Volcanic Examples and Incidents
Concentrations of sulphur dioxide (SO2) hazardous to human health have been recorded downwind of many volcanoes. The highest concentrations are often seen close to persistently degassing volcanoes:
Kilauea, Hawaii: Ambient concentrations of SO2 in a tourist car park during an episodic increase in activity in 1996 rose to 4.0 ppm (BGVN 21:01), nearly ten times higher than the USA 3-hour concentration guideline. From 1987-2001, the ambient SO2 concentration exceeded the US 24-hour primary health standard on more than 85 occasions at Hawaii Volcanoes National Park Headquarters (Elias, 2002). Such measurements at this popular tourist destination have prompted the introduction of the SO2 guidelines for the park.
Masaya, Nicaragua: Currently actively degassing and in the periods March-April 1998 and February-March 1999 mean concentrations of SO2 measured at downwind sites up to 44 km away had a range of <0.002 - 0.23 ppm (~5-600 µg m-3) (Delmelle et al., 2002). About 30 % of these measurements were above the World Health Organisation (WHO) 24-hour ambient guideline level. Maximum concentrations measured on the Llano Pacaya ridge 14 km away were 0.6 ppm (Horrocks, 2001). In May 2001, the maximum SO2 abundance recorded in the Masaya plume on the edge of the Santiago crater was 3.1 ppm (7950 µg m-3) (Allen et al., 2002). These concentrations indicate a potential risk to the health of the local population and complaints about eye sensitivity and inflammation, bronchitis, sore throats and headaches have been received from local people. It is estimated that ~ 50,000 people are at risk from SO2 and plume induced water pollution in the Masaya region.
Poas, Costa Rica: Residents and scientists in the vicinity of the volcano have complained of eye and throat irritation over time. Long-term measurements of SO2 in populated downwind areas showed mean concentrations up to ~0.28 ppm (730 µg m-3), with short-term measures up to 0.3-0.5 ppm (Nicholson et al., 1996). These levels, observed in 1991 and 1992, exceed the WHO 24-hour ambient guideline values and in some locations exceed the 15-minute level. The highest SO2 levels measured at Poas crater rim were ~ 35 ppm, substantially above all guideline levels.
Villarrica, Chile: SO2 concentrations measured at the crater rim showed that a concentration of 13 ppm (equivalent to the NIOSH 15 min occupational limit for SO2) was often exceeded (Witter and Delmelle, 2004). At the height of the summer tourist season, about 100 tourists climb to the summit of Villarrica volcano per day. A large number of these people are exposed to the noxious gases.
White Island, New Zealand: A pilot health study reported time-averaged measurements of personal exposure to SO2 for a 20 minute period spent downwind of fumaroles of ~6-75 ppm (Durand et al., 2004). These concentrations exceed short-term occupational exposure limits by up to 15 times.
Populations and cities can be seriously affected by SO2 emissions during more explosive volcanic activity:
Soufrière, Guadeloupe: During the 1976 eruption, the population complained of headaches associated with a strong SO2 odour (Le Guern et al., 1980).
Popocatepetl, Mexico: In Mexico City, directly downwind of the persistently active volcano, SO2 concentrations have exceeded 0.08 ppm (160 µg m-3) under the influence of volcanic emissions (Raga et al., 1999). This is more than four times the city's typical monthly average and above most of the recognised annual and 24 hour exposure guidelines.
Sakurajima, Japan: This volcano has been very active in recent history, fumigating a wide region downwind. Maximum hourly SO2 levels in Sakurajima city (~5 km from Sakurajima volcano) in 1980 were 0.84 ppm, exceeding Japanese ambient air quality standards (Yano et al., 1986). From September 1985 to February 1986, monthly average SO2 concentrations measured at the base of Sakurajima ranged from 0.015 ppm to 0.138 ppm, with an average of 0.079 ppm for the period (Kawaratani and Fujita, 1990). Epidemiological investigations into health in the region surrounding the volcano have shown positive associations between SO2 concentrations and adult mortality from bronchitis and neonatal mortality (Shinkuro et al., 1999; Wakisaka et al., 1988).
Miyakejima, Japan: In autumn 2000, southerly and southwesterly winds brought the volcanic gases emitted by Miyakejima to the main island and caused high concentrations of SO2 at many surface stations 100-400 km downwind (e.g. Naoe et al., 2003). At 88 km distance, maximum SO2 surface levels were ~0.114 ppm, compared to 0.0028 ppm at the same time in the previous year (An et al., 2003). At 4.5 km, the maximum recorded hourly concentration was 0.945 ppm. This is more than nine times the Japanese air-quality hourly value. The eruption influenced the air quality of the Tokyo metropolitan area, which has more than 30 million residents, some of whom reported smelling malodorous gas in the city (Fujita et al., 2003). From August to November 2000, SO2 levels at 623 air monitoring stations across Japan exceeded hourly air quality values (Fujita et al., 2003).
Other examples of SO2 concentrations and effects at varying distances:
Concepcion, Nicaragua: SO2 emissions from the crater in 1986 and 1993 measured 8-10 km downwind were sufficient to cause mild fumigation of populated areas (SEAN 11:05; BGVN 18:03).
Cerro Hudson, Chile: Sulphurous fumes on 11 October 1991 were so intense in the Huemules valley on the west flank of the volcano that some inhabitants became sick, resulting in vomiting and loss of consciousness (BGVN 16:09). (It is unclear what the composition of these fumes was and there may have been sulphate aerosol and/or hydrogen sulphide present).
St Augustine, Alaska: The plume from the 1 February 1976 eruption contained concentrations of gaseous sulphur (assumed by the investigators to be all sulphur dioxide) up to 10 ppm close to the volcano and 1 ppm 10 km downwind that caused minor throat irritation (Stith et al., 1978).
Yasur, Vanuatu: Hazardous levels of SO2 have been found in the plume at the crater rim. In September 1988, plume concentrations here were between 3 and 9 ppm (SEAN 13:12), exceeding many occupational air-quality standards.
Popocatepetl, Mexico: Near-vent concentrations of SO2 in February 1997 were ~3.8 ppm (10,000 µg m-3), which is double the NIOSH recommended time-weighted average (Goff et al., 1998).
Telica, Nicaragua: In March-June 1994, sulphur-rich steam from the crater moved down the slopes of the volcano and filled a valley with high concentrations of SO2. A sulphur odour was also reported on the NE slope (BGVN 19:07).
Taal, Philippines: Strong smells of SO2 were observed during the 1911 eruption and it has been suggested (Baxter 1990) that this may have contributed to the mortality caused by the eruption.
In other regions, people living and working close to volcanoes emitting SO2 may be unwittingly at risk from the gas. For example, mean SO2 levels by Lake Furnas in the caldera of the active Furnas volcano, Azores, have been measured at 0.115 ppm. This was recorded in an area where tourists and locals use the fumaroles for cooking and is several times higher than any listed annual guideline and higher than most 1- and 24-hour guideline levels. Levels in Furnas village centre (also in the caldera) had a range of 0.070-0.085 ppm (Baxter et al., 1999), also higher than any annual guideline levels.
Most known incidents related to SO2 poisoning have occurred at Aso volcano in Japan (see table). Here, 7 people have died from SO2 in the past 15 years and 59 people were hospitalised from inhalation of volcanic gas from January 1980 to October 1995. Over half of the fatalities had a history of asthma. Following autopsies of the dead, the SO2 evacuation criteria levels were reduced and strict warnings about the risks of exposure are given to visitors to protect those with asthma and respiratory diseases (Ng'Walali et al., 1999).
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