Environment
The Environment map has two layers: Pollution, the smoke from factories and power plants, and Heat, the warmth pavement and roofs add to the city’s nights.
Air pollution
Busy factories, coal plants, paper mills, petrochemical plants and warehouses give off particles while they work; an idle one gives off nothing. Each spreads a plume the same way in every direction: coarse dust that settles within a few blocks, and a finer haze that thins with distance but reaches across the city, so a big industrial district is felt everywhere. Every home gets an air pollution score from 0 to 100, where 100 is living next door to a working factory. Sources stack, up to the cap of 100, and a coal plant running flat out counts as three factories.
It is a game score, not an official air quality index, which would be defined per pollutant over set averaging periods. The map reads it as Clear below 30, Elevated from 30 to 39 and High from 40.
The standard breeze and today’s wind
Wind spreads smoke thinner: twice the wind, half the score, within limits. So that the map holds still while the weather changes, the Environment map scores every home in a standard breeze of 8 km/h, with the factories and plants running as they actually ran today. A line on the map gives today’s real wind.
Health uses the real wind. Still days make the air worse and windy ones better, and on the windy map air pollution runs well below what the map shows. A resident at a score of 100 is about half again as likely to fall ill. Trees near homes take a little off, at most 12% under full canopy, but the answer to a factory is where it stands and how hard it runs.
Night heat added by the city
Pavement, concrete and roofs soak up the day’s sun and give it back after dark, so a built-up neighbourhood stays warmer at night than the countryside around it. The Heat layer shows this night heat added by the city: a few tenths of a degree in a leafy suburb, up to about 3.5 °C in a district paved from wall to wall on a calm night. Busy factories add a little of their own.
Less pavement near homes is the strong lever. Trees cool afternoons far more than nights, water does not cool nights at all, and wind carries the heat away. Like Pollution, the layer draws homes in the standard breeze; tonight’s figures use today’s wind. Open water is left blank: a river holds no pavement or roofs for the city to warm, while smoke drifts over it like any air.
It matters on summer nights. A night whose low stays at 20 °C or above counts as a warm night, and warm nights make people ill, because the body recovers from a hot day overnight. The Heat layer counts the residents the city’s own heat pushed past 20 °C.
Room to Breathe
Room to Breathe goes to a city that, over twelve complete months in a row, averages 10,000 residents and keeps nine in ten of them out of High air pollution at home: no more than one resident-day in ten spent in High, scored in the standard breeze. Because the breeze is fixed, the city’s map wins the award, not a lucky windy year. Keep industry away from homes and plant trees near the rest. Progress shows on the Pollution layer and on the Energy map’s Year page.
Why heat has no award
The simplest way to keep a city’s nights cool is to spread it thin, which is not worth rewarding. Trees barely move night heat, and on the windy map the wind would decide the result for you. So heat stays on the map as information and as a health cost, and waits for a lever that does not reward sprawl.
Parameters
Each parameter names its basis. Measured: a published figure, converted to game units. Calibration: a game-scale coefficient whose direction and scale are grounded in sources, but whose exact value was chosen for play. Scenario: an authored assumption about this fictional region.
Uhi neighborhood radius
80
How far around a home its land cover is read when scoring its heat: 80 m. A bicycle survey of Madison, Wisconsin found tree canopy cools most when measured over a city block, 60–90 m around a point, and most strongly once canopy passes about 40%, so a grove works and a lone tree does not.
Basis: measured
Uhi night impervious warming
3.5
How much warmer the night is in a fully paved and built neighbourhood than in open country: the heart of the night heat added by the city. Asphalt, concrete and masonry store the day’s sun and give it back for hours after dark. EPA’s review of US studies puts night-time heat islands at 2–5 °F (1.1–2.8 °C), and Madison’s nights varied by about 2.1 °C across the city, rising with paved cover. 3.5 at full pavement puts real districts, never quite fully paved, in that range: 80% paved gives 2.8.
Basis: calibration
Source: US EPA — What Are Heat Islands?
Uhi day impervious warming
1.2
A fully paved neighbourhood’s daytime warming, kept much smaller than the night’s so that the city’s heat problem is mostly a night-time one. A model choice: Madison’s measurements found paving warms the afternoon less than canopy cools it, while EPA’s review still reports urban daytimes 1–7 °F (0.6–3.9 °C) warmer.
Basis: calibration
Uhi day canopy cooling
2.5
How much a full tree canopy offsets daytime warming: trees shade the surfaces that would store heat and evaporate water. Land cover never cools a home below the regional reading; canopy only cancels paving’s warming, so by day a home ranges from par to at most +1.2 °C before factory waste heat, and about half canopy (0.48) cancels full paving. A review of 308 studies found urban forests on average 1.6 °C cooler than non-green urban areas. Still the player’s strongest daytime lever.
