Nitrogen oxides

Source

The most natural way of forming nitrogen oxides [NO_x(g), where x may be 1 or 2] is lightning. Atmospheric nitrogen reacts with nearby oxygen to form nitrogen monoxide.

Nitrogen monoxide further reacts with oxygen to form nitrogen dioxide.

But this only generate limited amount of nitrogen oxides. The pollution caused can be accounted for the engines of vehicles and furnaces. Due to their high temperature, these gases are evolved easily. The great number of cars on Hong Kong roads deepens the problem.

Health Effects

Nitrogen dioxide is much less soluble than sulphur dioxide. It penetrates deeply into smaller airways and lung parenchyma, causes pulmonary oedema at high concentrations. It may also damage the blood vessels.

Nitrogen dioxide is a major component of photochemical smog. Photochemical smog causes headaches, eye, nose and throat irritations, impaired lung function, coughing and wheezing.

Yellowish brown nitrogen dioxide Social Effects

Nitrogen dioxide is acidic in nature. Therefore, besides sulphur dioxide, it is another gas that will cause acid rain.

The gas, together with hydrocarbons and particulates, forms photochemical smog under sunlight. Its brown coloration obscure the sky with a yellow haze that lowers the visibility. This drives away tourists from coming.