Aerosol particles formation

Ma kela JM, Aalto P, Jokinen V, Pohja T, Nissinen A, Palmroth S, Markkanen T, Seitsonen K, Lihavainen H, Kulmala M (1997) Observations of ultrafine aerosol particle formation and growth in boreal forest. Geophys Res Lett 24 1219-1222... 

When a liquid or solid substance is emitted to the air as particulate matter, its properties and effects may be changed. As a substance is broken up into smaller and smaller particles, more of its surface area is exposed to the air. Under these circumstances, the substance, whatever its chemical composition, tends to combine physically or chemically with other particles or gases in the atmosphere. The resulting combinations are frequently unpredictable. Very small aerosol particles (from 0.001 to 0.1 Im) can act as condensation nuclei to facilitate the condensation of water vapor, thus promoting the formation of fog and ground mist. Particles less than 2 or 3 [Lm in size (about half by weight of the particles suspended in urban air) can penetrate the mucous membrane and attract and convey harmful chemicals such as sulfur dioxide. In order to address the special concerns related to the effects of very fine, iuhalable particulates, EPA replaced its ambient air standards for total suspended particulates (TSP) with standards for particlute matter less than 10 [Lm in size (PM, ). 

Similarly, SO2 and SO3 (SOJ compounds are produced in combustion by the oxidation of sulfur compounds within the fuel source. SO , emitted into the atmosphere can be incorporated into aerosol particles and wet-deposited as corrosive sulfuric acid. Both NO , and SO , emissions contribute to acid rain content from wet deposition, due to their participation in the formation of nitric and sulfuric acid, respectively. 

Before discussing the three categories of delivery device, the nature of the emitted aerosol will be considered. Droplet formation may be characterized in terms of the nature of the propulsive force and the liquid being dispersed, and this topic is dealt with for specific situations in the following sections. However, dry particles, which are delivered from suspension in pMDIs or from DPIs alone or from a blend, must be prepared in respirable sizes. The production of respirable aerosol particles has traditionally been achieved by micronization of the drug [25]. This... 

The formation of aerosol particles was observed [60-63] when ammonia is injected, by reactions of HNOx with undissociated NH3 ... 

It has been found that the "unattached" fraction is an ultrafine particle aerosol with a size range of 0.5 to 3 nm. In order to initiate studies on the formation mechanism for these ultrafine particles, a series of experiments were made in the U.S. Bureau of Mines radon chamber. By introducing SO into the chamber, particles were produced with an ultrafine size distribution. It has been found that the particle formation mechanism is supressed by the presence of radical scavengers. These experiments suggest that radiolysis following the decay of Rn-222 gives rise to the observed aerosol and the properties of the resulting aerosol are dependent on the nature and the amount of reactive gas present. 

It has been found that the activity which is conventionally referred to as the "unattached" fraction is actually an ultrafine particle aerosol with a size range of 0.5 to 3 nm. The hydroxyl radical from water molecule radiolysis is a key element to the particle formation mechanism. By injecting different concentrations of S02 into the test chamber, a possible particle formation mechanism has been suggested as follows Oxidizable species such as S02 reacts promptly with hydroxyl radicals and form a condensed phase. These molecules coagulate and become ultrafine particles. 

In addition to these nuclear reactions, myriads of other gas-phase transformations produce low-vapor pressure species, with the oxidation of SO2 and other reduced sulfur species dominating aerosol formation and growth. Oxidation of SO2 in the gas phase produces H2SO4, a readily condensable species that either combines with other molecules (new particle formation) or condenses on existing aerosols. 

The basic principle for 210Pb dating is that gaseous 222Rn is emitted to the atmosphere from the lithosphere, surface waters and airborne dust and there decays to 210Pb. After formation in the troposphere, 2l0Pb becomes attached to aerosol particles which reside in the atmosphere for only 30 days or less depending on season, latitude, frequency of rainfall, size and altitude of the aerosols, Nevissi et al., [17]1, Schell [26], and Poet et al., [19]. — —... 

