Condensation Of Nitric Acid Research Articles

Experimental study of sticking probabilities for condensation of nitric acid — water vapor mixtures

In the present study condensational droplet growth rates in the binary vapor system HNO 3–H 2O were measured over a relatively wide range of vapor activitiesin order to investigate the mass accommodation coefficients in binary vapor mixtures. The measurements on condensational droplet growth rates were performed in an expansion chamber with a sensitive time of the order of 10 s . Droplet growth rates and the corresponding droplet number concentrations were determined by the Constant angle mie scattering (CAMS) method. In the present study the droplet radii cover a range from 0.5 to about 4 μm . The experiments were performed at constant temperature and total pressure near atmospheric conditions. The experimental growth curves determined in the binary vapor system HNO 3–H 2O are compared to corresponding model calculations. Thereby the mass and thermal accommodation coefficients can be determined. It can be concluded from the experiments that in binary supersaturated vapor mixtures of HNO 3–H 2O the sticking probability for nitric acid molecules is between 1.0 and 0.3 for the case of the sticking probability for the water molecules is set to unity. Especially at very low relative humidities below 75% very good agreement between experiment and theory can be established when the sticking probability of water as well as of nitric acid is regarded to be unity.

A prognostic physico-chemical model of secondary and marine inorganic multicomponent aerosols II. Model tests

The accuracy and efficiency of the sectional multicomponent aerosol model SEMA, described in the first part of this paper, are tested. Comparisons of results of an equilibrium version of SEMA with results of the equilibrium models SEQUILIB and AIM show good agreement for relative humidities above 60% and thus validate the thermodynamic portion of the model. Tests of the dynamic portion of SEMA show the reliability of the model down to a minimum number of four sections. The results of a model application give evidence that kinetic limitations may be important in the formation of secondary aerosol species by condensation of sulphuric acid, nitric acid, and ammonia on sea salt aerosol. The concentrations of the chemical components of marine aerosol may be substantially different from their thermodynamic equilibrium concentrations in the polluted coastal atmosphere.

A prognostic physico-chemical model of secondary and marine inorganic multicomponent aerosols I. Model description

In this paper, the physico-chemical basics of the sectional multicomponent aerosol model SEMA are described. SEMA includes condensation and evaporation of sulphuric acid, nitric acid, hydrogen chloride, ammonia, and water vapour. The model can be applied to predictions of the chemical composition and size distribution of aqueous tropospheric secondary and marine aerosols. In SEMA, multicomponent thermodynamics and particle-size-dependent condensation and evaporation are efficiently coupled by application of a new sectional approach.

Dissolution of sulfuric acid tetrahydrate at low temperatures and subsequent growth of nitric acid trihydrate

Crystalline sulfuric acid tetrahydrate (SAT) has been observed to change phase at temperatures below its melting point, in agreement with recent theoretical predictions of deliquescence. Dissolution of SAT was observed in 63% of experiments expected to show a phase change, leading to formation of a ternary HNO3/H2SO4/H2O solution. This solution, which still contained a portion of the original solid SAT, crystallized to form nitric acid trihydrate (NAT). NAT then continued to grow by condensation of additional nitric acid and water at temperatures several degrees above the ice frost point. This process of SAT dissolution followed by NAT crystallization and growth may offer a mechanism for the formation of type Ia polar stratospheric clouds on frozen sulfate aerosols when SNAT>15.

Hygroscopicity of pre-existing particle distribution and formation of cloud droplets: a model study

The effects of the hygroscopicity of a pre-existing particle distribution and condensation of nitric acid on cloud droplet formation were studied by using an air parcel and multicomponent condensation model. The pre-existing particle distribution used is a bimodal distribution in which the particles are assumed to be internally mixed, i.e. they are composed partly from ammonium nitrate salt and partly from some insoluble substance. The mean diameters of the distributions and the mass fraction of soluble salt were varied in the simulations. Generally, the number of activated cloud droplets was found to be increased, when the initial mass fraction of salt (i.e. the initial amount of salt) was increased. However, the effects of increased initial amount of salt on the cloud droplet formation were not straightforward in all cases studied. The effects of the condensing hygroscopic substance, with initial nitric acid concentrations of 0.1, 1.0 and 10.0 ppbv on the activation of cloud droplets were also studied. The number of activated droplets increased when the initial concentration of nitric acid was increased.

