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AIR_what are the pollutants

Everyone says that the air is polluted. But what are the pollutants which cause air pollution?

March 26, 2017

By Igor Ovsyannykov (via

All air pollution is caused by particles. These particles can be anything: smoke, dust, liquid, pollen. Together, these all are referred to as Particulate Matter (PM). Even among these, there are particles that can be seen by your eyes, such as the particles you can see floating around in sunlight. Then there are the particles you can’t see.

See your hair? Usually, the diameter of one hair strand is 50-70 micrometers. When you cut that down to 10 micrometers and below, till 2.5 micrometers, the particles with these diameters are called PM 10. When the particles are even smaller than 2.5 micrometers, they are PM 2.5.

There are now new studies presenting evidence that PM2.5 is more harmful than PM10. It does make sense – smaller the particle, more the probability that it will go deeper into your lungs and harm us. This is also one of the important reasons for WHO to push for all countries to have standards for PM2.5.

While the fraction of PM2.5 is higher in the PM10 fraction, for the most cities with pollution from transport and other combustion sources, an often neglected non-combustion source is dust re-suspension (from road dust and dust storms), which forms part of the coarser fraction (PM2.5 to PM10). If we suddenly stop measuring PM10, we will be neglecting this source.

[Why is PM2.5 often higher than PM10? Is PM10 still a relevant measure?]

Read more: What is Particulate Matter?

Where do they come from?

These particles come in many sizes and shapes and can be made up of hundreds of different chemicals. Some are emitted directly from a source, such as construction sites, unpaved roads, fields, smokestacks or fires. Most particles form in the atmosphere as a result of complex reactions of chemicals such as sulfur dioxide and nitrogen oxides, which are pollutants emitted from power plants, industries and automobiles [EPA].


Any form of burning, also known as combustion, can lead to particle pollution. Other sources of particulate matter include all mobile vehicles, especially those with diesel engines, road dust, certain industries, furnaces, and tobacco smoke [HealthLinkBC].

The Pollutants

PM 2.5

Causes: aggravation of asthma, heart and cardiovascular system diseases, lung cancer. Etc.

PM 10

Causes: chronic respiratory disease, aggravated asthma, acute respiratory symptoms, decrease in lung function and damage to lung tissue, cancer, and premature death [The Asthma Files].

Sulphur dioxide (SO2)

Generation of electricity through coal, oil, gas leads to formation of sulphur dioxide in the air.

Causes: coughing, difficulty in breathing, chest tightness, aggravation of existing asthma.

Read more: EPA-SO2 

Nitrogen dioxide (NO2)

The major source of NO2 is combustion processes; NO2 is showing alarmingly high increasing trend in Indian cities due to increase in number of vehicles. On inhalation, 70–90% of NO2 can be absorbed in the respiratory tract of humans, and physical exercise increases the total percentage absorbed

Causes: It has been established that continuous exposure with as little as 0.1 ppm NO2 over a period of one to three years, increases incidence of bronchitis, emphysema and leads to adverse effect on lung performance (WHO 2000). Excessive NO2 affects the defence mechanism leaving you susceptible to respiratory illness.


Emissions from industries and vehicle exhausts release chemicals, which in the presence of sunlight form ozone.

Causes: coughing due to irritation, aggravation of bronchitis, reduces lung capacity, asthma, heart disease, emphysema. Also, asthmatics are more severely affected.

Read more: EPA-Ozone


Emissions from vehicles, emissions from the burning of coal, and also, cigarette smoke.

Causes: No specific guideline value has been developed for air. Benzene is carcinogenic to humans, and no safe level of exposure can be recommended [WHO: Exposure to Benzene]

Carbon Monoxide

CO production mostly occurs from sources having incomplete combustion. Due to its toxicity and appreciable mass in atmosphere, it should be considered as an important pollutant in AQI scheme.

Causes: Headache, dizziness, drowsiness, and nausea. Prolonged exposure can lead to vomiting, loss of consciousness, and collapse.

Read more: Health Effects of Particulate Matter (WHO)



About the author: Hitesh Shetty
Dreams of writing a bestseller and changing the world. When awake, tries to figure out how to do both. | Get Tech Addicted...
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