Aerosols- A threat or Savior? - Seeker's Thoughts

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Aerosols- A threat or Savior?

What is Aerosol emission?

Aerosols are tiny particles and droplets floating around in the atmosphere. There are natural sources of aerosols, such as volcanic eruption and chemical released by the tiny sea creature. Human are also a source to produce aerosols through exhausts and burning fossil fuels and wood.

Effects of aerosols 
Aerosols tend to have a cooling effect on the Earth’s climate, by scattering incoming sunlight and help to raise clouds in form, preventing the sun’s energy reaching the earth’s surface.But these particles have also affected the the phases of the PDO means- the pacific decadal oscillation which is a pattern of pacific climate variability, the PDO can remain in the same phase for 20 to 30 years. 
In the map below, it can be seen how the concentration of aerosols in the atmosphere changed over the period of the slowdown. The red and orange areas show the increasing level of aerosols, predominantly over china. In contrast blue shading show the reduction over Europe and eastern US.

 The changing concentration of aerosols in the atmosphere caused local cooling over china and warming over Europe, north America, and the north Atlantic. This also effect on strengthening the pacific trade winds, and extends negative phased of the PDO, and eventually slowdown in surface temperature rise.

New study says about aerosols emission
Does pollution cool monsoon?
Study found that the Increased in emission of aerosols in to the atmosphere due to pollution are beginning to have a definite cooling effect of 1 degree Celsius during the Indian summer monsoon period.

The increased cooling is seen during the day, while the night time temperature is increasing, thus shrinking the day time temperature difference. The diurnal or a day time temperature difference is what drives the convection process (where water evaporates and reaches the atmosphere as water vapour and form the clouds)
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As in day time temperature decreases, the lower of the atmosphere reduce in height and come closer to the earth’s surface. This cause more aerosols to get in to the atmosphere, thus impacting the lower atmospheric turbulence, which may affect the distribution of moisture and rainfall. 
The increased concentration of aerosols in the atmosphere also tends to change the shape and characteristics of rain-bearing clouds, leading to extreme rainfall events but weakened monsoon rainfall.
Nature communications published a report which says rain- bearing clouds were found to increase in number and height when aerosol emission higher. The cloud also tends to have far higher number of ice particles that are smaller in size when aerosols loading is higher, thus reducing the efficiency of water droplets growth. 
When there are high aerosols loading, there will be more water droplets in the atmosphere. Once the droplets reach above the freezing level, ice formation begins. This acts as a fuel to make the cloud grow taller and thicker.

When aerosols loading higher, cloud top contains a greater number of smaller ice particles, which tends to reflect shortwave radiation from the top of the cloud, leading the increased cooling of the earth’s surface. 
Cooling by shortwave radiation surpasses warming by longwave radiation, leading to net reduction in day time temperature during the summer monsoon.
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