Basis: calibration
Source: US EPA — Benefits of Trees and Vegetation
Uhi night canopy cooling
0.5
Full canopy’s much weaker effect at night. Shade does nothing after dark, and Ziter et al. found night temperature followed paving, not trees. Keeping this small separates the two levers: plant trees to fix afternoons, take up pavement to fix nights.
Basis: calibration
Uhi day water cooling
1
Daytime cooling for a neighbourhood entirely surrounded by water. A meta-analysis of urban blue spaces found them about 2.5 °C cooler in the warmest months; the game uses a modest 1 °C, weaker than canopy, so a waterfront is pleasant but no substitute for planting. Like canopy, it only offsets paving’s warming and never cools a home below the region.
Basis: calibration
Uhi night water cooling
0
Water does not cool nights in this model. The thermal mass that holds a shore’s afternoon down gives the heat back after dark, so large water bodies keep their shores mild or even warmer at night. Zero is a simplification that stops a lake passing for a cure for a paved district’s nights.
Basis: calibration
Uhi canopy tile spread
2.2
How many tiles of canopy one planted tree counts as: 2.2. A tree stands on one 10 m tile, but its crown is 9–23 m across (see the tree blueprint), so a normally spaced row of street trees adds up to real canopy rather than a few isolated squares of green.
Basis: calibration
Uhi lawn canopy equivalent
0.35
What a tile of park grass counts for against a tile of tree canopy: about a third. Grass transpires and is not asphalt, but it casts no shade, and shade is most of what a tree does on a hot afternoon, so a lawn beats pavement and loses to trees. The ranking follows EPA; 0.35 is chosen for play.
Basis: calibration
Source: US EPA — Benefits of Trees and Vegetation
Uhi calm wind reference
8
Below this wind the heat island is at full strength; above it, it weakens as the square root of 8 ÷ wind, because wind mixes the warm city air into the cooler air above. The inverse-square-root law is Oke’s classic finding; pinning it to the calm map’s mean wind is a game choice. Windy Velaria (24 km/h) runs at about 58% of full strength.
Basis: calibration
Source: Oke (1973) — City size and the urban heat island (Atmospheric Environment)
Uhi factory waste heat
0.3
Extra warming beside a fully active factory from its waste heat: 0.3 °C at the fence, falling off with the pollution plume’s distance and added after the par floor. Modelling of Philadelphia found human waste heat can lift winter-night air temperatures by up to about 3 °C citywide, with smaller effects in summer; 0.3 per factory keeps industry a minority contributor next to paving.
Basis: calibration
Uhi max anomaly
5
A ceiling on how far above the region any home’s temperature can sit, after every term is added. Normal play tops out near 4 °C (full paving on a calm night beside factories); the ceiling stops a future term from producing a 12 °C city.
Basis: calibration
Hot day temperature
32
A city high at or above 32 °C (about 90 °F) counts as a hot day: US climate records have long counted days of 90 °F or more (90 °F is 32.2 °C). It is read on the city’s resident-weighted high, so the heat island can add hot days the countryside does not see.
Basis: measured
Source: NOAA NCEI — Comparative Climatic Data (days with a maximum of 90 °F or higher)
Warm night temperature
20
A night whose city low is at or above 20 °C counts as a warm night, after Europe’s ‘tropical night’ indicator, which counts nights whose low stays above 20 °C; the game’s ≥ 20 also counts exactly 20, a game threshold. The heat island moves this statistic most, and warm nights matter for health: the body recovers from a hot day overnight.
Basis: measured
Source: Climate-ADAPT (EEA) and Copernicus C3S — Tropical nights
Contamination decay distance
600
A source’s fine-particle (PM2.5) plume falls by a factor of e every 600 m. That is deliberately about four times the measured near-source gradient: near an oil refinery, elemental carbon predicted from measurements fell from 22.8 µgC/m³ at 192 m to 3.0 at 500 m, an e-fold of about 150 m. At the measured curve a district of forty factories was invisible from housing a kilometre away; stretched, a big industrial district is felt across the city while a single plant across town stays faint. The fine plume keeps about 85% of its strength 100 m out, a fifth at 1 km and under 2% at 2.5 km; with the faster coarse plume, a factory’s whole score loses about a quarter over the first 100 m.
Basis: calibration
Contamination range
3000
Beyond 3 km a source’s fine plume is ignored: five decay lengths out, less than 1% remains (e⁻⁵ ≈ 0.7%). Real fine particles travel far further, for days and hundreds of miles; the map is a local planning tool, not a regional transport model.
