (RH, 0 %–90 %); among the 11 organosulfates examined, only sodium methyl sulfate (methyl-OS), sodium ethyl sulfate (ethyl-OS), sodium octyl sulfate (octyl-OS) and potassium hydroxyacetone sulfate were found to deliquesce as RH increased, and their mass growth factors at 90 % RH were determined to be 3.65 ± 0.06, 3.58 ± 0.02, 1.59 ± 0.01 and 2.20 ± 0.03. Hygroscopic growth of methyl-, ethyl- and octyl-OS aerosols was also studied using a humidity tandem differential mobility analyzer (H-TDMA); continuous hygroscopic growth was observed, and their growth factors at 90 % RH were determined to be 1.83 ± 0.03, 1.79 ± 0.02 and 1.21 ± 0.02. We further investigated CCN activities of methyl-, ethyl- and octyl-OS aerosols, and their single hygroscopicity parameters (κccn) were determined to be 0.459 ± 0.021, 0.397 ± 0.010 and 0.206 ± 0.008. For methyl- and ethyl-OS aerosols, κccn values agree reasonably well with those derived from H-TDMA measurements (κgf) with relative differences being < 25 %, whereas κccn was found to be ∼ 2.4 times larger than κgf for octyl-OS, likely due to both the solubility limit and surface tension reduction.

The reaction of oleic acid monolayers with gas-phase ozone at the air water interface: the effect of sub-phase viscosity, and inert secondary components.

Organic films that form on atmospheric particulate matter change the optical and cloud condensation nucleation properties of the particulate matter and consequently have implications for modern climate and climate models. The organic films are subject to attack from gas-phase oxidants present in ambient air. Here we revisit in greater detail the oxidation of a monolayer of oleic acid by gas-phase ozone at the air-water interface as this provides a model system for the oxidation reactions that occur at the air-water interface of aqueous atmospheric aerosol. Experiments were performed on monolayers of oleic acid at the air-liquid interface at atmospherically relevant ozone concentrations to investigate if the viscosity of the sub-phase influences the rate of the reaction and to determine the effect of the presence of a second component within the monolayer, stearic acid, which is generally considered to be non-reactive towards ozone, on the reaction kinetics as determined by neutron reflectometry measurements. Atmospheric aerosol can be extremely viscous. The kinetics of the reaction were found to be independent of the viscosity of the sub-phase below the monolayer over a range of moderate viscosities, , demonstrating no involvement of aqueous sub-phase oxidants in the rate determining step. The kinetics of oxidation of monolayers of pure oleic acid were found to depend on the surface coverage with different behaviour observed above and below a surface coverage of oleic acid of ∼1 × 1018 molecule m-2. Atmospheric aerosol are typically complex mixtures, and the presence of an additional compound in the monolayer that is inert to direct ozone oxidation, stearic acid, did not significantly change the reaction kinetics. It is demonstrated that oleic acid monolayers at the air-water interface do not leave any detectable material at the air-water interface, contradicting the previous work published in this journal which the authors now believe to be erroneous. The combined results presented here indicate that the kinetics, and thus the atmospheric chemical lifetime for unsaturated surface active materials at the air-water interface to loss by reaction with gas-phase ozone, can be considered to be independent of other materials present at either the air-water interface or in the aqueous sub-phase.

Impacts of methanesulfonate on the cloud condensation nucleation activity of sea salt aerosol

Methanesulfonate, an important oxidation product of dimethyl sulfide, is abundant in marine aerosol particles. However, its impact on the cloud condensation nucleation (CCN) activity of marine aerosol is yet to be elucidated, largely because the CCN activity of methanesulfonate has been seldom investigated. In this work, we measured the CCN activities of three common methanesulfonates, and the single hygroscopicity parameters (κ) were determined to be 0.46 ± 0.02 for sodium methanesulfonate (NaMS), 0.37 ± 0.01 for calcium methanesulfonate, and 0.47 ± 0.02 for potassium methanesulfonate, respectively. In addition, we explored the effect of NaMS on the CCN activities of NaCl and synthetic sea salt. It was found that if presented with a mass ratio of 1:1, NaMS would significantly reduce the CCN activities of NaCl and sea salt, and the κ values of binary mixtures could be estimated using the simple mixing rule. Nevertheless, if only presented with a mass ratio of 1:10 (an environmentally relevant value), the effect of NaMS on the CCN activities of NaCl and sea salt was found to be small. Overall, we conclude that from our experimental data and its levels found in the troposphere, methanesulfonate may only have minor impacts on the CCN activity of marine aerosol.

