1. NITROGEN OXIDES Formation and Relevance

2. WHERE DO NITROGEN OXIDES COME FROM? The most important forms of reactive nitrogen in the air are nitrogen monoxide (NO) and nitrogen dioxide (NO 2 ) and together we call them NOx. The most important forms of reactive nitrogen in the air are nitrogen monoxide (NO) and nitrogen dioxide (NO 2 ) and together we call them NOx. Nitrogen oxides are formed in the atmosphere mainly from the breakdown of nitrogen gas (N 2 ). Nitrogen oxides are formed in the atmosphere mainly from the breakdown of nitrogen gas (N 2 ). Because the two nitrogen atoms in N 2 are bound very strongly together (with a nitrogen to nitrogen triple bond), it isn't easy to break N 2 down into its atoms. Because the two nitrogen atoms in N 2 are bound very strongly together (with a nitrogen to nitrogen triple bond), it isn't easy to break N 2 down into its atoms.

3. A few bacteria have developed special mechanisms to do this and very high temperatures can also break the molecule down. A few bacteria have developed special mechanisms to do this and very high temperatures can also break the molecule down. Vehicle engines operate at high enough temperatures and nitrogen oxides are emitted in the exhaust fumes. Catalytic converters fitted to cars decrease the production of these harmful compounds. Vehicle engines operate at high enough temperatures and nitrogen oxides are emitted in the exhaust fumes. Catalytic converters fitted to cars decrease the production of these harmful compounds. Nitrogen oxides can also be formed when biomass is burnt and during lightning. Nitrogen oxides can also be formed when biomass is burnt and during lightning.

4. WHERE ARE THEY INVOLVED? NOx (= NO + NO 2 ) and other nitrogen oxides are important in almost all atmospheric reactions. NOx (= NO + NO 2 ) and other nitrogen oxides are important in almost all atmospheric reactions. Another form of nitrogen oxide, the very reactive nitrate radical (NO 3 ) is formed in the dark and this controls the chemistry of the night time atmosphere. Another form of nitrogen oxide, the very reactive nitrate radical (NO 3 ) is formed in the dark and this controls the chemistry of the night time atmosphere.

5. Nitrogen oxides react with water to form nitric acid (HNO 3 ). Nitrogen oxides react with water to form nitric acid (HNO 3 ). Nitric acid is not only a major contributor to acid rain but is also the main way in which nitrogen oxides are removed from the air, either by dry deposition of the acid directly or by removal in rain. Nitric acid is not only a major contributor to acid rain but is also the main way in which nitrogen oxides are removed from the air, either by dry deposition of the acid directly or by removal in rain. Nitric acid is also important in polar stratospheric cloud chemistry. Here it occurs as nitric acid trihydrate and this species plays a part in the formation of the ozone hole. Nitric acid is also important in polar stratospheric cloud chemistry. Here it occurs as nitric acid trihydrate and this species plays a part in the formation of the ozone hole.

6. NAMES OF NITROGEN COMPOUNDS FormulaSystematic NameCommon Name NOnitrogen monoxidenitric oxide N2ON2Odinitrogen monoxidenitrous oxide NO 2 nitrogen dioxidenitrogen peroxide N2O5N2O5 dinitrogen pentoxidenitric anhydride N2O3N2O3 dinitrogen trioxidenitrous anhydride HNO 3 -nitric acid NH 3 -ammonia

7. NITROGEN AND THE OZONE LAYER Nitrogen oxides are very important in the formation and loss of tropospheric ozone. Nitrogen oxides are very important in the formation and loss of tropospheric ozone. They are involved in catalytic cycles and continuously react and reform. They are involved in catalytic cycles and continuously react and reform. Nitrogen dioxide (NO 2 ) is broken down by sunlight to form nitrogen monoxide (NO). Nitrogen dioxide (NO 2 ) is broken down by sunlight to form nitrogen monoxide (NO). This NO then re-reacts to form more NO 2. This NO then re-reacts to form more NO 2. Ozone and unstable oxygen compounds known as hydroxy-radicals can also be involved in this cycle. Ozone and unstable oxygen compounds known as hydroxy-radicals can also be involved in this cycle. We emit far too much of these nitrogen oxides during combustion processes, particularly from vehicles. The main aim of fitting catalytic converters to cars is to reduce the emission of these compounds into the air. We emit far too much of these nitrogen oxides during combustion processes, particularly from vehicles. The main aim of fitting catalytic converters to cars is to reduce the emission of these compounds into the air.

