Monitoring of airborne particulate matter during the eruption of Soufrière Hills Volcano, Montserrat

A programme of air quality monitoring was devised to investigate concentrations and behaviour of repirable ash in the air on Montserrat. Sampling strategies used were short environmental tests, occupational tests, and continuous environmental monitoring in periods of both high and low volcanic activity. The results obtained between September 1996 and July 1999 allow comparison of the contributions made to airborne particles by different eruptive styles. Vulcanian explosions and ash-venting increased average background concentrations (c.30 µg m -3 ) of airbrne particles (≤10 µm in diameter) by up to a factor of ten. Large dome collapses released large amounts of ash into the atmosphere in an extremely sort time and airborne particle concentrations reached more than 600 µg m -3 . Aggregates of ash particles broke up on impact wth the gournd and ash re-suspension by wind caused airborne particle concentrations of approximately 250 µg m -3 . which were sometimes significantly higher than those caused by tephra fallout. Airborne particle concentration decreased with distance from the ash source, and wind an drain effectively removed ash from the atmosphere. Generally, airborne particle concentrations in inhabited areas of Montserrat remained low, even during elevated volcanic activity, when volcanic products were carried away by winds