================================== DOCUMENT 1: SESSION 4 (S4) ================================== POLLUTION ABATEMENT (21CHO105T) Unit 1 - Session 4 I. MULTIPLE CHOICE QUESTIONS (MCQs) 1. Which greenhouse gas is mainly released from agricultural activities like rice cultivation and livestock farming? β Answer: b) Methane β Explanation: Enteric fermentation in livestock and anaerobic decomposition in flooded rice paddies produce significant amounts of methane ( ). πΆπ» 4 2. The natural greenhouse effect is essential because it: β Answer: a) Keeps Earth's average temperature suitable for life β Explanation: Without the natural greenhouse effect, Earth's average surface temperature would be approximately -18 Β° C instead of the current hospitable 15Β°C. 3. Which of the following gases has both natural and anthropogenic sources? β Answer: d) All of the above β Explanation: Carbon dioxide, methane, and nitrous oxide are all produced naturally (volcanoes, wetlands, soil processes) as well as by human activities (fossil fuel burning, agriculture, industrial operations). 4. Which health issue is most directly linked to ozone layer depletion? β Answer: b) Skin cancer β Explanation: Ozone layer depletion allows increased Ultraviolet-B (UV-B) radiation to reach the Earth's surface, causing DNA damage in skin cells leading to skin cancers and cataracts. 5. Which of the following is an environmental impact of ozone depletion? β Answer: a) Reduced crop yields β Explanation: Enhanced UV-B radiation damages plant tissues, impairs photosynthesis, and leads to reduced biomass and agricultural productivity. II. SHORT ANSWER QUESTIONS Q1. What is the greenhouse effect and how does it help maintain Earth's temperature? β Answer: β Definition: The greenhouse effect is a natural thermal process where certain gases in Earth's atmosphere trap outgoing longwave infrared radiation emitted by the Earth's surface. β Mechanism: Shortwave solar radiation passes through the atmosphere and warms the Earth's surface. The surface re-radiates this energy back toward space as longwave thermal infrared radiation. β Temperature Maintenance: Greenhouse gases (such as , , π» 2 π πΆπ 2 πΆπ» 4 ) absorb and re-emit this thermal radiation back toward the Earth, keeping the global average ambient temperature at a stable, life-supporting level of approximately 15Β°C. Q2. What are the main human activities responsible for ozone layer depletion? β Answer: 1. Release of Chlorofluorocarbons (CFCs): Use of CFCs in refrigeration, air conditioning units, and aerosol propellants. 2. Halons & Fire Extinguishers: Use of brominated compounds in fire suppression systems. 3. Industrial Solvents: Emissions of carbon tetrachloride ( ) and πΆπΆπ 4 methyl chloroform ( ) used in degreasing and dry cleaning. πΆπ» 3 πΆπΆπ 3 4. Agricultural Fumigants: Application of methyl bromide ( ) in πΆπ» 3 π΅π agricultural soil treatment. III. LONG ANSWER QUESTION 1. Explain the Greenhouse Effect. β Answer: 1. Concept and Mechanism The greenhouse effect is the natural process by which greenhouse gases in the atmosphere absorb and re-emit infrared radiation from the surface, insulating the planet. β Solar Radiation: Solar radiation enters the Earth's atmosphere predominantly as visible light and shortwave UV radiation. β Absorption and Re-radiation: The Earth absorbs this energy and re-radiates it as lower-energy, longwave terrestrial thermal infrared radiation. β Trapping Heat: Radiatively active atmospheric gases absorb this outgoing infrared radiation and re-radiate it in all directions, including back toward Earth's surface, preventing rapid heat loss. 2. Primary Greenhouse Gases β Water Vapor ( ): The most abundant natural contributor to thermal π» 2 π radiation absorption. β Carbon Dioxide ( ): Released through fossil fuel combustion, πΆπ 2 deforestation, and industrial processing. β Methane ( ): Emitted from enteric fermentation in livestock, anaerobic πΆπ» 4 paddy farming, and natural gas leakage. β Nitrous Oxide ( ): Generated via synthetic fertilizer use and industrial π 2 π chemical production. β Fluorinated Gases (CFCs, HCFCs, ): Synthetic halogenated compounds ππΉ 6 with high global warming potentials. 3. Distinction Between Natural and Enhanced Greenhouse Effect β Natural Greenhouse Effect: Maintains Earth's mean surface temperature at a hospitable 15Β°C (without it, the mean temperature would be -18Β°C). β Enhanced Greenhouse Effect: Accelerated greenhouse gas concentrations due to anthropogenic activities lead to excess thermal retention, causing global warming and severe climate disruption.