Basis: calibration
Source: US EPA — What is Particle Pollution?
Pm25 fine fraction
0.25
The share of a source’s particles counted as fine (PM2.5); the rest is coarse. One fraction serves every source, coal stacks and factory dust alike, as a simplification. It sits below measured stack fractions: German industrial plants’ particle emissions were usually 50–90% PM2.5, so 25% suits mechanical dust better than combustion. PM2.5 therefore caps at 25 points and the combined PM10 at 100.
Basis: calibration
Pm10 coarse decay distance
300
The coarse (2.5–10 µm) plume’s e-folding distance: 300 m, half the fine plume’s, because heavier particles settle sooner. A game choice: EPA’s fugitive-dust guidance gives the direction (the largest particles settle within metres, PM10 far more slowly), not the distance. Coarse dust dominates right at the fence and has mostly settled a few blocks out, leaving PM2.5 as most of the reading across town.
Basis: calibration
Source: US EPA AP-42, Section 13.2 — Introduction to Fugitive Dust Sources
Pm10 coarse range
1500
Beyond 1.5 km, five coarse decay lengths, a source’s coarse plume is ignored.
Basis: calibration
Contamination fence line score
100
The air pollution score at the fence of one fully active factory in the standard breeze: the anchor of the 0–100 scale. 100 means ‘as bad as living next door to a working factory’, 50 half that, and sources stack up to the cap of 100. A coal plant at full dispatch counts as three factories. It is a game score, not an air quality index: an AQI is defined per pollutant over set averaging periods, which this model does not attempt.
Basis: calibration
Source: AirNow — AQI Basics
Contamination wind reference
8
The standard breeze, 8 km/h: the wind in which scores are quoted. Room to Breathe and the Environment map both score in it, so layout decides the award and the weather does not. Today’s reading, which health uses, scales with 8 ÷ today’s wind, because a plume’s concentration falls in proportion to wind speed, clamped by CONTAMINATION_MAX_WIND_RELIEF. On windy Velaria (24 km/h) the factor is 0.33, clamped to 0.4, so air pollution reads 60% lower than in the standard breeze.
Basis: calibration
Source: E. Savory, Western University — Self-study notes: Gaussian plumes
Contamination max wind relief
2.5
Wind can divide air pollution by at most 2.5, and still air multiply it by at most 2.5: the wind factor is clamped to 0.4–2.5. Real dispersion stops improving once a plume is well mixed, and stagnation is bounded by the depth of air trapped under an inversion. Weather matters, but never erases a factory.
Basis: calibration
Source: NOAA Global Monitoring Laboratory — Temperature inversions and air pollution
Contamination canopy reduction
0.12
The most a neighbourhood under full tree canopy takes off its own air pollution score: 12%. Deliberately more than measured: a US study estimated urban trees improve air quality by typically under 1%, about 2% for particles under full canopy, and up to 8% in a single hour. Trees help, but the answer to a factory is where it stands and how hard it runs.
Basis: calibration
Contamination high threshold
40
A home scoring 40 or more in the standard breeze has high air pollution: the Room to Breathe line and the High band on the Environment map. A game rule, not a health or regulatory limit, and not an AQI. In the standard breeze one fully active factory holds homes at or above 40 out to about 320 m, roughly three blocks, and a coal plant at full dispatch out to about 750 m, so moving housing a few blocks away is a real fix.
Basis: calibration
Contamination sickness multiplier
0.45
A resident at air pollution 100 is 1.45× as likely to fall ill on a given day, scaling linearly from 1× in clean air. It uses today’s wind, not the standard breeze. Long-term particle exposure really does raise respiratory and cardiovascular illness; the size is a balance choice, so a badly sited district is a visible, fixable public-health problem.
Basis: calibration
Source: WHO — Global Air Quality Guidelines (2021)
Warm night severe temperature
26
The night-time low at which the heat health effect reaches full strength, phasing in from WARM_NIGHT_TEMPERATURE (20 °C). A city reaches it only by adding its own heat to an already hot night. A game threshold.
Basis: calibration
Heat sickness multiplier
0.35
A resident is up to 1.35× as likely to fall ill on the hottest nights, phasing in from the warm-night line to WARM_NIGHT_SEVERE_TEMPERATURE. It rides on the night alone, which is where the evidence points: a study of 11 southern European cities found hot nights raised the risk of death by 1.12× (France) to 1.37× (Portugal). The exact figure is a balance choice.
Basis: calibration
Source: Royé et al. (2021) — Effects of Hot Nights on Mortality in Southern Europe (Epidemiology)