Growth of sulphuric acid nanoparticles under wet and dry conditions

New particle formation, which greatly influences the number concentrations and size distributions of an atmospheric aerosol, is often followed by a rapid growth of freshly formed particles. The initial growth of newly formed aerosol is the crucial process determining the fraction of nucleated particles growing to cloud condensation nuclei sizes, which have a significant influence on climate. In this study, we report the laboratory observations of the growth of nanoparticles produced by nucleation of H₂SO₄ and water in a laminar flow tube at temperatures of 283, 293 and 303 K, under dry (a relative humidity of 1%) and wet conditions (relative humidity of 30%) and residence times of 30, 45, 60 and 90 s. The initial H₂SO₄ concentration spans the range from 2 × 10⁸ to 1.4 × 10¹⁰ molecule cm⁻³ and the calculated wall losses of H₂SO₄ were assumed to be diffusion limited. The detected particle number concentrations, measured by the Ultrafine Condensation Particle Counter (UCPC) and Differential Mobility Particle Sizer (DMPS), were found to depend strongly on the residence time. Hygroscopic particle growth, presented by growth factors, was found to be in good agreement with the previously reported studies. The experimental growth rates ranged from 20 nm h⁻¹ to 890 nm h⁻¹ at relative humidity (RH) 1% and from 7 nm h⁻¹ to 980 nm h⁻¹ at RH 30% and were found to increase significantly with the increasing concentration of H₂SO₄. Increases in the nucleation temperature had a slight enhancing effect on the growth rates under dry conditions. The influence of relative humidity on growth was not consistent – at lower H₂SO₄ concentrations, the growth rates were higher under dry conditions while at H₂SO₄ concentrations greater than 1 × 10¹⁰ molecule cm⁻³, the growth rates were higher under wet conditions. The growth rates show only a weak dependence on the residence time. The experimental observations were compared with predictions made using a numerical model, which investigates the growth of particles with three different extents of neutralization by ammonia, NH₃: (1) pure H₂SO₄ – H₂O particles; (2) particles formed by ammonium bisulphate, (NH₄)HSO₄; (3) particles formed by ammonium sulphate, (NH₄)₂SO₄. The highest growth rates were found for ammonium sulphate particles. Since the model accounting for the initial H₂SO₄ concentration predicted the experimental growth rates correctly, our results suggest that the commonly presumed diffusional wall losses of H₂SO₄ in case of long-lasting experiments are not so significant. We therefore assume that there are not only losses of H₂SO₄ on the wall, but also a flux of H₂SO₄ molecules from the wall into the flow tube, the effect being more profound under dry conditions and at higher temperatures of the tube wall. Based on a comparison with the atmospheric observations, our results indicate that sulphuric acid alone cannot explain the growth rates of particles formed in the atmosphere

Intercomparison and evaluation of global aerosol microphysical properties among AeroCom models of a range of complexity

Many of the next generation of global climate models will include aerosol schemes which explicitly simulate the microphysical processes that determine the particle size distribution. These models enable aerosol optical properties and cloud condensation nuclei (CCN) concentrations to be determined by fundamental aerosol processes, which should lead to a more physically based simulation of aerosol direct and indirect radiative forcings. This study examines the global variation in particle size distribution simulated by 12 global aerosol microphysics models to quantify model diversity and to identify any common biases against observations. Evaluation against size distribution measurements from a new European network of aerosol supersites shows that the mean model agrees quite well with the observations at many sites on the annual mean, but there are some seasonal biases common to many sites. In particular, at many of these European sites, the accumulation mode number concentration is biased low during winter and Aitken mode concentrations tend to be overestimated in winter and underestimated in summer. At high northern latitudes, the models strongly underpredict Aitken and accumulation particle concentrations compared to the measurements, consistent with previous studies that have highlighted the poor performance of global aerosol models in the Arctic. In the marine boundary layer, the models capture the observed meridional variation in the size distribution, which is dominated by the Aitken mode at high latitudes, with an increasing concentration of accumulation particles with decreasing latitude. Considering vertical profiles, the models reproduce the observed peak in total particle concentrations in the upper troposphere due to new particle formation, although modelled peak concentrations tend to be biased high over Europe. Overall, the multi-model-mean data set simulates the global variation of the particle size distribution with a good degree of skill, suggesting that most of the individual global aerosol microphysics models are performing well, although the large model diversity indicates that some models are in poor agreement with the observations. Further work is required to better constrain size-resolved primary and secondary particle number sources, and an improved understanding of nucleation and growth (e.g. the role of nitrate and secondary organics) will improve the fidelity of simulated particle size distributions

Size distribution, composition and origin of the submicron aerosol in the marine boundary layer during the eastern Mediterranean "SUB-AERO" experiment

