Would addition of HCl as an ISA precursor make the troposphere acidic?

Airborne organic and inorganic acids such as oxalic, nitric and sulfuric acids already exist quite naturally in the atmosphere. These generate a fairly constant level of HCl above the ocean from its sea salt aerosol haze, which is continually refreshed by the underlying ocean.

The main part of the troposphere proposed for ISA emission is the lowest layer above the ocean. The global mass of salt in sea spray is the order of billions of tons, whereas ISA will be limited to about 150,000 tons of iron. The maximum addition of HCl would be the same order of magnitude as that iron emission. Any raindrop falling through the ISA plume would absorb sea salt many times its mass of HCl, which would buffer any low acidic pH towards near neutral pH values.

Additionally, we propose generating this HCl by sea water electrolysis. This would produce an alkalinity at the ocean surface equivalent to the HCl acidity in the ISA plume, and provide a corresponding alkaline component to the natural sea-spray.

N.B. Flues of power plants that burn coal, biomass, or municipal waste already emit acids, including HCl, and HCl is a constituent of volcanic exhalations and eruptions.

Given that ISA depletes tropospheric ozone, could it reach the stratosphere and deplete ozone there?

No. ISA reinforces the ozone layer: It’s sunshine generated chlorine atoms oxidize chloro methane at a faster rate than hydroxyl radicals in the dust-free part of the troposphere.

Further, ISA is already emitted by coal and steel manufacturing plants, with no deleterious effect on stratospheric ozone. This is despite the temperature of their flue gases being quite high, leading them frequently to rise above the boundary layer.

Much more risky would be Cl and Br atoms generated by ISA reaching the stratosphere. However there is no scientific evidence that coal combustion is destroying the ozone layer by halogen generation.

N.B. Coal combustion also generates N2O which does destroy the ozone layer, however ISA does not generate N2O.

Could a point source of ISA occasionally induce a rising ‘chimney’ of warm air (created by latent heat from condensation) that sucks in surrounding ISA to make a big, high chimney, that then lifts the ISA column much higher than expected, making high altitude clouds?

ISA is a mimic of its natural equivalent – fine dust transported from dry surfaces over oceans and continents by wind. The main transport medium is the lower troposphere. (Huge volcanic dust eruptions are the exception.) At the time of writing we know of no evidence of cirrus clouds being generated from power plant emissions, which emit Iron Salt Aerosol from their hot flues.

In any case, high altitude clouds have a short life, with very short-lived effects compared to CO2 and CH4, whose effects are long lasting. Keep in mind that it is these greenhouse gases that ISA depletes.

Further, sulphates generated by phytoplankton (induced by ISA) will reduce cirrus clouds if they reach that high.



Similar to the above point, could a rising ISA chimney suddenly condense and get rained out, leading to an over-fertilised patch of ocean, and phytoplankton bloom that then turns anoxic?

The raining out of mineral dust (the natural equivalent of ISA) is of course common over the ocean and curtails its depletion of atmospheric warming agents. For this reason, and because a rained-out ISA plume is wasteful and might induce a phytoplankton bloom, emission will be stopped when it rains over our ISA sources.

Could ISA otherwise cause local algal blooms?

No.  Numerous hypothetical risks have been posed from adding iron to the ocean, relating to plankton blooms, oxygen levels and permanence of carbon removal. However, our calculation – to be validated by field testing – is that ISA will not cause any harm. The low iron concentration of ISA (3g fairly evenly distributed per km2 per day) is expected to generate phytoplankton growth that will increase biological activity up the entire food chain, delivering major benefits for biodiversity and cooling. Field trials will measure phytoplankton properties, to provide clear information on actual effects.

Could ISA affect jellyfish population?

Jellyfish blooms result from human impacts, including overfishing and warmer seas. ISA can counteract these problems by increasing the overall biomass in the ocean food chain, benefiting predators and competitors of jellyfish such as tuna and sardines. ISA could further reduce jellyfish numbers by cooling the ocean surface.

Could ISA change the downstream marine ecosystem?

Positive effects would far outweigh any localised adverse changes. ISA increases primary productivity at the base of the ocean food chain, increasing quantity and diversity of all kinds of fish and ocean life. As a result, different locations will undergo mainly increases (and possibly some decreases) in plankton consumption of the surface level macronutrients: nitrates, silicates and phosphates. Even in locations with low macronutrient levels we expect the ISA effect on phytoplankton mass increase to become enhanced by diurnal krill-induced nutrient increase. (See next: How will ISA affect ocean nutrient levels?) The scale and effect of these changes are expected to have major benefits for biodiversity. However, an important factor in any decision to scale up ISA application is scientific confirmation of these benefits from field tests.