Instrument artifacts lead to uncertainties in parameterizations of cloud condensation nucleation

Abstract. The concentrations of cloud condensation nuclei (CCN) modulate cloud properties, rainfall location and intensity, and climate forcings. This work assesses uncertainties in CCN measurements and the apparent hygroscopicity parameter (κapp), which is widely used to represent CCN populations in climate models. CCN measurements require accurate operation of three instruments: the CCN instrument, the differential mobility analyzer (DMA), and the condensation particle counter (CPC). Assessment of DMA operation showed that varying the ratio of aerosol to sheath flow from 0.05 to 0.30 resulted in discrepancies between the κapp values calculated from CCN measurements and the literature value. Discrepancies were found to increase from <1 % to 13 % for both sodium chloride and ammonium sulfate. The ratio of excess to sheath flow was also varied, which shifted the downstream aerosol distribution towards smaller particle diameters (for excess flow < sheath flow) or larger particle diameters (for excess flow > sheath flow) than predicted. For the CPC instrument, undercounting occurred at high concentrations, resulting in calculated κapp lower than the literature values. Lastly, undercounting by CCN instruments at high concentration was also assessed, taking the effect of supersaturation on counting efficiency into account. Under recommended operating conditions, the combined DMA, CPC, and CCN uncertainties in κapp are 1.2 % or less for 25 to 200 nm diameter aerosols.

A thermodynamic description for the hygroscopic growth of atmospheric aerosol particles

Abstract. The phase state of atmospheric particulate is important to atmospheric processes, and aerosol radiative forcing remains a large uncertainty in climate predictions. That said, precise atmospheric phase behavior is difficult to quantify and observations have shown that “precondensation” of water below predicted saturation values can occur. We propose a revised approach to understanding the transition from solid soluble particles to liquid droplets, typically described as cloud condensation nucleation – a process that is traditionally captured by Köhler theory, which describes a modified equilibrium saturation vapor pressure due to (i) mixing entropy (Raoult's law) and (ii) droplet geometry (Kelvin effect). Given that observations of precondensation are not predicted by Köhler theory, we devise a more complete model that includes interfacial forces giving rise to predeliquescence, i.e., the formation of a brine layer wetting a salt particle at relative humidities well below the deliquescence point.

Characterization of aerosol hygroscopicity, mixing state, and CCN activity at a suburban site in the central North China Plain

Abstract. This study investigates aerosol hygroscopicity, mixing state, and cloud condensation nucleation as part of the Atmosphere–Aerosol–Boundary Layer–Cloud Interaction Joint Experiment performed in the summer of 2016 at Xingtai (XT), a suburban site located in the center of the North China Plain (NCP). In general, the probability density function (PDF) of the hygroscopicity parameter (κ) for 40–200 nm particles had a unimodal distribution, and mean κ-PDF patterns for different sizes were similar, suggesting that the particles were highly aged and internally mixed because of strong photochemical reactions. The κ calculated from the hygroscopic growth factor in the daytime and at night suggests that photochemical reactions largely enhanced the aerosol hygroscopicity. This effect became weaker as the particle size increased. In addition, the aerosol hygroscopicity was much larger at XT than at other sites in the NCP. This is because new particle formation takes place much more frequently in the central NCP, which is heavily polluted from industrial activities, than elsewhere in the region. The evolution of the planetary boundary layer played a dominant role in dictating aerosol mass concentration. Particle size was the most important factor influencing the ability of aerosols to activate, whereas the effect of chemical composition was secondary, especially when supersaturation was high. Using a fixed value of κ=0.31 to calculate the cloud condensation nuclei number concentration in this region suffices.

