Air Pollution: Types, Indicators, and Measurements

Air + pollutants = Air pollution 

Air quality destruction due to releasing the pollutants in the air is known as air pollution. Pollutants like sulfur dioxide, carbon dioxide, ammonia, particulate matter, etc. These pollutants affect air quality. 

Types of Air Pollutants

Primary Air Pollutants:

Pollutants that are directly released into the air are known as primary air pollutants.

Examples of primary air pollutants

• Sulfur dioxide
• Carbon monoxide
• Nitrogen dioxide
• Particulate matter
• Hydrocarbons
• chlorofluorocarbons (CFC's)
• Ammonia 
• Metals like Lead, Cadmium, and Copper

Secondary Air Pollutants

Pollutants are formed by a combination of primary air pollutants.

Examples of Secondary air pollutants

• Ground level ozone
• Peroxyacetyl nitrate
• particulate matter formed by combinations.

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What are the indicators of Air pollution?

• Sulfur Dioxide: The most important indicator of air pollution.
• Smoke or soiling index: A specific amount of air is filtered through a filter paper and the

stain is measured by a photoelectric meter.

• Grit and dust measurement: Checks the dust, grit deposits and small particulate matter

present in the air.

• Coefficient of haze: Measures smoke and other aerosols in air.
• Air Pollution Index: A combined index that takes multiple air pollutants with defined upper limits into consideration.

Important facts about air pollution indicators 

• Best indicator of air pollution: Sulphur dioxide
• The recommended level of SO2 in 24 hours of exposure is <20 mcg/m3.
• Most common and widely distributed air pollutant: Carbon monoxide
• Best biological indicator of air pollution: Lichens
• McArdle's index is an indicator to measure air comfort. Also measures predictable sweat rate in 4 hours. It is not considered an air pollution indicator.

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Air Quality Index (AQI)

An indicator of air pollution. It is given by the Central Pollution Control Board (CPCB).

What are the components of the air quality index?

• Sulfur dioxide
• Nitrogen dioxide
• Carbon monoxide
• Particulate matter 2.5 and 10
• Measures Ozone level
• Measures Lead, Ammonia, Chlorofluorocarbons, Hydrogen sulfides, etc.

Central Pollution Control Board's (CPCB) Air Quality Standards

Air Quality Index (AQI) Category

0-50 Good

51-100 Satisfactory

101-200 Moderate

201-300 Poor

301-400 Very Poor

401-500 Severe

What are the Sources of Indoor Air Pollution?

• Fuel consumption: It release pollutants like Carbon monoxide, Polyaromatic hydrocarbons, and nitrogen oxides
• Tobacco consumption: carbon monoxide and polyaromatic hydrocarbons are the main pollutants released by tobacco consumption.
• Coal combustion: Releases Sulphur oxides, arsenic, and fluorine
• Furnishings, construction materials, cooking: Aldehydes
• Remodeling and destruction of construction materials: Asbestos
• Remodeling/demolition of painted surfaces, leaded fuels, smelting: Lead
• Building and construction materials: Radon
• Adhesives, solvents, aerosol sprays, resin products: Organic vapours like benzene and toluene.
• Incineration, coal burning, petroleum burning: Hydrocarbons

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What is Air comfort, and how can we measure it?

Air comfort, or comfort zone, is the range of corrected effective temperature in which the individual or worker in an industry feels comfortable. It considers temperature, humidity, cooling power of air, velocity of air, and mean radiant heat.

Measurement of air comfort zone 

Cooling Power of Air:

• Determines the capacity of the atmosphere to dissipate the metabolite heat generated by humans.
• Includes 3 components: Air temperature, Air humidity, and Air velocity.
• Measured by a Kata thermometer.

Heat Stress Index:

The ratio of evaporation required to maintain heat balance to maximum evaporation, maintained in a particular environment, is expressed as a percentage.

• Related to body sweating.
• It ranges from 0 to 100.
• Severe heat strain: 40 to 60
• Very severe heat strain: 70 to 90
• Upper limit of heat tolerance: 100

Effective Temperature:

• Measures heat stress index.
• Includes air temperature, air humidity, and air flow.

Correct effective temperature:

• A better indicator of air comfort than effective temperature.
• Includes 4 components: Air temperature, air humidity, air velocity, and mean radiant heat.
• A globe thermometer is an instrument used to measure corrected effective temperature.

Predictable 4-hour sweat rate:

• Air comfort is measured using McArdle's index.
• It tells about predictable 4-hour sweat rate
• P4SR classifies thermal comfort levels as:
  • Comfort zone: 1 to 3 litres
  • Just tolerable: 3 to 4.5 litres
  • Intolerable: >4.5 litres

Corrected range of comfort zone 

• Corrected Effective Temperature: 25 to 27°c
• Relative humidity: 30 to 65%
• Dry Kata: 6 and above
• Wet Kata: 20 and above
• Predicted 4 hour sweat rate: 1 to 3 litres.

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Which Instruments are Used to Measure Air Quality?

Kata thermometer:

• Identification: A Kata thermometer has a red coloured narrow, and thin bulb that is used to measure low air velocity and cooling power of air.
• More reserved for low air velocity measurement.
• The cooling power of air is an indicator of air comfort. Not very reliable estimates are provided of the cooling power of air by the Kata thermometer.
• Dry Kata reading is more than 6 and wet Kata reading is more than 20—indicating thermal comfort.

Globe thermometer:

• In the Globe thermometer, there is a thick and wide bulb present.
• A globe thermometer is used to measure corrected effective temperature or radiant heat.

Which Instruments Are Used to Measure the Humidity of Air?

Air humidity is the moisture content of the air. It can be measured by the following instruments:

• Hygrometer: It measures the humidity of air. It is the most commonly used to measure the air humidity.
• Sling psychrometer: It is another method of measuring air humidity. In this there are two thermometers. One is a dry bulb thermometer, and the other is a wet bulb thermometer.
• Dry and wet bulb hygrometer: 
• Assman psychrometer: It is used to measure the air temperature and humidity of the air.

Some Other Instruments

• Robinson Cup Anemometer: It measures air velocity in the early days. Robinson cup anemometers are of three types: plate anemometer, Robinson cup nemometer, and windmill anemometer.
• Barometer: It is an instrument to measure atmospheric pressure. In this, an asteroid barometer and a mercury barometer are present.
• Campbell stokes sunshine recorder: It measures amount of sunlight absorbed with 24 hours
• Stevenson screen: It measures air temperature

Points to Remember

• Sulfur dioxide is the best air pollution indicator.
• Lichen is the best biological indicator of air pollution
• McArdle's index is an indicator to measure air comfort.
• A psychrometer is used to measure air humidity.
• Kyoto protocol is one of the initiatives to control global warming
• The Kyoto Protocol called for a 90% reduction in greenhouse gas emissions.
• There is no very severe category in AQI.

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