8. OTHER IMPORTANT NITROGEN GASES Nitrous oxide (N 2 O) which is formed during microbiological degradation processes. It is an important greenhouse gas but does not react in the troposphere. In the stratosphere it destroys ozone. Nitrous oxide (N 2 O) which is formed during microbiological degradation processes. It is an important greenhouse gas but does not react in the troposphere. In the stratosphere it destroys ozone. Ammonia (NH 3 ) is the most important basic gas in the atmosphere. It comes mainly from agriculture, both from the storage of animal wastes and from fertiliser use. It reacts in the atmosphere with acid species like nitric acid to form aerosol particles. Ammonia (NH 3 ) is the most important basic gas in the atmosphere. It comes mainly from agriculture, both from the storage of animal wastes and from fertiliser use. It reacts in the atmosphere with acid species like nitric acid to form aerosol particles.

9. NITROGEN OXIDES – AT THE CENTRE OF ATMOSPHERIC CHEMISTRY Nitrogen oxides are really at the centre of atmospheric chemistry. Most chemical compounds which are oxidised and removed from the air or are transformed into other chemical species come into touch directly or indirectly with NO or NO 2. Nitrogen oxides are really at the centre of atmospheric chemistry. Most chemical compounds which are oxidised and removed from the air or are transformed into other chemical species come into touch directly or indirectly with NO or NO 2. For Further Information check out http://www.atmosphere.mpg.de/enid/9e6bcfb50de0564f365187fd4bec79d6,0/basics /3__Ozone_and_nitrogen_oxides_239.html For Further Information check out http://www.atmosphere.mpg.de/enid/9e6bcfb50de0564f365187fd4bec79d6,0/basics /3__Ozone_and_nitrogen_oxides_239.html http://www.atmosphere.mpg.de/enid/9e6bcfb50de0564f365187fd4bec79d6,0/basics /3__Ozone_and_nitrogen_oxides_239.html http://www.atmosphere.mpg.de/enid/9e6bcfb50de0564f365187fd4bec79d6,0/basics /3__Ozone_and_nitrogen_oxides_239.html

10. THE NITROGEN CYCLE The complex interrelationship between atmospheric nitrogen, nitrate, nitrate and ammonium ions found in soils, and organic nitrogen compounds found in living matter, is called the nitrogen cycle. The complex interrelationship between atmospheric nitrogen, nitrate, nitrate and ammonium ions found in soils, and organic nitrogen compounds found in living matter, is called the nitrogen cycle. The nitrogen cycle keeps the nitrogen content of the atmosphere constant. The nitrogen cycle keeps the nitrogen content of the atmosphere constant. Nitrogen fixation refers to the conversion of nitrogen gas into nitrogen compounds. Nitrogen fixation refers to the conversion of nitrogen gas into nitrogen compounds. Nitrification is the process of converting one nitrogen compound to another. Nitrification is the process of converting one nitrogen compound to another. Denitrification is the process of releasing nitrogen gas back into the atmosphere. Denitrification is the process of releasing nitrogen gas back into the atmosphere.

11. N 2 gas in the atmosphere can be changed into soluble nitrogen compounds in the soil. N 2 gas in the atmosphere can be changed into soluble nitrogen compounds in the soil. Electrical storms can produce small quantities of nitrates (NO 3 - ) and nitrates (NO 2 - ) which are carried to earth in rain. Electrical storms can produce small quantities of nitrates (NO 3 - ) and nitrates (NO 2 - ) which are carried to earth in rain. Some plants, like legumes, can convert atmospheric N 2 gas into nitrogen compounds which can be converted by bacteria into nitrates (NO 3 - ), which plants can use to make plant proteins. Some plants, like legumes, can convert atmospheric N 2 gas into nitrogen compounds which can be converted by bacteria into nitrates (NO 3 - ), which plants can use to make plant proteins. Soluble nitrogen compounds in soil can be taken up by plants to make plant proteins. Soluble nitrogen compounds in soil can be taken up by plants to make plant proteins. Animals eat the plants and by the process of digestion convert the plant proteins to animal proteins. Animals eat the plants and by the process of digestion convert the plant proteins to animal proteins. Plants and animals die and their decomposing cells release N 2 gas back into the atmosphere. Plants and animals die and their decomposing cells release N 2 gas back into the atmosphere.

12. THE NITROGEN CYCLE DIAGRAM

13. THE NITROGEN CYCLE IS THE OXIDATION AND REDUCTION OF NITROGEN Nitrogen Cycle N 2(g) → NH 4 + (aq) → NO 2 - (aq) → NO 3 - (aq) Nitrogen Cycle N 2(g) → NH 4 + (aq) → NO 2 - (aq) → NO 3 - (aq) Oxidation No of N 0 → -3 → +3 → +5 Oxidation No of N 0 → -3 → +3 → +5 Reaction Type reduction oxidation oxidation Reaction Type reduction oxidation oxidation