promoting the sustainable and responsible use of cobalt in all forms

Cobalt in the atmosphere

This short article aims to bring together information on cobalt in the atmosphere.

What are the sources for cobalt in the air?

As cobalt is a non-volatile material, it is rarely found in the atmosphere alone. Typically it is found in the air attached to anthropogenic pollutant particles, with a fraction of the cobalt found in natural dust. Natural sources of cobalt-containing dust include the weathering of local rocks and soils, volcanic eruptions, forest fires and seawater spray.

Cobalt is released into the air from both natural processes and man-made activities.

There are also a number of sources for cobalt-containing particles resulting from man’s activities. Small amounts of cobalt may be released into the atmosphere from coal-fired power plants and incinerators, vehicular exhaust, industrial activities relating to the mining and processing of cobalt-containing ores, and the production and use of cobalt alloys and chemicals (Faroon et al. 2004). In many countries, there is a limit on the amount of cobalt which industrial plants can release. Cobalt from combustion sources is primarily in the form of oxides (Kim et al. 2006). Coarse particles with diameters greater than 2µm may be deposited within 10km of the point of emission, whilst smaller particles may travel further.


How much cobalt is in the atmosphere?

Friberg et al (1986) reported average natural background levels of cobalt in the atmosphere at around 1.0x10-9mg/m3 and stated that the atmospheric concentrations of cobalt in remote areas is very low (less than 1.0x10-10mg/m3 in the Antarctic) while in urban areas the ambient air concentration is usually higher (in the order of 1.0x10-6mg/m3 and exceeding 1.0x10-5mg/m3 in heavily industrialised cities). Seiler et al (1988) reported the cobalt concentrations in ambient air in several places in North and South America and in the United Kingdom and found that the levels were in the range 7.0x10-8 to 5.0x10-6mg/m3. Over the open ocean, cobalt concentrations ranged from 0.0004 to 8.0x10-8mg/m3 (Chester et al. 1991)

Khan et al (2003) investigated dustfall in Peshawar (Pakistan) and found levels of cobalt in collected dust samples at around 68µg/g. These levels were ascribed to industrial uses such as the manufacture of alloys and its use as an industrial catalyst, although no direct evidence was given for this relationship.


Where does the cobalt end up?

Ultimately, 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 stays in the atmosphere depends upon factors such as meteorological conditions, particle size, density and form.

Rainwater washes out any soluble cobalt species which are in the atmosphere. Studies have identified mean cobalt concentrations in rainwater to be between 0.3µg/L in rural areas and 1.7µg/L in highly industrial areas (Arimoto 1985; Hansson et al. 1988). Data from the Swedish Environmental Research Institute (ECOLAS, personal communication) indicate that cobalt levels in precipitation over rural areas were below 0.039µg/L between 2001 and 2003. Similar values were seen in the Netherlands for 1999 and 2000 with the annual concentration of cobalt in rainwater being 0.35µg/L and 0.59µg/L respectively, translating to a mean annual cobalt wet deposition rate of 47.1µg/m2 in the Netherlands for 1999 and 2000. In comparison a wet deposition level of 12µg/m2 was found in Massachusetts Bay as part of a total (wet and dry) of 47µg/m2 between September 1992 and September 1993 (Golomb et al. 1997).

Studies in the UK have shown that between 33 and 44% of the cobalt occurred as stable organic complexes (Nimmo and Fones, 1997), meaning it was not bio-available to soil dwelling or aquatic organisms. Total cobalt deposition flux at a site in the Rhone delta in southern France in 1988-1989 was 420±230µg/m2 year with 150µg/m2 year in the form of wet deposition (Guieu et al. 1991).


References and further reading


DISCLAIMER

This summary is intended to provide general information about the topic under consideration. It does not constitute a complete or comprehensive analysis, and reflects the state of knowledge and information at the time of its preparation. This summary should not be relied upon to treat or address health, environmental, or other conditions.