A power-plant stack releases SO2 and NOx into the wind-driven
plume (yellow-grey haze). Over seconds-to-minutes of atmospheric
residence, these gases oxidize with water vapour into sulfuric
and nitric acid aerosol (the plume shifts amber → magenta).
Switch on rain to let that acid aerosol condense and fall — it
lowers lake pH where droplets land in the water, and damages
trees where droplets land in the forest.
SO2 + [O] + H2O → H2SO4 (sulfuric acid)
NOx + [O] + H2O → HNO3 (nitric acid)
pH = 7 − k · D (D = cumulative deposition, mol/m²)
health' = −c · max(0, 5.6 − pH_local) (damage only below natural rain pH 5.6)
- Emission rate — SO2/NOx released per second before scrubbing.
- Wind speed — how fast the plume drifts toward the lake and forest; higher wind spreads it thinner but further.
- Scrubber efficiency — fraction of emissions captured at the stack before release (flue-gas desulfurization); real plants reach 90%+.
- Rain toggle — without rain, acid aerosol just disperses in the air (tracked as SO2/NOx ppb); with rain it precipitates and deposits on the ground.
This mirrors the real 1970s–80s acid-rain crisis: unscrubbed
coal-plant SO2 acidified thousands of lakes and forests
downwind, and the 1990 US Clean Air Act's scrubber mandates
(and similar EU rules) cut deposition and let many lakes
slowly recover.