ENHANCED ATMOSPHERIC METHANE OXIDATION RESEARCH FIELD EXPERIMENTS

Methane is the second most important greenhouse gas and has a 100-year global warming potential of 32 compared to CO2. The rise in atmospheric methane has been accelerating in recent years and this extra methane burden was not included in greenhouse gas emissions scenarios at the time of the Paris agreement. If the rise of methane levels continues, it becomes very difficult to meet the Paris goals.

But because methane is such a large part of climate forcing, it also presents an opportunity for addressing the problem, especially because its atmospheric lifetime is relatively short (about 10 years). Although methane control cannot replace the necessity of reaching “net‐zero” emissions of CO2, significant reductions in the methane burden would ease the timescales required to reach required CO2 reduction targets. And the good news is that this could be done at a cost that is low relative to the parallel and necessary measures being taken to reduce CO2.

In addition to increased methane emissions by human and natural sources, another possible cause for increasing methane levels is a decline in the oxidative capacity of the atmosphere. The oxidative capacity is the natural cleansing power of the atmosphere, driven mainly by OH radicals, and to a lesser extent by chlorine atoms. Chlorine is estimated to be responsible for a few % of the global methane sink, and Cl has the advantage that it reacts much faster with methane than OH. Heterogeneous reactions of sea-salt aerosol is one of the main sources of atmospheric chlorine atoms.

This Xploration is about facilitating a field campaign to further investigate the workability of removing methane from the atmosphere by restoring or increasing the oxidative power of the atmosphere using chlorine atoms generated by sea-salt aerosols.

In smog chamber tests it has been shown that the presence of iron in salt-aerosols can increase the generation of chlorine atoms by at least one order of magnitude (shown in salt pans and in salt aerosols). These smog chamber test results mean that if soluble iron particles interact with sea-salt aerosols, it could substantially increase the generation of chlorine atoms. Because marine fuel oil combustion from shipping is the main source of soluble iron above the oceans, the shipping industry may have an important impact on chlorine chemistry and thus on the reduction of methane in the atmosphere.

The hypothesis that we want to test in this Xploration is that iron emissions by ships are catalyzing the generation of chlorine radicals in shipping plumes, and in this way enhancing the oxidative power of the atmosphere.

Our aim is to test the hypothesis by experimentally observing chlorine chemistry in the plume of a ship,in which the plume contains iron emissions.