Atmospheric aerosol particles

The aerosol particles in the atmosphere are liquid or solid particles. Their sizes range from a fraction of a micron to several hundreds of microns (pm). Various names, such as Aitken nuclei, smokes, fumes or hazes (for the smaller particles) and dusts, mists, fogs or ash (for larger ones) have been used in the nomenclature of atmospheric aerosols. 

All aerosol particles are formed by condensation of gases or vapours or by mechanical processes. They may be transformed by coagulation or condensation at the same time as they are transported by air movement and dilution. They might disappear from the atmosphere and settle on some surfaces which act as a sink. The residence times of aerosol particles in the atmosphere vary from some days near the earth s surface in the troposphere to a year or more in the stratosphere. 

As is known, the size of an atom is of the order of 10 m or 10 pm or 0.1 nm (the Bohr radius r = 0.5292 x 10 m), while the size of an atomic nucleus is of the order of 10 m or 10 pm or 10 nm. Thus an aerosol particle having a diameter of some nanometres (or 10 pm) is a hundred times or more larger than an atom and so includes some number of atoms or clusters of atoms. 

Primary particles, such as road dust, salt (sea-) spray from the oceans and cement dust do not change form after emission, whereas a substantial fraction of mass of the secondary particles, such as photochemically produced sulfates and photochemical smog, is formed by in situ chemical reactions involving gases. 

Monitoring and particular aerosol characterisation studies have led to a revolution in both our knowledge and our understanding of atmospheric aerosols. Atmospheric sciences, particle technology, industrial hygiene and health effect studies of pollutants are different contributing fields in that context. 

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Table 7-4 Oxyacids, their salts, and ionized forms that could exist in atmospheric aerosol particles...

Gill, P. S., T. E. Graedel, and C. J. Weschler, Organic Films on Atmospheric Aerosol Particles, Fog Droplets, Cloud Droplets, Raindrops, and Snowflakes, Rev. Geophys. Space Phys., 21, 903-920 (1983). 

Indeed, based on the number, surface, and volume distributions shown in Fig. 9.6, Whitby and co-workers suggested that there were three distinct groups of particles contributing to this atmospheric aerosol. Particles with diameters >2.5 yu,m are identified as coarse particles and those with diameters 2.5 pm are called fine particles. The fine particle mode typically includes most of the total number of particles and a large fraction of the mass, for example, about one-third of the mass in nonurban areas and about one-half in urban areas. The fine particle mode can be further broken down into particles with diameters between 0.08 and 1-2 yxm, known as the accumulation range, and those with diam-... 

Kerminen, V.-M., and A. S. Wexler, Growth Laws for Atmospheric Aerosol Particles An Examination of the Bimodality of the Accumulation Mode, Atmos. Environ., 29, 3263-3275 (1995). 

Noble, C. A., and K. A. Prather, Real-Time Size Measurement of Correlated Size and Composition Profiles of Individual Atmospheric Aerosol Particles," Environ. Sci. Technol., 30, 2667-2680 (1996). 

Quinn, P. K., D. S. Covert, T. S. Bates, V. N. Kapustin, D. C. Ranisey-Bell, and L. M. Mclnnes, Dimethylsulfide Cloud Condensation Nuclei Climate System Relevant Size-Resolved Measurements of the Chemical and Physical Properties of Atmospheric Aerosol Particles, J. Geophys. Res., 98, 10411-10427 (1993). 

Eichel, C., M. Kramer, L. Schiitz, and S. Wurzler, The Water-Soluble Fraction of Atmospheric Aerosol Particles and Its Influence on Cloud Microphysics, J. Geophys. Res., 101, 29499-29510 (1996). 

Vented Underground Burst. An underground detonation which produces no visible fireball, but which results in the release of volatile radionuclides through fissures or other vents, produces a single particle class— atmospheric aerosol particles with condensable radionuclides deposited on their surface. Radionuclide abundance is independent of particle size. 

Measuring the Strong Acid Content of Atmospheric Aerosol Particles... 

The climate effects of atmospheric aerosol particles are a matter of continuous interest in the research community. The aerosol-climate effects are divided into two groups The direct effect represents the ability of the particle population to absorb and scatter short-wave radiation - directly affecting the radiation balance. These direct effects depend primarily on the aerosol optical properties and particle number size distribution, as the particle size significantly affects the scattering efficiency of... 

Addition of EGA to the analysis of atmospheric aerosol particles has permitted an independent speciation and determination of the nitrogenous component for samples which have not had chemical or physical pretreatment. The discovery from ESCA analyses that a substantial fraction of the particulate nitrogen exists chemically bound to the carbonaceous fraction has been confirmed by EGA. The indication from ESCA and EGA that inorganic sulfate... 

