Particle Condensational Growth Research Articles

Toxicity assessment of CeO₂ and CuO nanoparticles at the air-liquid interface using bioinspired condensational particle growth

CeO2 and CuO nanoparticles (NPs) are used as additives in petrodiesel to enhance engine performance leading to reduced diesel combustion emissions. Despite their benefits, the additive application poses human health concerns by releasing inhalable NPs into the ambient air. In this study, a bioinspired lung cell exposure system, Dosimetric Aerosol in Vitro Inhalation Device (DAVID), was employed for evaluating the toxicity of aerosolized CeO2 and CuO NPs with a short duration of exposure (≤10 min vs. hours in other systems) and without exerting toxicity from non-NP factors. Human epithelial A549 lung cells were cultured and maintained within DAVID at the air-liquid interface (ALI), onto which aerosolized NPs were deposited, and experiments in submerged cells were used for comparison. Exposure of the cells to the CeO2 NPs did not result in detectable IL-8 release, nor did it produce a significant reduction in cell viability based on lactate dehydrogenase (LDH) assay, with a marginal decrease (10%) at the dose of 388 μg/cm2 (273 cm2/cm2). In contrast, exposure to CuO NPs resulted in a concentration dependent reduction in LDH release based on LDH leakage, with 38% reduction in viability at the highest dose of 52 μg/cm2 (28.3 cm2/cm2). Cells exposed to CuO NPs resulted in a dose dependent cellular membrane toxicity and expressed IL-8 secretion at a global dose five times lower than cells exposed under submerged conditions. However, when comparing the ALI results at the local cellular dose of CuO NPs to the submerged results, the IL-8 secretion was similar. In this study, we demonstrated DAVID as a new exposure tool that helps evaluate aerosol toxicity in simulated lung environment. Our results also highlight the necessity in choosing the right assay endpoints for the given exposure scenario, e.g., LDH for ALI and Deep Blue for submerged conditions for cell viability.

On numerical broadening of particle-size spectra: a condensational growth study using PyMPDATA 1.0

Abstract. This work discusses the numerical aspects of representing the condensational growth of particles in models of aerosol systems such as atmospheric clouds. It focuses on the Eulerian modelling approach, in which fixed-bin discretisation is used for the probability density function describing the particle-size spectrum. Numerical diffusion is inherent to the employment of the fixed-bin discretisation for solving the arising transport problem (advection equation describing size spectrum evolution). The focus of this work is on a technique for reducing the numerical diffusion in solutions based on the upwind scheme: the multidimensional positive definite advection transport algorithm (MPDATA). Several MPDATA variants are explored including infinite-gauge, non-oscillatory, third-order terms and recursive antidiffusive correction (double-pass donor cell, DPDC) options. Methodologies for handling coordinate transformations associated with both particle-size spectrum coordinate choice and with numerical grid layout choice are expounded. Analysis of the performance of the scheme for different discretisation parameters and different settings of the algorithm is performed using (i) an analytically solvable box-model test case and (ii) the single-column kinematic driver (“KiD”) test case in which the size-spectral advection due to condensation is solved simultaneously with the advection in the vertical spatial coordinate, and in which the supersaturation evolution is coupled with the droplet growth through water mass budget. The box-model problem covers size-spectral dynamics only; no spatial dimension is considered. The single-column test case involves a numerical solution of a two-dimensional advection problem (spectral and spatial dimensions). The discussion presented in the paper covers size-spectral, spatial and temporal convergence as well as computational cost, conservativeness and quantification of the numerical broadening of the particle-size spectrum. The box-model simulations demonstrate that, compared with upwind solutions, even a 10-fold decrease in the spurious numerical spectral broadening can be obtained by an apt choice of the MPDATA variant (maintaining the same spatial and temporal resolution), yet at an increased computational cost. Analyses using the single-column test case reveal that the width of the droplet size spectrum is affected by numerical diffusion pertinent to both spatial and spectral advection. Application of even a single corrective iteration of MPDATA robustly decreases the relative dispersion of the droplet spectrum, roughly by a factor of 2 at the levels of maximal liquid water content. Presented simulations are carried out using PyMPDATA – a new open-source Python implementation of MPDATA based on the Numba just-in-time compilation infrastructure.