Liquid–liquid phase separation in particles containing secondary organic material free of inorganic salts

Abstract. Particles containing secondary organic material (SOM) are ubiquitous in the atmosphere and play a role in climate and air quality. Recently, research has shown that liquid–liquid phase separation (LLPS) occurs at high relative humidity (RH) (greater than ∼ 95 %) in α-pinene-derived SOM particles free of inorganic salts, while LLPS does not occur in isoprene-derived SOM particles free of inorganic salts. We expand on these findings by investigating LLPS at 290 ± 1 K in SOM particles free of inorganic salts produced from ozonolysis of β-caryophyllene, ozonolysis of limonene, and photo-oxidation of toluene. LLPS was observed at greater than ∼ 95 % RH in the biogenic SOM particles derived from β-caryophyllene and limonene while LLPS was not observed in the anthropogenic SOM particles derived from toluene. This work combined with the earlier work on LLPS in SOM particles free of inorganic salts suggests that the occurrence of LLPS in SOM particles free of inorganic salts is related to the oxygen-to-carbon elemental ratio (O : C) of the organic material. These results help explain the difference between the hygroscopic parameter κ of SOM particles measured above and below water saturation in the laboratory and field, and have implications for predicting the cloud condensation nucleation properties of SOM particles.

Inter-annual variability of transparent exopolymer particles in the Arctic Ocean reveals high sensitivity to ecosystem changes

Transparent exopolymer particles (TEP) are a class of marine gel particles and important links between surface ocean biology and atmospheric processes. Derived from marine microorganisms, these particles can facilitate the biological pumping of carbon dioxide to the deep sea, or act as cloud condensation and ice nucleation particles in the atmosphere. Yet, environmental controls on TEP abundance in the ocean are poorly known. Here, we investigated some of these controls during the first multiyear time-series on TEP abundance for the Fram Strait, the Atlantic gateway to the Central Arctic Ocean. Data collected at the Long-Term Ecological Research observatory HAUSGARTEN during 2009 to 2014 indicate a strong biological control with highest abundance co-occurring with the prymnesiophyte Phaeocystis pouchetii. Higher occurrence of P. pouchetii in the Arctic Ocean has previously been related to northward advection of warmer Atlantic waters, which is expected to increase in the future. Our study highlights the role of plankton key species in driving climate relevant processes; thus, changes in plankton distribution need to be accounted for when estimating the ocean’s biogeochemical response to global change.

Interactions of Water with Mineral Dust Aerosol: Water Adsorption, Hygroscopicity, Cloud Condensation, and Ice Nucleation.

Mineral dust aerosol is one of the major types of aerosol present in the troposphere. The molecular level interactions of water vapor with mineral dust are of global significance. Hygroscopicity, light scattering and absorption, heterogneous reactivity and the ability to form clouds are all related to water-dust interactions. In this review article, experimental techniques to probe water interactions with dust and theoretical frameworks to understand these interactions are discussed. A comprehensive overview of laboratory studies of water adsorption, hygroscopicity, cloud condensation, and ice nucleation of fresh and atmspherically aged mineral dust particles is provided. Finally, we relate laboratory studies and theoretical simulations that provide fundemental insights into these processes on the molecular level with field measurements that illustrate the atmospheric significance of these processes. Overall, the details of water interactions with mineral dust are covered from multiple perspectives in this review article.

New approaches to quantifying aerosol influence on the cloud radiative effect

The topic of cloud radiative forcing associated with the atmospheric aerosol has been the focus of intense scrutiny for decades. The enormity of the problem is reflected in the need to understand aspects such as aerosol composition, optical properties, cloud condensation, and ice nucleation potential, along with the global distribution of these properties, controlled by emissions, transport, transformation, and sinks. Equally daunting is that clouds themselves are complex, turbulent, microphysical entities and, by their very nature, ephemeral and hard to predict. Atmospheric general circulation models represent aerosol−cloud interactions at ever-increasing levels of detail, but these models lack the resolution to represent clouds and aerosol−cloud interactions adequately. There is a dearth of observational constraints on aerosol−cloud interactions. We develop a conceptual approach to systematically constrain the aerosol−cloud radiative effect in shallow clouds through a combination of routine process modeling and satellite and surface-based shortwave radiation measurements. We heed the call to merge Darwinian and Newtonian strategies by balancing microphysical detail with scaling and emergent properties of the aerosol−cloud radiation system.

