A Atmospheric composition

Air pollution makes the transmissivity of urban atmospheres significantly lower than that of nearby rural areas. During the period 1960 to 1969, the atmospheric transmissivity over Detroit averaged 9 per cent less than that for nearby areas, and reached 25 per cent less under calm conditions. The increased absorption of solar radiation by aerosols plays a role in daytime heating of the boundary layer pollution dome (see Figure 12.23A) but is less important within the urban canopy layer, which extends to mean rooftop height (see Figure 12.23B). Table 12.2 compares urban and rural energy budgets for the Cincinnati region during summer 1968

Figure 12.25 Diurnal variation of energy balance components for a N-S-oriented urban canyon in Vancouver, British Columbia, having white concrete walls, no windows, and a width/height ratio of 1:1, during the period 9 to 11 September 1973. (A) The average for the E-facing wall. (B) The average for the floor. (C) Averages of fluxes through the canyon top.

Figure 12.25 Diurnal variation of energy balance components for a N-S-oriented urban canyon in Vancouver, British Columbia, having white concrete walls, no windows, and a width/height ratio of 1:1, during the period 9 to 11 September 1973. (A) The average for the E-facing wall. (B) The average for the floor. (C) Averages of fluxes through the canyon top.

Source: After Nunez and Oke, from Oke (1978).

under anticyclonic conditions with < 3/10 cloud and a wind speed of <2 m s-1. The data show that pollution reduces the incoming short-wave radiation, but a lower albedo and the greater surface area within urban canyons counterbalance this. The increased urban Ln at 12:00 and 20:00 LST is largely offset by anthropogenic heating (see below).

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Renewable Energy 101

Renewable Energy 101

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable. The usage of renewable energy sources is very important when considering the sustainability of the existing energy usage of the world. While there is currently an abundance of non-renewable energy sources, such as nuclear fuels, these energy sources are depleting. In addition to being a non-renewable supply, the non-renewable energy sources release emissions into the air, which has an adverse effect on the environment.

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