Environmental Chemistry: Atmosphere and Water - SS2 Chemistry Past Questions and Answers - page 2

The Earth's atmosphere is primarily composed of nitrogen (about 78%) and oxygen (about 21%), with trace amounts of other gases, including argon, carbon dioxide, and water vapour. These major components play crucial roles in supporting life on Earth. Oxygen is essential for respiration, allowing living organisms to extract energy from food. Nitrogen is important for the synthesis of proteins and other organic compounds.

Human activity significantly impacts the composition of the atmosphere. The burning of fossil fuels releases carbon dioxide and other greenhouse gases into the air, leading to an increase in global temperatures and climate change. Deforestation reduces the number of trees that absorb carbon dioxide, exacerbating the greenhouse effect. Additionally, industrial processes release pollutants, such as sulphur dioxide and nitrogen oxides, which can lead to acid rain and smog, affecting both human health and the environment.

The Earth's atmosphere can be divided into distinct layers based on temperature changes with increasing altitude. These layers, from the surface upwards, are the troposphere, stratosphere, mesosphere, thermosphere, and exosphere.

The variations in temperature and composition are primarily influenced by the absorption of solar radiation and the interactions between different gases. The troposphere, closest to the Earth's surface, experiences a decrease in temperature with altitude due to the absorption of solar radiation by the Earth's surface. The stratosphere, on the other hand, exhibits an increase in temperature with altitude because of the presence of the ozone layer, which absorbs and filters out harmful ultraviolet (UV) radiation.

The mesosphere experiences a drop in temperature again, whereas the thermosphere witnesses a significant increase in temperature because it absorbs extreme ultraviolet and X-ray radiation from the Sun. The exosphere is the outermost layer, where atoms and molecules can escape into space due to low density and high temperatures.

The ozone layer in the stratosphere plays a vital role in shielding life on Earth from harmful ultraviolet (UV) radiation. Ozone (O3) is formed when oxygen molecules (O2) in the stratosphere are split into individual oxygen atoms by solar UV radiation. These oxygen atoms then combine with other oxygen molecules to form ozone.

The ozone layer absorbs most of the Sun's harmful UV-B and UV-C radiation, preventing these high-energy rays from reaching the Earth's surface. UV radiation is known to cause skin cancer, cataracts, and other harmful effects on living organisms. Therefore, the presence of the ozone layer is crucial for protecting life on Earth and maintaining the delicate balance of ecosystems.