How would ammonia affect an otherwise breathable atmosphere? [duplicate]

Question

I'm looking into an otherwise breathable but dense Nitrogen/Oxygen atmosphere, that happens to have 0.5-1% Ammonia in it - it roughly comes out to around 0.02 atm for Partial Pressure in total.

For humans, I imagine that's basically toxic, but I'm more interested in the implications for Native Life, and whether it could be a boon or an impairment on the life of the planet.

Are there any considerations that come up with ammonia at that quantity, like acid rain, or the color of the sky/clouds, that might affect life on the planet?

Answer 1

Look up the Nitrogen Cycle

Ammonium using or nitrate-producing organisms will go wild

It's worth looking up the nitrogen cycle.

Every form of nitrogen is used by at least a few organisms. Some plants and bacteria use ammonia to live on, and if they can handle the pH and high concentrations, they'll boom.

Nitrifying plants and bacteria convert ammonia (ammonium salts, to be more precise) into nitrates; they will also benefit, as will all the downstream organisms that like nitrate but can also ignore the ammonia.

Mass extinction will happen to many others

The pH of the sea and almost all soils will be very high. On Earth, this would be a mass extinction event. Nonetheless, there will.be survivors.

You need an explanation

Because of the nitrogen cycle, a one off addition of NH3 will be worked through over time. So there needs to be some source (a bacterium, maybe, or giant robotic Haber Process chemical plants) that has changed the equilibrium permanently. Unless one-off is all you're after.

Answer 2

It won't affect the color of the sky or clouds, and it won't produce acid rain... but it will produce alkaline rain, which will significantly increase chemical weathering of rocks, putting a lot more silica and metal ions into the water.

Bioavailable nitrogen is a limiting nutrient for most life forms, which is why we put nitrogen in fertilizer, and having that much ammonia available will completely remove that restriction, so, all else being equal, plants life could be much more productive, with associated increases in biomass and biodiversity all the way up the food chain.

However... in an otherwise-breathable atmosphere, ammonia is not stable. It will react with oxygen, and it will react with carbon dioxide (or more accurately, with carbonic acid), leaching CO2 out of the atmosphere. Fortunately (?), ammonia is itself a greenhouse gas... or would be, if it had a longer residence time in the atmosphere.

The biggest problem is that it doesn't have a long residence time in the atmosphere. If you've got that much ammonia floating around along with enough oxygen to be otherwise-breathable, something is constantly producing it in gargantuan quantities, and whatever that is will have significant additional effects on life on this planet, which more likely than not completely invalidates that previous assumption of "all else being equal".