Model simulation of the amount of soluble mass during cloud droplet formation

The development of the amount of hygroscopic material from nitric acid vapour in nascent cloud droplets has been studied. This phenomenon was approached first by simple calculations in order to find out maximum values of condensed hygroscopic material in droplets and in cloud water. Then, a more detailed parcel model with the binary condensation of water and nitric acid vapours was used for the simulations of the development of droplet distribution and the composition of droplets. In the parcel model vapours are condensing on the ammonium nitrate particles. According to the results of this study condensation of nitric acid could increase considerably the amount of nitrate ions in the droplets, if we compare this to the amount of nitrate ions from ammonium nitrate salt. This can lead to the enhanced amount of activated cloud droplets.

Metabolism of nitrate esters by a consortium of two bacteria.

The products of condensation of organic alcohols and nitric acid are nitrate esters with the general structure C-O-NO2. These products are widely employed as vasodilators and explosives, and are true xenobiotic compounds, as they do not occur in nature. We have isolated and characterized a consortium of two microorganisms, Arthrobacter ilicis and Agrobacterium radiobacter, that mineralized recalcitrant ethylene glycol dinitrate. The Arthrobacter strain was the actual degrading microorganism, although the second microbe facilitated mineralization. The biodegradation of ethylene glycol dinitrate by A. ilicis involved the progressive elimination of the nitro groups from the organic molecule to generate ethylene glycol, which was then mineralized. Waters polluted with ethylene glycol dinitrate have been shown amenable to biological treatment in a pilot plant with wastewaters generated during the synthesis of the chemical in a factory.

Laboratory studies of the formation of polar stratospheric clouds: Nitric acid condensation on thin sulfuric acid films

Thin sulfuric acid films were exposed to 5 × 10−8 − 8 × 10−7 torr HNO3 and 2 − 3 × 10−4 torr H2O and cooled to temperatures near the ice frost point. Fourier transform infrared (FTIR) spectroscopy was used to probe the condensed‐phase species during isothermal experiments, and gas pressures were monitored with mass spectrometry. Supercooled liquid sulfuric acid films exposed to HNO3 (6 ≤ SNAT ≤ 114) showed indications of HNO3 uptake to form ternary solutions of approximately 4 wt % HNO3, 38 wt % H2SO4, and 59 wt % H2O, followed by crystallization of nitric acid trihydrate (NAT). NAT crystallization did not initiate significant crystallization of the supercooled H2SO4, but the H2SO4 often crystallized to sulfuric acid tetrahydrate (SAT) upon warming. In contrast, when crystalline SAT films were exposed to HNO3 and water, NAT did not condense within several hours, even at HNO3 saturation ratios of 30 or higher. Calculations of the contact parameter from experimental data indicate that m <0.76 for NAT on SAT. Our film studies suggest that crystalline polar stratospheric cloud (PSC) growth is most easily accomplished when stratospheric sulfate aerosols (SSAs) remain liquid, absorb HNO3, and produce crystalline nitric acid trihydrate via heterogeneous nucleation. If SSAs crystallize to SAT at some point during the winter, nitric acid condensation is hindered, and PSC formation could become more difficult.

Possible nitric acid coating formation over Pinatubo aerosols inferred with a microphysical code: A case study during EASOE

Lidar observations at Sodankylä (Finland) on January 9 and 11 1992, made as part of the European Arctic Stratospheric Ozone Experiment (EASOE), showed very different profiles of backscattering ratio. A prominent layer was seen between potential temperatures of 420 and 445K on January 9, which was nearly absent in the backscattering profile between these isentropic surfaces on the 11th. Examination of the trajectories of the airmasses reaching Sodankylä on these days lead us to suggest that the larger returns on January 9th could arise from the formation of a nitric acid coating on volcanic aerosols. Simulations using a microphysical model produce results consistent with this suggestion. We conclude that nitric acid condensation on January 9 can explain the measurements, but that independent information would be needed to quantify the characteristics of the aerosol substrate.

Simultaneous ozone and polar stratospheric cloud observations at South Pole station during winter and spring 1991

Simultaneous polar stratospheric cloud (PSC) and ozone measurements were made over South Pole Station using a two‐wavelength backscattersonde. This instrument produces aerosol profiles similar to those obtained with a ground‐based lidar system but with higher vertical resolution. In one sounding, depolarization of the PSCs was also measured. The backscattersondes were supplemented with occasional frost point soundings. The measurements made before the appearance of PSCs do not show clear evidence of particle deliquescence, suggesting that the background sulfate particles may be frozen solids rather than liquids. PSCs began appearing at ∼20 km when the temperature at that altitude dropped to −80°C (193 K). Initially, there was apparent evidence of supersaturation (with respect to nitric acid trihydrate) associated with some type I PSCs, while other examples indicated that the condensation of nitric acid was in quantitative agreement with that expected from the saturation vapor pressure and available nitric acid vapor. The apparent supersaturated layers (which occurred within the first 2 weeks of the onset of PSCs) can alternatively be interpreted as denitrified regions. The wavelength dependence of the backscatter is used to deduce rough particle sizes, and in particular, type Ia and Ib population types can be readily identified by the backscattersonde when not occurring as mixed systems. The mode radius of the first observed PSCs of the season was ∼0.5 μm. In the polarization sensitive sounding, two varieties of type I PSCs were observed, one of which exhibited significant depolarization and another which produced very little depolarization. This observation would be consistent with the classification of types Ia and Ib, respectively. At the precise time that sunlight was returning to the stratosphere near South Pole Station, a strong inverse correlation in the structure of PSCs and ozone mixing ratio was observed. Using trajectory analysis, it is argued that the effect is probably the result of chemical depletion rather than transport processes. This chance observation is consistent with enhanced ozone depletion occurring in association with sunlit PSCs during the early spring.

