Pollution

Pollution is the namesake of the game: a poisonous haze that hangs over the world, spreads with the wind and water, and slowly kills what it touches. It is simulated all the time, even while you are at home or in a raid.

The pollution field

The world is split into cells of 8 × 8 tiles, each with a pollution level from 0% (clean) to 100% (the worst). Every 10 min of game time the field moves on:

• Sources add pollution around them: industrial parks (0.8% a step, and they grow by 3% of that every game week), toxic waste dumps (2% a step: small but strong), nuclear power plants (3% a step, steady, the strongest source) and the crater and slope vents of volcanic islands (1.2% a step).
• It spreads to neighbouring cells. Water carries it 1.5 times as well as land; rock walls let only 30% through.
• The wind blows it downwind and slowly turns over the weeks. It is strongest in winter (×1.75) and autumn (×1.5) and weakest in summer (×0.5), so smog builds up in calm summers.
• It fades by 0.2% a step, about 25% a game day, if nothing feeds it.
• Rain washes it out: drizzle up to 2.1%, rain up to 6% and storm up to 9% of a cell’s pollution per game hour. Falling snow holds it in place, and so does a winter snow cover until the thaw. See Weather.

The world is already polluted when you start: the field runs for 14 game days before your first day.

You can see it: polluted ground takes on a sickly tint, and in poor air a haze closes in around you.

Air quality

Air	Level	What it means
Clean	below 5%	Safe to breathe.
Fair	5%–15%	Your body clears it as fast as you breathe it in up to about 15%.
Poor	15%–45%	Toxicity builds up slowly.
Toxic	45% and up	Toxicity builds up fast. Wear a gas mask.

Toxicity

Breathing air above 5% builds up toxicity in your body, from 0% to 100%. The worse the air, the faster it climbs. Your body clears 1.2% a minute on its own, 4 times as fast while Antitox Pills work. As it rises you go through three stages:

Stage	Toxicity	Effect
Toxic (mild)	25%+	stamina pool −20%
Toxic (strong)	50%+	move speed −5%; stamina pool −40%; aim sway +30%; no healing
Toxic (severe)	75%+	move speed −10%; stamina pool −60%; aim sway +30%; no healing; you lose 2 ml of blood a second, up to 6 ml at 100%

How long it takes to get there from clean, in play time:

Air	Mild	Strong	Severe	Mild, with a gas mask
Poor air (25%)	21 min	41 min 30 s	1 h	never
A factory’s core (35%)	10 min 30 s	21 min	31 min 30 s	never
A toxic dump (60%)	4 min 30 s	9 min 30 s	14 min	never
The worst air (100%)	2 min 30 s	5 min	7 min 30 s	never

Mild toxicity takes about 21 min of clean air to clear, or 5 min with antitox pills.

Gas masks and filters

A Gas Mask keeps out 95% of the pollution in the air. Its filter wears only while the air is above 5%, and lasts 30 min of that. Fit a fresh Gas Filter when it runs out. A mask you find has a fresh filter.

Foul water and food

• Water is foul where the level is 20% or more, or within 24 tiles of a toxic dump. A drink of it adds 8% toxicity and makes you Sick for 10 min. A canteen filled there stays foul.
• Berries and mushrooms picked where the level is 20% or more are foul too: each one adds 4% toxicity and 5 min of sickness.
• Traders pay only part of the price for polluted goods; see Trading.

Plants and animals

• Above 25% trees start to die, faster the worse the air. Dead trees do not come back.
• Healthy animals move away from air at 30% or more. Those that live there are sick, and so are their carcasses.
• At 65% and up, animals come as mutants. A mutant’s bite adds 5% to your toxicity. See Wildlife.
• Zombie hordes that raid your home on polluted air can bring toxic mutants, whose hits poison you.

Fighting back

You can clean up the land around you:

• Dig out toxic dumps. Each barrel takes 3 s of Shovel swings. A dump gives off less with every barrel gone, and nothing once it is empty.
• Shut down factories. A shut industrial site gives off only 10% of what it started with, and stops growing.
• Filter the air at home. An air filter on a powered network cuts your home’s air to 25% of the level outside. Each Gas Filter loaded gives 48 game hours of filtering, and it holds 4.
• Plant trees. A Sapling grows into a tree in 3 game days, but withers into a stump if the level is above 20%. Felling a living tree drops a sapling 25% of the time.
• Grow food in clean air. A planter grows only while it is watered and the home’s air (after the filter) is at most 30%; in worse air the crop withers and dies. Picking berries and mushrooms gives a seed 25% of the time.

Crop	Sown with	Ripe after	Harvest
Berries	Berry Seeds	2 game days of watered time	4 × Berries, and the seed back
Mushrooms	Mushroom Spores	3 game days of watered time	3 × Mushrooms, and the seed back

A watering lasts 24 game hours, and a planter holds at most 48.