Cloud condensation nucleation activities of calcium carbonate and its atmospheric ageing products.

Aerosol particles can serve as cloud condensation nuclei (CCN) to form cloud droplets, and its composition is a main factor governing whether an aerosol particle is an effective CCN. Pure mineral dust particles are poor CCN; however, changes in chemical composition of mineral dust aerosol particles, due to heterogeneous reactions with reactive trace gases in the troposphere, can modify their CCN properties. In this study we investigated the CCN activities of CaCO3 (as a surrogate for mineral dust) and its six atmospheric ageing products: Ca(NO3)2, CaCl2, CaSO4, Ca(CH3SO3)2, Ca(HCOO)2, and Ca(CH3COO)2. CaCO3 has a very low CCN activity with a hygroscopicity parameter (κ) of 0.001-0.003. The CCN activities of its potential atmospheric ageing products are significantly higher. For example, we determined that Ca(NO3)2, CaCl2 and Ca(HCOO)2 have κ values of ∼0.50, similar to that of (NH4)2SO4. Ca(CH3COO)2 has slightly lower CCN activity with a κ value of ∼0.40, and the κ value of CaSO4 is around 0.02. We further show that exposure of CaCO3 particles to N2O5 at 0% relative humidity (RH) significantly enhances their CCN activity, with κ values increasing to around 0.02-0.04. Within the experimental uncertainties, it appears that the variation in exposure to N2O5 from ∼550 to 15,000 ppbv s does not change the CCN activities of aged CaCO3 particles. This observation indicates that the CaCO3 surface may be already saturated at the shortest exposure. We also discussed the atmospheric implications of our study, and suggested that the rate of change in CCN activities of mineral dust particles in the troposphere is important to determine their roles in cloud formation.

CCN activity of size-selected aerosol at a Pacific coastal location

Abstract. As one aspect of the NETwork on Climate and Aerosols: addressing key uncertainties in Remote Canadian Environments (NETCARE), measurements of the cloud condensation nucleation properties of 50 and 100 nm aerosol particles were conducted at Ucluelet on the west coast of Vancouver Island in August 2013. The overall hygroscopicity parameter of the aerosol (κambient) exhibited a wide variation, ranging from 0.14 ± 0.05 to 1.08 ± 0.40 (where the uncertainty represents the systematic error). The highest κ values arose when the organic-to-sulfate ratio of the aerosol was lowest and when winds arrived from the west after transport through the marine boundary layer. The average κambient during this time was 0.57 ± 0.16, where the uncertainty represents the standard deviation. At most other times, the air was predominantly influenced by both marine and continental emissions, which had lower average PM1 κambient values (max value, 0.41 ± 0.08). The two-day average aerosol ionic composition also showed variation, but was consistently acidic and dominated by ammonium (18–56% by mole) and sulfate (19–41% by mole), with only minor levels of sodium or chloride. Average κorg (hygroscopicity parameter for the aerosol's organic component) values were estimated using PM1 aerosol composition data and by assuming that the ratio of aerosol organic to sulfate mass is related directly to the composition of the size-selected particles.