Microphysical characteristics of precipitating cumulus cloud based on airborne Ka-band cloud radar and droplet measurements

Based on cloud-probe data and airborne Ka-band cloud radar data collected in Baoding on 5 August 2018, the microphysical structural characteristics of cumulus (Cu) cloud at the precipitation stage were investigated. The cloud droplets in the Cu cloud were found to be significantly larger than those in stratiform (STF) cloud. In the Cu cloud, most cloud particles were between 7 and 10 μm in diameter, while in the STF cloud the majority of cloud particles grew no larger than 2 μm. The sensitivity of cloud properties to aerosols varied with height. The cloud droplet effective radius showed a negative relationship with the aerosol number concentration (Na) in the cloud planetary boundary layer (PBL) and upper layer above the PBL. However, the cloud droplet concentration (Nc) varied little with decreased Na in the high liquid water content region above 1500 m. High Na values of between 300 and 1853 cm−3 were found in the PBL, and the maximum Na was sampled near the surface in August in the Hebei region, which was lower than that in autumn and winter. High radar reflectivity corresponded to large FCDP (fast cloud droplet probe) particle concentrations and small aerosol particle concentrations, and vice versa for low radar reflectivity. Strong updrafts in the Cu cloud increased the peak radius and Nc, and broadened cloud droplet spectrum; lower air temperature was favorable for particle condensational growth and produced larger droplets.摘要在积云中, 大多数云粒子的直径在7到10微米之间, 而在层云中, 大多数云粒子的直径不超过2微米. 云滴有效半径与云中行星边界层(PBL)及PBL上层的气溶胶数浓度(Na)呈负相关. 在1500米以上的高液态水含量区域, 云滴浓度(Nc)变化不大, Na含量降低. 高雷达反射率对应于大的FCDP云粒子浓度和小的气溶胶粒子浓度. 积云中的强上升气流增加了云滴的峰值半径和数浓度, 拓宽了云滴谱; 较低的空气温度有利于粒子的凝结增长, 并产生较大的液滴.

The dependence of pool scrubbing decontamination factor on particle number density: modeling based on bubble mass and energy balances

ABSTRACT Pool scrubbing is one of the promising means for mitigating radioactive aerosol release into the environment in nuclear severe accident scenarios. The influence of operational conditions on its performance is therefore of much interest. This paper focuses on the influence of particle number density found in our experiments. The experiments, conducted for insoluble monodispersed (0.5 µm) particles, indicated a sharp decrease in the decontamination factor (DF) for inlet number densities higher than ~1 × 1011 m−3. A model is proposed based on a hypothesis that particle removal becomes inefficient at high number densities because particle condensational growth is limited by the depletion of vapor supersaturation in rising bubbles. The model calculates the magnitude of supersaturation from the bubble mass and energy balances considering the condensational vapor consumption and heat addition by all particles in the bubble, where the rate of condensation on each particle is dependent on supersaturation. The particle size, condensationally growing with time, is then used in the calculation of centrifugal particle removal. It is shown that the model reproduces qualitatively the experimental dependence of DF on particle number density, providing further proof that such dependence is a physical reality deserving attention in the evaluation of pool scrubbing performance.

