Atmospheric dispersion, environmental effects and potential health hazard associated with the low-altitude gas plume of Masaya volcano, Nicaragua

Abstract

Masaya volcano (560 m a.s.l.), Nicaragua, re- sumed its degassing activity in mid-1993 with the con- tinuous emission of SO 2 at rates increasing from 600 metric tons (t) day -1 (7.0 kg s -1 ) in 1995 to 1800 t day -1 (21.0 kg s -1 ) in 1999. The low-altitude gas plume is typically blown westward by the prevailing wind across the Masaya caldera and Las Sierras high- lands, which are at a higher elevation than the gas vent. In this study, the areal distribution of atmospheric SO 2 concentrations was monitored within 44 km of the vent with a network of passive samplers. Measured SO 2 air concentrations ranged from <2 to 90 ppbv in 1998 and from <2 to 230 ppbv in 1999. The data suggest that the volcanic emissions influenced air quality across a 1,250- km2 area downwind. Local topography exerts a strong control on plume dispersal, and hilltops are particularly prone to fumigation and thus, to high ambient SO 2 lev- els. In a zone 22 km2 in size located within 15 km of the source, the response of vegetation to sustained exposure to high atmospheric dose of volcanic SO 2 and HF result- ed in a strong reduction in the number of plant communi- ties. A transition zone of somewhat indefinite boundary surrounds the devastated zones and exhibits vegetation damage in the form of leaf injury. In addition to the envi- ronmental impacts of the volcanic emissions, both short- and long-term public health hazards may exist in areas most exposed to the plume. The harmful effects of the volcanic emissions on cultivated vegetation could be di- minished by using windbreaks made of gas-tolerant trees and shrubs such as Eugenia jambos, Brosimum utile and Clusia rosea. The current gas crisis at Masaya volcano provides an unique opportunity for investigating the at- mospheric, environmental and medical impacts of volca- nic gases and aerosols.