Natural sources of nickel to the atmosphere include soil dust, forest fires, particle releases from vegetation and sea salt. Anthropogenic sources of nickel released to the atmosphere are primarily from fossil fuel (oil and coal) combustion, high-temperature metallurgical operations, nickel primary production operations, and municipal waste incineration. Other sources include coke ovens, cement manufacturing, asbestos mining/milling, and cooling towers.
In major nickel producing countries such as Canada, the most important anthropogenic sources of nickel to air are the primary base metal smelter and refineries, followed by fossil fuel combustion. Nickel in air is mainly in the particulate form, with particle sizes ranging from 0.1 to 2 μm. Nickel associated with these particles is mainly in the form of nickel sulphate, nickel chloride, nickel nitrate, and nickel oxide, the sulphates resulting from the oxidation of nickel by sulphur dioxide. Airborne nickel particles eventually end up being precipitated with rainfall and therefore end up in water and soil.
Adverse health effects from the inhalation of nickel can occur and these are associated with inhalation of the inorganic form. The respiratory system is the prime target of nickel inhalation toxicity in both animals and humans. Further information on the health effects of nickel can be found here.