Urban atmospheric dusts

Fig. 1. The size distribution of particles in an urban atmospheric dust showing the three size modes. Based on Whitby, 1977 4).

Table I Characteristics of the Three Size Modes of Urban Atmospheric Dust...

Diverse techniques have been employed to identify the sources of elements in atmospheric dust (and surface dust) (Table V). Some involve considering trends in concentration and others use various statistical methods. The degree of sophistication and detail obtained from the analyses increases from top left to bottom right of the Table. The sources identified as contributing the elements in rural and urban atmospheric dusts are detailed in Table VI. The principal sources are crustal material, soil, coal and oil combustion emissions, incinerated refuse emissions, motor vehicle emissions, marine spray, cement and concrete weathering, mining and metal working emissions. Many elements occur in more than one source, and they are classified in the... 

Since the majority of the elements in surface dust arise from deposited aerosol and added soil it is not surprising to find strong linear relationships between the concentrations of the elements in an atmospheric dust and street or house dust. This is illustrated by the two examples given in Fig. 8 for remote house dust vs urban atmospheric dust and street dust vs rural atmospheric dust. As discussed above crustal/soil material is a major component of atmospheric dust and the soil based elements in the atmospheric dust are Al, Ca, Fe, Mg, Mn, Ni, K, Si and Ti. The elements As, Br, Cd, Cl, Co, Cu, Pb, Rb, Se, V, and Zn are, on the other hand, enriched in atmospheric dust. The same elemental distribution applies to surface dust, but in this case their concentrations (compared on a mass basis) are reduced presumably due to dilution with soil. However, the elements enriched in the atmosphere remain enriched in the surface dusts. 

Fig. 8. Relationship between the concentration of elements in surface and atmospheric dusts (a) house dust vs urban atmospheric dust, (b) street dust vs rural atmospheric dust [M] is the concentration of element M.

It is remarkable that, except for local hot-spots such as around industrial sites, mining areas and volcanoes, the elemental compositions of atmospheric dust in similar locations, such as remote or rural or urban are relatively constant over the world. This suggests either common sources, or a dominant source, or good mixing and transport of the dust around the globe. In fact all three factors have a role in determining the uniformity. Because of the consistent composition it is possible to estimate the median concentrations of the elements in atmospheric dusts in similar, but widely separated, locations. These estimates are given in columns 2 to 7 in Table n. The concentrations of the elements in the atmospheric dust are expressed as mass per volume of air. For remote locations (columns 2 to 5) the concentrations are in ng m 3, whereas for rural and urban areas (columns 6 and 7) the elemental concentrations are in xg m-3. 

Coal ash, coal fly ash, power station fly ash, incinerator ash, vehicle exhaust particulates, urban dust, atmospheric dust, metal smelter dust, welding dust, diesel particulates, particulates on filter media Sewage sludge, wastewater... 

The chemical composition of groundwaters depends on many causes rainwaters have a notable chemical charge, especially in marine salts (M. Schoeller, 1962) and in elements which originate from atmospheric dusts (silts, clays, pollen and bacteria) or from urban and industrial activity (Crozat, 1978 Dessfevre Delepoule, 1978). 

Middleton N, Yiallouros P, Kleanthous S et al (2008) A 10-year time-series analysis of respiratory and cardiovascular morbidity in Nicosia, Cyprus the effect of short-term changes in air pollution and dust storms. Environ Health 7 39 Millan M, Salvador R, Mantilla E et al (1997) Photo-oxidant dynamics in the Mediterranean basin in summer results from European research projects. J Geophys Res 102 8811-8823 Millan MM, Sanz Ml, Salvador R et al (2002) Atmospheric dynamics and ozone cycles related to nitrogen deposition in the western Mediterranean. Environ Pollut 118 167-186 Mostafa AR, Hegazi AH, El-Gayar MS et al (2009) Source characterization and the environmental impact of urban street dusts from Egypt based on hydrocarbon distributions. Fuel 88 95-104... 

Vallius M, Ruuskanen J, Mirme A et al (2000) Concentration and estimated soot content of PMj, PM2.5 and PMio in a subarctic urban atmosphere. Environ Sci Technol 34 1919-1925 Vrekoussis M, Liakakou E, Kocak M et al (2005) Seasonal variability of optical properties of aerosols in the Eastern Mediterranean. Atmos Environ 39 7083-7094 Waisel Y, Ganor E, Epshtein V et al (2008a) Airborne pollen, spores, and dust across the East Mediterranean Sea. Aerobiology 24 125-131... 

The significance of dust is mentioned above. Industrial and urban atmospheres contain more or less solid particles consisting of carbon, soot, sand, oxides, and salts, e.g. chloride and sulphate. Many of these substances attract moisture from the air some of them also attract polluting and corrosive gases. The salts cause high conductivity, and carbon particles can lead to a large number of small galvanic elements because the particles act as efficient cathodes after deposition on the surface. 

Sources of lead in surface water or sediment include deposits of lead-containing dust from the atmosphere, waste water from industries that handle lead (primarily iron and steel industries and lead producers), urban runoff, and mining piles. 

Road transport is an important contributor to primary emissions of PM (soot, wear particles and road dust) and also a source of secondary particles formed by condensation of gaseous species (mainly S- and N-compounds and organics) emitted by the tailpipe and partly also by the wear of brakes and tyres. Thus, PM emissions from road traffic are responsible for an important proportion of the exceedances of the PM10 and PM25 Air Quality Limit Values established by the European legislation for the protection of the human health (2008/50/EC [17]). The daily (50 pg m-3) and annual (40 pg m 3 ) limit values for PM10 (atmospheric particles with mean aerodynamic diameter <10 pm) and the annual limit value for PM2.5 (25 pg m-3) (in force from 2015) concentrations in ambient air are indeed exceeded mostly in the urban areas (Fig. 1 [17]). 

Deb, M.K., Thakur, M., Mishra, R.K. and Bodhankar, N. (2002) Assessment of atmospheric arsenic level in airborne dust particulates of an urban city of central India. Water Air and Soil Pollution, 140(1-4), 57-71. 

Despite the low average consumption of pesticides, in the sporadic reports available, it could be seen that even the roadside dusts, rural and urban soils and the underwater sediments are contaminated. Many pesticides are degrading the Indian environment, even though faster dissipation and possible degradation of POPs chemicals like HCHs and DDTs were observed in Indian soils by the tropical climate of India (Pillai, 1986). Such a phenomenon of dissipation in the dry season was substantiated by Ramesh et al. (1991) in the river sediments (Fig. 9.2). Further, the relative flux of residues into the aquatic environment is smaller than the amount volatilized to the atmosphere in tropical countries like India (Tanabe et al., 1991). 

These few examples show the desperate need for further research and assessment in the chemistry and all aspects of air pollution. One might question whether we have knowledge of all urban sources of hydrocarbons that are important to atmospheric interactions. Does all rubber dust from automotive tires remain as dust What is the contribution of asphalt roadways to atmospheric hydrocarbons Is the contribution from such unassessed and other unknown anthropogenic sources sufficient in itself to account for health-damaging levels of ozone These and other questions require immediate attention if we are to realize the goal of effective pollution control. 

The budgets of the separate boxes are discussed first. Concerning the continental atmosphere it is, to begin with, subdivided into three smaller boxes, i.e., the atmosphere over industrial and urban regions, dusty continental atmosphere, meaning arid regions hit by wind blown dust, and clean continental atmosphere. 

---