Particle size distributions of smaller particles have been made using electrical mobility analyzers and diffusion batteries, (9-11) instruments which are not suited to chemical characterization of the aerosol. Nonetheless, these data have made major contributions to our understanding of particle formation mechanisms (1, 1 ). At least two distinct mechanisms make major contributions to the aerosols produced by pulverized coal combustors. The vast majority of the aerosol mass consists of the ash residue which is left after the coal is burned. At the high temperatures in these furnaces, the ash melts and coalesces to form large spherical particles. Their mean diameter is typically in the range 10-20 pm. The smallest particles produced by this process are expected to be the size of the mineral inclusions in the parent coal. Thus, we expect few residual ash particles smaller than a few tenths of a micrometer in diameter (12). 

Because the aerosol size and composition distributions depend so strongly on the combustion conditions, substantial differences in fine particle formation and emissions are expected between different furnaces, fuels, and operating conditions with the greatest variation in particles smaller than a few tenths of a micron in diameter. 

Improved control devices now frequently installed on conventional coal-utility boilers drastically affect the quantity, chemical composition, and physical characteristics of fine-particles emitted to the atmosphere from these sources. We recently sampled fly-ash aerosols upstream and downstream from a modern lime-slurry, spray-tower system installed on a 430-Mw(e) coal utility boiler. Particulate samples were collected in situ on membrane filters and in University of Washington MKIII and MKV cascade impactors. The MKV impactor, operated at reduced pressure and with a cyclone preseparator, provided 13 discrete particle-size fractions with median diameters ranging from 0,07 to 20 pm with up to 6 of the fractions in the highly respirable submicron particle range. The concentrations of up to 35 elements and estimates of the size distributions of particles in each of the fly-ash fractions were determined by instrumental neutron activation analysis and by electron microscopy, respectively. Mechanisms of fine-particle formation and chemical enrichment in the flue-gas desulfurization system are discussed. 

Flagan, R.C. and Friedlander, S.K. "Particle Formation in Pulverized Coal Combustion-A Review," presented at Symposium on Aerosol Science and Technology, Eight-Second National Meeting of the American Institute of Chemical Engineers, Atlantic City, N.J. 29 August -1 September 1976. 

Hoffmann, T R. Bandur, U. Marggraf, and M. Linscheid, Molecular Composition of Organic Aerosols Formed in a-Pinene/Oj Reaction Implications for New Particle Formation Processes, J. Geophys. Res., 103, 25569-25578 (1998). 

Notholt et al. (1992) and Andres-Hernandez et al. (1996) measured HONO, NO, N02, and aerosol surface areas at both urban and nonurban locations. They observed that at Ispra, Italy, HONO concentrations tended to correlate with N02, NO, and aerosol surface areas. Such studies support the formation of HONO from heterogeneous reactions of N02 at the surfaces of aerosol particles, fogs, buildings, and the ground. 

Different mechanisms of aerosol growth give rise to different so-called growth laws, which are expressions relating the change in particle size (e.g., volume or diameter) with time to the particle diameter. Because different mechanisms of particle formation give rise to different growth laws, one can test experimental data to see which mechanism or combination of mechanisms is consistent with the observations. For a more detailed discussion of this approach, see Friedlander (1977), Heisler and Friedlander (1977), McMurry and Wilson (1982), Pandis et al. (1995), and Kerminen and Wexler (1995). 

Hoppel, W. A., G. M. Frick, J. W. Fitzgerald, and R. E. Larson, Marine Boundary Layer Measurements of New Particle Formation and the Effects Nonprecipitating Clouds Have on Aerosol Size Distribution, J. Geophys. Res., 99, 14443-14459 (1994). 

Evidence for the contribution of the CIO + BrO interaction is found in the detection and measurement of OCIO that is formed as a major product of this reaction, reaction (31a). This species has a very characteristic banded absorption structure in the UV and visible regions, which makes it an ideal candidate for measurement using differential optical absorption spectrometry (see Chapter 11). With this technique, enhanced levels of OCIO have been measured in both the Antarctic and the Arctic (e.g., Solomon et al., 1987, 1988 Wahner and Schiller, 1992 Sanders et al., 1993). From such measurements, it was estimated that about 20-30% of the total ozone loss observed at McMurdo during September 1987 and 1991 was due to the CIO + BrO cycle, with the remainder primarily due to the formation and photolysis of the CIO dimer (Sanders et al., 1993). The formation of OCIO from the CIO + BrO reaction has also been observed outside the polar vortex and attributed to enhanced contributions from bromine chemistry due to the heterogeneous activation of BrONOz on aerosol particles (e.g., Erie et al., 1998). 

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