Abstract
Abstract. Atmospheric dispersal of a gas denser than air can threat the environment and surrounding communities if the terrain and meteorological conditions favour its accumulation in topographic depressions, thereby reaching toxic concentration levels. Numerical modelling of atmospheric gas dispersion constitutes a useful tool for gas hazard assessment studies, essential for planning risk mitigation actions. In complex terrains, microscale winds and local orographic features can have a strong influence on the gas cloud behaviour, potentially leading to inaccurate results if not captured by coarser-scale modelling. We introduce a methodology for microscale wind field characterisation based on transfer functions that couple a mesoscale numerical weather prediction model with a microscale computational fluid dynamics (CFD) model for the atmospheric boundary layer. The resulting time-dependent high-resolution microscale wind field is used as input for a shallow-layer gas dispersal model (TWODEE-2.1) to simulate the time evolution of CO2 gas concentration at different heights above the terrain. The strategy is applied to review simulations of the 1986 Lake Nyos event in Cameroon, where a huge CO2 cloud released by a limnic eruption spread downslopes from the lake, suffocating thousands of people and animals across the Nyos and adjacent secondary valleys. Besides several new features introduced in the new version of the gas dispersal code (TWODEE-2.1), we have also implemented a novel impact criterion based on the percentage of human fatalities depending on CO2 concentration and exposure time. New model results are quantitatively validated using the reported percentage of fatalities at several locations. The comparison with previous simulations that assumed coarser-scale steady winds and topography illustrates the importance of high-resolution modelling in complex terrains.
Highlights
IntroductionThe atmospheric dispersion of gases (of natural, accidental or intentional origins) can be very hazardous to life and the environment
The atmospheric dispersion of gases can be very hazardous to life and the environment
We introduce a methodology for local wind field characterisation based on transfer functions that couple mesoscale numerical weather prediction (NWP)
Summary
The atmospheric dispersion of gases (of natural, accidental or intentional origins) can be very hazardous to life and the environment. Historic examples of tragic accidents include the dioxin release in Seveso (Italy, 1976), the methyl isocyanate in Bophal (India, 1984), or the petroleum gas explosions in Mexico City (Mexico, 1984), among several others (e.g. Britter, 1989). Many gas manifestations in Central and Southern Italy, characterised by persistent CO2 emissions, have caused several periodic accidents (Chiodini et al., 2004). Another case of natural origin, much rarer than diffuse emissions but potentially much more hazardous, are limnic eruptions triggered during overturning of CO2 -rich volcanic lakes Another case of natural origin, much rarer than diffuse emissions but potentially much more hazardous, are limnic eruptions triggered during overturning of CO2 -rich volcanic lakes (e.g. Zhang, 1996), such as the eruptions that occurred
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
