Urban aerosols

Hansen, J. E., W. C. Wang, and A. A. Lacis, 1979. Climatic effects of atmospheric aerosols, Proc. Conf. on Aerosols Urban and Rural Characteristics, Source and Transport Studies, New York Academy of Sciences, New York. 

In the cases that accurate measurements of UV flux at the earth s surface have been published and discussed in the literature, an attenuation of UV flux (global, i.e. direct plus diffuse) is apparent for absorbing aerosols, urban or rural (see figure 3 ) [Lorente at al., 1993].The authors describe different types of aerosol according to their climatology (origin). The four cases in Barcelona, Spain correspond to ... 

Keywords Cloud chemistry Dust Heterogeneous chemistry Ice photochemistry Organic aerosols Urban grime Vibrational overtone absorption... 

Fig. 6. Size distribution of an urban aerosol showing the three modes containing much of the aerosol mass. The fine mode contains particles produced by condensation of low volatility gases. The mid-range, or accumulation mode, results from coagulation of smaller aerosols and condensation of gases on preexisting particles. Coarse particulates, the largest aerosols, are usually generated mechanically.

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, ). 

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. 

Table VI. Sources of Elements, Anions and Cations in Urban and Rural Aerosols ...

Stephanou EG, N Stratigakis (1993) Oxocarboxylic and a,co-dicarboxylic acids photooxidation products of biogenic unsaturated fatty acids present in urban aerosols. Environ Sci Technol 27 1403-1407. 

Dragoescu, C., Friedlander, S. (1989) Dynamics of the aerosol products of incomplete combustion in urban atmospheres. Aerosol... 

For the Great Lakes, especially for the Lake St. Clair collection site, industrial sources and urban lead aerosol fallout from the Detroit area were major sources. 

Pyrethroids are a class of synthetic chemicals that are similar in structure to natural pyrethrins. They have been used in field crops and urban pest management for nearly 30 years, and within the last 5 to 10 years new products have been registered for specific use against stored-product insects. Resmethrin is labeled for use as an aerosol in food plants, mills, and warehouse facilities, but could have potential side effects such as discoloration of surfaces and odor contamination and may be more appropriate for use in empty facilities. Labels generally state to cover any food prior to application. The pyrethroids esfenvalerate (Conquer) and prallethrin (Etoc) are also labeled for use in some situations as an aerosol space treatment in... 

Hamester, M., Stechmann, H., Steiger, M. and Dannecker, W. (1994). The origin of lead in urban aerosols - a lead isotopic ratio study. Science of the Total Environment 146/7 321-323. 

The first scientists to investigate the coastal atmospheric presence of APs were Van Ry and Dachs, in a study conducted in the Hudson river estuary. GC-MS analyses showed that atmospheric NP isomer mixtures have a similar composition to technical mixtures, with relatively high total concentrations in the range of 0.0002—0.069 xg m-3 in the gas phase, and 0.0001-0.051 p,gm-3 in the aerosol phase. These concentrations are higher than those of polycyclic aromatic hydrocarbons and up to two orders of magnitude higher than polychlorinated biphenyl concentrations in impacted urban-industrial areas [32]. 

Convincing new information on the health effects of oxidant exposure has emerged from controlled studies on humans, from which tentative dose-response curves have been constructed. These data are reviewed in Chapter 9, with the types of experimental facilities now available for such measurements. The new data show reduced pulmonary function in healthy smokers and nonsmokers after exposure to ozone at 0.37 ppm and higher for 2 h. The federal standard is 0.08 ppm for a I-h exposure.) Other gases and aerosols found in an urban atmosphere were not present in these experiments. 

Organic aerosols formed by gas-phase photochemical reactions of hydrocarbons, ozone, and nitrogen oxides have been identified recently in both urban and rural atmospheres. Aliphatic organic nitrates, such dicarboxylic acids as adipic and glutaric acids, carboxylic acids derived from aromatic hydrocarbons (benzoic and phenylacetic acids) and from terpenes emitted by vegetation, such as pinonic acid from a pinene, have been identified. The most important contribution in this held has been that of Schuetzle et al., who used computer-controlled... 

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