Nitrogen Dioxide (NO2 ) is one of a group of reactive gases known as oxides of nitrogen or nitrogen oxides (NOx). Other nitrogen oxides include nitrous acid and nitric acid.
NO2 along with other NOx reacts with other chemicals in the air to form both particulate matter and ozone. Both of these are also harmful when inhaled due to effects on the respiratory system.
The most prominent source of NO2 for the public is internal combustion engines burning fossil fuels. Indoors, exposure can arise from cigarette smoke, boilers, ovens and wood burners.
Medical Effects of NO2
According the respected worldwide pollutant data source, the US Environmental Protection Agency, breathing air with a high concentration of NO2 can irritate airways in the respiratory system. Exposures over short periods can aggravate respiratory diseases, particularly asthma, leading to respiratory symptoms (such as coughing, wheezing or difficulty breathing), hospital admissions and visits to A&E. Longer exposures to elevated concentrations of NO2 can contribute to the development of asthma and potentially increase susceptibility to respiratory infections. People with asthma, as well as children and the elderly are generally at greater risk from NO2 health effects.
In terms of the more exact medical effects, gaseous NO2 diffuses into the epithelial lining fluid (ELF) of the respiratory epithelium and dissolves, and chemically reacts with antioxidant and lipid molecules in the ELF; NO2‘s health effects are caused by the reaction products or their metabolites, which are reactive nitrogen species and reactive oxygen species that can drive bronchoconstriction, inflammation, reduced immune response, and may have effects on the heart. These findings have been derived from experimental animal studies and evidence from controlled human exposure studies.
Sources of NO2 in London
According to Cleaner Air for London (2010 data) in the capital, 63% of NO2 is from ground based transport. Gas consumption accounts for 16% with domestic 7% and non-domestic 9%; construction accounts for 12%, with regulated industrial processes 6% and 3% from other sources.
Of the transport sources, cars are the highest at 28%, with Heavy Goods Vehicles at 18%; buses and coaches 16%; ground based aviation and rail, both at 12%; with shipping and motorcycles both contributing 1%.