The study described here demonstrates that ESCA provides information regarding the chemical nature of the surface of an unperturbed sample which would be difficult to acquire by other methods. A major weakness of ESCA, the necessity of exposing the sample to vacuum, together with its attendant problem of sample volatilization, can also be one of its strengths. The volatility of some nitrogenous species in atmospheric aerosol particles can be used to provide strong evidence for chemical identity of ionic compounds (e.g., ammonium nitrate) rather than simply ionic identities as provided by wet chemical methods. This volatility is accelerated by x-ray irradiation, so that similar results could be achieved only by extended vacuum exposure alone if another analytical technique were used. Also, with ESCA, volatile losses can be conveniently monitored since the sample remains in the spectrometer throughout the process. 

Molnar, A., Meszaros, E., Hansson, H. C., Karlsson, H., Gelencser, A., Kiss, G., and Krivacsy, Z. (1999).The importance of organic and elemental carbon in the fine atmospheric aerosol particles. Atmos. Environ. 33, 2745-2750. 

Pio, C. A., Castro, L. M., and Ramos, M. O. (1993). Differentiated determination of organic and elemental carbon in atmospheric aerosol particles by a thermal-optical method. In Physico-Chemical Behaviour of Atmospheric Pollutants, Report EUR 15609/2 EN, Ange-letti, G., and Restelli, G, eds., Proceedings of the Sixth European Symposium, Vol. 2, Varese, 18-22 October, pp. 706-711. 

Figure 7.1 Major sources and modes of atmospheric aerosol particles and principal removal mechanisms (Whitby and Cantrell, 1976 Seinfeld and Pandis, 1998).

Dod, R.L., Gundel, L.A., Benner, W.H. and Novakov, T. (1984) Non-ammonium reduced nitrogen species in atmospheric aerosol-particles. Sci. Total Environ., 36, 277-282. 

Gill, P.S., Graedel, T.E. and Weschler, C.J. (1983) Organic films on atmospheric aerosol-particles, fog droplets, cloud droplets, raindrops and snowflakes. Rev. Geophys., 21, 903-920. 

Shimmo, M., A. Piia, K. Hartonem, et al. 2004. Identification of organic compounds in atmospheric aerosol particles by on-line supercritical fluid extraction-liquid chromatography-gas chromatography-mass spectrometry./. Chromatogr. A 1022 151-159. 

However, the thermal fluctuations are not the only process that could perturb the propagation of ultrashort laser pulses through the atmosphere. Aerosol particles, like water droplets or dust, can have dimensions of several tens of microns, comparable with the filament diameter they could seriously harm the delicate dynamical balance required to propagate filaments. 

Figure 1. Chemical processes associated with an atmospheric aerosol particle.

Figure 1 shows a schematic of a typical atmospheric aerosol particle (if such an entity can be assumed to exist). The particle consists of sulfates, nitrates, water, ammonium, elemental and organic carbon, metals, and dust. After a primary particle is emitted, gas-phase reactions occur, converting oxides of nitrogen to nitric acid, sulfur dioxide to sulfuric acid, and hydrocarbons to oxidized, low-vapor-pressure condensable organics. 

Atmospheric aerosol particles modify the radiative transfer in the atmosphere and they have an impact on the cloud formation. Therefore, they alter the weather and they have an impact on climate. The anthropogenic part of this modification of the state of the atmosphere is currently not well understood and it raises the largest uncertainties with respect to climate change (see the IPCC report 2007). We developed a new on-line model system to investigate the aerosol-radiation-interaction on the regional scale. 

Hanel G. and Thudium J., Mean bulk densities of samples of dry atmospheric aerosol particles a summary of measured data. Pageoph. , 115, 199-803 (1977). 

Meszaros a., On the size distribution of atmospheric aerosol particles of different composition. Atmos. Environ. , 11, 1075-1081 (1977). 

There has been recent interest in a somewhat different aspect of adsorption and reaction on metal oxides photocatalysis. The interest stems partially from that role that some transition-metal oxides can play in photochemical reactions in the atmosphere. Atmospheric aerosol particles can act as substrates to catalyze heterogeneous photochemical reactions in the troposphere. Most tropospheric aerosols are silicates, aluminosilicates and salts whose bandgaps are larger than the cutoff of solar radiation in the troposphere (about 4.3 eV) they are thus unable to participate directly in photoexcited reactions. However, transition-metal oxides that have much smaller bandgaps also occur as aerosols — the most prevalent ones are the oxides of iron and manganese — and these materials may thus undergo charge-transfer excitations (discussed above) in the pres-... 

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