The environmental effects of the eruption have been routinely monitored throughout the eruption. This has included the measurement of ambient sulphur dioxide (SO2) concentrations at ground level, the monitoring of fine dust particles in the air, and the measurement of the pH of rainwater.

Diffusion tubes positioned at various sites beneath the volcanic plume on the northwest and west of the volcano measure the concentration of SO2 at ground level. Only once (during 1998) has the concentration of SO2 increased above the World Health Organisation's safety guidelines for people working and living in this area.

The pH of rainwater is monitored beneath the plume and is often as low as about 2 directly downwind of the volcano. This leads to the rapid corrosion of metal structures and cars left in the exclusion zone.

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