Chemistry and morphology of dried‐up pollen suspension residues

Pollen grains are covered with lots of different biochemical compounds, like proteins, saccharides and lipids, which are only loosely attached to the pollen. Therefore, they can be separated from the pollen by suspending them in water. Since these compounds play a key role in many atmospheric processes (e.g. cloud condensation nucleation, ice nucleation, aerial allergen exposure), their separation and analyzing are of interest.The chemical composition of whole pollen grains is compared by both Raman and infrared spectroscopy with material that could be extracted from pollen with water. The dominant signals in the pollen grain Raman spectra are those from sporopollenin and carotenoids. These bands decrease in the washing water spectra, since sporopollenin is high molecular and thus is not extractable. The released material shows in turn a chemical composition that differs significantly between species, what is quite expected, since they differ even in the optical properties of their aqueous suspensions. The FTIR spectra show some additional bands to appear in comparison to the Raman spectra.Furthermore, we investigated the pollen rupturing and material release in the aqueous suspensions by drying them up and picturing the residues with a scanning electron microscope. We saw that corn pollen ejected loads of micrometer‐sized organelles, which are most likely starch granules. The more the pollen disrupted, the more the measured samples were covered with an amorphous film, which consists of the extracted pollen material, like lipids, sugars, and proteins – the same substances we detected by spectroscopy. Copyright © 2013 John Wiley & Sons, Ltd.

Thermochemical, Cloud Condensation Nucleation Ability, and Optical Properties of Alkyl Aminium Sulfate Aerosols

Alkyl aminium sulfates have been postulated to constitute important components of nucleation and accumulation mode atmospheric aerosols. In this study we present laboratory data on the thermochemical, cloud condensation nuclei (CCN) activity, and optical properties of selected aminium sulfate compounds of atmospheric relevance (monomethyl aminium sulfate (MMAS), dimethyaminium sulfate (DMAS), trimethylaminium sulfate, monoethylaminium sulfate (MEAS), diethylaminium sulfate (DEAS), and triethylaminium sulfate (TEAS)). We found that the vapor pressure of these aminium salts is 1–3 orders of magnitude lower than that of ammonium sulfate and as such they can contribute to new aerosols and secondary aerosols formation. We infer that these species have very high CCN activity, with hygroscopicity parameter that is similar to that ammonium sulfate. Finally, between 360 and 420 nm, these aminium sulfate salts scatter light less efficiently than ammonium sulfate, and do not absorb light. These derived parameters can contribute to the better understanding and characterization of the role that these compounds play in atmospheric chemical reactions, gas–solid partitioning and their possible contribution to the microphysical and radiative effects of atmospheric aerosols.

Quantitative and time-resolved nanoparticle composition measurements during new particle formation

The chemical composition of 20 nm diameter particles was measured with the Nano Aerosol Mass Spectrometer (NAMS) in a rural/coastal environment during days when new particle formation (NPF) occurred and days when NPF did not occur. NAMS provides a quantitative measure of nanoparticle elemental composition with high time resolution. These measurements show that nanoparticle chemical composition is dynamic on both types of days and that changes in nanoparticle chemical composition do not necessarily correlate with changes in aerosol mass or number concentration. On NPF days, NAMS can distinguish between elements associated with particle formation and early mass growth from those associated with later mass growth. In the early stage of NPF, the particle phase sulphur mole fraction (S) increases simultaneously with the increase in gas phase sulphuric acid. This composition change occurs before the mode diameter has grown into the NAMS-measured size range and is quantitatively described by sulphuric acid condensation. The nitrogen mole fraction (N) also increases during this time period. The N/S mole ratio is approximately 2, indicating that particulate sulphate is fully neutralized. As the mode diameter passes into and through the NAMS-measured size range, N increases at a faster rate than S (N/S mole ratio increases above 2), indicating that a separate, nitrogen-based growth process exists, possibly involving aminium salts, inorganic nitrate and/or organonitrates. Carbonaceous matter is the most abundant component (-50% by mass) of the growing nanoparticles, but it is the inorganic species that are preferentially enhanced during NPF relative to other times of day. Concurrent measurements of cloud condensation nucleation activity during NPF events suggest that these newly formed particles are hygroscopic. Nanoparticle composition on non-NPF days also shifts toward a more inorganic composition during the daytime, but the chemical species are different from NPF days and the particles are less hygroscopic. Incorporation of S into growing nanoparticles is adequately explained by existing models, but currently no models exist to satisfactorily explain incorporation of nitrogen-containing species or carbonaceous matter.

