Aerosol Pollution

About Aerosols:

• Aerosols are defined as a combination of liquid or solid particles suspended in a gaseous or liquid environment.
• They tend to hang in the atmosphere near their source, or move as localised or regional masses via air currents.
• They range in size from a few atoms across to the width of a human hair.
• In the atmosphere, these particles are mainly situated in the low layers of the atmosphere (< 1.5 km) since aerosol sources are located on the terrestrial surface.
• However, certain aerosols can still be found in the stratosphere, especially volcanic aerosols ejected into the high altitude layers.
• They include:
  • Crystals of sulphate,
  • Balls of almost pure black carbon (commonly, though not entirely accurately, called soot),
  • Droplets of nitric or sulfuric acid, spores of pollen.
• They may be salt freed from the crests of breaking waves, or desert sand whipped up by the wind.

Types of Aerosols:

• Natural Aerosols:
  • One of the largest natural sources of aerosols are plankton, which breathe out dimethyl sulphide (DMS), a strong-smelling chemical that gives the sea it’s familiar pungent odour.
  • DMS reacts with oxygen to produce clouds of sulfuric acid.
  • Sulphur dioxide released by volcanoes does the same.
  • Ninety percent of aerosols in the atmosphere are naturally occurring, but their levels have remained relatively constant over time.
• Anthropogenic Aerosols:
  • On the other hand anthropogenic, or human-made aerosols are emitted from:
    • Vehicle exhausts
    • Smokestacks of factories,
    • Ships and coal-burning powerplants
    • Farmers burning field stubble and land grabbers clearing Amazon forest with fire
    • Gas flares on oil rigs and discarded plastic shopping bags.
  • Even tumble driers release microplastic fibres that float skyward.
  • These sources have increased dramatically over the industrial period, roughly in step with greenhouse gases.

What Aerosols Do?

• Most aerosols help cool the planet by reflecting sunlight back out into space, reducing the amount of radiant energy that reaches Earth’s surface.
• They also help create clouds or brighten existing clouds, by acting as condensation nuclei around which water vapor condenses.
• Aerosols first came to public attention in the 1970s, not so much because of their cooling impact, but due to acid rain.
• The worst aerosols are very fine particulates that can penetrate deep into the lungs and may even enter the blood stream exacerbating respiratory and cardiovascular conditions.

PRACTICE QUESTION:

Consider the following statements:

1. Aerosols are mainly situated in the stratosphere

2. The origin of atmospheric aerosols can be both natural and anthropogenic

Which of the statements given above is/are correct?

(a) 1 only

(b) 2 only

(c) Both 1 and 2

(d) Neither 1 nor 2

Answer