Effect On Ozone
Ozone depletion is another mean by which the Earth is warmed after a volcanic eruption; fortunately, it is not the Troposphere that is affected but the Stratosphere. The chlorine gas within the Volcano reacts with hydrogen to produce the Halide acid HCl. Recent studies have indicated that this tends to be confined within the Troposphere where it condenses and falls as precipitation. In 1991 however, Mount Pinatubo erupted producing a plume thirty four kilometres high. The plume reached the stratosphere and satellite imagery indicated ozone depletion between altitudes 16 – 28 kilometres declined by 33%.[1] Directly, the Hydrogen Chloride was not the source of Ozone depletion yet it influences the activation of Chlorine Radicals which estimated to account for just 3% of Chlorine within the Stratosphere in 1991. However, one Chlorine radical can destroy 100,000 molecules of Ozone; hence, even an emission of just 3% can pose great damage. Below are the reactions by which HCl reacts within the Atmosphere to produce Chlorine and other Chlorine containing compounds.
HCl(g) + HOCl(g) -> H20(g) + Cl2(g)
HCl(g) + ClONO2(g) -> HNO3(g) + Cl2(g)
N2O5(g) + HCl(g) -> HNO3 + CLONO
[1] http://en.wikipedia.org/wiki/Mount_Pinatubo
HCl(g) + HOCl(g) -> H20(g) + Cl2(g)
HCl(g) + ClONO2(g) -> HNO3(g) + Cl2(g)
N2O5(g) + HCl(g) -> HNO3 + CLONO
[1] http://en.wikipedia.org/wiki/Mount_Pinatubo
When ultraviolet radiation meets a Chlorine molecule a Cl – Cl bond is broken during the initiation stage, to produce a radical; a species with an unpaired electron. They are very reactive and once generated will react with a molecule of O3. The breakdown of Ozone begins during the Propagation stage, which divides again into two steps.
Initiation:
· Cl2 -> Cl• + Cl•
· ClONO -> ClO• + NO2•
Propagation:
· Cl• + O3 -> ClO• + O2
· ClO• + O3 -> Cl• + 2O2
Initiation:
· Cl2 -> Cl• + Cl•
· ClONO -> ClO• + NO2•
Propagation:
· Cl• + O3 -> ClO• + O2
· ClO• + O3 -> Cl• + 2O2
This chain reaction will continue converting Ozone to Oxygen until two radicals meet to form a molecule. This is referred to as the termination stage of radical substitution; in this case the Oxygen produced may then react with other Oxygen molecules within the atmosphere to produce Ozone thus allowing the cycle to continue. Below are examples of termination with reference to the reactions above.
· ClO• + ClO• -> Cl2 + O2
· Cl• + Cl• -> Cl2
· Cl• + CLO• -> CL2[2]
[2] OCR Chemistry, Dave Gent and Rob Ritchie Page 228
It is not only Chlorine radicals to cause Ozone Depletion but also Bromine containing compounds. As the plume migrates once it has erupted the extreme temperatures cause Bromine to react with oxygen to produce BrO. The Bromine monoxide although in quantities 100 times less than that of Chlorine it is 10x more potent to the atmosphere.[3] The Bromine species again would convert Ozone to Oxygen via the free radical substitution mechanism which in the Troposphere would be beneficial to life but as previously stated not within the Stratosphere.
It is not only Hydrochloric Acid that may contribute to Ozone depletion. During eruptions the sulphur dioxide aerosols emitted allow heterogeneous reactions to occur between halogen containing compounds (HCl, HOCl) that become activated initiating reactions with O3 molecules. Again this is an indirect effect on the cause of Ozone depletion as it is not the actual gases that react with the O3 molecules that catalyse reactions between pre-existing chlorofluorocarbons produced by man. I believe this positive correlation between the emissions of Sulphur Dioxide and increased Ozone depletion show apparent evidence that they are in fact the causative agent as to why Ozone depletion occurs.
[3]http://hvo.wr.usgs.gov/volcanowatch/archive/2005/05_07_28.html
· ClO• + ClO• -> Cl2 + O2
· Cl• + Cl• -> Cl2
· Cl• + CLO• -> CL2[2]
[2] OCR Chemistry, Dave Gent and Rob Ritchie Page 228
It is not only Chlorine radicals to cause Ozone Depletion but also Bromine containing compounds. As the plume migrates once it has erupted the extreme temperatures cause Bromine to react with oxygen to produce BrO. The Bromine monoxide although in quantities 100 times less than that of Chlorine it is 10x more potent to the atmosphere.[3] The Bromine species again would convert Ozone to Oxygen via the free radical substitution mechanism which in the Troposphere would be beneficial to life but as previously stated not within the Stratosphere.
It is not only Hydrochloric Acid that may contribute to Ozone depletion. During eruptions the sulphur dioxide aerosols emitted allow heterogeneous reactions to occur between halogen containing compounds (HCl, HOCl) that become activated initiating reactions with O3 molecules. Again this is an indirect effect on the cause of Ozone depletion as it is not the actual gases that react with the O3 molecules that catalyse reactions between pre-existing chlorofluorocarbons produced by man. I believe this positive correlation between the emissions of Sulphur Dioxide and increased Ozone depletion show apparent evidence that they are in fact the causative agent as to why Ozone depletion occurs.
[3]http://hvo.wr.usgs.gov/volcanowatch/archive/2005/05_07_28.html