What is nitrate?
In an engine combustion chamber a series of reactions occur that oxidise a small part of the nitrogen in the charge air and the majority of the nitrogen in the fuel oil so that nitric oxide (NO) is formed. In the cooler exhaust after the combustion chamber approximately 5-10% of the NO is then converted to nitrogen dioxide (NO2) in the presence of excess oxygen [3]. Collectively NO and NO2 are often referred to as NOx.
When NO2 is dissolved in water it is converted by a series of reactions to nitric acid (HNO3), which is then readily ionised to nitrate (NO3-).
Relevant Chemistry
2NO (nitric oxide) + O2 <> 2NO2 (nitrogen dioxide)
2NO2 + H2O <> HNO2 (“nitrous acid”) + HNO3 (nitric acid)
Note: nitrous acid is only known in solution and in the form of nitrite (NO2-) salts
3HNO2 <> HNO3 + 2NO + H2O
2NO + O2 <> 2NO2
So overall
4NO2 + 2H2O + O2 <> 4HNO3 (nitric acid)
Nitrate is an important nutrient in the sea, and over-enrichment is known as eutrophication. If sufficient this promotes growth of organisms such as algae. A rapid increase or accumulation in the population of algae is known as an algal bloom, which can disrupt functioning of an aquatic system, causing a variety of problems such as a lack of oxygen in the water needed for fish and shellfish to survive [8].