Summarization: A period of intensive physical and chemical aerosol characterisation measurements was held over 5 days during July 2000 as part of the European SUB-AERO experiment.. Concurrent measurements were performed at the Finokalia remote coastal site on the island of Crete (Greece) and onboard the R/V “Aegaeon” which cruised in south part of the Aegean Sea northwards of Crete. The objective of the study was to investigate the spatial and temporal variability of microphysical parameters of the submicron aerosol and their dependence on airmass origin and chemical composition. The results reflect the submicron aerosol properties during airmass transport from the north including Europe and the Balkans and are in line with other studies on the aerosol properties of polluted continental air entering the marine boundary layer (MBL). Concentrations of submicron particulate matter (PM) mass were relatively higher at sea (20 μg m−3) compared to the coastal site (16 μg m−3). Concentrations of both organic carbon and sulphate, being the major water soluble component, were also higher at sea than at land. The high concentrations of ammonium and those of the water soluble organics, such as oxalate, can be attributed to emissions from mainland forest fires. The submicron aerosol number size distribution was unimodal with mobility mean diameters (dg) ranging from 98 to 144 μm and standard deviations (σg) from 1.56 to 1.9. Aerosol number concentrations at Finokalia were at least 50% lower especially when R/V Aegaeon sampled polluted air, but the modal parameters of the size distribution were very similar (dg: 111–120, σg: 1.55–1.91). The surface MBL, under these conditions, was an aerosol rich environment where aerosol particles were transported both by the surface wind, advected from higher layers, chemically processed by interactions with gaseous precursors and physically altered by water vapour. The number to volume ratio for the submicrometer aerosol fraction reflected the effect of these mechanisms on the size distribution.Παρουσιάστηκε στο: Atmospheric Environmen

Dry powder inhaler of colistimethate sodium for lung infections in cystic fibrosis: optimization of powder construction

Colistimethate sodium (CMS) for treatment of lung infections in cystic fibrosis patient was transformed into a dry powder for inhalation by spray drying. Design of Experiment was applied for understanding the role of the spray-drying process parameters on the critical quality attributes of the CMS spray-dried (SD) powders and agglomerates thereof. Eleven experimental SD microparticle powders were constructed under different process conditions according to a central composite design. The SD microparticles were then agglomerated in soft pellets. Eleven physico-chemical characteristics of SD CMS microparticle powders or agglomerates thereof were selected as critical quality attributes. The yield of SD process was higher than 75%. The emitted fraction of agglomerates from RS01 inhaler was 75–84%, and the fine particle fraction (particles <5 µm) was between 58% and 62%. The quality attributes of CMS SD powders and respective agglomerates that were significantly influenced by spray-drying process parameters were residual solvent and drug content of the SD microparticles as well as bulk density and respirable dose of the agglomerates. These attributes were also affected by the combination of the process variables. The air aspiration rate was found as the most positively influential on drug and solvent content and respirable dose. The residual solvent content significantly influenced the powder bulk properties and aerodynamic behavior of the agglomerates, i.e. quality attributes that govern drug metering in the device and the particles lungs deposition. Agglomerates of CMS SD microparticles, in combination with RS01 DPI, showed satisfactory results in terms of dose emitted and fine particle fraction

Characterisation of indoor/outdoor PM in suburban area of Prague: Chemical and elemental size

Μη διαθέσιμη περίληψηNot available summarizationΠαρουσιάστηκε στο: European Aerosol Conferenc

Time and size resolved indoor/outdoor particles in an empty room

Summarization: Finding the concentration Cin of a non-reacting pollutant in a room of volume V is the main objective of indoor air modeling. Cin is controlled by the ventilation rate of indoor and outdoor air (with concentration Cout), sources Q, and sinks S. Here we measured time and size resolved indoor and outdoor particle concentrations and compared the experimental results with the prediction based on simple mass balance model. MODELLING OF INDOOR PARTICLE CONCENTRATIONS The temporal evolution of the indoor concentration including contaminant sources and sinks can be under well mixed conditions described by the first-order linear differential equation dCin/dt = ? (Cout - Cin) + q (1) Here q = (Q-S)/V is combined sources and sinks term divided by the room volume. For constant ?, Cout, and q and for the initial condition Cin = Cin (0), the equation (1) has the solution Cin = e-?t Cin (0) + (1 - e-?t ) (q/? + Cout ) (2) As can be seen the solution has a decay following a single time exponent ?. After infinitely long time the equation (2) has the stationary limit Cin (?) Š q/? + Cout (3) RESULTS Indoor and outdoor particle size measurements were made using two Scanning Mobility Particle Sizers (SMPS) model 3936N25 and 3934C, and Aerodynamic Particle Sizer (APS) model 3320. The instruments covered particle size range from 3 nm to 20 microm. The same instruments were used for sampling both indoor and outdoor aerosol using valve system that allowed the aerosol samples to be drawn in alternating time periods from inside and outside the room. The measurements were conducted in an empty office (without any furniture and any activity inside) and outside the window. To prevent possible generation of aerosol by the measuring system all the instruments and pumps were located in a room different from the office where the air samples were taken. Usually three 5 min sampling cycles for indoor sampling followed by three cycles for outdoor sampling were used. The measurements were corrected for multiple charging, efficiency of CPC counters, and particle losses in sampling trains. To observe the dynamics of the process the office was equilibrated from time to time during the measurements with the outside environment. For this purpose the windows of the office were opened for about 2 hours to exchange air between the office and surroundings.Παρουσιάστηκε στο: Sixth International Aerosol Conferenc