Search

This 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. Key Points: A simple but accurate expression is presented for the equilibrium radius of an inorganic aerosol particle at relative humidities 99–100%This expression explicitly illustrates the dependences on relative humidity and dry solute massThe factors that contribute to the uncertainty in this expression are examined [ABSTRACT FROM AUTHOR]

The cloud condensation nuclei (CCN) closure study was performed to exemplify the effect of aerosol chemical composition on the CCN activity of aerosols at Mahabaleshwar, a high altitude background site in the Western Ghats, India. For this, collocated aerosol, CCN, Elemental Carbon (EC), Organic Carbon (OC), sub-micron aerosol chemical speciation for the period from 3rd June to 19th June 2015 was used. The chemical composition of non-refractory particulate matter (<1 μm) as measured by Time of Flight – Aerosol Chemical Speciation Monitor (ToF-ACSM) was dominated by organics with average concentration of 3.81 ± 1.6, 0.32 ± 0.06, 0.15 ± 0.02, 0.13 ± 0.03 and 0.95 ± 0.12 μg m −3 for organics, ammonium, chloride, nitrate and sulphate, respectively. The PM 1 number concentration as obtained by Wide Range Aerosol Spectrometer (WRAS) varied from 750 to 6480 cm −3 . The average mass concentration of elemental carbon (EC) as measured by OC-EC analyzer was 1.16 ± 0.4 μg m −3 . The average CCN concentrations obtained from CCN counter (CCNC) at five super-saturations (SS's) was 118 ± 58 cm −3 (0.1% SS), 873 ± 448 cm −3 (0.31% SS), 1308 ± 603 cm −3 (0.52% SS), 1610 ± 838 cm −3 (0.73% SS) and 1826 ± 985 cm −3 (0.94% SS). The CCN concentrations were predicted using Köhler theory on the basis of measured aerosol particle number size distribution, size independent NR-PM1 chemical composition and calculated hygroscopicity. The CCN closure study was evaluated for 3 scenarios, B-I (all soluble inorganics), B-IO (all soluble organics and inorganics) and B-IOOA (all soluble inorganic and soluble oxygenated organic aerosol, OOA). OOA component was derived from the positive matrix factorization (PMF) analysis of organic aerosol mass spectra. Considering the bulk composition as internal mixture, CCN closure study was underestimated by 16–39% for B-I and overestimated by 47–62% for B-IO. The CCN closure result was appreciably improved for B-IOOA where the knowledge of OOA fraction was introduced and uncertainty reduced to within 8–10%. [ABSTRACT FROM AUTHOR]

Insights into the hygroscopicity of nanoparticles is critically important in determining their growth and subsequent climate implications. A significant knowledge gap in the traditional Köhler (TK) model is the lack of size dependence of physicochemical properties of nanoparticles. Here, we present the modified Köhler curves of nanoparticles containing ammonium sulfate (AS) and alkylaminium sulfates (AASs), including monomethylaminium sulfate (MMAS), dimethylaminium sulfate (DMAS), and trimethylaminium sulfate (TMAS), by considering the curvature-correction of surface tension (σ) obtained from polarizable molecular dynamic (MD) simulations. It is found that sulfates can cause a non-monotonic relation between σ and droplet size with a maximum at several nanometers. The modified Köhler curves demonstrate that, for sulfate particles with diameters over 10 nm, accounting σ -correction can apparently affect the inverse of critical supersaturation (S c − 1 ), but still give the consistent S c − 1 order with the model without σ -correction (S c − 1 (AS) > S c − 1 (MMAS) > S c − 1 (DMAS) > S c − 1 (TMAS)). While for ultra-small particles (d = ∼3 nm), the curvature correction of σ is much more significant, which even alters the order of S c − 1 (S c − 1 (MMAS) ≈ S c − 1 (DMAS) > S c − 1 (AS) > S c − 1 (TMAS)). The present study shows that the curvature correction of surface tension is necessary to accurately predict the hygroscopicity of nucleation mode particles, and MMAS/DMAS-containing nanoparticles can demonstrate easier water-uptake than that of AS-containing nanoparticles with ∼3 nm diameter, thereby leading to higher growth rate and stronger climate impacts. [Display omitted] • Modified Köhler curves for ammonium/alkylaminium sulfate nanoparticles are derived. • The importing of curvature correction of surface tension can increase the accuracy of Köhler curve. • For ultra-small particles (d = ∼3 nm), the MMAS/DMAS have higher hygroscopic capacity than that of AS. [ABSTRACT FROM AUTHOR]

Abstract: In this study, we use a Tandem Differential Mobility Analyser (TDMA) system combining particle volatilization and humidification conditioning (VH-TDMA) to test the effect of the gentle volatilization of a small fraction of the atmospheric particles on the particle hygroscopic growth in several environments (urban to remote). We first give an overview of the Hygroscopic Growth Factors (HGF) in these various environments, showing that in most of them, aerosol particles are externally mixed. We then show that the particle hygroscopicity can either be increased or decreased after thermal conditioning of the particle at moderate temperatures (50–110 °C). The hygroscopic growth factor changes induced by volatilization indicate that some volatile compounds, although present at low concentrations, can significantly influence the hygroscopic growth of particles in a way that can most of time be theoretically explained if simplified assumptions are used. However, simplified assumptions occasionally fail over several hours to explain hygroscopic changes, kinetic/surface effects observed at remote environments are suspected to be important. [Copyright &y& Elsevier]

