Lester, Ron
The marine boundary layer naturally contains sulphuric acid aerosol, which is the oxidation product of sulphur dioxide, itself the oxidation product of dimethyl sulphide emissions from phytoplankton. Cloud condensation nuclei in the marine boundary layer therefore usually contain a high sulphuric acid content.
Modern jetliners fly in the lower stratosphere and any particles, including sulphuric acid droplets, catalyse ozone destruction. The general rule for temperate to tropical regions is that low-lying clouds provide an overall cooling effect, and high altitude clouds provide an overall warming effect. Therefore releasing sulphur emissions into the upper troposphere to form aircraft tracks would likely have an increased warming effect.
OTOH NOx emissions from aircraft tend to catalyse methane destruction, and methane that drifts into the stratosphere readily oxidises there to form water vapour. Water vapour is the source of the polar stratospheric clouds that are now appearing in early spring in polar regions, producing the ozone holes there in recent years.
Clive
--On 27/06/2023 23:06 BST Lester Wyborny <[email protected]> wrote:Since ships emit their pollutants, such as sulphate particles, in the lower atmosphere, it would create a greater breathing problem for people who would be exposed to the high sulfate and other particulate matter emissions from these ships. Although you are suggesting that these particles would be emitted over the open ocean, they would still be transported to land areas via atmospheric weather patterns where it would create breathing and other associated health issues. This is why the ships were forced to reduce their sulfur levels.A better idea would be to dose jet fuel with sulfur-containing chemicals when the jets are operating at high altitudes to emit the sulfate particles in the upper atmosphere which is less likely to expose the human population and also remain there for longer periods. The concern with this idea is that changes in the fuels used by passenger airlines creates a concern about the potential impact on their safe operation, and agreeing to such a change would take many years to test out and implement. It has been a while since I reviewed the data on this, but the jet fuel typically contains ~700 ppm sulfur. Conversely ship bunker fuel, before the standards forced these vessels to use lower sulfur fuel, contained ~3%, or ~30,000 ppm sulfur, so a lot more sulfur/sulfate emissions.
On Tue, Jun 27, 2023 at 1:07 PM Ron Baiman <[email protected]> wrote:Dear Colleagues,A bunch of us (in forums and communications within the groups in the lists above) have been discussing a potential immediate practical step (that earlier has been raised by others) that may provide at least a modicum of cooling especially over the oceans: a relaxation of the "bunker fuel" sulfur content regulations that just came into effect in 2020 (https://www.theguardian.com/environment/2020/jan/01/shipping-fuel-regulation-to-cut-sulphur-levels-comes-into-force ) for inter-port "high seas" shipping. The idea is that cargo ships and tankers would be able to use the old dirty sulfur laden fuel in the open ocean but switch to the cleaner fuel when they are near ports or human habitation. Apparently many ships have multiple fuel tanks so that they may be able to switch fuels in transit.To be clear, we would stress that we fully support getting off of fossil fuels, but if fossil fuels are going to be used anyway it makes no sense not to at least benefit from fossil fuel burning maritime sulfur aerosol generation that is known to have a significant cooling effect (how much is currently being re-estimated using the "termination shock" signal from the 2020 abrupt change in sulfur emissions due to the regulation). Looking forward this also points the way to including effective (and hopefully less harmful to human health) tropospheric aerosol generators in future non GHG emitting replacements for the bunker fuel (see the HPAC direct climate cooling petition for some possible options: https://drive.google.com/file/d/1yHe2Fe6fU11odfcH-4GwdYDNTCk7uB-J/view?usp=sharing ).Any thoughts or data on this that might be helpful in working up (or not) this proposal would be appreciated.For example, the last sentence in this excerpt from a quote in this Guardian piece (https://www.theguardian.com/environment/2023/jun/19/marine-heatwave-uk-irish-coasts-threat-oysters-fish-high-temperatures) shared in recent ocean heat spike thread: https://www.theguardian.com/environment/2023/jun/19/marine-heatwave-uk-irish-coasts-threat-oysters-fish-high-temperature suggests that this may be a factor causing the recent unprededented spike in ocean heating:"Piers Forster, a professor of climate physics at the University of Leeds, said: “Both Met Office and NOAA analyses of sea-surface temperature show temperatures are at their highest ever level – and the average sea-surface temperature breached 21C for the first time in April. These high temperatures are mainly driven by unprecedented high rates of human-induced warming. Cleaning up sulphur from marine shipping fuels is probably adding to the greenhouse gas driven warming...""
Best,Ron--
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