Ammonium Sulfate Particles Research Articles

Point and column aerosol radiative closure during ACE 1: Effects of particle shape and size

We used data collected during the First Aerosol Characterization Experiment (ACE 1) to study point and column aerosol radiative closure over the remote ocean. To test point closure, total and hemispheric backscattering coefficients calculated with a Mie single‐scattering model were compared with measurements made by ship and aircraft at three wavelengths (400, 550, and 700 nm). On the ship, assuming spherical particles, calculated total scattering was usually within 10% of measurements (closure obtained in >80% of the cases) but calculated backscattering was usually 15–25% lower than measurements (closure obtained in <50% of the cases). When a model for particle nonsphericity was applied to the dried sea spray, assuming the particles to be ideal cubes or irregular convex and concave crystals resulted in overestimation of backscattering. However, when nonsphericity parameters were fit to the measurements, calculated backscattering was also usually within 10% of measurements (closure obtained in >80% of the cases). On the aircraft, however, calculated scattering and backscattering were usually lower than measurements by 20–45% regardless of assumed particle shape (closure obtained in <50% of the cases), likely owing to differences in the aerosol inlet penetration efficiencies to each instrument or unidentified uncertainties in the measured number size distributions or scattering coefficients. To test column closure, aerosol extinction profiles calculated from in situ observations (below 5.5 km) and satellite observations (above 5.5 km) were vertically integrated, and the resulting aerosol optical depth was compared with measurements made on the ship during two clear‐sky days at three wavelengths (500, 778, and 862 nm). Calculated spectral optical depths were usually within 25% of measurements (closure obtained at one or more wavelengths on both days), and agreement at longer wavelengths was improved when satellite measurements were spectrally scaled using in situ model results. On both days, large sea salt particles produced a spectrally neutral aerosol optical depth in the marine boundary layer whereas smaller ammonium sulfate particles contributed to greater optical depth at shorter wavelengths in the overlying upper atmosphere.

Dissolution Kinetics of Ulexite in Ammonium Sulfate Solutions

The dissolution kinetics of ulexite in ammonium sulfate solutions was investigated. The effects of ammonium sulfate concentration, particle size, solid/liquid ratio, stirring speed, and reaction temperature on the dissolution rate have been evaluated. It was found that the dissolution rate increased with increasing ammonium sulfate concentration, stirring speed, and reaction temperature. However, increasing the particle size and solid/liquid ratio decreased the dissolution rate. Experimental data were examined by the heterogeneous and homogeneous models. The heterogeneous diffusion-controlled ash or product layer may describe the dissolution rate. The following mathematical model was used to represent the reaction kinetics: 1 − 3(1 − X)2/3 + 2(1 − X) = 3.9 × 107C0.64D-0.85(S/L)-1.06ω0.40e-10050/Tt, where X is the fractional conversion, C the ammonium sulfate concentration, D the particle size, S/L the solid-to-liquid ratio, ω the stirring speed, T the reaction temperature, and t the reaction time.

Single-particle characterization of urban aerosol particles collected in three Korean cites using low-Z electron probe X-ray microanalysis.

A recently developed single-particle analytical technique, called low-Z electron probe X-ray microanalysis (low-Z EPMA), was applied to characterize urban aerosol particles collected in three cities of Korea (Seoul, CheongJu, and ChunCheon) on single days in the winter of 1999. In this study, it is clearly demonstrated that the low-Z EPMA technique can provide detailed and quantitative information on the chemical composition of particles in the urban atmosphere. The collected aerosol particles were analyzed and classified on the basis of their chemical species. Various types of particles were identified, such as soil-derived, carbonaceous, marine-originated, and anthropogenic particles. In the sample collected in Seoul, carbonaceous, aluminosilicates, silicon dioxide, and calcium carbonate aerosol particles were abundantly encountered. In the CheongJu and ChunCheon samples, carbonaceous, aluminosilicates, reacted sea salts, and ammonium sulfate aerosol particles were often seen. However, in the CheongJu sample, ammonium sulfate particles were the most abundant in the fine fraction. Also, calcium sulfate and nitrate particles were significantly observed. In the ChunCheon sample, organic particles were the most abundant in the fine fraction. Also, sodium nitrate particles were seen at high levels. The ChunCheon sample seemed to be strongly influenced by sea-salt aerosols originating from the Yellow Sea, which is located about 115 km away from the city.