Cloud condensation nucleation activity of biomass burning aerosol

We examine the hygroscopic properties of particles freshly emitted from laboratory biomass burning experiments conducted during the second Fire Lab At Missoula Experiment (FLAME‐II). Values of the hygroscopicity parameter, kappa, were derived from both hygroscopic growth measurements and size‐resolved (30–300 nm in diameter) cloud condensation nuclei (CCN) measurements for smokes emitted by the open combustion of 24 biomass fuels from the United States and Asia. To analyze the complex cloud condensation nuclei response curves we propose a new inversion scheme that corrects for multiple charge effects without the necessity of prior assumptions about the chemical composition and mixing state of the particles. Kappa varied between 0.02 (weakly hygroscopic) and 0.8 (highly hygroscopic). For individual smokes, kappa was a function of particle size, with 250 nm particles being generally weakly hygroscopic and sub‐100 nm particles being more hygroscopic. At any given size the emissions were often externally mixed, showing more and less hygroscopic growth modes and bimodal CCN activation spectra. Comparisons between growth factor‐derived and CCN‐derived hygroscopicities were consistent when taking this heterogeneity into account. A conceptual model of biomass burning emissions suggests that most particles are CCN active at the point of emission and do not require conversion in the atmosphere to more hygroscopic compositions before they can participate in cloud formation and undergo wet deposition.

Deliquescence‐controlled activation of organic aerosols

We examine the cloud condensation nucleation behavior expected for dry submicron particles composed of organic species having limited solubility in water and thus exhibiting deliquescence only under water‐supersaturated conditions. If saturated solution water activities aw are approximately 0.97 < aw < 1, then deliquescence is likely to control the supersaturation required to activate submicron particles, leading to high sensitivity of critical supersaturation to dry diameter. Similar behavior may occur for species, including polymeric compounds, that exhibit limited miscibility in water until very dilute conditions. Treating the sparingly‐soluble or limited‐miscibility species as insoluble aerosol components in calculations of their hygroscopic growth does not reproduce the predicted strong dependence of critical supersaturation on dry particle size. Lack of information on the solubility characteristics of organic‐species‐dominated atmospheric particulate matter may thus lead to discrepancies between predicted and measured droplet activation, even when particle composition and size are well‐constrained by measurements.

Aerosol chemistry and climate: Laboratory studies of the carbonate component of mineral dust and its reaction products

The hygroscopicity, cloud condensation nucleation (CCN) activity and infrared optical extinction of CaCO3, a reactive component of mineral dust aerosol, and Ca(NO3)2, a product of atmospherically‐aged CaCO3 through reaction with nitrogen oxides, have been measured. The hygroscopic growth and CCN activity of Ca(NO3)2 are orders of magnitude greater than CaCO3 and more similar to ammonium sulfate. Ca(NO3)2 particles also reflect a greater amount of near infrared radiation at higher relative humidity. These measurements provide the first quantitative assessment of the important changes in climate forcing that can occur as mineral dust aerosol is transported, reacted and aged in the atmosphere.

Biological micro‐particles in rain water

This work constitutes the first report on the morphology and chemical identification of biological micro‐particles in rain water at two sites (Shizuoka and Tsukuba) from Japan. Micro‐particles in rain water were deposited directly onto electron microscopic grids using ultracentrifugation. Particles with diameters more than 0.2 µm were examined using an electron microscope equipped with an energy‐dispersive X‐ray analyzer. Biological particles in rain water were found to be bacteria and leaf debris, and most of those particles were associated with minerals. Peaks of phosphorus and potasium in the X‐ray spectra, which are characterized as chemical components of bacteria or leaves, were observed in all the biological particles. These particles in rain water were present in number percentages of 23 to 34% of the total insoluble particles, with concentrations of 1.6×104 to 2.4×104 cm−3 of rain water. This finding suggests that these biological particles are captured effectively in cloud water and/or precipitation, and that they may play a role in cloud condensation and/or ice nucleation.