Measurements of stratospheric gaseous nitric acid in the winter Arctic vortex using a novel rocket‐borne mass spectrometric method

The altitude distribution of stratospheric gaseous nitric acid was measured on 30 January, 1989 at Esrange (68°N, 20°E; Northern Sweden) in a particularly cold stratosphere (lowest temperature 190 K) using a novel rocket‐borne ACIMS (Active Chemical Ionisation Spectrometry)‐ instrument. Within the coldest layer (18.5–22.6 km) gaseous nitric acid was found to be strongly depleted. Probably this depletion was caused by local nitric acid condensation leading to NAT (Nitric Acid Trihydrate) aerosols, which were still present in the same layer, and/or HNO3‐removal from that layer by sedimentation of HNO3‐containing aerosols. Threshold temperatures for nitric acid condensation of about 195–193 K (18.5 km) and 193 K (22.6 km) can be inferred from the present data being roughly consistent with theoretical model predictions.

Nitric acid in polar stratospheric clouds: Similar temperature of nitric acid condensation and cloud formation

As shown independently by two different techniques, nitric acid aerosols and polar stratospheric clouds both form below similar threshold temperatures. This supports the idea that the polar stratospheric cloud (PSC) particles involved in chlorine activation and ozone depletion in the winter polar stratosphere are composed of nitric acid. One technique used to show this is inertial impaction of nitric acid aerosols using an ER‐2 aircraft; the other method is remote sensing of PSCs by the Stratospheric Aerosol Measurement (SAM II) satellite borne optical sensor. Both procedures were in operation during the Arctic Airborne Stratospheric Expedition in 1989, and the Airborne Antarctic Ozone Experiment in 1987. Analysis of Arctic particles gathered in situ indicates the presence of nitric acid below a “first appearance” temperature Tfa = 202 K. This is the same highest temperature a at which PSCs are seen by the SAM II satellite. In comparison, a “first appearance” temperature Tfa = 198 K was found for the Antarctic samples.

Evidence for stratospheric nitric acid condensation from balloon and rocket measurements in the Arctic

Strong evidence for nitric acid condensation at altitudes of about 18–23 km is provided by balloon-and rocket-borne measurements made near Kiruna, northern Sweden, in January 1989. Nitric acid con-densation is believed to be a necessary step in the chemical pre-conditioning required for chlorine-catalysed ozone destruction.

Stratospheric nitric acid vapour measurements in the cold Arctic vortex: implications for nitric acid condensation

STRATOSPHERIC nitric acid condensation has recently been proposed1, 2 to take place in the cold winter polar vortex, priming it for chlorine-catalysed ozone destruction. This idea has been developed subsequently3–8. Condensation, thought to proceed via a heterogeneous heteromolecular mechanism involving stratospheric water vapour and pre-existing H2SO4/H2O aerosols, which serve as condensation nuclei, leads to solid nitric acid trihydrate (NAT; HNO3.3H2O) aerosols. It is expected1, 2, 8 that the condensation temperature, Tc(NAT), is significantly greater than that of water-ice, Tc(H2O-ice), given the stratospheric abundances of gaseous nitric acid and water and the thermodynamic properties of stratospheric aerosols8. Knowledge of Tc(NAT) is important because it determines the spatial and temporal extent of NAT aerosols and hence possibly of polar ozone destruction. Here we report in situ measurements of the detailed height distribution of gaseous nitric acid in the cold arctic vortex, using a balloon-borne technique9–16, which offers a much better altitude resolution (30 m) than previous satellite measurements17, 18. Our data set an upper limit to Tc(NAT) of 195 K at 23 km, and are consistent with model predictions based on the present gaseous nitric acid data, typical water vapour abundances and thermodynamic data8 of macroscopic NAT mixtures. However, our upper limit to Tc(NAT) is markedly lower than some of the early model estimates1, 2.