One important physical effect of urban air pollution is that it reduces visibility and illumination. A smog layer can cut illumination by 10 percent in summer and 20 percent in winter. Ultraviolet radiation is absorbed by smog, which at times completely prevents these wavelengths from reaching the ground. Reduced ultraviolet radiation may prove to be of importance in permitting increased bacterial activity at ground level. City smog cuts horizontal visibility to some one-fifth to one-tenth of the distance normal for clean air. Where atmospheric moisture is sufficient, the hygroscopic particles acquire water films and can cause formation of true fog with near-zero visibility. Over cities, winter fogs are much more frequent than over the surrounding countryside.
A related effect of the urban heat island is the general increase in cloudiness and precipitation over a city, as compared with the surrounding countryside. This increase results from intensified convection generated by heating of the lower air. For example, it has been found that thunderstorms over the city of London produce 30 percent more rainfall over the city than over the surrounding country. Increased precipitation over an urban area is estimated to average from 5 to 10 percent over the normal for the region in which it lies.
A large city produces a heat island. Within this warm air layer, pollutants are trapped beneath an inversion lid. The layer of polluted air takes the form of a broad pollution dome centered over the city when winds are very light or near calm. However, when there is general air movement in response to the pressure gradient field, the pollutants are carried far downwind to form a pollution plume. In this situation pollution from one city affects another and generally the pollutants remain over the land, contaminating suburban and rural areas over a wide zone.
Locals hypothesize that the legacy of Italian blood and culture in Cologne, colonized by the Romans more than 1500 years ago, makes the people more jovial and lighthearted. Cologne is the largest city on the Rhine.
Kolsch is not only the dialect spoken here but, also the name of their own top-fermented beer. There are more than 4,000 pubs, restaurant's and brewery taverns in Cologne.
Unlike many of the world's large cities, Cologne, with a population of over a million, gets better every day, there are more things to do and see, more new and innovative buildings... more
Travel is an opportunity to learn, whether geography, languages, history or other subjects.
Cologne is situated on the beautiful Rhine River.