Numerical study on the effect of the supersaturated vapor on the performance of a gas cyclone

Gas cyclones are widely used to purify waste gases but are not effective in collecting fine particles. The cloud-air-purifying (CAP) technology was recently developed to overcome this deficiency by unitizing the supersaturated vapor in the cyclone. This paper presents a CFD study on the CAP cyclone. The condensational growth of particles is implemented in the CFD model. Its positive effect on the collection efficiency is confirmed and more clearly understood from microscopic investigations. Particles with the same initial size can grow into a narrow size distribution, yet the average growth ratio is increased with the increase of the supersaturation ratio and the decrease of the initial size, resulting in a significant improvement of the collection efficiency for fine particles, particularly in controlling those escaping through the middle-reverse flow. A predictive model is developed to consider the effect of the vapor. These results can help understand and optimize the CAP cyclone.

Investigation into water vapor and flue gas temperatures on the separation capability of a novel cyclone separator

Using water mist or vapor to help collect fine particles has been attracting increasing attention. A new fine particle separation technology which combines the centrifugal force field with the supersaturated vapor is recently proposed to realize the high removal efficiency of PM2.5 in gas cyclones. Different from the operation of a traditional cyclone, in this new cyclone, the operational temperature can be a key variable that determines the particle condensational growth and the related separation efficiency, which has not been studied in cyclones. Therefore, this paper investigates the effect of the temperatures in such purification process. Both the temperatures of the water vapor and the flue gas are studied. The effects of the two temperatures on the performance of the cyclone are studied in terms of the overall removal efficiencies, grade removal efficiencies and the morphology change of the dust particles by SEM. Additionally, the experimental results are analyzed based on the classical heterogeneous nucleation theories. The results indicate that higher water vapor temperature can improve the removal through decreasing the surface tension, which makes the particles easier to nucleate and grow in size. On the contrary, higher flue gas temperature leads to a decrease in efficiency, because the saturation deceases although the nucleation rate and critical supersaturation for particle nucleation shows conducive to nucleation.

Condensational particle growth device for reliable cell exposure at the air-liquid interface to nanoparticles.

A first-of-its-kind aerosol exposure device for toxicity testing, referred to as the Dosimetric Aerosol in Vitro Inhalation Device (DAVID), was evaluated for its ability to deliver airborne nanoparticles to lung cells grown as air-liquid interface (ALI) cultures. For inhalation studies, ALI lung cell cultures exposed to airborne nanoparticles have more relevancy than the same cells exposed in submerged culture because ALI culture better represents the respiratory physiology and consequently more closely reflect cellular response to aerosol exposure. In DAVID, water condensation grows particles as small as 5 nm to droplets sized > 5 μm for inertial deposition at low flow rates. The application of DAVID for nanotoxicity analysis was evaluated by measuring the amount and variability in the deposition of uranine nanoparticles and then assessing the viability of ALI cell cultures exposed to clean-air under the same operational conditions. The results showed a low coefficient of variation, < 0.25, at most conditions, and low variability in deposition between the exposure wells, trials, and operational flow rates. At an operational flow rate of 4 LPM, no significant changes in cell viability were observed, and minimal effects observed at 6 LPM. The reliable and gentle deposition mechanism of DAVID makes it advantageous for nanoparticle exposure.

Optimization of fibrous air filter on the basis of particle condensational growth during the air cooling and de-humidification process using mathematical modeling

Indoor ultra-fine particles have significantly adverse effects on human health. Under the condition of high concentration, the widely used HEPA (High-Efficiency Particulate Air) requires expensive operation cost. Previous study indicated that air cooling and dehumidification system could greatly increase particle size (from dozens of nanometers to several micrometers) due to the condensation effect during the process of air conditioning in hot and humid regions. Because of the condensational growth of particles, low-grade air filters can be used to achieve high efficiency and lower cost. This study developed mathematical model to predict particle size variation in cooling and dehumidification process and investigate its effect on fibrous filter performance. The steps are as follows: 1) Based on the state-space model, distributions of supersaturation ratio in condensational dehumidification process were simulated; 2) The modified Lagrangian method and SSR-based model were used to simulate particle trajectory and size increase; 3) Based on the prediction of condensational growth of particles, the air filter performance model were adopted to investigate the condensation effect on fibrous filter performance. The results shows that condensational dehumidification improve the filtration efficiency of middle-efficiency fibrous from 72% to 92%, quality factor from 0.016 to 0.031. Utilization of condensational dehumidification could decrease energy consumption of fibrous filtration system by 53%. This study is of great significance to improve the effectiveness and economy through the coordinated control for indoor pollutants, temperature and humidity control in humid and hot climate region.

