Jorma Joutsensaari

An amorphous solid state of biogenic secondary organic aerosol particles

Secondary organic aerosol (SOA) particles are formed in the atmosphere from condensable oxidation products of anthropogenic and biogenic volatile organic compounds (VOCs). On a global scale, biogenic VOCs account for about 90% of VOC emissions and of SOA formation (90 billion kilograms of carbon per year). SOA particles can scatter radiation and act as cloud condensation or ice nuclei, and thereby influence the Earth’s radiation balance and climate. They consist of a myriad of different compounds with varying physicochemical properties, and little information is available on the phase state of SOA particles. Gas–particle partitioning models usually assume that SOA particles are liquid, but here we present experimental evidence that they can be solid under ambient conditions. We investigated biogenic SOA particles formed from oxidation products of VOCs in plant chamber experiments and in boreal forests within a few hours after atmospheric nucleation events. On the basis of observed particle bouncing in an aerosol impactor and of electron microscopy we conclude that biogenic SOA particles can adopt an amorphous solid—most probably glassy—state. This amorphous solid state should provoke a rethinking of SOA processes because it may influence the partitioning of semi-volatile compounds, reduce the rate of heterogeneous chemical reactions, affect the particles’ ability to accommodate water and act as cloud condensation or ice nuclei, and change the atmospheric lifetime of the particles. Thus, the results of this study challenge traditional views of the kinetics and thermodynamics of SOA formation and transformation in the atmosphere and their implications for air quality and climate.

Airway Exposure to Silica-Coated TiO2 Nanoparticles Induces Pulmonary Neutrophilia in Mice

The importance of nanotechnologies and engineered nanoparticles has grown rapidly. It is therefore crucial to acquire up-to-date knowledge of the possible harmful health effects of these materials. Since a multitude of different types of nanosized titanium dioxide (TiO(2)) particles are used in industry, we explored their inflammatory potential using mouse and cell models. BALB/c mice were exposed by inhalation for 2 h, 2 h on 4 consecutive days, or 2 h on 4 consecutive days for 4 weeks to several commercial TiO(2) nanoparticles, SiO(2) nanoparticles, and to nanosized TiO(2) generated in a gas-to-particle conversion process at 10 mg/m(3). In addition, effects of in vitro exposure of human macrophages and fibroblasts (MRC-9) to the different particles were assessed. SiO(2)-coated rutile TiO(2) nanoparticles (cnTiO(2)) was the only sample tested that elicited clear-cut pulmonary neutrophilia. Uncoated rutile and anatase as well as nanosized SiO(2) did not induce significant inflammation. Pulmonary neutrophilia was accompanied by increased expression of tumor necrosis factor-alpha (TNF-alpha) and neutrophil-attracting chemokine CXCL1 in the lung tissue. TiO(2) particles accumulated almost exclusively in the alveolar macrophages. In vitro exposure of murine and human macrophages to cnTiO(2) elicited significant induction of TNF-alpha and neutrophil-attracting chemokines. Stimulation of human fibroblasts with cnTiO(2)-activated macrophage supernatant induced high expression of neutrophil-attracting chemokines, CXCL1 and CXCL8. Interestingly, the level of lung inflammation could not be explained by the surface area of the particles, their primary or agglomerate particle size, or radical formation capacity but is rather explained by the surface coating. Our findings emphasize that it is vitally important to take into account in the risk assessment that alterations of nanoparticles, e.g., by surface coating, may drastically change their toxicological potential.

Generation of nanometer-size fullerene particles via vapor condensation

Abstract Ultrafine (30–40 nm) fullerene particles were generated via vapor condensation in a continuous flow system starting from pure C 60 and mixed fullerene extract (C 60 /C 70 ). Gas-phase particle size distributions were measured using a condensation particle counter and differential mobility analyzer. Particle morphology and crystallinity were studied by SEM and TEM. Particles were partly amorphous at 400°C, and became crystalline C 60 when processed above 500°C. The particles had an average size of 30, 35 and 40 nm and total number concentrations of 2.2×10 6 , 3.5×10 6 , and 5.0×10 6 number of particles/cm 3 , respectively at 500, 525 and 550°C.

Estimating the Viscosity Range of SOA Particles Based on Their Coalescence Time

Copyright 2014 American Association for Aerosol Research

Mobility size development and the crystallization path during aerosol decomposition synthesis of TiO2 particles

Abstract Size and morphology transformation as well as the crystallization path of monodisperse titanium dioxide particles were studied in aerosol flow reactor. Solid, hydrated titanium oxide particles were prepared from titanium alkoxide by a droplet hydrolysis and a subsequent size classification. The particles were carried to a reactor in air at temperature range of 20–1500°C. The inlet particle size of 100 and 200 nm gradually decreased 40% with increasing temperature as investigated by a tandem differential mobility analyzer (TDMA) system. The decrease was due to decomposition of the hydrated Ti–O particles, densification of the forming TiO2 particles, and a phase change from anatase to rutile. Above 1000°C the mobility size increased due to crystal-habit formation that created faceted, elongated particles and consequently an increased dynamic shape factor. Microstructure investigations with a transmission electron microscope (TEM) showed that nanocrystalline anatase particles were present at 600°C and transformed to rutile up to 1100°C with simultaneous crystallite growth. Single-crystal rutile particles were observed at temperatures with the increased mobility diameters.

