An aerosol is a suspension of a solid or liquid particle in the air. For health purposes, aerosol or particulate matter (PM) is typically defined by size, with the smaller particles having more health impact. Commonly quoted values for PM are total particulate matter (TPM) or total suspended particles (TSP); particles with a diameter <10 µm (PM10); and particles with a diameter <2.5 µm (PM2.5). The effects and guidelines given here apply only to the size of the aerosol, but surface properties, chemical composition, and multi-species interactions may also be important in governing impacts and these require further study. Halogen and some sulphate aerosols are acidic, and it is thought that acidic PM may pose a greater risk to health than non-acidic. Metals contained in volcanic plumes, such as mercury, iridium, arsenic, and others, can catalyse reactions, and particularly in combination with acid gases and aerosols, increase health effects. In addition, volcanic aerosols are typically PM2.5 (e.g. Allen et al., 2002), a size fraction that is able to penetrate into the deepest parts of the lung. Fine ash is an aerosol and may also be acidic if it has adsorbed acid gases in the plume. Certain types of ash also may have an associated silicosis risk (e.g. Baxter et al., 1999). These extended impacts are not considered here.
CAUTION: Most studies of exposure effects are based on urban pollution and so are not representative of volcanic pollution. A high proportion of volcanic aerosol is acidic and there is concern that acidic aerosol may be more severe on the respiratory system than non-acidic aerosol. The effects and guidelines provided here should thus be taken as indicative only.
Since the depth to which particulate matter can penetrate the respiratory system is dependent on size, fine particles (PM2.5) have a higher probability of deposition in the alveoli of the lungs and are associated with a greater health risk than larger particles. Particles of this small size also have residence times of days to weeks in the troposphere and can travel distances of hundreds to thousands of kilometres allowing them to be widely dispersed. The effects of even smaller "ultrafine" particles (<0.1 µm in diameter) on health are not well understood, but are of current concern. Recent studies suggest that, even at low levels (<100 µg m-3), short-term exposure to PM of any size range is associated with health effects (WHO, 1999), and that strong aerosol acidity or high sulphate content may contribute to the effects associated with PM2.5. Epidemiological studies have shown that both daily mortality and hospital admissions increase with increasing PM in the surface boundary layer and that the effects for PM2.5 are amplified over those for PM10 (e.g. Braga et al., 2001). The scale of these increases is only on the order of half to a few percent and these associations are only valid over a period of a few days. Once the exposure to air pollution has finished there are generally no long-term effects unless the initial dosage was very high (this is more likely in an industrial accident than in a volcanic context). The short-term impacts of PM are on the respiratory and pulmonary systems of the body. Asthmatics and people with existing respiratory problems may experience reactions at lower concentrations than others.
Ambient and occupational guidelines exist for particulate matter. Some guidelines are for total particulate matter (TPM), whereas others are for particular size fractions - usually PM10 or PM2.5. Guidelines for acidic aerosol do not exist. In 1971, the USA Environmental Protection Agency (EPA) set the level of particulate matter that could cause significant harm to the health of persons at 1000 µg m-3 (24-hour average). Importantly, this level is reduced when sulphur dioxide is also present at elevated concentrations. The tables show that this EPA value is considerably lower than the present USA occupational guidelines. Inhalation of aerosol can be prevented using respirators of an appropriate standard.