Simulation of fine polydisperse particle condensational growth under an octadecane–nitrogen atmosphere

The evolution of particle size distribution (PSD) of fine polydisperse particles at high number concentrations (>105cm−3) was simulated through a combined model employing direct quadrature method of moments (DQMOM) with heat and mass transfer equations. The PSD was assumed to retain log-normal distribution during the heterogeneous condensation process. The model was first verified by exact solution and experimental data prior to investigating the influence of initial conditions on final PSD under an octadecane–nitrogen atmosphere. Low particle number concentrations and high vapor concentrations were beneficial to shift the PSD to larger particles having a narrower distribution. Additionally, vapor depletion has more influence on the final PSD than the heat release parameter for a number concentration of 106cm−3. This study may assist the design process of a gas–solid separating cyclone, to eliminate dust from high-temperature volatiles by pyrolysis of solid fuels.

P.4.b.014 - The prevalence of posttraumatic stress disorder and mental health of Korean Vietnam War veterans 40 years after the war

The public health impact of particulate matter in ambient air with a size of 2.5 μm or smaller (PM2.5) has been of great concern. It is well known that PM2.5 is much more harmful to human health than coarse particles. To remove PM2.5, most air purifiers on the market have been equipped with a high efficiency particulate air (HEPA) filter. Under the circumstances that generate PM2.5 aerosols at high concentrations such as during indoor cooking or in work places, HEPA-grade filters are neither durable nor applicable because of their high replacement cost. Thus, a large number of cooks and workers are exposed to intensive emissions of PM2.5 without proper filtration. In this paper, we introduce a novel concept to remove PM2.5 without HEPA filters. A key idea is to use the condensational growth of particles. Once the particles have grown to a few micron, they are much easier to remove because of their increased inertia. Based on this, we developed the first prototype of a filter-free particle filtration unit consisting of an air saturator (equipped with water spray nozzles), a condenser in which humid air is cooled down to a supersaturation state and thereby allows particles to grow by condensation, and a multi-nozzle-impactor assembly for collecting the grown particles downstream of the condenser. We started with a small-scale model, and then demonstrated that a large-scale prototype could remove organic, inorganic, and metallic ultrafine particles with a collection efficiency of larger than 80% at a volume flow rate of 50–92 L/s.

CCN production by new particle formation in the free troposphere

Abstract. Global models predict that new particle formation (NPF) is, in some environments, responsible for a substantial fraction of the total atmospheric particle number concentration and subsequently contributes significantly to cloud condensation nuclei (CCN) concentrations. NPF events were frequently observed at the highest atmospheric observatory in the world, on Chacaltaya (5240 m a.s.l.), Bolivia. The present study focuses on the impact of NPF on CCN population. Neutral cluster and Air Ion Spectrometer and mobility particle size spectrometer measurements were simultaneously used to follow the growth of particles from cluster sizes down to ∼ 2 nm up to CCN threshold sizes set to 50, 80 and 100 nm. Using measurements performed between 1 January and 31 December 2012, we found that 61 % of the 94 analysed events showed a clear particle growth and significant enhancement of the CCN-relevant particle number concentration. We evaluated the contribution of NPF, relative to the transport and growth of pre-existing particles, to CCN size. The averaged production of 50 nm particles during those events was 5072, and 1481 cm−3 for 100 nm particles, with a larger contribution of NPF compared to transport, especially during the wet season. The data set was further segregated into boundary layer (BL) and free troposphere (FT) conditions at the site. The NPF frequency of occurrence was higher in the BL (48 %) compared to the FT (39 %). Particle condensational growth was more frequently observed for events initiated in the FT, but on average faster for those initiated in the BL, when the amount of condensable species was most probably larger. As a result, the potential to form new CCN was higher for events initiated in the BL (67 % against 53 % in the FT). In contrast, higher CCN number concentration increases were found when the NPF process initially occurred in the FT, under less polluted conditions. This work highlights the competition between particle growth and the removal of freshly nucleated particles by coagulation processes. The results support model predictions which suggest that NPF is an effective source of CCN in some environments, and thus may influence regional climate through cloud-related radiative processes.

