Effect of dimethylamine on the gas phase sulfuric acid concentration measured by Chemical Ionization Mass Spectrometry

Sulfuric acid is widely recognized as a very important substance driving atmospheric aerosol nucleation. Based on quantum chemical calculations it has been suggested that the quantitative detection of gas phase sulfuric acid (H2SO4) by use of Chemical Ionization Mass Spectrometry (CIMS) could be biased in the presence of gas phase amines such as dimethylamine (DMA). An experiment (CLOUD7 campaign) was set up at the CLOUD (Cosmics Leaving OUtdoor Droplets) chamber to investigate the quantitative detection of H2SO4 in the presence of dimethylamine by CIMS at atmospherically relevant concentrations. For the first time in the CLOUD experiment, the monomer sulfuric acid concentration was measured by a CIMS and by two CI-APi-TOF (Chemical Ionization-Atmospheric Pressure interface-Time Of Flight) mass spectrometers. In addition, neutral sulfuric acid clusters were measured with the CI-APi-TOFs. The CLOUD7 measurements show that in the presence of dimethylamine (<5 to 70 pptv) the sulfuric acid monomer measured by the CIMS represents only a fraction of the total H2SO4, contained in the monomer and the clusters that is available for particle growth. Although it was found that the addition of dimethylamine dramatically changes the H2SO4 cluster distribution compared to binary (H2SO4-H2O) conditions, the CIMS detection efficiency does not seem to depend substantially on whether an individual H2SO4 monomer is clustered with a DMA molecule. The experimental observations are supported by numerical simulations based on A Self-contained Atmospheric chemistry coDe coupled with a molecular process model (Sulfuric Acid Water NUCleation) operated in the kinetic limit

Evolution of particle composition in CLOUD nucleation experiments

Sulphuric acid, ammonia, amines, and oxidised organics play a crucial role in nanoparticle formation in the atmosphere. In this study, we investigate the composition of nucleated nanoparticles formed from these compounds in the CLOUD (Cosmics Leaving Outdoor Droplets) chamber experiments at CERN (Centre européen pour la recherche nucléaire). The investigation was carried out via analysis of the particle hygroscopicity, ethanol affinity, oxidation state, and ion composition. Hygroscopicity was studied by a hygroscopic tandem differential mobility analyser and a cloud condensation nuclei counter, ethanol affinity by an organic differential mobility analyser and particle oxidation level by a high-resolution time-of-flight aerosol mass spectrometer. The ion composition was studied by an atmospheric pressure interface time-of-flight mass spectrometer. The volume fraction of the organics in the particles during their growth from sizes of a few nanometers to tens of nanometers was derived from measured hygroscopicity assuming the Zdanovskii–Stokes–Robinson relationship, and compared to values gained from the spectrometers. The ZSR-relationship was also applied to obtain the measured ethanol affinities during the particle growth, which were used to derive the volume fractions of sulphuric acid and the other inorganics (e.g. ammonium salts). In the presence of sulphuric acid and ammonia, particles with a mobility diameter of 150 nm were chemically neutralised to ammonium sulphate. In the presence of oxidation products of pinanediol, the organic volume fraction of freshly nucleated particles increased from 0.4 to ~0.9, with an increase in diameter from 2 to 63 nm. Conversely, the sulphuric acid volume fraction decreased from 0.6 to 0.1 when the particle diameter increased from 2 to 50 nm. The results provide information on the composition of nucleated aerosol particles during their growth in the presence of various combinations of sulphuric acid, ammonia, dimethylamine and organic oxidation products

Thermodynamics of the formation of sulfuric acid dimers in the binary (H2SO4-H2O) and ternary (H2SO4-H2O-NH3) system