Ambient air quality guidelines for particulate matter/aerosol
|Averaging period||Guideline type||Date of implemen-
|Argentina||TPM||150||1 month||16 April 1973||Ley 20.284||a|
|Chile||TPM||260||24 hours||not to be exceeded more than once per year||22 June 1978||Resolución No. 1215||a|
|75||Annual||22 June 1978||Resolución No. 1215||a|
|PM10||150||24 hours||24-hr standard not to be exceeded by the annual 98th percentile||25 May 1998||Decreto Supremo No 59/98||a|
|24 hours||January 1996||GB 3095-1996||a|
|Annual||January 1996||GB 3095-1996||a|
|24 hours||January 1996||GB 3095-1996||a|
|Annual||January 1996||GB 3095-1996||a|
|Columbia||TPM||400||24 hours||not to be exceeded more than once per year||11 January 1982||Decreto No. 2||a|
|100||Annual||11 January 1982||Decreto No. 2||a|
|Costa Rica||TPM||240||24 hours||not to be exceeded more than once per year||Reglamento sobre inmisión de contaminantes atmosféricos||a|
|90||Annual||Reglamento sobre inmisión de contaminantes atmosféricos||a|
|PM10||150||24 hours||not to be exceeded more than once per year||Reglamento sobre inmisión de contaminantes atmosféricos||a|
|50||Annual||Reglamento sobre inmisión de contaminantes atmosféricos||a|
|Ecuador||TPM||250||24 hours||not to be exceeded more than once per year||15 July 1991||Registro Oficial No. 726||a|
|80||Annual||15 July 1991||Registro Oficial No. 726||a|
|EU||PM10||50||24 hours||not to be exceeded more than 35 times a calendar year||1 January 2005||COUNCIL DIRECTIVE 1999/30/EC||b|
|40||Annual||1 January 2005||COUNCIL DIRECTIVE 1999/30/EC||b|
|Japan||PM10 (SPM)||200||1 hour||8 May 1973||c|
|100||24 hours||8 May 1973||c|
|Mexico||TPM||260||24 hours||Not to be exceeded||23 December 1994||NOM-024-
|75||Annual||23 December 1994||NOM-024-
|PM10||150||24 hours||Not to be exceeded more than once per year||23 December 1994||NOM-025-SSA1-
|50||Annual||23 December 1994||NOM-025-
|New Zealand||PM10||50||24 hours||May 2002||d|
|UK||PM10||50||24 hours||not to be exceeded more than 35 times a calendar year||31 December 2004||The Air Quality (England) Regulations 2000||e|
|40||Annual||31 December 2004||The Air Quality (England) Regulations 2000||e|
|USA||PM10||150||24 hours||Primary & Secondary||1990||NAAQS||f|
|50||Annual||Primary & Secondary||1990||NAAQS||f|
|PM2.5||65||24 hours||Primary & Secondary||1990||NAAQS||f|
|15||Annual||Primary & Secondary||1990||NAAQS||f|
- (i) Sensitive areas of special protection; (ii) typical urban and rural areas and (iii) special industrial areas.
- European Commission Guidelines Website
The ambient particulate matter guidelines table above demonstrates the tremendous range of international guidelines that exist. Difference between country's guidelines may be explained by the age of the guideline, the practical achievement of a standard based on current and predicted pollution levels or the data from which the standard was set (e.g. epidemiological study versus actual pollution levels). The table below summarises the range of main guideline values for each particle size.
Summary of the ranges of ambient particulate matter guideline levels
Occupational guidelines for particulate matter/aerosol
|Averaging period||Guideline type||Relevant Law||Ref.|
|USA||TPM||15000||8 hour TWA||Permissible Exposure Limit (PEL)||OSHA Regulations (Standards - 29 CFR)||a|
|PM10||5000||8 hour TWA||Permissible Exposure Limit (PEL)||OSHA Regulations (Standards - 29 CFR)||a|
Volcanic particulate emissions cause problems over a range of distances from the vent and the highest levels of particulate matter may be found in areas tens of km away from the volcano (e.g. Yano et al., 1990). In addition, at degassing volcanoes, levels of sulphate aerosol (SO42-) close to the vent can be dangerously high:
- Masaya, Nicaragua: Maximum sulphate concentrations recorded on the crater rim in December 2001 were ~165 µg m-3 (6-hour average) (Mather et al., 2003). The mean value was ~125 µg m-3, which is almost double the USA 24-hour ambient guideline for PM2.5, although not nearly as high as the PM10 occupational guidelines. Since sulphate aerosol is consistently in the PM2.5 size range, and is likely strongly acidic, these measurements imply a possible health hazard to volcanologists working at the crater and tourists visiting the crater-rim car park. The adverse impact of acid deposition downwind is also well recognised here (Delmelle et al., 2002).
