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What is the danger of NO2? How can it make you sick?

NO2 or nitrogen dioxide is a compound released during combustion processes. Air composes of approximately 80% nitrogen (N2), which is oxidised to nitrogen monoxide (NO) and partially to NO2 by reactions with oxygen (O2) at high temperatures. NO is further oxidised to NO2, which is a strong oxidant, in the atmosphere. NO2 can cause irritation of eyes, nose and throat and when inhaled might cause lung irritations and decreased lung function. In areas with higher levels of nitrogen dioxide, a greater chance of asthma attacks and an increase in hospital stays because of respiratory complaints are observed. It was thought for a long time that NO2 was an indicator for the complex mixture of traffic-related air pollution rather than being harmful itself. A good correlation exists between NO2 and other compounds, such as diesel soot, which makes it difficult to tell which of the two is (the most) harmful. Recent studies however indicate that nitrogen dioxide is more than a proxy for air pollution, but that is harmful as a seperate molecule as well.