Development of filter-free particle filtration unit utilizing condensational growth: With special emphasis on high-concentration of ultrafine particles

The public health impact of particulate matter in ambient air with a size of 2.5 μm or smaller (PM2.5) has been of great concern. It is well known that PM2.5 is much more harmful to human health than coarse particles. To remove PM2.5, most air purifiers on the market have been equipped with a high efficiency particulate air (HEPA) filter. Under the circumstances that generate PM2.5 aerosols at high concentrations such as during indoor cooking or in work places, HEPA-grade filters are neither durable nor applicable because of their high replacement cost. Thus, a large number of cooks and workers are exposed to intensive emissions of PM2.5 without proper filtration. In this paper, we introduce a novel concept to remove PM2.5 without HEPA filters. A key idea is to use the condensational growth of particles. Once the particles have grown to a few micron, they are much easier to remove because of their increased inertia. Based on this, we developed the first prototype of a filter-free particle filtration unit consisting of an air saturator (equipped with water spray nozzles), a condenser in which humid air is cooled down to a supersaturation state and thereby allows particles to grow by condensation, and a multi-nozzle-impactor assembly for collecting the grown particles downstream of the condenser. We started with a small-scale model, and then demonstrated that a large-scale prototype could remove organic, inorganic, and metallic ultrafine particles with a collection efficiency of larger than 80% at a volume flow rate of 50–92 L/s.

Efficient collection of viable virus aerosol through laminar‐flow, water‐based condensational particle growth

State-of-the-art bioaerosol samplers have poor collection efficiencies for ultrafine virus aerosols. This work evaluated the performance of a novel growth tube collector (GTC), which utilizes laminar-flow water-based condensation to facilitate particle growth, for the collection of airborne MS2 viruses. Fine aerosols (<500 nm) containing MS2 coliphage were generated from a Collison nebulizer, conditioned by a dilution dryer and collected by a GTC and a BioSampler. The GTC effectively condensed water vapour onto the virus particles, creating droplets 2-5 μm in diameter, which facilitated collection. Comparison of particle counts upstream and downstream revealed that the GTC collected >93% of the inlet virus particles, whereas the BioSampler's efficiency was about 10%. Viable counts of the GTC-collected viruses were also one order of magnitude higher than those of the BioSampler (P = 0·003). The efficiency of the GTC for the viable collection of MS2 viruses exceeds that of industry standard instrument, the BioSampler, by a factor of 10-100. This study reveals that the GTC is an effective collector of viable MS2 aerosols, and concludes the instrument will be an effective tool for studying viable virus aerosols and the inhalation risks posed by airborne viruses.

Combustion of nano-sized aluminum particles in steam: Numerical modeling

A model of the dynamics and mechanism of combustion of an ensemble of nanoscale aluminum particles in a steam is theoretically studied for adiabatic conditions. The formation of condensed phase is modeled for conditions when the homogeneous nucleation of gaseous Al2O3 species, processes of condensation/evaporation and coagulation of particles are taken into account. The model is used for studying the effects of the particle size, equivalence ratio, and chemical kinetics on the burning characteristics of aluminum-particle/steam mixtures. The calculated rate of combustion is limited by the rate of condensation growth of particles contained thermally unstable Al2O3 species. The details of the mechanism of interaction of the gas-phase reactions and the formation of particles are discussed. The results of numerical calculations are compared with experimental results of nano-aluminum dust combustion.

