Anthropogenic activities particle

Inorganic and organic compounds are often present in the environment in complex forms. Levels of contaminating metals and molecules are variable, depending on the natural conditions and anthropogenic activities. The contaminants may be airborne as vapour, droplets or dust particles, and in the soil in aqueous or particulate forms. In the case of aqueous systems, they can exist as emulsions, as dissolved ions or molecules and as suspended or sedimentary particles. Environmental particles have been reviewed in the first two volumes of this series [1,2]. 

K-means cluster analysis is an excellent method for the reduction of individual-partide datai if extra clusters are used to allow for the non-spherical shape and natural variability of atmospheric particles. The "merge" method for choosing seedpoints is useful for detecting the types of lew abundance particles that are interesting for urban atmospheric studies. Application to the Phoenix aerosol suggests that the ability to discriminate between various types of crustal particles may yield valuable information in addition to that derived from particle types more commonly associated with anthropogenic activity. 

In remote alpine areas where anthropogenic pollution is limited, the retention of nutrients associated with trapped particles may become apparent. Case studies in two Rocky Mountain lakes (Kootenay and Arrows) indicated a reduced biological productivity, which is not compensated - as is usually the case in the European Alps -by enhanced nutrient input due to anthropogenic activities in the catchment [5]. 

The first major link between the indirect effects of aerosol particles and climate is whether there has been an increase in particles and in CCN due to anthropogenic activities. As discussed in Chapter 2, anthropogenic emissions of particles and of gas-phase precursors to particles such as S02 have clearly increased since preindustrial times, and it is reasonable that CCN have also increased. Ice core data provide a record of some of the species that can act as CCN. Not surprisingly, sulfate and nitrate in the ice cores have increased substantially over the past century (Mayewski et al., 1986, 1990 Laj et al., 1992 Fischer et al., 1998). For example, Figure 14.43 shows the increases in sulfate and nitrate since preindustrial times in an ice core in central Greenland (Laj et al., 1992). Sulfate has increased by 300% and nitrate by 200%. This suggests that sulfate and nitrate CCN also increased, although not necessarily in direct proportion to the concentrations in the ice core measurements. 

As discussed in Section C.la, sea salt particles in the marine boundary layer have been shown to likely play a major role in backscattering of solar radiation (Murphy et al., 1998), i.e., to the direct effect of aerosol particles. However, they also contribute to the indirect effect involving cloud formation, since they can also act as CCN. Since such particles are a natural component of the marine atmosphere, their contribution will not play a role in climate change, unless their concentration were somehow to be changed by anthropogenic activities, e.g., through changes in wind speed over the... 

On the other hand, aerosol particles from anthropogenic activities tend to be concentrated over or near industrial regions in the continents. Because both the direct and indirect effects of particles are predominantly in terms of scattering solar radiation, their effects are expected primarily during the day. 

Particles in the atmosphere arise from natural sources, such as windbome dust, sea spray and volcanoes, and from anthropogenic activities, such as combustion of fuels. Emitted directly as particles (primary aerosol) or formed in the atmosphere by gas-to-particle conversion processes (secondary aerosol), atmospheric aerosols are generally considered to be the particles that range in from a few nanometres to tens of micrometres in diameter [1]. 

Several authors confirm that elements related to anthropogenic activities, are concentrated into very small size particles, with a mean aerodynamic diameter less than 2 pm, in the atmosphere. At the same time heavy metals, whose emissions in the atmosphere are related to natural sources, are concentrated into coarse particles with a mean aerodynamic diameter greater than 2 pm (4-10). 

Methods for correcting for grain-size effects in studies on heavy metal concentrations in estuarine and coastal sediments have been discussed by Ackermann (1980). There is, unfortunately, no one standard method for particle-size normalisation and a wide range of techniques are in use (Table 2.3). The method which often involves the least effort is the correction which uses comparison with rubidium (Rb) as a conservative element (Ackermann, 1980). This technique relies on the fact that Rb has a similar ionic radius to potassium (K) and so substitution of Rb for K will take place in clay minerals. Furthermore, Rb is present in the sand fraction in very much smaller concentrations than in the clay or silt fraction and concentrations of the element in sediments are rarely influenced by anthropogenic activity. Another advantage of the use of Rb is that it is often routinely analysed by X-ray fluorescence along with a suite of pollutant trace metals. 

Strontium is widely distributed in the earth s crust and oceans. Strontium is released into the atmosphere primarily as a result of natural sources, such as entrainment of dust particles and resuspension of soil. Radioactive strontium is released into the environment as a direct result of anthropogenic activities. Stable strontium can be neither created nor destroyed. However, strontium compounds may transform into other chemical compounds. Radioactive strontium is formed by nuclear reactions. Radioactive decay is the only mechanism for decreasing the concentration of radiostrontium. The half-life of 90Sr is 29 years. 

The long-range transport of Saharan and Asian dust has been identified as the dominant source of mineralic particles over the Atlantic, the Arctic, and the Pacific (SCOPE 1979 Rahn et al. 1979 Duce et al. 1980 Uematsu etal. 1983 Parrington and Zoller 1984). Other important sources of naturally emitted metal compounds are volcanoes (Zoller 1983), forest fires which may be of natural occurrence as well as originate from anthropogenic activities and exudations from vegetation (Pacyna 1986a, b). 

Mineral dust is emitted from both natural and anthropogenic activities. Natural emissions arise by wind acting on undisturbed source regions. Anthropogenic emissions result from human activity, including (1) land-use changes that modify soil surface conditions and (2) climate modifications that, in turn, alter dust emissions. Such modifications include changes in windspeeds, clouds and precipitation, and the amounts of airborne soluble material, such as sulfate, that may become attached to mineral dust particles and render them more susceptible to wet removal. 

Natural emissions include lead released from volcanoes, seawater sprays, forest fires, and wind-bome soil particles in remote areas. These releases are typically to the atmosphere and are set forth in Table 4.2. Cumulative atmospheric releases in the natural source category average 19,000 MT/year and a median of 12,000 MT/year (Nriagu, 1989). It should be noted that one has to distinguish between tme natural sources and emissions and those which are more inclusive, i.e., background lead estimates. Such background levels can represent releases to the atmosphere and subsequent deposition of reentrained dusts contaminated with lead from past anthropogenic activities. 

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