In some cases, in-plume aerosol concentrations can be quite low. For instance, plume concentrations of SO42- 10-300 km downwind of Etna, Italy in September 1983 were of order of magnitude 0.1-10 µg m-3 (Bergametti et al., 1984; Martin et al., 1986) and in 1989-90 mean PM10 levels tens of km downwind of the active Kilaeua vent on the Island of Hawaii were 11.1 µg m-3. Both of these examples are within ambient levels. However, one-hour averages of PM2.5 >80 µg m-3 have been measured at the popular National Park Visitor Center at the summit of Kilauea, during specific wind conditions (National Park Service, 2003 unpublished data). From 1987-1991, during the continuous phase of the Kilauea eruption, emergency room visits and hospital admissions for chronic obstructive pulmonary disease and asthma increased on the Island of Hawaii (Mannino et al., 1996), as compared to rates from 1981-1986, but a direct link between this increase and volcanic PM or gas emissions could not be established. The presence of metals and acid aerosol in the Kilauea plume also raises concerns regarding the health effects of volcanic pollution. The acidic mixture of volcanic gas and aerosol produced by Kilauea has been named "vog".
Further downwind of active volcanoes particulate levels can be raised intermittently depending on the activity of the volcano and weather conditions.
- Popocatepetl, Mexico: Particulate sulphate levels in Mexico City can be doubled by emissions from Popocatepetl (Moya et al., 2003; Raga et al., 1999). PM10 levels in the city already exceed the Mexican 24-hour standard on most days of the year due to vehicular and fixed emission sources (Moya et al., 2003) so the contribution of volcanic aerosol substantially increases the health hazard. From December 1994 to April 1995, the peak concentration of total suspended particles from Popocatepetl emissions ~15 km away from the volcano was 1440 µg m-3 (Rojas-Ramos et al., 2001), more than five times Mexico's 24-hr TPM standard.
- Volcan de Colima, Mexico: There is some evidence that fine (PM1.5 - PM2.5) S, Cl, Cu and Zn aerosol is increased in the city of Colima, Mexico by emissions from the volcano during favourable wind conditions (Miranda et al., 2004).
- Sakurajima, Japan: Hourly average TSP concentrations recorded ~35 km from the erupting volcano were >200 µg m-3 on 53 occasions in 1980, with a maximum value of 345 µg m-3 exceeding Japanese ambient air quality standards (Yano et al., 1986). In January 1986, the maximum PM10 concentrations 25 km downwind were similarly >340 µg m-3 (Yano et al., 1990).
- Soufrière Hills, Montserrat: Ambient concentrations of PM10 and respirable dust in the region immediately downwind of the volcano were frequently in the range of 100-500 µg m-3 during the ongoing eruption in 1997 and 1998 (Searl et al., 2002), exceeding UK air quality standards. Much of this was resuspended ash, meaning that personal exposure levels were considerably higher for certain activities, such as sweeping, when occupational exposures were frequently exceeded.
Large eruptions cause problems due to the amount of fine ash they erupt; these health impacts have been reviewed by Horwell & Baxter, 2006:
- Mt St Helens, USA: Following the 18 May 1980 eruption, total suspended particulate levels downwind averaged 33402 µg m-3 and remained above 1000 µg m-3 for a week (compared to the mean level of 80 µg m-3) (Baxter et al., 1983), exceeding the ambient and EPA significant harm standards. The majority of the deposited tephra was PM10 and this was found to be responsible for increases in respiratory morbidity (Bernstein et al., 1986). The groups most heavily exposed to resuspended ash following the eruption were emergency workers and police officers (Baxter et al., 1981).
- Pinatubo, Philippines: Ash is suspected to have been the cause of increased mortality due to respiratory infection in the area of Pinatubo in the months following its 1991 eruption (Mason, 2002).
Anecdotal evidence from many volcanoes shows that ash and acid aerosol in the vicinity of volcanic plumes can be an irritant to the eyes, skin and respiratory system, but relatively few studies have examined the impacts of volcanic particulate matter on human health. These studies include investigations of health effects related to the eruptions of Kilauea, Hawaii (e.g., Mannino et al., 1996); Mount St. Helens, USA (e.g., Baxter et al., 1981; Baxter et al 1983; Bernstein et al., 1986); Mt. Spurr (Choudhury et al., 1997; Gordian et al., 1996); Popocatepetl, Mexico (Rojas-Ramos et al., 2001); Ruapehu, New Zealand (Hickling et al., 1999); Sakurajima, Japan (e.g., Wakisaka et al., 1988, Yano et al., 1986); Soufrière Hills, Montserrat (e.g. ,Forbes et al. 2003); and Soufriere, St Vincent (e.g., Leus et al., 1981). In some of these studies, positive associations between increased volcanic particulate and certain health outcomes have been found for both acute and chronic exposure. However, it is difficult to separate the effects of ash, gas, and aerosols of various chemical compositions. In addition, the health measures examined in the studies were variable, with some more appropriate for discerning effects than others. Further work is required to determine the direct contribution of volcanic aerosol to ill health.
