Abstract
Abstract. The 1783–1784 AD Laki flood lava eruption commenced on 8 June 1783 and released 122 Tg of sulphur dioxide gas over the course of 8 months into the upper troposphere and lower stratosphere above Iceland. Previous studies have examined the impact of the Laki eruption on sulphate aerosol and climate using general circulation models. Here, we study the impact on aerosol microphysical processes, including the nucleation of new particles and their growth to cloud condensation nuclei (CCN) using a comprehensive Global Model of Aerosol Processes (GLOMAP). Total particle concentrations in the free troposphere increase by a factor ~16 over large parts of the Northern Hemisphere in the 3 months following the onset of the eruption. Particle concentrations in the boundary layer increase by a factor 2 to 5 in regions as far away as North America, the Middle East and Asia due to long-range transport of nucleated particles. CCN concentrations (at 0.22% supersaturation) increase by a factor 65 in the upper troposphere with maximum changes in 3-month zonal mean concentrations of ~1400 cm−3 at high northern latitudes. 3-month zonal mean CCN concentrations in the boundary layer at the latitude of the eruption increase by up to a factor 26, and averaged over the Northern Hemisphere, the eruption caused a factor 4 increase in CCN concentrations at low-level cloud altitude. The simulations show that the Laki eruption would have completely dominated as a source of CCN in the pre-industrial atmosphere. The model also suggests an impact of the eruption in the Southern Hemisphere, where CCN concentrations are increased by up to a factor 1.4 at 20° S. Our model simulations suggest that the impact of an equivalent wintertime eruption on upper tropospheric CCN concentrations is only about one-third of that of a summertime eruption. The simulations show that the microphysical processes leading to the growth of particles to CCN sizes are fundamentally different after an eruption when compared to the unperturbed atmosphere, underlining the importance of using a fully coupled microphysics model when studying long-lasting, high-latitude eruptions.
Highlights
The 1783–1784 AD Laki eruption commenced on 8 June 1783 and emitted ∼122 Tg of sulphur dioxide (SO2) into the upper troposphere/lower stratosphere above Iceland
We used the dataset provided by Thordarson and Self (2003) to specify the SO2 emissions and, recognising that such an eruption is likely to occur again, we investigated the sensitivity of aerosol microphysical processes to the timing of the eruption by simulating a hypothetical Laki eruption commencing in December
Our principal finding is that the Laki eruption had the potential to dramatically impact global condensation nuclei (CN) and cloud condensation nuclei (CCN) concentrations, with an increase of the total particle concentration in the upper troposphere by a factor of ∼16 over large parts of the Northern Hemisphere during the first 3 months after the onset of the eruption
Summary
The 1783–1784 AD Laki eruption commenced on 8 June 1783 and emitted ∼122 Tg of sulphur dioxide (SO2) into the upper troposphere/lower stratosphere above Iceland. Thordarson and Self (2003) presented a comprehensive review of the course of the Laki eruption, including a detailed volatile release budget and a contemporary account of the atmospheric and environmental consequences observed for around two years following the eruption This comprehensive review has enabled the impacts of the Laki eruption to be studied using numerical models (Stevenson et al, 2003; Highwood and Stevenson, 2003; Chenet et al, 2005; Oman et al, 2006a,b). In contrast to previous studies, we use a dedicated global aerosol microphysics model to simulate the driving aerosol processes, such as nucleation, condensation and coagulation, as well as the subsequent evolution of the aerosol size distribution, thereby allowing us to assess the impact on the global budget of total particle number concentration and cloud condensation nuclei (CCN). Timmreck et al (2009) suggested that it is crucial to use fully coupled chemistry and microphysics models in order to simulate the volcanic aerosol size distribution and correctly constrain the effect of very large volcanic eruptions on temperature, aerosol optical depth, and subsequently the environmental impact
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