Primary air pollutants are the pollutants that are emitted directly from the source to the atmosphere whereas secondary air pollutants are formed in the lower atmosphere.
Primary air pollutants include oxides of sulfur, carbon, and nitrogen, volatile organic compounds, suspended particulate matter, H₂S, etc.
These pollutants are of concern as they are harmful to humans, animals and plants. They can also be the source of secondary air pollutants. Let's now see some of the primary air pollutants.
Sulfur oxide
About 95% of sulfur oxide is sulfur dioxide SO₂. It is a colourless gas with a pungent odour. They are mostly emitted by industries and the burning of fossil fuels. Effects of Sulfur oxide are:
It interferes with the function of the mucous membrane.
It creates breathing problems and causes a deficit of oxygen in the body.
They combine with the rainwater and create acid rain which affects the building's appearance.
Carbon monoxide
It is mostly due to vehicular exhaust, due to incomplete burning of fossil fuels. It is a colourless, odourless toxic gas. Ill effects on humans are:
It combines with haemoglobin in the blood and forms complex substances that result even in death.
Nitrogen oxides
They are generally suspended in the atmosphere by fly ash, tobacco smoke, smog, etc. Effects on human health include:
It creates eye and nasal irritation.
It also causes respiratory problems.
Hydrocarbons
They are compounds of hydrogen and carbon. They undergo photochemical reactions and formaldehyde and ketone which are very harmful.
Suspended particulate matter
They are the mixture of solid particles and liquid droplets which are found in the air. PM2.5 and PM10 are types of particulate matter based on their size.
PM10 are inhalable coarse particles
PM2.5 are fine particles.
Ill effects: respiratory problems, lung cancer
Other pollutants
Some other primary air pollutants like Lead can cause damage to the liver and kidneys, Aromatic hydrocarbons from automobile exhaust are carcinogens that causes cancer.
Photochemical smog is formed due to the interaction of oxides of nitrogen with sunlight. They give rise to peroxyacetyl nitrate (PAN) and ozone which are very harmful.
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