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Learn · Air Quality & Health

Invisible Dangers in the Air

Understanding what the sensors detect and why it matters for health

Grades 6–8 30 min observation live IESH data

Students take their first air quality readings, learn what CO and mixed gases mean for health, and identify common sources of air pollution in Nepali homes and communities.

Learning objectives

  • Identify carbon monoxide (CO) as a product of incomplete combustion and explain why it is dangerous.
  • Read relative air quality sensor values and describe what changes in those values might indicate.
  • List common sources of indoor and outdoor air pollution in Nepal.
  • Explain the link between cooking fuel type and respiratory health.

Background

Carbon monoxide (CO) is a colourless, odourless gas produced whenever carbon-containing materials burn without sufficient oxygen. This "incomplete combustion" happens in wood fires, charcoal stoves, vehicle engines and burning crop waste. CO is dangerous because it binds to haemoglobin in the blood 200 times more strongly than oxygen, preventing blood from carrying oxygen to organs. Even low concentrations cause headaches, dizziness and fatigue; high concentrations cause death.

The MQ-135 sensor detects a range of gases including ammonia (from animal waste and fertiliser), CO₂ (from breathing and combustion), benzene and other volatile organic compounds. It gives a single "air quality" reading rather than identifying individual gases. Both sensors produce a higher raw ADC value when gas concentrations increase — but the readings require calibration against known gas concentrations to convert to ppm (parts per million).

Nepal's air quality challenges span indoor and outdoor environments. In Kathmandu valley, trapped by surrounding hills and filled with vehicle exhaust, brick kiln smoke and dust from rapid construction, the valley regularly ranks among South Asia's most polluted urban areas in winter. In rural areas, the main threat is indoor pollution from cooking. Both contexts are important, and both show up — in different ways — in sensor readings.

Procedure

  1. Read the current MQ-7 (CO) and MQ-135 (air quality) raw values from the dashboard. Record them.
  2. The bar next to each reading shows how high the value is relative to the maximum (4095). What percentage of maximum is each reading at?
  3. Open a window or door if possible. Wait 5 minutes. Do the readings change? Why might fresh air affect the values?
  4. Brainstorm as a class: list 5 sources of air pollution inside a typical Nepali home and 5 sources outside.
  5. For each source, predict whether it would affect the MQ-7 reading, the MQ-135 reading, or both.
  6. Read the Nepal context above. Calculate: if 13,000 people die per year from household air pollution, how many is that per day? Per hour?

Discussion

  1. Why is carbon monoxide particularly dangerous compared to other pollutants — even though you can't see or smell it?
  2. Women and young children in Nepal are most affected by indoor air pollution. Why?
  3. What changes to a kitchen design could reduce indoor air pollution from a wood cooking fire?

Worksheet

1. Record MQ-7 reading: ___ and MQ-135 reading: ___ . Calculate each as a percentage of the maximum 4095. [3 marks]

Answer guide (for teachers)

Check arithmetic: (reading ÷ 4095) × 100. Values around 5–15% are typical in clean indoor air.

2. Explain in three sentences why carbon monoxide is dangerous to humans, even in small amounts. [3 marks]

Answer guide (for teachers)

CO is colourless and odourless so you cannot detect it. It binds to haemoglobin in blood 200× more strongly than oxygen. This prevents blood from carrying oxygen to the brain and organs, causing illness or death.

3. Name THREE sources of indoor air pollution common in Nepal and suggest one practical way to reduce indoor pollution in a rural Nepali kitchen. [4 marks]

Answer guide (for teachers)

Sources: wood fire cooking, burning incense, kerosene lamps, animal dung fuel, smoking. Solutions: improved cookstoves with chimneys, switching to LPG or biogas, opening windows and doors, cross-ventilation in kitchen design.

Vocabulary

Carbon Monoxide (CO)
A colourless, odourless toxic gas produced by incomplete combustion of carbon-containing fuels.
Incomplete Combustion
Burning that occurs with insufficient oxygen, producing CO and soot rather than CO₂ and water.
Haemoglobin
The protein in red blood cells that carries oxygen from the lungs to the rest of the body.
Indoor Air Pollution
Contamination of the air inside buildings, most commonly from cooking fires, heating and cleaning products.

Extension

Research "improved cookstove" programmes in Nepal. Find one organisation working on this and write a 150-word summary of their approach, who they target, and what evidence they have for health improvements.

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