Hygroscopic properties of mixed ammonium sulfate and carboxylic acids particles

AbstractThe hygroscopic growth of internally mixed ammonium sulfate and carboxylic acid particles was measured as a function of relative humidity by using a tandem differential mobility analyzer (TDMA). In TDMA experiments the organic compounds with different solubilities act in several ways, ranging from the behavior of totally insoluble substance to that of soluble compounds. The hygroscopic properties for mixtures containing either adipic acid or phthalic acid together with ammonium sulfate indicate that the organic fraction of the particles behaves as an inert mass and does not contribute to water uptake. The mixtures involving malonic acid or succinic acid increased the water uptake of the ammonium sulfate part only. The results indicate that the solubility of the organic fraction in individual aerosol particles clearly influences the aerosol–water interaction.

Detection of negative ions from individual ultrafine particles.

Aerosol mass spectrometers can be used to classify individual airborne particles on the basis of chemical composition. While positive ion mass spectra are normally used to characterize ultrafine particles (defined here as particles smaller than 200 nm in diameter), negative ion mass spectra can provide complementary information. To effectively utilize the negative ion mass spectra of ultrafine particles, it is important to understand biases in the formation and detection of negative ions. It is found that the intensity of negative ions is generally less than that of positive ions, due to the creation of electrons in the ablation process that must react to form negative ions. The ablation efficiency, defined as the probability that an ablated particle produces a detectable ion signal, exhibits both size and composition dependencies. The ablation efficiency for detection of negative ions follows the same trends as the ablation efficiency for the detection of positive ions: sodium chloride and ammonium nitrate have higher ablation efficiencies than oleic acid, and the ablation efficiency decreases with the particle diameter. The ablation efficiency of negative ions is less than or equal to the ablation efficiency of positive ions, and the relative difference increases as the particle diameter decreases. Pure ammonium sulfate particles exhibit an ablation efficiency too low to be measured in the present experiments. However, trace amounts of sulfate in mixed-composition particles can be readily detected in the negative ion mass spectra.

硫酸アンモニウム及び硫酸ナトリウム粒子による銅の腐食

硫酸アンモニウム及び硫酸ナトリウム粒子による銅の腐食

A novel tandem differential mobility analyzer with organic vapor treatment of aerosol particles

Abstract. A novel method to characterize the organic composition of aerosol particles has been developed. The method is based on organic vapor interaction with aerosol particles and it has been named an Organic Tandem Differential Mobility Analyzer (OTDMA). The OTDMA method has been tested for inorganic (sodium chloride and ammonium sulfate) and organic (citric acid and adipic acid) particles. Growth curves of the particles have been measured in ethanol vapor and as a comparison in water vapor as a function of saturation ratio. Measurements in water vapor show that sodium chloride and ammonium sulfate as well as citric acid particles grow at water saturation ratios (S) of 0.8 and above, whereas adipic acid particles do not grow at S < 0.96. For sodium chloride and ammonium sulfate particles, a deliquescence point is observed at S = 0.75 and S = 0.79, respectively. Citric acid particles grow monotonously with increasing saturation ratios already at low saturation ratios and no clear deliquescence point is found. For sodium chloride and ammonium sulfate particles, no growth can be seen in ethanol vapor at saturation ratios below 0.93. In contrast, for adipic acid particles, the deliquescence takes place at around S = 0.95 in the ethanol vapor. The recrystallization of adipic acid takes place at S < 0.4. Citric acid particles grow in ethanol vapor similarly as in water vapor; the particles grow monotonously with increasing saturation ratios and no stepwise deliquescence is observed. The results show that the working principles of the OTDMA are operational for single-component aerosols. Furthermore, the results indicate that the OTDMA method may prove useful in determining whether aerosol particles contain organic substances, especially if the OTDMA is operated in parallel with a hygroscopicity TDMA, as the growth of many substances is different in ethanol and water vapors.

Deliquescence of ammonium sulfate particles at sub‐eutectic temperatures

To better understand atmospheric aerosol phase transitions under free tropospheric conditions, the behavior of ammonium sulfate (AS) particles mounted on a silicon substrate has been investigated between 229 and 295 K. Experiments were performed in a chamber where water partial pressure and particulate infrared spectra were monitored as the temperature was lowered. Deliquescence experiments at temperatures above the eutectic (254 K) are not new, however results defining deliquescence relative humidity (DRH) at temperatures below the eutectic have been lacking. At sub‐eutectic temperatures the system is supersaturated with respect to ice, therefore both deliquescence and ice formation were possible. Within experimental error, deliquescence was observed at the thermodynamically predicted value both above and below the eutectic. The lack of a significant kinetic barrier to deliquescence implies that AS particles could form supercooled solution droplets at high relative humidities, and function as ice nuclei if these droplets homogeneously freeze.

