--- title: "Kathmandu air pollution and topography" subject: "Technology, Environment and Society" chapter: 5 key: "semester_7/technology_environment_and_society:kathmandu-air-topography" source: https://www.bctengineer.com/q/semester_7/technology_environment_and_society/kathmandu-air-topography site: BCT Engineering --- # Kathmandu air pollution and topography Technology, Environment and Society · Chapter 5: Water and Air Pollution - Asked in: 2083 Bhadra, 4 marks - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_7/technology_environment_and_society/kathmandu-air-topography - Whole chapter: https://www.bctengineer.com/md/semester_7/technology_environment_and_society/chapter-5 ## Question List the major sources of air pollution in the Kathmandu valley and explain why its topography worsens air quality. ## Short answer Major sources include vehicles, road and construction dust, brick kilns, open waste burning, industries, and household fuels. The valley's bowl shape and surrounding hills trap pollutants, winter temperature inversions create a lid preventing vertical mixing, and low wind with little dry-season rain concentrates pollution. ## Answer Kathmandu valley often records PM2.5 levels many times above the WHO guideline, especially in winter and spring. #### Major sources of air pollution in Kathmandu valley 1. **Vehicles** – the fastest-growing source; old diesel buses, trucks and the large number of motorcycles emit PM, CO, NOₓ and hydrocarbons; traffic jams increase emissions. 2. **Road and construction dust** – unpaved, dug-up roads (drinking water pipe and road widening works), building construction and open transport of sand. 3. **Brick kilns** – mainly in Bhaktapur and Lalitpur, burning coal and biomass in the dry season. 4. **Open burning of waste** – plastics and garbage burnt in streets. 5. **Industries** – cement, small factories, diesel generators. 6. **Household fuel** – firewood, kerosene and LPG in some homes. 7. **Forest fires and trans-boundary pollution** – smoke from fires in Nepal and haze from the Indo-Gangetic plain in spring. #### Why topography worsens air quality 1. **Bowl-shaped valley** – Kathmandu is surrounded by hills (Shivapuri, Phulchowki, Chandragiri, Nagarjun) rising 700–1,500 m above the valley floor. Air cannot move out easily and pollutants are trapped. 2. **Temperature inversion** – on winter nights the ground cools fast and cold dense air settles on the valley floor under a layer of warmer air. This "lid" stops vertical mixing, so smoke and dust stay near the ground until late morning. ```text warm air layer (lid) ~~~~~~~~~~~~~~~~~~~~~~~~ / cold, polluted air \ / hills [city] hills \ ``` 3. **Low wind speed** – especially in winter mornings; pollutants are not dispersed. 4. **Little rain in the dry season** (November–May) – no washing out of particles. 5. **High density** – dense settlements and narrow roads in a closed basin concentrate sources. So the same emission gives a much higher concentration in Kathmandu than in an open plain. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Which source of air pollution in Kathmandu valley is described as the fastest-growing? A. Brick kilns B. Vehicles C. Forest fires D. Household LPG use Answer: B. Vehicles, especially old diesel buses, trucks and many motorcycles, are the fastest-growing source, emitting PM, CO, NOx and hydrocarbons. (Key point: Fastest-growing source) 2. How does a winter temperature inversion worsen air quality in the valley? A. Warm air near the ground rises quickly and carries smoke away B. Strong winds blow pollutants into the valley from outside C. Cold dense air under a warmer layer acts as a lid and stops vertical mixing D. Rain washes pollutants down onto the valley floor Answer: C. On winter nights cold dense air settles on the floor beneath warmer air, so smoke and dust cannot mix upward and stay near the ground until late morning. (Key point: Temperature inversion) 3. Why does the bowl shape of Kathmandu valley raise pollutant concentration? A. Surrounding hills 700-1,500 m high stop air moving out, so pollutants are trapped B. The hills produce extra dust that adds to emissions C. The valley floor is hotter than the hills, so pollutants sink D. The hills increase wind speed through the valley Answer: A. The surrounding hills prevent easy air movement out of the valley, trapping pollutants, so the same emission gives a higher concentration than on an open plain. (Key point: Bowl-shaped valley) ## Related in Technology, Environment and Society - [Kathmandu air pollution: causes, effects, mitigation](https://www.bctengineer.com/question.md?key=semester_7%2Ftechnology_environment_and_society%3Akathmandu-air-pollution-causes) — Technology, Environment and Society, chapter 5 - [Kathmandu air pollution and livable city](https://www.bctengineer.com/question.md?key=semester_7%2Ftechnology_environment_and_society%3Akathmandu-livable-city) — Technology, Environment and Society, chapter 5 - [Indoor air pollution and Kathmandu air problems](https://www.bctengineer.com/question.md?key=semester_7%2Ftechnology_environment_and_society%3Aindoor-air-kathmandu-health) — Technology, Environment and Society, chapter 5 - [Water pollution: sources, causes and impacts](https://www.bctengineer.com/question.md?key=semester_7%2Ftechnology_environment_and_society%3Awater-pollution-sources-impacts) — Technology, Environment and Society, chapter 5 - [Sources and types of water pollution](https://www.bctengineer.com/question.md?key=semester_7%2Ftechnology_environment_and_society%3Awater-pollution-sources-types) — Technology, Environment and Society, chapter 5 - [Air pollution: causes, effects and mitigation](https://www.bctengineer.com/question.md?key=semester_7%2Ftechnology_environment_and_society%3Aair-pollution-causes-mitigation) — Technology, Environment and Society, chapter 5, asked 3× ## Related in other subjects - [Report on sound pollution in Kathmandu Valley](https://www.bctengineer.com/question.md?key=semester_5%2Fcommunication_english%3Areport-sound-pollution-kathmandu) — Communication English, chapter 9 - [Research article on air pollution in Kathmandu](https://www.bctengineer.com/question.md?key=semester_5%2Fcommunication_english%3Aresearch-article-air-pollution-kathmandu) — Communication English, chapter 10, asked 3× - [Air pollution, pollutants, sources and remedies](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Aair-pollution-sources-remedies) — Engineering Chemistry, chapter 3 - [Major sources and selection factors](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Asources-and-selection-factors) — Water Supply Engineering, chapter 2, asked 2×