CFC substitutes - characteristics

The substitute for CFCs should be safe, low cost, increased energy efficiency of CFC replacement technology, effective refrigerants with low ozone layer depletion potential (ODP) and low global warming potential (GWP).

CFC-12 (R-12) is a widely used refrigerant. HFC 134a (R-134a) is the most promising alternative (R-143a) and (R-152a) can also be used.

19.1.3. Nitrogen Oxides: Source

The sources of nitrogen oxides are mainly explosions of thermonuclear weapons, industrial emissions and agricultural fertilizers.

The chemical reaction

Nitric oxide (NO) catalytically destroys ozone.

Nitric oxide

+ ozone

Nitrogen dioxide + monoxide

Nitric oxide + Oxygen

Nitrogen dioxide + Oxygen

The escape of N2O

Nitrous oxide (N2O) is released from solid through denitrification of nitrates under anaerobic conditions and nitrification of ammonia under aerobic conditions. This N2O can gradually reach the middle of the stratosphere, where it is photolytically destroyed to yield nitric oxide which in turn destroys ozone.

Other substances:

Bromine containing compounds called halons and HBFCs, i.e. hydrobromo fluorocarbons [both used in fire extinguishers and methyl bromide (a widely used pesticide)]. Each bromine atom destroys hundred times of more ozone molecules than what a chlorine atom does.

Bromine + ozone —

Bromine monoxide

+ Oxygen

Bromine monoxide —► + chlorine monoxide Oxygen + Bromine + chlorine

2. The second type of clouds contain nitric acid instead of pure water.

3. The third type of clouds have the same chemical composition as nacreous clouds, but form at a slower rate, which results in a larger cloud with no iridescence.

The chlorine released by the breakdown of CFCs exists initially as pure chlorine or as chlorine monoxide (active chlorine / instable) but these two forms react further to form compounds Chlorine nitrate and HCL that are stable (inactive chlorine).

Chlorine + methane —kHCl + methyliumcation (CH3)

Bromine (Br) combines with ozone forming bromine monoxide (BrO) and Oxygen (O2). The BrO further reacts with chlorine monoxide (ClO) to give oxygen (O2) and free atoms of bromine (Br) and chlorine (Cl). This free atoms can further react with ozone.

Sulphuric acid particles: These particles free chlorine from molecular reservoirs, and convert reactive nitrogen into inert forms thus preventing the formation of chlorine reservoirs.

Carbon tetrachloride (a cheap, highly toxic solvent) and methyl chloroform (used as a cleaning solvent for clothes and metals, and a propellant in a wide range of consumer products, such as correction fluid, dry cleaning sprays, spray adhesives) and other aerosols.