Background aerosols

Measurements of ozone concentration in the ozone layer in the stratosphere are made in the less intense Huggins band to avoid complete absorption of the laser radiation. Again, the two or three wavelength DIAL method is used to make allowance for background aerosol scattering. A suitable laser for these measurements is the XeCl pulsed excimer laser (see Section 9.2.8) with a wavelength of 308 nm, close to the peak absorption of the Huggins... 

Lannefors H, Hansson HC, Granat L. 1983. Background aerosol composition in southern Sweden — Fourteen micro and macro constituents measured in seven particle size intervals at one site during one year. Atmos Environ 17 87-101. 

Charlson, R. J., A. H. Vanderpol, D. S. Covert, A. P. Waggoner, and N. C. Ahlquist, H2S04 (NH4)2S04 Background Aerosol Optical Detection in the St. Louis Region, Atmos. Environ., 8, 1257-1267 (1974a). 

Clarke, A. D., and R. J. Charlson, Radiative Properties of the Background Aerosol Absorption Component of Extinction, Science, 229, 263-265 (1985). 

Covert, D. S., North Pacific Marine Background Aerosol Average Ammonium to Sulfate Molar Ratio Equals 1, J. Geophys. Res., 93, 8455-8458 (1988). 

Borrmann, S S. Solomon, J. E. Dye, D. Baumgardner, K. K. Kelly, and K. R. Chan, Heterogeneous Reactions on Stratospheric Background Aerosols, Volcanic Sulfuric Acid Droplets, and Type I Polar Stratospheric Clouds Effects of Temperature Fluctuations and Differences in Particle Phase, J. Geophys. Res., 102, 3639-3648 (1997b). 

Zhang, R M.-T. Leu, and M. J. Molina, Formation of Polar Stratospheric Clouds on Preactivated Background Aerosols, Geophys. Res. Lett., 23, 1669-1672 (1996). 

Fieure8 One hour averages of (a) JN02 and (b) JO( D) as a function of solar zenith angle under cloudless conditions. The solid line represents a best fit of the upper limit of measured photolysis frequencies, corresponding to a clear atmosphere with background aerosol load. The broken lines denote the results of model simulations based on different model aerosol scenarios (from figure 6 of Reuder and Schwander 1999). 

Niemi JV, Saarikoski S, Tervahattu H, Makela T, Hillamo R, Vehkamaki H, Sogacheva L, Kulmala M (2006) Changes in background aerosol composition in Finland during polluted and clean periods studied by TEM/EDX individual particle analysis. Atmos Chem Phys 6 5049-5066... 

Vester BP, Ebert M, Bamert EB et al (2007) Composition and mixing state of the urban background aerosol in the Rhein-main area (Germany). Atmos Environ 41 6102-6115... 

Querol X, Alastuey A, Pey J, Cusack M, Perez N, Mihalopoulos N, Theodosi C, Gerasopoulos E, Kubilay N, Kofak M (2009) Variability in regional background aerosols within the Mediterranean. Atmos ChemPhys 9 4575 -591. doi 10.5194/acp-9-4575-2009... 

Perez N, Castillo S, Pey J, Alastuey A, Viana M, Querol X (2008) Interpretation of the variability of regional background aerosols in the Western Mediterranean. Sci Total Environ 407 527-540... 

Hidy, G., and Blanchard, C. L. (2005). The Midlatitude North American Background Aerosol and Global Aerosol Variation. /. Air Waste Manage. Assoc. 55,1585-1599. 

It is important to understand the sources and loss mechanisms of stratospheric sulfate aerosols. These aerosols are linked to the decrease in ozone at mid-latitudes because they hydrolyse N2O5, reducing the amount of NOx that would otherwise limit the efficiency of chlorine-catalysed ozone depletion. In addition these aerosols scatter light, cooling the planet [127]. Their concentration increases dramatically following major volcanic eruptions however they are always present at background levels. The source of these background aerosols is a matter of debate. In 1976 Paul Crutzen presented the idea that sulfate aerosols result from the photolysis of carbonyl sulphide [128] ... 

The problem of the global background aerosol has been briefly discussed above. The sophisticated nature and substantial uncertainty of this notion have been mentioned. Apparently, of all the global regions most favourable for studies of GBA the Antarctic continent is the best. 

The non-sea spray effects on the levels of Ca, Cl, K, Mg and Na as well as sulfate in snow samples from Terra Nova Bay were ascertained (66). Sampling mode and analytical approach (based on IC) fully complied with criteria previously set up. For Ca and K it was concluded that a nearly uniform background aerosol characterizes the area investigated, which adds to the contribution of marine spray. The oxidation of DMS, in turn, is the dominant source of non-sea spray sulfate. 

Physical and chemical evolution of target aerosol system in isolation and externally-mixed with a different seed background aerosol population with gas phase photochemistry. 

The results of the experiment (Chen and Lelevkin, 2000) show, that before the Pinatubo volcano eruption, in the background period the area of 24-29 km was marked out with local minimmns in the correlation function at which the main mass of flie background aerosol was concentrated. This happened at the height of the maximum ozone concentration (24-27 km), not in the field of the Junge aerosol layer, so one can expect that the ozone accumulation takes place there, i.e. 6)3 is generated from the photooxidation of SO2 by air oxygen (Ivlev et. al., 1990) S02 C ) + 2 0( P). 

The foregoing discussion, excluding the photooxidation of DMS, is summarized in Fig. 17 (Kellogg et al., 1972). It can be seen that the sulfuric acid droplets formed are generally neutralized by ammonia. This is the reason why background aerosol particles consist mainly of ammonium sulfate (see Chapter 4). 

It follows from this discussion that the study of properties and effects of atmospheric aerosol particles exceeds the scope of air chemistry. Considering the complexity of the problem, we restrict our discussion in the following to the presentation of formation processes and principal physical and chemical properties of background aerosol in the troposphere and stratosphere. 

It should be mentioned that the size distributions presented in Figs 26 and 27 are typical of a polluted atmosphere. Unfortunately, very little information is available about the background aerosol filling 80-90 % of the troposphere. These... 

An important step in the understanding of the formation and composition of tropospheric background aerosol was provided by the work of Fenn et al. (1963) who demonstrated that in aerosol samples collected in Greenland13, 40 % of the large particles consisted of sulfate. This finding was confirmed by American authors... 

The composition of background aerosol particles, including a part of Aitken range, was investigated by morphological identification by A. Meszaros and Vissy (1974) on the basis of membrane filter samples collected in remote oceanic air in the Southern Hemisphere. They found that 75-95 % of the particles was composed of the following four substances (Fig. 33) ... 

Because the mass of ammonium sulfate and sulfuric acid particles is mainly in the size range of active condensation nuclei, it is believed that this process provides a very effective removal mechanism for the tropospheric background aerosol. However, we have to emphasize that other processes are also operating in the cloud to remove small aerosol particles, of which the most important process is the coagulation of particles and cloud drops. As we have seen (Subsection 4.1.1), thermal coagulation is particularly effective in the range of very small particles inactive in condensation. To estimate this process, let us consider a cloud in which the number concentration of drops with radius rc is Nc. If the number concentration... 

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