Dense Gas Dispersion and Modelling at Fagradalsfjall, Iceland

冰岛Fagradalsfjall正在进行的火山喷发为观察和模拟密集火山气体的行为提供了一个难得的机会。二氧化硫（SO2）是富熔岩喷发的主要排放物，比如在fagradalsjall火山。当空气的分子量增加一倍以上时，很容易表现出密集的气体分散特性，如沉淀，有可能显著影响数百公里尺度上的分散。这可能导致低浓度的浓度增加，对空气质量和人类健康造成影响。该项目旨在(a)收集地面空气质量和气象数据集，(b)生成能够模拟稠密气体的建模框架，并根据(a)对其进行验证。目前还不存在这样一个框架。这是一次重大的、有时间限制的、可接近的火山喷发事件，如果现在对其作出反应，可以在科学认识和未来管理方面取得重大进展，可能更大的火山喷发会产生严重的气体危害。(A)我们将加强在Fagradalsfjall附近现有的空气质量观测，建立一个网络，在50-100公里范围内提供密集火山气体扩散的综合评估。这一独特的数据集将首次为具有致密气体能力和地表加热耦合的完整气象预测模型提供独立验证（见下文）。(B)最近的模式开发工作已证明，利用NCAR天气研究和预报模式的改编版本进行有效的火山气体分散预测。该系统被用于成功地解释冰岛Katla火山（冰下）二氧化碳分散的飞机测量结果，并首次定量解释了导致1986年尼奥斯湖灾难的密集气体二氧化碳行为，该灾难看到密集的二氧化碳聚集并排出山谷，造成约1700人死亡。这些应用都没有考虑（或需要）加热表面。然而，Fagradalsfjall火山喷发现在正处于有熔岩喷泉报道的阶段，因此在任何模型中都需要考虑地表加热的影响，包括稠密气体、加热表面和底层气象之间复杂的相互作用和反馈。在开发和验证之后，该模型将在未来作为一种可操作的危害预测系统，并可能显著提高英国国家应对密集气体释放的能力。这包括人为释放，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.