Allen, A.G., Oppenheimer, C., Ferm, M., Baxter, P.J., Horrocks, L.A., Galle, B., McGonigle, A.J.S. and Duffell, H.J., 2002. Primary sulfate aerosol and associated emissions from Masaya Volcano, Nicaragua. Journal of Geophysical Research 107(D23).
Baxter, P.J., Ing, R., Falk, H. and Plikaytis, B., 1983. Mount St. Helens eruptions: the acute respiratory effects of volcanic ash in a North American community. Archives of Environmental Health, 38(3): 138-143.
Baxter, P.J., Ing, R., Falk, H., French, J., Stein, G.F., Bernstein, R.S., Merchant, J.A. and Allard, A., 1981. Mount St Helens eruptions, May 18 to June 12, 1980. Journal of the American Medical Association, 246(22): 2585-2589.
Baxter, P.J., Bonadonna, C., Dupree, R., Hards, V.L., Kohn, S.C., Murphy, M.D., Nichols, A., Nicholson, R.A., Norton, G., Searl, A., Sparks, R.S.J. and Vickers, B.P., 1999. Cristobalite in volcanic ash of the Soufrière Hills volcano, Montserrat, British West Indies. Science, 283: 1142-145.
Bergametti, G., Martin, D., Carbonnelle, J., Faivre-Pierret, R. and Vie Le Sage, R., 1984. A mesoscale study of the elemental composition of aerosols emitted from Mt. Etna Volcano. Bulletin of Volcanology, 47(4(2)): 1107-1114.
Bernstein, R.S., Baxter, P.J., Falk, H., Ing, R., Foster, L. and Frost, F., 1986. Immediate public health concerns and actions in volcanic eruptions: lessons from the Mount St. Helens eruptions, May 18 - October 18, 1980. American Journal of Public Health, 76(Supplement): 25-37.
Braga, A.L.F., Zanobetti, A. and Schwartz, J., 2001. The lag structure between particulate air pollution and respiratory and cardiovascular deaths in 10 US cities. Journal of Occupational and Environmental Medicine, 43(11): 927-933.
Choudhury, A.H., Gordian, M.E. and Morris, S.S., 1997. Associations between respiratory illness and PM10 air pollution. Archives of Environmental Health, 52(2): 113-117.
Delmelle, P., Stix, J., Baxter, P.J., Garcia-Alvarez, J. and Barquero, J., 2002. Atmospheric dispersion, environmental effects and potential health hazard associated with the low-altitude gas plume of Masaya volcano, Nicaragua. Bulletin of Volcanology 64(6), 423-434.
Forbes, L., Jarvis, D., Potts, J. and Baxter, P.J., 2003. Volcanic ash and respiratory symptoms in children on the island of Montserrat, British West Indies. Occupational and Environmental Medicine, 60(3): 207-211.
Gordian, M.E., Özkaynak, H., Xue, J., Morris, S.S. and Spengler, J.D., 1996. Particulate air pollution and respiratory disease in Anchorage, Alaska. Environmental Health Perspectives, 104(3): 290-297.
Hickling, J., Clements, M., Weinstein, P. and Woodward, A., 1999. Acute health effects of the Mount Ruapehu (New Zealand) volcanic eruption of June 1996. International Journal of Environmental Health Research, 9(2): 97-107.
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Martin, D., Ardouin, B., Bergametti, G., Carbonnelle, J., Faivre-Pierret, R., Lambert, G., Le Cloarec, M.F. and Sennequier, G., 1986. Geochemistry of sulfur in Mount Etna plume. Journal of Geophysical Research, 91(B12): 12,249-12,254.
Mason, B., 2002. Pinatubo dust is still a killer. New Scientist, 175(2351): 7.
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Moya, M., Castro, T., Zepeda, M. and Baez, A., 2003. Characterization of size-differentiated inorganic composition of aerosols in Mexico City. Atmospheric Environment, 37(25): 3581-3591.
Raga, G.B., Kok, G.L., Baumgardner, D., Baez, A. and Rosas, I., 1999. Evidence for volcanic influence on Mexico City aerosols. Geophysical Research Letters, 26(8): 1149-1152.
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