Measurement of individual particle atomic composition by aerosol mass spectrometry.

Advances in instrumentation used for particle compositional analysis have enabled real-time identification and classification of individual particles. However, precise quantitation of individual particle compositions has been elusive. Here, we demonstrate that real-time quantitative single-particle compositional analysis is possible. This is illustrated for individual particles of sodium chloride (70 nm), ammonium sulfate (70 nm), and silica (40-2000 nm) using a real-time aerosol mass spectrometer. Atomic fractions for major components (> 1% concentration) of individual multicomponent particles have been measured within +/-20% accuracy. Trace element detection limits of 20 ppm are also demonstrated when individual particle compositions are ensemble averaged.

Enhancing the detection of sulfate particles for laser ablation aerosol mass spectrometry.

A major limitation to the application of laser ablation aerosol mass spectrometry for the detection of particles less than 200 nm in diameter is a low ablation efficiency for sulfate particles. (Ablation efficiency is the probability that an ablated particle produces a detectable ion signal.) A method is described here to enhance the ablation efficiency of sulfate particles by coating them with a UV-absorbing compound. The method can be applied in-line with the aerosol mass spectrometer in a manner that does not significantly alter the aerosol size distribution. It is shown that a 12-nm coating of 1-naphthyl acetate increases the ablation efficiency of 136-nm ammonium sulfate particles by at least a factor of 20, while similar coatings on oleic acid and ammonium nitrate particles do not significantly alter the ablation efficiency. The results suggest that "undetected" particles, presumably sulfate, in ambient aerosol can be assessed.

The size effect of hematite and corundum inclusions on the efflorescence relative humidities of aqueous ammonium sulfate particles

Mineral dusts inside aqueous atmospheric particles provide surfaces that induce crystallization during episodes of decreasing relative humidity (RH). Submicron aqueous ammonium sulfate particles containing hematite (α‐Fe2O3) and corundum (α‐Al2O3) inclusions are investigated in an aerosol flow tube at 298 K. As compared to 35% RH where homogeneous nucleation is rapid, the heterogeneous nuclei regulate the RH from 35% up to 60% RH as the inclusion size varies from 50 to 450 nm. The strong size dependence can be rationalized by an active site model. Model optimization yields 1010.4 sites cm−2 and m < 0 for α‐Al2O3 and 109 sites cm−2 and m=0.04 for α‐Fe2O3 particles.

Measurement-based aerosol forcing calculations: The influence of model complexity

On the basis of ground-based microphysical and chemical aerosol measurements a simple ‘ two-layer-singlewavelength’ and a complex ‘ multiple-layer-multiple-wavelength’ radiative transfer model are used to calculate the local solar radiative forcing of black carbon (BC) and (NH 4)2SO4 (ammonium sulfate) particles and mixtures (external and internal) of both materials. The focal points of our approach are (a) that the radiative forcing calculations are based on detailed aerosol measurements with special emphasis of particle absorption, and (b) the results of the radiative forcing calculations with two different types of models (with regards to model complexity) are compared using identical input data. The sensitivity of the radiative forcing due to key input parameters (type of particle mixture, particle growth due to humidity, surface albedo, solar zenith angle, boundary layer height) is investigated. It is shown that the model results for external particle mixtures (wet and dry) only slightly differ from those of the corresponding internal mixture. This conclusion is valid for the results of both model types and for both surface albedo scenarios considered (grass and snow). Furthermore, it is concluded that the results of the two model types approximately agree if it is assumed that the aerosol particles are composed of pure BC. As soon as a mainly scattering substance is included alone or in (internal or external) mixture with BC, the differences between the radiative forcings of both models become signie cant. This discrepancy results from neglecting multiple scattering effects in the simple radiative transfer model. Zusammenfassung

Excimer laser fragmentation-fluorescence spectroscopy as a method for monitoring ammonium nitrate and ammonium sulfate particles

Excimer laser fragmentation-fluorescence spectroscopy (ELFFS) is shown to be an effective detection strategy for ammonium nitrate and ammonium sulfate particles at atmospheric pressure and room temperature. Following photofragmentation of the ammonium salt particle, fluorescence of the NH fragment is observed at 336 nm. The fluorescence signal is shown to depend linearly on particle surface area for laser intensities varying from 1.2×10 8 to 6×10 8 W/cm 2. The 100 shot (1 s) detection limits for ammonium nitrate range from 20 ppb for 0.2 μm particles to 125 ppb for 0.8 μm particles, where these concentrations are expressed as moles of ammonium ion per mole of air. For ammonium sulfate, the 100 shot (1 s) detection limits vary from 60 ppb for 0.2 μm particles to 500 ppb for 1 μm particles. These detection limits are low enough to measure ammonium salt particles that form in the exhaust of combustion processes utilizing ammonia injection as a nitric oxide control strategy.

