Dense Gas Dispersion and Modelling at Fagradalsfjall, Iceland

冰岛Fagradalsfjall正在进行的喷发为观察和模拟稠密火山气体的行为提供了一个难得的绝佳机会。二氧化硫(SO2)是富含熔岩的喷发的主要排放物，如Fagradalsfjall。由于空气的相对分子质量是空气的两倍以上，这很容易表现出稠密的气体分散特性，如沉淀，可能会显著影响数百公里范围内的分散。这可能会导致低水平的浓度升高，从而对空气质量和人类健康造成影响。该项目的目标是：(A)收集地面空气质量和气象数据集；(B)制作能够模拟稠密气体的模拟框架，并对照(A)进行验证。目前还不存在这样的框架。这是一个重大的、有时间限制和可获得的喷发事件，如果现在对其作出反应，可以在科学理解和管理方面取得重大进展，因为未来可能会发生更大规模的喷发，由此产生严重的气体危险。(A)我们将加强Fagradalsfjall附近现有的空气质量观测，建立一个网络，对50-100公里范围内密集的火山气体扩散进行全面评估。这一独特的数据集将为具有稠密气体能力和地面加热(见下文)的完整气象预测模型提供第一次独立验证。(B)最近的模型开发工作证明，使用NCAR天气研究和预报(WRF)模型的改编版本，可以有效地预测火山气体扩散。该系统被用来成功地解释飞机对冰岛(冰下)卡特拉火山二氧化碳扩散的测量，并首次定量解释了导致1986年尼奥斯湖灾难的致密气体二氧化碳的行为，导致密集的二氧化碳汇集和排入山谷，造成约1700人死亡。这两种应用都不考虑(或要求)加热表面。然而，Fagradalsfjall喷发现在正处于已有熔岩喷泉报告的阶段，因此在任何模拟中都需要考虑地表加热的影响，以包括稠密气体、受热表面和底层气象之间的复杂相互作用和反馈。经过开发和验证后，该模型将在未来作为一个可操作的危险预测系统使用，并可能导致英国国家应对稠密气体泄漏的能力显著提高。这包括人为排放，例如工业事故和火灾。

The ongoing eruption at Fagradalsfjall in Iceland presents an outstanding and rare opportunity to observe and model the behaviour of dense volcanic gases. Sulphur Dioxide (SO2) is the principal emission from lava-rich eruptions such as at Fagradalsfjall. With more than double the molecular weight of air, this is prone to exhibiting dense gas dispersion characteristics such as settling, with the potential to significantly affect the dispersion over scales of hundreds of kilometers. This can lead to enhanced concentrations at low levels with consequences for air quality and human health. This project aims to (a) collect a surface air quality and meteorological dataset and (b) produce a modelling framework capable of simulating dense gas and validate it against (a). Such a framework does not exist at present. This is a significant, time-limited and accessible eruption event which, if responded to now, can lead to major advances in both scientific understandings and in the management of future, possibly larger, eruptions from which there is a serious gas hazard. (A) We will enhance existing air quality observations in the vicinity of Fagradalsfjall, creating a network to provide a comprehensive assessment of dense volcanic gas dispersion on a scale of 50-100 km. This unique dataset will provide the first independent verification for a full meteorological prediction model with dense gas capability coupled with surface heating (see below).(B) Recent model development work has demonstrated effective volcanic gas dispersion predictions using an adapted version of the NCAR Weather Research and Forecasting (WRF) model. This system was used to successfully interpret aircraft measurements of CO2 dispersion from the (subglacial) Katla volcano in Iceland and to explain quantitatively, for the first time, the dense gas CO2 behaviour which led to the Lake Nyos disaster in 1986 that saw dense CO2 pooling and draining down valleys, causing ~1700 deaths. Neither of these applications considered (or required) a heated surface. However, the Fagradalsfjall eruption is now in a phase where lava fountains have been reported, and so the effect of surface heating will need to be considered in any modelling, to include the complex interactions and feedbacks between a dense gas, a heated surface, and the underlying meteorology. The model, after development and verification, will be available in the future as an operational hazard prediction system and and could lead to significant improvements in the UK national capability to respond to dense gas releases. This includes anthropogenic releases, for example industrial accidents and fires.