Saturday, July 11, 2009

These days, I’m sort of hooked up to the environs, so to say. Environment friendliness has become the mantra for many --- unleashing the Earth Hour, etc.

Caught up in a fierce windstorm that sent trees crashing around him and branches flying around his head…swaying violently in the roaring winds, he studied the effects of the storm valley… and closed his eyes to listen to “music of storm”

The primary causes of acid rain—emissions of sulfur dioxide and nitrogen oxide—result mainly from industrial activities that pollute the air. In fact, about two-thirds of the emissions of sulfur dioxide and one-fourth of nitrogen oxide derive from electric-power generation that relies on burning fossil fuels, such as coal. Most coal contains small amounts of sulfur, which is converted to sulfur dioxide when the coal is burned. Although modern power plants use precipitators to remove small particles from the coal smoke, sulfur dioxide is a gas and passes freely up the chimneys.

As it travels in the atmosphere, some sulfur dioxide settles to the ground and is slowly absorbed by soil and plants, but most of it stays in the air for several days. Under the action of sunlight, sulfur dioxide slowly reacts with oxygen and water droplets in the air to form sulfuric acid. If there is ammonia in the air, some of the acid is neutralized to form ammonium sulfate, and a mixture of this chemical and sulfuric acid remains airborne in the form of fine particles and droplets. In dry weather, these particles form a haze that can limit visibility to a few miles. In wet weather, the particles and droplets dissolve in water and are brought to the ground in rain or snow. In this way, production of sulfur dioxide by burning coal in power plants can make the rain acidic hundreds of miles downwind from the source.

Although electric power plants are the most significant producers of the pollutants that cause acid rain, other important sources are industries that use high-sulfur oil as a fuel, and smelters that produce copper and other metals from sulfide ores. There are even natural sources that release sulfur dioxide into the air, such as volcanoes and forest fires.

Acid rain may also result from the conversion of nitrogen oxides in the air to nitric acid. Nitrogen oxides are produced in many processes when coal, oil, or natural gas are burned and are released in large quantities by electric power plants, automobiles, and oil refineries. Once in the air, the nitrogen oxides gradually react with oxygen and moisture to produce nitric acid, in the same way that sulfur dioxide is converted to sulfuric acid. Both types of acid occur together in rain and snow.

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