Cities create climatic conditions of their own through their physical structure and urban activities. A. The amount of heat produced in a city will be reduced when cities use the heat from cars to warm homes. B. The built-up landscape of the city readily becomes a heat island, with greater water runoff and special climatic conditions such as low relative humidity and increased air turbulence. C. The materials from which cities are built and the effects of pollution domes help make urban areas warmer than rural areas. D. Cities tend to be warmer than their surrounding areas, in part because they produce heat by burning fuel for heating, powering vehicles, and industrial production. E. In most cities, the heating that results from solar radiation is intensified by carbon dioxide, a gas that is present at very high concentrations in cities' atmospheres. F. During periods without rainfall, the air in cities heats up and causes winds to slow down, with the result that pollutants are not dispersed.