Types of weather modification.

7/28/2019 Types of weather modification.

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(1) Cloud Seeding

(2) Acid Rain

(3) Clean Coal Technology



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Cloud Seeding

Cloud seeding, a form of weather modification, is the attempt to

change the amount or type of precipitation that falls from clouds,by dispersing substances into the air that serve as cloud condensation

or ice nuclei, which alter the microphysical processes within the cloud.

- Intent is to increase precipitation (rain or snow).

- Chemicals used for cloud seeding include Silver Iodide and

dry ice (frozen CO2).

- Seeding of clouds requires that they contain supercooled liquid water

(liquid water colder than zero degrees Celsius).

- Introduction of AgI, which has a crystalline structure similar to that of ice,

will induce freezing nucleation.



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There are three cloud seeding methods: hygroscopic, static, and dynamic.

Hygroscopic method disperses salts through flares or explosives in the

lower portions of clouds. The salts grow in size as water joins with them.

Eg. NaOH, KOH, ZnCl2, CaCl2, NaCl etc

Static cloud seeding involves spreading a chemical like silver iodide into clouds.

The silver iodide provides a crystal around which moisture can condense.

The moisture is already present in the clouds, but silver iodide essentially

makes rain clouds more effective at dispensing their water.

Dynamic cloud seeding aims to boost vertical air currents, which encourages

more water to pass through the clouds, translating into more rain.



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Static Cloud Seeding



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Crystal Structure of Silver Iodide

Structure of Ice Crystal



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Weather Modification Method

- Chinese scientists use rocket launchers and shoot silver iodide pellets

into wisps of passing cloud.

- Predicted 20% increase in rain fall.

- When the rocket is launched, rocket activates the spraying of the

seeding material along the rocket’s trajectory.

- Once the cloud seeding is completed, the parachute will be opened,

allowing the rocket to land slowly and safely.

Launching system of rainfall-enhancement and

hail-suppression rocket (Source: Nature)



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Acid rain describes any form of precipitation with high levels of

nitric and sulfuric acids.

It can also occur in the form of snow or fog.

When humans burn fossil fuels, SO2

and NOx

are released

into the atmosphere.

NOx = NO + NO2

SO2 and NOx become sulfuric and nitric acids when they enter

the atmosphere and react with water vapor.

Acid Rain



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Emissions of sulfur dioxide and nitrogen oxides react

with water vapor in the atmosphere to create sulfuric

and nitric acids.



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The pH scale is a measure of acidity and alkalinity.

Acid rain has a pH of 5.6 or less.

Acid deposition weakens trees

and pollutes surface waters



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Coal which is primarily used for electricity generation is the second

largest contributor of CO2, a greenhouse gas contributing to global

warming, and sulfur dioxide responsible for causing acid rains.

Clean coal technology aims to reduce the environmental

impact of coal energy generation by making the coal burn clean.

Clean Coal Technology



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Only 40% energy efficient

Traditional Thermal Power Plant



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Burning coal, such as for power generation, gives rise to a variety of wastes.

- including that of global warming due to CO2 releases to the atmosphere.

Clean Coal Methods:

Coal cleaning by 'washing' reduces emissions of ash and SO2

when the coal is burned.

Gasification avoids burning coal altogether. Steam and hotpressurized air or oxygen combined with coal in a reaction

that forces carbon molecules apart. The resulting syngas,

a mixture of CO and H2, is then cleaned and burned in a gas

turbine to make electricity.

Low-NOx burners allow coal-fired plants to reduce nitrogen oxide

emissions by up to 40%.

Sequestration refers to disposal of liquid carbon dioxide,

once captured, into deep geological strata.

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Photochemical Smog

Noxious mixture of highly reactive and oxidizing

air pollutants including:

• Troposphere Ozone

• Oxides of Nitrogen (NOx)

• Volatile organic compounds (VOC)

• Peroxyacetyl Nitrates (PAN)

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Generation Mechanism:

Three ingredients required:

• Ultraviolet Light

• Hydrocarbons

• Nitrogen oxides

• HC

• NO

UV

Light

• O3

• PANs

• Other Oxidants

Photochemical Reaction

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Schematic Diagram of

Photochemical Smog Formation

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N2(g) + O2(g) 2NO(g)

At the high temperatures of the car's combustion chamber:

Some of the nitric oxide reacts with oxygen to form nitrogen dioxide:

2NO(g) + O2(g) 2NO2(g)

When the nitrogen dioxide (NO2) concentration is well above clean air levels

and there is plenty of sunlight, then

This oxygen atom (O) can react with oxygen molecules (O2) in the air

to form ozone:

O + O2

O3

NO2(g) + hv NO(g) + O

Formation of NOx, and O3

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Peroxyacetylnitrate (PAN) Production

Nitrogen dioxide (NO2), oxygen (O2) and hydrocarbons (unburnt petrol)

react in the presence of sunlight to produce peroxyacetylnitrate:

NO2(g) + O2(g) + HC + hv CH3CO-OO-NO2(g)

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Effects on human health:

• Ozone

– Cause acute respiratory problems – Aggravate asthma

– Cause temporary decreases in lung function

– Impair the body's immune system

• Peroxyacetylnitrate (PANs) – Respiratory and eye irritants

– Mutagenic- causing skin cancer

• Volatile organic compounds (VOCs) – Global warming - Methane

– Carcinogenic - Benzene

– Form Ozone

Types of weather modification.

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