Cobalt in the atmosphere

Cobalt is released into the air both from natural processes and from man’s activities.

As a non-volatile material, cobalt is rarely found in the atmosphere alone, but is more generally attached to particles in the air generated by man-made pollution, while a fraction of cobalt is found in natural dust originating from weathering of rocks and soils, volcanic eruptions, forest fires and seawater spray.

Sources for cobalt-containing particles in the atmosphere resulting from man’s activities include small amounts released from coal-fired power plants and incinerators, vehicle exhausts, mining and processing of cobalt-containing ores, and the production and use of cobalt alloys and chemicals.

Many countries limit the amount of cobalt which industrial plants can release. Cobalt from combustion sources is primarily in the form of oxides.

Coarse particles with diameters greater than 2 µm may be deposited within 10 km of the point of emission, whilst smaller particles may travel further.

Natural sources of cobalt-containing dust include volcanic eruptions, forest fires and seawater spray.

Average natural background levels of cobalt in the atmosphere are reported to be approximately 1.0 ng/m3 while atmospheric concentrations of cobalt in remote areas are very low (less than 1.0 x 10-3ng/m3 in the Antarctic) but usually higher in urban areas (in the order of 10 ng/m3 in source areas). Cobalt concentrations in ambient air in several places in North America and in Europe have been found at levels in the range 0.1 to 48 ng/m3.

When dust settles out of the atmosphere it can either land on soil, where it will eventually add to the soil concentration of cobalt, or into water where it will find its way to bottom sediments, both of which are discussed in other documents available on this website. The length of time that cobalt remains in the atmosphere depends on factors such as meteorological conditions, particle size, density and form.

Rainwater washes out any soluble cobalt in the atmosphere. Studies have identified mean cobalt concentrations in rainwater to be between 0.3 µg/L in rural areas and 1.7 µg/L in highly industrial areas.

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