Multiply twinned C60 and C70 nanoparticles

Abstract Nanoparticles of C 60 and C 70 prepared by aerosol flow reactor method show a well developed morphology when produced at sufficiently high temperatures. Hexagonal plate shaped, icosahedral and decagonal particles of C 60 and C 70 are formed. Morphology and internal structure are studied by scanning and transmission electron microscopy. The plate-like particles are lamellar–twinned and grow preferentially on the side-faces by nucleation of new molecular layers along re-entrant corners. The decagonal multiply twinned nanoparticles are strained and show a distinct deviation from cubic symmetry. Some of the C 70 particles exhibit a modulated structure to accommodate the internal stress; this is possible because of the ellipsoidal shape of the C 70 molecule.

Contrasting responses of silver birch VOC emissions to short- and long-term herbivory

There is a need to incorporate the effects of herbivore damage into future models of plant volatile organic compound (VOC) emissions at leaf or canopy levels. Short-term (a few seconds to 48 h) changes in shoot VOC emissions of silver birch (Betula pendula Roth) in response to feeding by geometrid moths (Erannis defoliaria Hübner) were monitored online by proton transfer reaction time-of-flight mass spectrometry (PTR-TOF-MS). In addition, two separate field experiments were established to study the effects of long-term foliage herbivory (FH, 30-32 days of feeding by geometrids Agriopis aurantiaria (Clerck) and E. defoliaria in two consecutive years) and bark herbivory (BH, 21 days of feeding by the pine weevil (Hylobius abietis L.) in the first year) on shoot and rhizosphere VOC emissions of three silver birch genotypes (gt14, gt15 and Hausjärvi provenance). Online monitoring of VOCs emitted from foliage damaged by geometrid larvae showed rapid bursts of green leaf volatiles (GLVs) immediately after feeding activity, whereas terpenoid emissions had a tendency to gradually increase during the monitoring period. Long-term FH caused transient increases in total monoterpene (MT) emissions from gt14 and sesquiterpene (SQT) emissions from Hausjärvi provenance, mainly in the last experimental season. In the BH experiment, genotype effects were detected, with gt14 trees having significantly higher total MT emissions compared with other genotypes. Only MTs were detected in the rhizosphere samples of both field experiments, but their emission rates were unaffected by genotype or herbivory. The results suggest that silver birch shows a rapid VOC emission response to short-term foliage herbivory, whereas the response to long-term foliage herbivory and bark herbivory is less pronounced and variable at different time points.

Effective Density and Morphology of Particles Emitted from Small-Scale Combustion of Various Wood Fuels

The effective density of fine particles emitted from small-scale wood combustion of various fuels were determined with a system consisting of an aerosol particle mass analyzer and a scanning mobility particle sizer (APM-SMPS). A novel sampling chamber was combined to the system to enable measurements of highly fluctuating combustion processes. In addition, mass-mobility exponents (relates mass and mobility size) were determined from the density data to describe the shape of the particles. Particle size, type of fuel, combustion phase, and combustion conditions were found to have an effect on the effective density and the particle shape. For example, steady combustion phase produced agglomerates with effective density of roughly 1 g cm(-3) for small particles, decreasing to 0.25 g cm(-3) for 400 nm particles. The effective density was higher for particles emitted from glowing embers phase (ca. 1-2 g cm(-3)), and a clear size dependency was not observed as the particles were nearly spherical in shape. This study shows that a single value cannot be used for the effective density of particles emitted from wood combustion.

Generation of nanophase fullerene particles via aerosol routes

Abstract Nanocrystalline and nanometer-size fullerene particles have been generated by aerosol routes starting from a solution of mixed fullerene extract in toluene. Nanocrystalline fullerene particles have been produced by spray drying, and ultrafine particles have been formed by vapor condensation. Gas-phase particle size distributions were determined with a differential mobility analyzer, and particle morphology and crystallinity were studied by scanning and transmission electron microscopies. When the processing temperature was increased from 20 to 400 °C, the average particle size was reduced from 140 to 100 nm due to particle densification. At higher temperatures of 500 and 600 °C, nanometer-size (about 20 nm), spherical fullerene particles were formed via vapor condensation. Transmission electron microscopy analysis indicated that a few nanometer-size crystallites were formed already at 200 °C and the crystallite size was increased to about 10 nm at 500 °C.

On the determination of electrostatic precipitator efficiency by differential mobility analyzer

Abstract In order to determine penetration curve of the electrostatic precipitator (ESP) as a function of aerosol particle diameter in the range of 10–1000 nm measurement series were carried out in real scale power plant conditions. Differential mobility particle sizing (DMPS) system was used to measure the particle mobility distributions before and after ESP. MICRON -algorithm (constrained regularization) was used to invert mobility distribution to the corresponding number distributions. Penetration curve was calculated from the measured number distributions.