Posts Tagged ‘sulphur’
an excursus into… important biological stuff
According to Morton, and planetary science in general, there are four periods, or eons, in our planetary history, the Hadean, the Archaean, the Proterozoic and the Phanerozoic. That’s in order from the earliest to the current. The Hadean largely covers Earth’s formation, from around 4.6 billion years ago to 4 billion. The Archaean takes us from 4 to 2.5 billion, with the planet cooling and the first life-forms. The Proterozoic, which was the longest eon (so far), took us from 2.5 billion to about 539 million years ago, and its defining event for us was the great oxygenation and the snowball earth in the early part of that period. The Phanerozoic kicked off or was kicked off by the Cambrian explosion and the emergence of complex life.
So, to the long Proterozoic, which has been dubbed the ‘boring billion’, it’s been argued that the most important of the atmospheric changes in this period has to do with sulphur:
The oxidised surface of the planet would have provided the oceans with a greatly increased supply of sulphate, which microbes in the oxygen-free depths of the ocean would reduce into sulphides (Morton, p212).
Most of this stuff isn’t particularly comprehensible to me, so I’ll try to understand. First, something about ‘nitrogen-fixing’:
To be useful to life, nitrogen has to be fixed from the gaseous form in the atmosphere to a reduced form, the ammonium ion. No eukaryotes have the energy-intensive electron transfer chains and associated enzymes needed to pump the necessary electrons into the nitrogen; but various bacteria, including some cyanobacteria, do (ibid. p212).
So I’ll have to do more research into nitrogen fixation. Nitrogen gas is inert, which is to say, unreactive. It’s different, though, from the chemically inert gases of the periodic table (helium, argon, neon – the ‘noble gases’). As a diatomic molecule, N2, it’s an extremely stable, triple bonded element.
So, nitrogen, sulphur (sulphate and sulphides), ammonium and cyanobacteria.. But let me go to another source, Wikipedia, on nitrogen fixation.
Nitrogen fixation is a chemical process by which the abundant but relatively inert molecular dinitrogen (N2) is converted into bioavailable nitrogen compounds such as ammonia (NH3) and nitrates (NO3).[1] It occurs both biologically and abiologically, the latter either naturally through weather phenomena (e.g. lightning) or artificially by chemical industries. Biological nitrogen fixation or diazotrophy is catalyzed by enzymes called nitrogenases,[2] produced by microorganisms such as cyanobacteria and rhizobia. These enzyme complexes are encoded by the Nif genes (or Nif homologs) and contain iron, often with a second metal (usually molybdenum, but sometimes vanadium).[3]
So … where does sulphur come in, if anywhere?
Sulphur is essential for biological nitrogen fixation. Without enough sulphur, legume-rhizobium symbioses form fewer and smaller root nodules, produce less nitrogenase enzyme, and struggle to convert atmospheric nitrogen into plant-usable forms. Sulphur acts as a key metabolic partner to nitrogen in building proteins and chlorophyll.
Somehow I can’t quite picture this, though I’m sure it’s all true. So how do you add an elegant sufficiency of sulphur? Well, I’ve found a website that explains not only why sulphur is essential but how nitrogen fixation works. It’s referenced below, but I’m going to try describe the process in my own words.
So, in North America, where wheat and corn are grown, legumes (plants in the pea family Fabaceae) are used as a rotational crop, as they increase nitrogen levels in the soil, reducing the need for nitrogen fertiliser. There’s a common bacterium in soil called rhizobia, which likes to inhabit the root nodules of legumes. It produces enzymes called nitrogenases, which are in the habit of converting atmospheric nitrogen into ammonia. I know this was explained, sort of, in the Wikipedia quote, but my skull is thick. Plants convert ammonia into ammonium (NH4+) somehow, which they then absorb through their roots to build important/essential planty stuff, like amino acids, proteins and chlorophyll. They also have special enzymes – e.g. glutamine synthetase – which change the ammonia, which is toxic in large amounts, into, er, something less toxic.
So now back to sulphur, for some reason. It’s apparently essential for nitrogen fixation in legumes. It’s absorbed from the soil as sulphate ions, by the roots, and it works with nitrogen ‘to convert raw nutrients into usable plant proteins’.
And all of this, perhaps, is related to the emergence of complex eukaryotic life…
