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Instituto de Investigação
em Vulcanologia e Avaliação de Riscos
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Referência Bibliográfica

VIVEIROS, F., FERREIRA, T., SILVA, C., HIPOLITO, A., GASPAR, J.L. (2008) – Meteorological influences on the indoor CO2 concentrations at Azores archipelago (Portugal) – Public health hazard. IAVCEI 2008 General Assembly, Reykjavik, 17 - 25 Agosto (comunicação Oral).


Azores archipelago is a volcanic region where the main degassing areas include fumarolic fields, thermal and CO2 cold springs and soil diffuse degassing areas. CO2 is the main gas released diffusely by soil degassing and consequently is one of the most hazardous gases in this region. Indoor CO2 concentration monitoring programmes, using CO2 infrared detectors, were started in dwellings located in some of the islands due to several respiratory and neurological symptoms described by the population.


The first monitoring test was performed in S. Miguel Island in a dwelling at Furnas village, in Furnas volcano caldera, built over an area where soil CO2 concentrations range from 25 to 50 % vol. Indoor CO2 values at ground floor level reached values as high as 20.8 % vol. being the average value 4.7 % vol. A similar monitoring experiment is being done at Mosteiros village, on the west flank of Sete Cidades volcano, since March 2006. This house is under monitoring due to the several symptoms described by the residents that were attributed to exposition effects to high CO2 concentrations. In this case the detector was set in a room from the 1st floor and the registered CO2 values ranged between 0 and 17.4% vol. In Faial Island, the surveyed dwelling displayed CO2 values between 0.2 and 91.1% at ground floor despite the low soil CO2 values measured in the surrounding ground. Due to these high and lethal values the residents were obliged to move to another house.


Even though all the monitored houses are placed in distinct volcanic systems and in areas with different soil CO2 concentrations it was found that the observed sharp indoor CO2 increases resulted from a fast response of diffuse degassing to stormy weather conditions, marked by significant decreases in the barometric pressure and high rainfall periods. This work emphasizes the presence of a hidden permanent risk to public health in degassing zones that can be triggered just by significant changes in meteorological conditions.