Ice nucleation in sulfuric acid and ammonium sulfate particles

Cirrus clouds are composed of ice particles and are expected to form in the upper troposphere when highly dilute sulfate aerosols cool and become supersaturated with respect to ice. In the laboratory we have used Fourier transform infrared spectroscopy to monitor ice nucleation from sulfate particles for relevant compositions of sulfuric acid/water and ammonium sulfate/water aerosols. Measured freezing temperatures are presented as a function of aerosol composition, and results are compared to existing aerosol data. We find that sulfuric acid solution aerosol exhibits greater supercooling than ammonium sulfate solution aerosol of similar weight percent. Ice saturation ratios based on these measurements are also reported. We find that ammonium sulfate solution aerosol exhibits a relatively constant ice saturation of S∼1.48 for ice nucleation from 232 to 222 K, while sulfuric acid solution aerosol shows an increase in ice saturation from S∼1.53 to S∼1.6 as temperature decreases from 220 K to 200 K. These high‐saturation ratios imply selective nucleation of ice from sulfate aerosols.

Homogeneous ice nucleation in aqueous ammonium sulfate aerosol particles

The mechanisms involved in cloud formation affect the resulting cloud radiative properties. Therefore, accurate cloud formation models and related global warming models require freezing data for ammonium sulfate particles, a major constituent of upper tropospheric clouds. Homogeneous ice nucleation in aqueous ammonium sulfate particles has been studied by several laboratory groups; however, there is significant disagreement in the reported data. In the present work, the ice freezing temperatures are measured by sending (NH4)2SO4 particles, generated by vapor condensation, through a temperature‐controlled flow cell, where ice formation is detected with infrared spectroscopy. To determine possible explanations for disparate results among several laboratories, the experimental methods used in this study are closely examined. Experiments are performed to preclude artifacts, and experimental conditions are varied to develop a complete understanding of processes involved in particle freezing. All experiments produce consistent results. Mass transfer calculations for the aerosol flow tube technique employed in the current study suggest that one frozen particle in 104 to 106 may scavenge sufficient water vapor from surrounding supercooled aqueous particles such that a single ice particle accumulates enough mass to yield a positive freezing event in the infrared spectrum. This result appears to partially explain the confusing and conflicting results coming from several laboratories employing different experimental methods to observe homogeneous ice nucleation in ammonium sulfate. Six lower limit J (cm−3 s−1) values are determined as 1.1×106 (233±1 K, x = 0.013±0.001), 1.1×106 (231±1 K, x = 0.029±0.004), 1.7×106 (227±1 K, x = 0.066±0.015), 2.8×106 (226±1 K, x = 0.071±0.018), 8.4×106 (224±1 K, x = 0.097±0.034), and 8.4×108 (221±1 K, x = 0.153±0.076), where the associated temperatures and solute mole fraction aqueous compositions (x) are noted in parentheses.

Ice Formation by Sulfate and Sulfuric Acid Aerosol Particles under Upper-Tropospheric Conditions

Ice formation in ammoniated sulfate and sulfuric acid aerosol particles under upper-tropospheric conditions was studied using a continuous flow thermal diffusion chamber. This technique allowed for particle exposure to controlled temperatures and relative humidities for known residence times. The phase states of (NH4)2SO4 and NH4HSO4 particles were found to have important impacts on their ice formation capabilities. Dry (NH4)2SO4 particles nucleated ice only at high relative humidity (RH ≥ 94%) with respect to water at temperatures between −40° and −60°C. This result suggested either an impedance or finite time dependence to deliquescence and subsequent homogeneous freezing nucleation. Ammonium sulfate particles that entered the diffusion chamber in a liquid state froze homogeneously at relative humidities that were 10% lower than where ice nucleated on initially dry particles. Likewise, crystalline or partially crystallized (as letovicite) NH4HSO4 particles required higher relative humidities for ice nucleation than did initially liquid bisulfate particles. Liquid particles of size 0.2 μm composed of either ammonium sulfate or bisulfate froze at lower relative humidity at upper-tropospheric temperatures than did 0.05-μm sulfuric acid aerosol particles. Comparison of calculated homogeneous freezing point depressions suggest that size effects on freezing may be more important than the degree of ammoniation of the sulfate compound.