Towards the identification of molecular constituents associated with the surfaces of isoprene-derived secondary organic aerosol (SOA) particles

Abstract. Secondary organic aerosol (SOA) particle formation ranks among the least understood chemical processes in the atmosphere, rooted in part in the lack of knowledge about chemical composition and structure at the particle surface, and little availability of reference compounds needed for benchmarking and chemical identification in pure and homogenous form. Here, we synthesize and characterize SOA particle constituents consisting of the isoprene oxidation products α-, δ-, and cis- and trans-β-IEPOX (isoprene epoxide), as well as syn- and anti-2-methyltetraol. Paying particular attention to their phase state (condensed vs. vapor), we carry out a surface-specific and orientationally selective chemical analysis by vibrational sum frequency generation (SFG) spectroscopy of these compounds in contact with a fused silica window. Comparison to the vibrational SFG spectra of synthetic isoprene-derived SOA particle material prepared at the Harvard Environmental Chamber yields a plausible match with trans-β-IEPOX, suggesting it is an abundant species on their surfaces, while the other species studied here, if present, appear to be SFG inactive and thus likely to be localized in a centrosymmetric environment, e.g., the particle bulk. No match is found for authentic SOA particle material collected at the site of the Amazonian Aerosol Characterization Experiment (AMAZE-08) with the surface SFG spectra of the compounds surveyed here, yet we cannot rule out this mismatch being attributable to differences in molecular orientation. The implications of our findings for SOA formation are discussed in the context of condensational particle growth and reactivity.

Moderated, Water-Based, Condensational Particle Growth in a Laminar Flow.

Presented is a new approach for laminar-flow water condensation that produces saturations above 1.5 while maintaining temperatures of less than 30°C in the majority of the flow and providing an exiting dew point below 15°C. With the original laminar flow water condensation method, the particle activation and growth occurs in a region with warm, wetted walls throughout, which has the side-effect of heating the flow. The "moderated" approach presented here replaces this warm region with a two sections - a short, warm, wet-walled "initiator", followed by a cool-walled "moderator". The initiator provides the water vapor that creates the supersaturation, while the moderator provides the time for particle growth. The combined length of the initiator and moderator sections is the same as that of the original, warm-walled growth section. Model results show that this new approach reduces the added heat and water vapor while achieving the same peak supersaturation and similar droplet growth. Experimental measurements confirm the trends predicted by the modeling.

Temperature-dependent accumulation mode particle and cloud nuclei concentrations from biogenic sources during WACS 2010

Abstract. Submicron aerosol particles collected simultaneously at the mountain peak (2182 m a.s.l.) and at a forested mid-mountain site (1300 m a.s.l.) on Whistler Mountain, British Columbia, Canada, during June and July 2010 were analyzed by Fourier transform infrared (FTIR) spectroscopy for quantification of organic functional groups. Positive matrix factorization (PMF) was applied to the FTIR spectra. Three PMF factors associated with (1) combustion, (2) biogenics, and (3) vegetative detritus were identified at both sites. The biogenic factor was correlated with both temperature and several volatile organic compounds (VOCs). The combustion factor dominated the submicron particle mass during the beginning of the campaign, when the temperature was lower and advection was from the Vancouver area, but as the temperature started to rise in early July, the biogenic factor came to dominate as a result of increased emissions of biogenic VOCs, and thereby increased formation of secondary organic aerosol (SOA). On average, the biogenic factor represented 69% and 49% of the submicron organic particle mass at Whistler Peak and at the mid-mountain site, respectively. The lower fraction at the mid-mountain site was a result of more vegetative detritus there, and also higher influence from local combustion sources. The biogenic factor was strongly correlated (r~0.9) to number concentration of particles with diameter (Dp)&gt; 100 nm, whereas the combustion factor was better correlated to number concentration of particles with Dp&lt;100 nm (r~0.4). The number concentration of cloud condensation nuclei (CCN) was correlated (r~0.7) to the biogenic factor for supersaturations (S) of 0.2% or higher, which indicates that particle condensational growth from biogenic vapors was an important factor in controlling the CCN concentration for clouds where S≥0.2%. Both the number concentration of particles with Dp&gt;100 nm and numbers of CCN for S≥0.2% were correlated to temperature. Considering the biogenic influence, these results indicate that temperature was a primary factor controlling these CCN concentrations at 0.2% supersaturation.