Sulfuric acid is an important gas influencing atmospheric new particle formation (NPF). Both the binary (H2SO4-H2O) system and the ternary system involving ammonia (H2SO4-H2O-NH3) may be important in the free troposphere. An essential step in the nucleation of aerosol particles from gas-phase precursors is the formation of a dimer, so an understanding of the thermodynamics of dimer formation over a wide range of atmospheric conditions is essential to describe NPF. We have used the CLOUD chamber to conduct nucleation experiments for these systems at temperatures from 208 to 248 K. Neutral monomer and dimer concentrations of sulfuric acid were measured using a chemical ionization mass spectrometer (CIMS). From these measurements, dimer evaporation rates in the binary system were derived for temperatures of 208 and 223 K. We compare these results to literature data from a previous study that was conducted at higher temperatures but is in good agreement with the present study. For the ternary system the formation of H2SO4 center dot NH3 is very likely an essential step in the formation of sulfuric acid dimers, which were measured at 210, 223, and 248 K. We estimate the thermodynamic properties (dH and dS) of the H2SO4 center dot NH3 cluster using a simple heuristic model and the measured data. Furthermore, we report the first measurements of large neutral sulfuric acid clusters containing as many as 10 sulfuric acid molecules for the binary system using chemical ionization-atmospheric pressure interface time-of-flight (CI-APi-TOF) mass spectrometry.Peer reviewe

Combustion fume structure and dynamics. Period of performance: 8/16/91--2/15/92

During pulverized coal combustion, a fume of submicron particles is formed when minerals that have volatilized from the parent coal nucleate to form new particles. The particles thus generated are extremely small, but they grow rapidly due to Brownian coagulation. Much has been learned about these fine particles in experimental studies of the particles formed in coal combustion. Measurements of the variation of chemical composition with particle size clearly demonstrate that the particles smaller than about 0.1 {mu}m in diameter are formed from vapors while larger particles are dominated by residues from the mineral matter in the coal. Theoretical predictions of the evolution of the particle size distribution suggest that the nuclei should produce a sharp peak which may approach 0.1 {mu}m, but they are unlikely to grow much beyond that size in the limited time available in practical combustors. The focus of this research program is on elucidating the fundamental processes that determine the particle size distribution, composition, and agglomerate structures of coal ash fumes. The ultimate objective of this work is the development and validation of a model for the dynamics of combustion fumes, describing both the evolution of the particle size distribution and the particle morphology. The study employs model systems to address the fundamental questions and to provide rigorous validation of the models to be developed. This first phase of the project has been devoted to the development of a detailed experimental strategy that will allow agglomerates with a broad range of fractal dimensions to be studied in the laboratory

Thermally induced structural changes in coal combustion

The effects of the temperature-time history during coal devolitization and oxidation on the physical properties and the reactivity of resulting char were studied experimentally for temperatures and residence times typical of pulverized combustion. Experiments were also carried out at somewhat lower temperatures and correspondingly longer residence times. An electrically heated laminar flow reactor was used to generate char and measure the rates of oxidation at gas temperatures about 1600K. Partially oxidized chars were extracted and characterized by gas adsorption and mercury porosimetry, optical and scanning electron microscopy, and oxidation in a thermogravimetric analysis system (TGA). A different series of experiments was conducted using a quadrople electrodynamic balance. Single particles were suspended electrodynamically and heated by an infrared laser in an inert or oxygen-containing atmosphere. During the laser heating, measurements were taken of particle mass, size/shape, and temperature

Water Activities of NH4NO3/(NH4)2SO4 Solutions

Water activities for mixed ammonium nitrate/ammonium sulfate solutions at relative humidities of 0.35-0.75 were measured using a spherical void electrodynamic balance. The concentrations of singly levitated droplets of nitrate to sulfate mole ratio of n = 1/5, 1/3, 1/2, 1, 2 and 4 in equilibrium with an ambient environment of prescribed relative humidity were measured. To avoid uncertainty in determining the composition of the solid particles, solution properties were determined relative to the known properties at about 80% relative humidity. The concentration of this reference state was estimated by three models of mixed electrolyte solutions, the Zdanovskii-Stokes-Robinson(ZSR), the Kusik and Meissner(KM) and the Pitzer models. The measured total mass fraction of solute of the mixed solutions differed by less than 0.5% when different models were used to calculate the reference state concentration. The water activity data were obtained at ionic strengths as high as 108 molal and used to evaluate predictions from these three models. For n = 1/5 and 1/3, deviations of model predictions from experimental data are within 2%. Generally, predictions of the ZSR model are most consistent with our data. Maximum deviations occur at n = 2; 6% for ZSR, 8% for KM and 5% for Pitzer, The deviations can be attributed to binary and ternary solute-solute interactions that the ZSR, KM and elementary version of the Pitzer models do not consider. However, no simple characterization of the interaction parameters is possible; they seem to be strong functions of the fractional ionic strength of the solute and the total ionic strength of the solutions