How will ISA affect ocean nutrient levels?

The world’s oceans have abundant phosphate and nitrate nutrients in the oxygen reduced deep water, but at the surface, the nutrient level is mostly less.  In large regions, more than sixty million square kilometres or 20% of the world ocean surface, lack of iron creates ocean deserts with low biological activity – High Nutrient Low Chlorophyll or HNLC regions. ISA will result in water becoming mixed from different ocean levels, increasing total biomass and primary productivity.

Contributing factors to ocean mixing include:

  • ocean circulation strengthened by brine production from enhanced winter ice freezing;
  • less stratification of ocean water, by reduced ice cap melting;
  • increased krill swarms, due to greater volume of phytoplankton.

Huge swarms of krill move up and down hundreds of meters every day, eating plankton on the surface at night and resting in the deep water in the day. The krill move through a barrier called the thermocline, in and out of the deep ocean water where nutrient levels are higher, helping to fertilize the surface water. By increasing plankton growth, ISA will increase krill population, thereby increasing the daily transport of deep water into the top layer. In this way, krill volumes concomitant with plankton growth provide a negative feedback (stabilising) process, that keeps surface nutrients re-supplied.

How does ISA affect the ocean’s oxygen level?

The most scalable way to fertilize oceanic plankton at low and even dosage is from airborne particles that contain bio-available iron. But additionally, ISA’s multiple ocean surface cooling effects enable the ocean to absorb more oxygen. Further, ISA protects against low oxygen (anoxia) by promoting increased vertical cycling of the ocean water.

Is there an upper limit for iron uptake by ocean life?

The main issues for upper limits are theorised with far higher iron concentration than that delivered by ISA, and include downstream nutrient depletion and anoxia. Depleting all the available nutrients in one region with added iron would constitute the upper limit, but our proposed ISA volume is well below these levels, and nutrient uptake is expected to be counteracted by an increased volume of krill bringing up deep water nutrients. However, while increasing total productivity and biodiversity, the impact of iron fertilisation in sensitive locations needs careful measurement, in case unexpected limits are reached. Similarly, depletion of oceanic oxygen levels from concentrated plankton blooms constitute a limiting factor, as seen in dead zones caused by agricultural runoff from rivers. Once again, the concentrations of iron proposed from enhanced ISA application are well below the level where these effects are expected to occur. We suggest the very low risk of these deleterious effects is outweighed by the broad benefit for biodiversity of increasing overall uptake of otherwise unused nutrients, and a corresponding increase in ocean biomass.

Ocean ecosystems survive with infinitesimal amounts of iron that arrives largely in rare and widely distributed dust fall events, that cause ‘bloom and bust’ cycles. So continuous atmospheric distribution of iron salt aerosol sounds like a dangerous idea. Instead shouldn’t large ocean areas be allowed to lie fallow for long periods to keep their ecosystems in balance?

During the ice ages wind-blown dust over the Southern Ocean appears to have been 15-20 times the current rate, and photosynthetic activity at that time reduced atmospheric CO2 down from 280 to 200ppm. This was despite reduced terrestrial vegetation from the preponderance of ice sheets over northern latitudes.

Further, before the advent of steamships, when human activity began significantly reducing ocean biomass with industrial scale whaling and fishing, ocean biomass existed at far higher levels than today. Those creatures large and small, would have mixed nutrients around the oceans in all directions, creating more of a turquoise planet than today’s blue one characterised by large ocean deserts.

None of this suggests a particular need for ecosystems to lie fallow.

Having said that, ISA application is proposed initially just for the Arctic polar and sub-polar regions and the Southern Ocean, i.e. in locations where polar winters exist.

Neither methane depletion, nor albedo reduction, nor photosynthetic activity take place during the dark months of the polar winter, therefore it makes no sense to emit ISA during those periods. For reasons of economics we propose not applying ISA during seasons when the period between sunrise and sunset is shorter than 3 or 4 hours.

Could ISA help clean up marine plastic?

Given that plastics are a significant form of ocean pollution, research is planned to determine the extent to which iron delivered with ISA can activate microbes that consume, degrade and deplete marine micro plastics. We know that these microbes use certain enzymes to adhere to and metabolise plastic, and some of the enzymes contain iron, which ISA supplies.



Could an enhanced Iron Salt Aerosol program result in acid rain?

No. See answer to question above: ‘Would addition of HCl as an ISA precursor make the troposphere acidic?’ 

In short, proposed dispersion volumes are too low to affect the acidity of rain appreciably, and our use of electrolysis will anyway render the effect of rained-out ISA neutral. 


Please email your questions to  


Next: Deployment Issues