Development and evaluation of a novel bioaerosol amplification unit (BAU) for improved viral aerosol collection

A novel bioaerosol amplification unit (BAU) that increases the size of viral particles by condensational growth has been designed and evaluated for improved viral aerosol collection. In the BAU, water was used as the condensing vapor to preserve viability of virus, and supersaturation conditions for condensational growth of particles were achieved by either conductive cooling or mixing with hot, water-saturated air. MS2 bacteriophage (28 nm) was used as the test agent, and changes in collection efficiency of an SKC Biosampler with and without the BAU were determined by assaying plaque-forming units (PFUs) in the collection medium. Results showed that the mixing-type BAU (mBAU) was a promising device for improved viral aerosol sampling. The number of viruses (PFU) collected in the Biosampler increased 2–3 fold after passing through the mBAU. However, PFU increases in the cooling-type BAU (cBAU) were insignificant. APS results likewise showed that the mBAU was better in growing particles than the cBAU. After growth, number concentrations of particles larger than 327 nm in the cBAU and mBAU increased 1.3 and 15.0 fold, respectively. The relatively high molecular diffusivity of water vapor compared to the thermal diffusivity of air and the temperature gradient in the cBAU tube limited particle growth by causing condensation to occur predominantly at the colder wall.

Influence of chemical composition and microstructure on the hygroscopic growth of pyrogenic aerosol

The hygroscopic properties of a model smoke aerosol series including ammonium sulfate, levoglucosan, and oxalic and humic acids were investigated. The condensation growth of particles and the relative humidity of direct and inverse particle-droplet phase transitions were measured with a tandem differential mobility analyzer. The data were obtained in the range of relative humidity from 4 to 95% at 298 K. Experimental growth factors were compared to the results of Koehler theory by using contemporary models of water activity in particles. It was shown that the hygroscopic properties of the aerosols were substantially different from the hygroscopic properties of the corresponding bulk phases. It was found that a complex microstructure of nanoparticles resulted in excess volume absorption of water, in some cases causing their full deliquescence at lower relative humidities than in macrosystems of identical composition. From the measurement data, a parametrization of hygroscopic particle growth was performed. The results of parametrization can be used to construct refined models of a smoke aerosol.

Atmospheric new particle formation at Utö, Baltic Sea 2003-2005

Nearly 3 yr (March 2003–December 2005) of continuous particle number size distribution measurements have been conducted at the island of Utö in the Baltic Sea. The measured particle size range was from 7 to 530 nm. During the measurement period, a total of 103 regional new-particle formation events were observed. The characteristics of the nucleation events at Utö were similar to those reported in the literature in other Nordic sites, though measured condensation sinks were rather high (geometric mean of 3.8 × 10-3 s-1) during event days. Clear evidence was found that new particles nucleate regionally near Utö, rather than are transported from greater distances. However, the Baltic Sea seems to have an inhibiting effect on new-particle formation. The boreal forest areas in the continental Finland were found to have an enhancing effect on the nucleation probability in Utö, suggesting that at least some of the precursor gases for nucleation and/or condensational growth of particles originate from these forests. In addition to regional new-particle formation events, a total of 94 local events were observed in Utö. These are short-lived events with a small footprint area, and can at least partly be tracked down to the emissions of ship traffic operating at Utö.