Parameterization of cloud droplet size distributions: comparison with parcel models and observations

Journal of Geophysical Research, Vol. 114, D11205The article of record as published may be located at http://dx.doi.org/10.1029/2008JD011387This work examines the efficacy of various physically based approaches derived from one-dimensional adiabatic parcel model frameworks (a numerical model and a simplified parameterization) to parameterize the cloud droplet distribution characteristics for computing cloud effective radius and autoconversion rate in regional/global atmospheric models. Evaluations are carried out for integrations with single (average) and distributions of updraft velocity, assuming that (1) conditions at smax are reflective of the cloud column or (2) cloud properties vary vertically, in agreement with one-dimensional parcel theory. The predicted droplet distributions are then compared against in situ cloud droplet observations obtained during the CRYSTAL-FACE and CSTRIPE missions. Good agreement of droplet relative dispersion between parcel model frameworks indicates that the parameterized parcel model essentially captures one-dimensional dynamics; the predicted distributions are overly narrow, with relative dispersion being a factor of 2 lower than observations. However, if conditions at cloud maximum supersaturation are used to predict relative dispersion and applied throughout the cloud column, better agreement is seen with observations, especially if integrations are carried out over the distribution of updraft velocity. When considering the efficiency of the method, calculating cloud droplet spectral dispersion at smax is preferred for linking aerosol with droplet distributions in large-scale models

Resonance Structures in Elastic and Raman Scattering for Microspheres

To study the interactions between Mie scattering and Raman emissions of spherical particles, we measured the Raman spectra together with the elastically scattered light of the excitation source of an evaporating aqueous sodium nitrate droplet. Resonance structures were observed in the temporal profiles of the elastically scattered light and Raman nitrate and water emissions. The resonance structures in these three profiles occurred in a concerted mode but sometimes occurred independently of each other. A model of inelastic scattering by microspheres by Kerker et al. ["Raman and Fluorescent Scattering by Molecules Embedded in Spheres with Radii up to Several Multiples of the Wavelength," Appl. Opt. 18, 1172-1179 (1979); "Lorenz-Mie Scattering by Spheres: Some Newly Recognized Phenomena," Aerosol Sci. Technol. 1, 275-291 (1982); "Inelastic Light Scattering," in Aerosol Microphysics I: Particle Interaction, W.H. Marlow, Ed. (Springer-Verlag, New York, 1980); "Model for Raman and Fluorescent Scattering by Molecules Embedded in Small Particles," Phys. Rev. A 13, 396-404 (1976)] and the behavior of low order Mie resonances were used to explain the data. This type of data can be used for the determination of chemical compositions of spherical particles

Airborne analysis of the Los Angeles aerosol

Atmospheric Environment, 34, 4155-4173.As part of the Southern California ozone study (SCOS), a research aircraft was employed during August and September of 1997 to characterize the physical and chemical properties of the aerosol present over the Los Angeles Basin. Aerosol size distributions measured using a di!erential mobility analyzer and two optical particle counters were combined with "lter-based composition measurements to derive a physicochemical description of the aerosol sampled. The accuracy of this description was evaluated through comparison of derived and directly measured aerosol properties including mass, absorption coe$cient, hemispherical backscattering coe$cient, and total scattering coe$cient at two di!erent relative humidities. The sampled aerosol exhibited a complex vertical structure possessing multiple elevated aerosol layers. The most pronounced of these layers were observed to form by injection of aerosol above the ground-level mixed layer along the southern edge of the San Gabriel Mountains, which form the northern boundary of much of the Los Angeles Basin. Over multiple inland areas, additional layers were observed at about 2500 m above sea level (asl), while o! the coast of Santa Monica, thin but concentrated layers were detected about 500 m asl. In addition to the sharp vertical gradients in aerosol concentration observed, horizontal gradients at multiple locations were found to be su$cient to result in more than 50% variability within a 5!5 km computational grid cell commonly used in atmospheric models. Vertically resolved aerosol measurements made over one location during several #ights, as well as over several locations during a morning and afternoon #ight on the same day, were used to investigate the temporally and spatially resolved impact the aerosol had on gas-phase photolysis rates. These calculations predict that for a 103 zenith angle the sampled aerosol enhanced photolysis rates by up to about 5%, although a slight decrease was often observed near ground level