References
https://en.wikipedia.org/wiki/Nitrogen_fixation
4 Reasons Sulphur Is Necessary for Nitrogen Fixation in Legumes.
the shipping industry – a bit of a global warming headache
Ok, that’s sulphur oxides, nitrogen oxides, carbon dioxide, particulate matter and non-methane volatile organic compounds
I’ve been alerted, by a brief piece on a New Scientist podcast, and then by some passages in Tim Smedley’s book Clearing the air: the beginning and end of air pollution, about some pretty disturbing stats on the polluting and greenhouse impact of the world’s shipping industry – a factor we don’t often consider when we attempt to reduce our personal environmental impact. We tend to focus on the products we consume, the cars we drive, the homes we heat, the plane trips we take and so forth. But once it’s pointed out to us it becomes obvious. We’re the recipients of a vast global trading network involving foodstuffs, appliances and gadgetry of all sorts, as well as bulk supplies of crude oil, iron ore and a host of other raw materials, brought to us by more or less massive marine vessels.According to an article in Chemical & Engineering News (C&EN), goods weighing 11 billion tonnes were shipped across our oceans in 2019, a 3-billion tonne increase from a decade before. And the increase is expected to … increase. So how are these vessels powered? To quote from the C&EN article,
“The shipping industry uses more than 300 million tons of fossil fuels every year, roughly 5% of global oil production,” says Camille Bourgeon, a specialist in air pollution and energy efficiency in the marine environment at the IMO [the International Maritime Organisation – an agency of the UN]. In 2018, global shipping activity emitted roughly 1.05 billion t of carbon dioxide into the atmosphere, accounting for about 2.9% of the total global anthropogenic CO2 emissions for that year, according to the IMO’s 2020 greenhouse gas study.
What’s worse is that for decades the shipping industry has been using the lowest grade, most noxious fuels, ‘the stuff no-one else wants’, as one maritime engineer describes it. This ‘residual fuel’ is also called HFO, for ‘heavy fuel oil’, which the oil industry has been more than happy to provide to the shipping industry rather than having to get rid of it some other, more expensive way. And when you’re out in the middle of the ocean, who’s going to check your emissions? The fuel used has seriously high sulphur content, and once ships come into port, the cargo is offloaded onto diesel trucks and then often onto diesel locomotives. Here are some of Tim Smedley’s opening remarks on the industry:
[Shipping] is easily the transport sector with the worst history. Shipping emissions contribute nearly 15% of NOx [nitrogen oxides including nitric oxide and nitrogen dioxide, some of the worst air pollutants] and 13% of sulphur dioxide emissions globally, and these numbers are increasing. Due to growing populations and consumer spending, more and more supertankers set sail every year. Since 1985 global container shipping has increased by about 10% annually, with only brief dips for each recession.
There seems to be no stopping this growth, and about a quarter of this transport is fuelled by crude oil. As Smedley points out, this ‘gives us the headache-inducing fact that a quarter of all shipping emissions come from shipping the fuel needed to produce the emissions’.
As mentioned, sulphur dioxide is a major constituent of HFO. On the website of Aeroqual, a company that provides air monitoring systems, I found this disturbing claim – the sulphur dioxide of HFO is 2700 times higher than that of road fuel. Sulphur dioxide emissions have been dropping for years in developed countries – a 76% decrease in Europe between 1990 and 2009 – leaving shipping as the primary source.
As also mentioned, ports are some of the most atmospherically noxious places on the planet. Most of them use diesel-powered machinery for off-loading and transportation. Diesel emissions significantly increase cancer risks according to a host of epidemiological studies, and various engine improvements have barely kept up with improvements in emissions monitoring, which have highlighted further dangers. But the diesel issue probably requires a whole new post.
The shipping industry, setting aside all those smelly and sick-making ports, and the sulphur dioxide problem, is a major contributor to greenhouse emissions, releasing over 3% of our carbon dioxide, a percentage that is set to rise in the aftermath of the covid pandemic. A website called ship technology sets out a plan to address the issues, which reminds me of the plans regularly emanating from the IPCC, requiring targets which seem to be seldom met by the major emissions culprits. The plan includes improved ship-to shore data feed technology, exhaust emission technology, behavioural change such as slow steaming (yes, that just means slowing down) and more preventive maintenance, and alternative fuels such as LNG, hydrogen and even solar. LNG is the most touted alternative fuel due to requiring fewer alterations to shipping infrastructure, though it’s surely an interim solution.
The IMO has been rather defensive about its role as the shipping regulator, and the degree of progress made in reducing emissions. Certainly it’s a difficult industry to police, with many nations and companies involved, including military vessels worldwide, which have other priorities, to put it mildly. But it’s clear that shipping officials are feeling the pressure. As one of them put it:
“… can shipping reduce more greenhouse gas emissions? I’m sure it will. But it’s difficult to say how much particularly not knowing the consequences from regional regulations. There seems to be a wish to require unrealistic emission reductions in order to collect money from ships.”
These remarks make me wonder whether money is being collected from land-based greenhouse emitters, and if not, why not? Interestingly, the same official has this to say in the industry’s defence:
“When discussing short-term measures, the figure over the next 10 years will bring the shipping carbon intensity reduction in 2030 to more than 40%, below the year 2008. This is a remarkable achievement by a sector that is, and will remain, the most efficient mode of transportation”.
This appears to be saying that the most efficient form of transport in the shipping sector is, and always will be, shipping. Or maybe I’m reading it wrong. In any case, they’re on the case, which is great. Must remember to have another look in 2030.
References
https://cen.acs.org/environment/greenhouse-gases/shipping-industry-looks-green-fuels/100/i8
Tim Smedley, Clearing the air: the beginning and the end of air pollution, 2019
https://www.aeroqual.com/blog/ship-pollution-port-air-quality
https://en.wikipedia.org/wiki/Diesel_exhaust
https://www.ship-technology.com/analysis/guidelines-and-goals-reducing-shippings-emissions/