Abstract: In this paper we present a construction of 3-designs by using a 3-design with resolvability. The basic construction generalizes a well-known construction of simple 3- designs by Jungnickel and Vanstone (1986). We investigate the conditions under which the designs obtained by the basic construction are simple. Many infinite families of simple 3-designs are presented, which are closely related to some known families by Iwasaki and Meixner (1995), Laue (2004) and van Tran (2000, 2001). On the other hand, the designs obtained by the basic construction possess various properties: A theory of constructing simple cyclic 3- designs by Köhler (1981) can be readily rebuilt from the context of this paper. Moreover many infinite families of simple resolvable 3-designs are presented in comparison with some known families. We also show that for any prime power q and any odd integer n there exists a resolvable 3- design. As far as the authors know, this is the first and the only known infinite family of resolvable t- designs with and . Those resolvable designs can again be used to obtain more infinite families of simple 3-designs through the basic construction. [ABSTRACT FROM AUTHOR]

Abstract: We report the design and characterization of a continuous-flow horizontal thermal gradient cloud condensation nucleus spectrometer (CCNS). The calibration of supersaturation inside the CCNS chamber using monodisperse NaCl aerosols shows that it is important to experimentally determine the supersaturation profile of the instrument, rather than relying on theoretical calculations based on measurements of the temperature gradient. The latter method significantly overestimates the actual supersaturation, mainly because of the discrepancy between measured and actual temperature gradients and the non-ideality in droplet samplings. Laboratory experiments were also performed to validate the instrumental performance and to compare the cloud condensation nuclei (CCN) activation results with theoretical predictions based on Köhler theory. In the current configuration, the operational range of the CCNS has been verified to be between 0.08% and 0.9% supersaturation, with potential for further range enhancement. Using a computer-controlled motorized sampling system, we have demonstrated that CCN activation experiments can be routinely performed with much higher time resolution, suggesting excellent potential of this CCNS instrument for airborne measurements. [Copyright &y& Elsevier]

Aerosol–cloud condensation nuclei (CCN) closure was studied in a semi-rural location 80km north of Toronto, Canada at the Centre for Atmospheric Research Experiments outside of Egbert, Ontario during the fall of 2005. This site is subject to both polluted air from southern Ontario and clean air from the north. The purpose of the investigation was to evaluate the degree to which closure is attained at a supersaturation of 0.32% when size-resolved aerosol compositions from an Aerodyne Quadrupole Aerosol Mass Spectrometer are made alongside measurements of CCN number density and aerosol size distribution. Attention was given to assessing the sensitivity of closure to assumptions made concerning the water solubility and surface tension of the organic fraction of the aerosol in the Köhler analysis. By assuming that the organics are insoluble and that the growing droplet has the surface tension of water, a good overall degree of closure is attained throughout the analysis time period, with the predicted numbers of CCN within 15% of the modelled numbers, which is within our estimated systematic uncertainties. However, for the specific periods during which the organic content of the aerosol is high, the degree of closure is significantly lower. Sensitivity analyses indicate that some degree of organic water solubility and/or surface tension reduction is necessary to achieve the best agreement and least variance between the modelled and measured numbers of CCN. A general conclusion is that significant uncertainties arise in predicting CCN levels only when the level of soluble inorganic species is below approximately 25% by mass. [Copyright &y& Elsevier]

Abstract: We present a parameterization for numbers of water and ammonia molecules in an equilibrium droplet with fixed number of sulfuric acid molecules at known relative humidity, ammonia mixing ratio and temperature. The radius of the droplet is also parameterized. The parameterizations are based on macroscopic model of solution droplets and up-to-date thermodynamics. The binary parameterizations are valid for temperatures 190–330 K and relative humidities 1–99%. The ternary parameterization can be used at temperatures 240–300 K, relative humidities 5–95%, and ammonia mixing ratios 10−4–100 ppt. In both cases the parameterizations are valid for droplets containing up to 1011 sulfuric acid molecules. The droplet composition is always between the limits of pure ammonium bisulfate and pure ammonium sulfate. [Copyright &y& Elsevier]

Abstract: The cloud condensation nuclei (CCN) activation of 19 organic species with water solubilities (C sat) ranging from 10−4 to 102 g solute100g−1 H2O was measured. The organic particles were generated by nebulization of an aqueous or an alcohol solution. Use of alcohols as solvents enables the measurement of low solubility, non-volatile organic CCN activity and reduces the likelihood of residual water in the aerosol. The activation diameter of organic species with very low solubility in water (C sat<0.3g100g−1 H2O) is in agreement with Köhler theory using the bulk solubility (limited solubility case) of the organic in water. Many species, including 2-acetylbenzoic acid, aspartic acid, azelaic acid, glutamic acid, homophthalic acid, phthalic acid, cis-pinonic acid, and salicylic acid are highly CCN active in spite of their low solubility (0.3g100g−1 H2O

Abstract: The ability of mixed ammonium sulfate/organic acid particles to act as cloud condensation nuclei (CCN) has been studied in the laboratory using a continuous flow, thermal-gradient diffusion chamber operated at supersaturations between 0.3% and 0.6%. The organic acids studied were malonic acid, azelaic acid, hexanoic acid, cis-pinonic acid, oleic acid and stearic acid, and the particles were largely prepared by condensation of the organic vapor onto a dry ammonium sulfate core. For malonic acid and hexanoic acid, the mixed particles activated as predicted by a simple Köhler theory model where both species are assumed to be fully soluble and the droplet has the surface tension of water. Three low-solubility species, cis-pinonic acid, azelaic acid and oleic acid, are well modeled where the acid was assumed to be either partially or fully insoluble. Interestingly, although thin coats of stearic acid behaved in a manner similar to that displayed by oleic and cis-pinonic acid, we observed that thick coats led to a complete deactivation of the ammonium sulfate, presumably because the water vapor could not diffuse through the solid stearic acid. We observed no CCN behavior that could be clearly attributed to a lowering of the surface tension of the growing droplet by the presence of the organic constituents, some of which are highly surface active. [Copyright &y& Elsevier]