Life on Earth could not exist without the protective shield of the ozone layer

	Sources	Features
Chloro Fluoro Carbons CFC Also HCFC	Refrigerants, propellants, solvents, fire retardants, foaming agents in plastic manufacturing,� solvents for cleaning electronic and metallic components, for freezing foods	CFC are non-corrosive, non-inflammatory, low toxicity, chemical stability CFCs cannot be eliminated from atmosphere by usual scavenging processes like photo dissociation(under light), rain-out, oxidation Thermally Stable in Troposphere (move to Stratosphere by random diffusion) Unstable in Stratosphere as exposed to UV radiation Residence time in atmosphere b/w 40-150 years CFC-12 (R-12) widely used refrigerant [HFC 134A promising with low ODP]
Halons (Bromides), HBFC Hydro Bromo Fluoro Carbons	Halons and HBFC - used in fire extinguishers Methyl Bromide used in pesticides	Bromide destroys Ozone more powerful than Chlorine
Nitrogen Oxides	Thermonuclear explosions, agricultural fertilizers, industrial emission, volcanic eruptions , production of adipic acid	Denitrification of nitrites under anaerobic conditions releases Nitrous Oxide Nitrification of Ammonia under aerobic conditions� releases Nitrous Oxide
Sulphuric Acid particles	burning coal (60 %), mainly in thermal power plants + Petroleum products + in production of paper & smelting of metals Volcanic eruptions	These particles free Chlorine atoms from its reservoirs (HCL / ClONo2) and convert reactive nitrogen to inert forms thus prevents reservoirs of Chlorine molecules implies that more Chlorine atoms destroys Ozone
Carbon Tetrachloride	Cheap , Highly toxic solvent
Methyl Chloroform	Cleaning solvent for clothes, metals, correction fluid, dry cleaning sprays, spray adhesives
Aerosols

*CFC and HBFC are Ozone depleting substances while HFC, PFC are GHGs

ODP - Ozone Depletion Potential
Ozone in troposphere is bad- acid rains, smog, GHG; Ozone in stratosphere is good - UV protection blanket
Depletion of O3 is catalystic- one atom destroys thousands of ozone molecule before becoming inactive/inert form(HCL / ClONo2)

Stable compounds of Chlorine in Stratosphere(reservoirs) are HCL / ClONo2
After destroying thousands of Ozone molecules, Chlorine forms stable compounds by reacting with Nitrites and Hydrides
Ozone formed due to Sunlight + Volatile Organic Compound VOC + No2
CFC-12 (R-12)
HCFC-22 - popularly as R22
India will no longer permit the release of HFC-23, a potent greenhouse gas, released when local companies produce the refrigerant HCFC-22

Polar Stratospheric Clouds in Ozone Depletion

Ice particles of PSC forms as good substratum for chemical reactions that frees Chlorine from its reservoirs (HCL / ClONo2-ChlorineNitrate)

HCl + ClONo2 -> Cl2

This makes the Ozone depletion possible
Also, they absorb the reactive nitrogen making the stability of Chlorine slower
Besides, Dimer Chlorine Monoxide Cl2O2 is formed (formed by ClO reacting with itself) and this dimer is easily disassociated by sunlight giving rise to free chlorine at oms which further react to destroy ozone

Ozone depletion is more at poles

Because of Polar Stratospheric clouds which makes depletion at faster rate

Why Antarctic Ozone depletion is more than that of Arctic Ozone depletion

Polar Stratospheric Clouds are at much lower altitude
Strong and longevity Polar Vertex over Antarctica th an Arctic pole
Very Cold temperature than Arctic (formation of more clouds and strong vortex)

Ozone Measurement

Dobson Spectrophotometer

Umheher Technique
Thickness of Ozone column(Compressed at Standard Temperature and Pressure) in millicm
One Dobson Unit = 2.69 * 1020 molecules per square meter

M83 - Filter ozonometer
Total Ozone Mapping Spectrometer TOMS in Nimbus-7 satellite

History of Ozone depleting Substances

First Generation

CFC[R12]

High ODP

Montreal protocol

Phased out

Developed countries by 2000
Developing countries by 2010

Second Generation

HCFC [R22]

Low ODP but high GWP

Montreal protocol amended

	Freeze	Phase out
Developed countries	2004	2020
Developing countries	2013	2030

As per Indian Ozone Depleting Substances Rules,2000, HCFC phaseout is 2040

India banned HFC-R23 (byproduct of HCFC R22)

Third Generation

HFC [R134a]

No ODP but high GWP

Kigali Deal Nov 2017 came into force.

Target from Jan 1, 2019

Richest countries like US and few in Europe	Freeze 2018	Reduce to about 15% of 2012 levels by 2036
China, Brazil, all of Africa	Freeze 2024	Reduce to about 20% of 2021 levels by 2045
India, Iran, Pakistan, Saudi	Freeze 2028	Reduce to about 15% of 2025 levels by 2047

Fourth generation

Hydrofluroolefins

No ODP and low GWP

Hydrofluroolefins

Specifically designed to have no ODP and low GWP
They are Chemical compounds consists of Hydrogen, Fluorine, Carbon
The difference with that of HFC is HFC is derivates of Carbon alkanes while olefins is derivates of carbon alkenes
Olefins have very short atmospheric life time [few days]
Cons

Some US companies have developed these and patented. Without addressing IPR, countries cannot go forward since of high costs
Hydrofluroolefins degrade quickly and produce a chemical called Trifluoracetic acid which is water soluble and persistent. Hence it bioaccumulate

Ozone Depletion Substances ODS