Control Methods for Air Pollution

This section explores various techniques to mitigate air pollution, focusing on methods to reduce emissions of sulphur dioxide, nitrogen oxides, and hydrocarbons.

Flue gas desulphurization is a key method for reducing sulphur dioxide emissions. There are two main approaches:

1. Wet flue gas desulphurization: Flue gases are passed through a bed of crushed calcium carbonate. Sulphur dioxide reacts with the calcium carbonate, producing solid calcium sulphate.

2. Dry flue gas desulphurization: Hydrated lime is used to absorb the SO2, producing calcium sulphide which is then disposed of in landfills or used to make cement.

Vocabulary: Flue gas - The gas exiting to the atmosphere via a flue, which is a pipe or channel for conveying exhaust gases from a fireplace, oven, furnace, boiler or steam generator.

For reducing nitrogen oxide emissions, flue gas denitrification can be used in power stations. This process involves injecting ammonia or urea, which converts NOx into harmless nitrogen gas.

Highlight: Reducing peak temperatures in any form of combustion will decrease NOx formation, offering another strategy for emission control.

To control hydrocarbon emissions, several methods are employed:

1. Catalytic converters: These devices oxidize hydrocarbons to CO2 and H2O.
2. Vapor collection and incineration: Gases are collected and condensed at filling stations, then returned to the main fuel supply.
3. Activated carbon filters: Vapors can be passed through an activated carbon filter where hydrocarbons are absorbed onto carbon particles.

Example: Modern vehicles are equipped with catalytic converters as a standard feature to reduce harmful emissions.

Improving combustion efficiency is another crucial strategy. This involves operating boilers with an optimum amount of excess air to ensure complete combustion of fuels.

Acid Rain and Its Impacts

Acid rain is a significant environmental issue with far-reaching consequences. This section explores the causes and impacts of acid rain on both living and non-living entities.

Definition: Acid rain is precipitation that has become acidic due to atmospheric pollution, primarily from the combustion of fossil fuels and emission of photochemical smog.

The effects of acid rain on buildings and monuments are particularly severe. Limestone structures are especially vulnerable, as the acidic rain dissolves their surface layer. Metal structures such as railways, water pipes, and overhead power lines are also susceptible to damage from acid rain.

Example: The deterioration of historic buildings and monuments in cities with high pollution levels is a visible consequence of acid rain.

The acid rain effects on the environment extend to living organisms as well. Lichens, which are composite organisms formed from algae and fungi, are particularly sensitive to acidic conditions. Their size, health, and abundance can serve as indicators of sulphur dioxide levels in the environment.

Highlight: The impact of acid rain on soil pH and nutrient availability can lead to toxic levels of copper and zinc, further affecting plant and animal life.

The acid rain effects on humans are primarily indirect, through damage to the environment and food sources. However, direct effects can include:

1. Protein damage: Low pH can denature proteins in cell membranes and inhibit enzyme action.
2. Damage to exoskeletons: Invertebrates with calcium-based exoskeletons may die as acids dissolve these protective structures.
3. Respiratory issues: When combined with sulphur dioxide, acid rain can exacerbate breathing difficulties and increase the frequency of respiratory problems.

Vocabulary: Denaturation - The process by which proteins lose their structure, potentially leading to loss of function.