The urban atmosphere

In the section above we began to look at human influence on the atmosphere. The changes wrought by humans are important, though often subtle on the global scale. It is in the urban atmosphere where human influence shows its clearest impact, so it is necessary to treat the chemistry of the urban atmosphere as a special case. 

In urban environments there are pollutant compounds emitted to the atmosphere directly and these are called primary pollutants. Smoke is the archetypical example of a primary pollutant. However, many compounds undergo reactions in the atmosphere, as we have seen in the section above. The products of such reactions are called secondary pollutants. Thus, many primary pollutants can react to produce secondary pollutants. It is the distinction between primary and secondary pollution that now governs our understanding of the difference 

---

Jantunen, M. (1999). Risks, estimation, management and jxircepnon. In The Urban Atmosphere and Its Effects (P. Brimblecomhe and B. Maynard, Eds.). Imperial College Press (in press). 

The sewer processes take place in a complex system. They proceed in one or more of the five phases the suspended water phase, the biofilm, the sewer sediments, the sewer atmosphere and the sewer walls, and by exchange of relevant substances across the interphases. Processes that proceed in the sewer system affect other parts of the urban system, i.e., the urban atmosphere with malodorous substances. Furthermore, wastewater treatment plants and local receiving waters receive not just those substances discharged into the sewer but also products that are the result of the sewer processes (Figures 1.1 and 1.3). 

The first three aspects are related to the release of volatile substances into the gas phase of the sewer and from there into the urban atmosphere. These volatile compounds are H2S and organic odorous compounds produced under anaerobic conditions in the wastewater or associated biofilm and sediment. 

Exchange of volatile compounds across the air-water interface, e.g., oxygen (reaeration that affects aerobic or anaerobic conditions) and release of odorous substances Release of odorous substances to the urban atmosphere and change of reaeration due to a lower atmospheric oxygen concentration Extent of the processes... 

If ozone-olefin adducts are stable in the gas phase, as a recent study hinted, then they are almost certainly present in the urban atmosphere. Their concentrations will depend on their stability in the sunlit atmosphere. If present, they are expected to be very reactive. 

Sawicki, E., S. P. McPherson, T. W. Stanley, J. Meeker, and W. C. Elbert. Quantitative composition of the urban atmosphere in terms of polynuclear aza heterocyclic compounds and aliphatic and polynuclear aromatic hydrocarbons. Int. J. Air Water Pollut. 9 515-524, 1%5. 

Rogge WF, Hildemann LM, Mazurek MA, Cass GR, Simoneit BRT, Sources of fine organic aerosol 6. Cigarette smoke in the urban atmosphere. Environ Sci Technol 28 1375-1388, 1994. 

Baek, S. O., M. E. Goldstone, P. W. W. Kirk, J. N. Lester, and R. Perry, Phase Distribution and Particle Size Dependency of Polycyclic Aromatic Hydrocarbons in the Urban Atmosphere, Chemosphere, 22, 503-520 (1991b). 

Harrison, R. M M. Jones, and G. Collins, Measurements of the Physical Properties of Particles in the Urban Atmosphere, Atmos. Environ., 33, 309-32f (f999). 

Cardelino, C. A., and W. L. Chameides, An Observation-Based Model for Analyzing Ozone Precursor Relationships in the Urban Atmosphere, J. Air Waste Manage. Assoc., 45, 161-180 (1995). 

Duncan, B. N., and W. L. Chameides, Effects of Urban Emission Control Strategies on the Export of Ozone and Ozone Precursors from the Urban Atmosphere to the Troposphere, J. Geophys. Res., 103, 28159-28179 (1998). 

Kumar P, Robins A, Vardoulakis S, Britter R (2010) A review of the characteristics of nanoparticles in the urban atmosphere and the prospects for developing regulatory controls. Atmos Environ 44 5035-5052... 

Kumar P, Ketzel M, Vardoulakis S, Pirjola L, Britter R (2011) Dynamics and dispersion modelling of nanoparticles from road traffic in the urban atmospheric environment -a review. J Aerosol Sci 42 580-603... 

Shi JP, Evans DE, Khan AA, Harrison RM (2001) Sources and concentration of nanoparticles (<10 nm diameter) in the urban atmosphere. Atmos Environ 35 1193-1202... 

Dall Osto M, Thorpe A, Beddows DCS, Harrison RM, Barlow IF, Dunbar T, Williams PI, Coe H (2011) Remarkable dynamics of nanoparticles in the urban atmosphere. Atmos Chem Phys 11 6623-6637... 

Shi PJ, Khan AA, Harrison RM (1999) Measurements of ultra fine particle concentration and size distribution in the urban atmosphere. Sci Total Environ 235 51-64... 

Caricchia, A.M., Chiavarini, S., Pezza, M., 1999. Polycyclic aromatic hydrocarbons in the urban atmospheric particulate matter in the city of Naples (Italy). Atmos. Environ. 33, 3731-3738. 

We have employed two multi-elemental techniques (INAA and ICP-AES) to determine sulphur, halogens and 14 other trace elements in urban summer rainfall. Quality control was assured using NBS reference materials. The overall accuracy and precision of these two methods makes possible the routine analysis of many environmentally important trace elements in acid rain related investigations. Enrichment factor calculations showed that several elements including S, Cu, Zn and Cr were abnormally enriched in the urban atmosphere. A comparison of three separate sites showed a strong gradient of metal deposition from the industrial to the outlaying areas. 

A marked by-product of oxidation in the urban atmosphere, often associated, but not exclusive to, urban air pollution is PAN. PAN is formed by... 

Farrar, N.J., Hamer, T., et al. (2004a) Field deployment of thin film passive air samplers for persistent organic pollutants a study in the urban atmospheric boundary layer. Environmental Science and Technology, 39(1) 42-A8. 

Kwamena, N.O.A., Clarke, J.P., et al (2007) Assessing the importance of heterogeneous reactions of polycyclic aromatic hydrocarbons in the urban atmosphere using the multimedia urban model. Atmospheric Environment, 41(1) 37-50. 

Tn the presence of sunlight and oxides of nitrogen (NOa,), hydrocarbons react to form new products, some of which are called oxidants. The most commonly investigated photochemically produced oxidants in the urban atmosphere are ozone (O3), nitrogen dioxide (NO2), and peroxy-acetylnitrate (PAN). 

Aldehydes are primary and secondary pollutants in the urban atmosphere, and since laboratory studies indicate that they photo-oxidize to form peroxides, the presence of peroxides in the atmosphere seems evident. 

In the early 1950 s Haagen-Smit (8) stated that the oxidizing effect of smog resulted from the combined action of NO2 and O3 and peroxides. However no quantitative or qualitative study of hydroperoxides in the urban atmosphere has been reported. 

Whether or not H2O2 is present in the urban atmosphere and, if it is, the concentration at which it exists are studied here. 

---