Hygroscopic growth of ultrafine ammonium sulphate aerosol measured using an ultrafine tandem differential mobility analyzer

An ultrafine tandem differential mobility analyzer has been developed for measurements of the hygroscopicity of ultrafine aerosol particles, between 8 and 50 nm in mobility diameter. In this paper, the main operation features of the device are presented along with a detailed evaluation for the limits of its operation. The instrument is suitable for both laboratory‐generated and atmospheric aerosol measurements. Hygroscopic growth data are presented for ammonium sulphate particles in the ultrafine size range, and comparisons are made with both experimental literature data and with theory. The data include determination of hygroscopic growth curves, deliquescence behavior, and hysteresis. These data will find applications in studies of the formation and growth of atmospheric aerosols.

AN ALTERNATIVE METHOD OF STUDYING THE OPTICAL PROPERTIES OF HIGHLY NON-ABSORBING SPHERICAL MONODISPERSE AEROSOL USING A CELL TRANSMISSOMETER

An approximate and convenient experimental method of studying the basic optical properties of a highly non-absorbing monodisperse spherical aerosol has been developed using a cell transmissometer equipped with a laser beam at 632.8 nm. The method is based on a linearization of the Lambert–Beer law which relates the light transmission measurements with the particle concentration measurements within the cell under stirred gravitational settling conditions. Applying Stokes’ law, the diameter of the particles, which is needed as an input parameter, was deduced taking into account a parameterization procedure to evaluate the particle density. In order to have high scattering, spherical and monodisperse ammonium sulphate particles generated from a dilute solution and with a compressed-air nebulizer were used as test aerosol. A linear regression fit was applied to obtain values for the scattering and absorption coefficient efficiencies; as a result, the single-scattering albedo was evaluated and an indirect estimation of the refractive index, the asymmetry factor, the specific scattering coefficient, and the mass-scattering efficiency could be made. The method has the potential advantage of avoiding the use of instruments like integrating nephelometers as well as being applied to a highly non-scattering spherical monodisperse aerosol. Comparison with other methods indicates that the results are reasonably precise, and comparison with Mie calculations shows that the method is reasonably accurate.

A high-flow humidograph for testing the water uptake by ambient aerosol

A “humidograph” with an air flow rate of 0.4 m 3 s −1 was built to investigate the uptake of water and its effect on sizing, collection and light scattering of ambient aerosol. In the humidograph the relative humidity (RH) can be scanned over a large RH trajectory. Its performance was assessed with laboratory particles of ammonium nitrate, ammonium sulfate and sodium chloride that are the major hygroscopic components of ambient aerosol. The increase in size at the deliquescence points, which ideally is a stepwise function of RH, occurs over a range of 3% RH units. This is shown to be an optimum value in a system of such large dimensions. Because the vapor pressure of ammonium nitrate increases significantly with temperature, its evaporative loss was investigated as a function of heating/drying temperature. The loss of pure test aerosol, with a mass distribution similar to that in the ambient atmosphere, was found to be acceptable for drying temperatures of up to 40°C. The sizing of deliquesced aerosol by LAS-X monitors was tested and found to be a complex function of RH. In Berner low-pressure impactors growth of hygroscopic aerosol was not observed, not even at an RH approaching saturation.

Electrostatic Enhancement of the Collection Efficiency of Stainless Steel Fiber Filters

This study investigated the effect of using a stainless steel fibrous filter as the ground electrode of a point-to-plate electrostatic precipitator on particle penetration. The effect of the electrical field on particle penetration was investigated at 4 different filter face velocities (25, 50, 100, and 125 cm/s) for monodisperse PSL and silica particles (size range 0.05-1 m) as well as polydis perse ammonium sulfate, ammonium nitrate, and ultrafine indoor air particles. Particle penetration was greatly reduced by the application of the electrical field. By comparison, the performance of electrically active fibrous filters has been shown to rapidly degrade as particle loading exceeds 2-3 g/m2. The effect of particle loading on particle penetration was also investigated at a filter face velocity of 50 cm/s. Particle penetration seemed to slightly decrease with particle loading and was independent of particle size. These results indicated that the accumulation of nonconductive particles up to 15 cm3/ m2 doe...