# Air pollution ## Microsim (three.js) <div class="microsim-player"> <iframe src="https://wikitube-3d-microsims.netlify.app/Air_pollution.html" width="100%" height="620" frameborder="0" loading="lazy" sandbox="allow-scripts allow-same-origin"></iframe> </div> *Part of the COSMOS hub's atmospheric strand, this sketch shows how a stable Boundary layer traps Aerosol particles once nighttime cooling drains Sensible heat from the ground — the same stratification that, carried to its extreme, defines the [[Stratosphere]].* > A **temperature inversion** occurs when a layer of warm air rests on top of cooler air near the surface, reversing the atmosphere's usual cooling-with-height and forming a stable "lid." Because rising parcels cannot punch through this lid, vertical mixing collapses and any pollutant emitted beneath it accumulates instead of dispersing — the recipe for smog. This microsim lets you release particles from a ground source, blow them downwind, and tighten or relax the inversion to watch concentrations build or clear. Strengthen the lid and a dense haze pools near the ground; add wind and the domain ventilates. ## About this microsim The microsim exposes three sliders — **Wind Speed** (0–10 m/s, default 3.0), **Emission Rate** (0–80 particles/s, default 35), and **Inversion Strength** (0–1, default 0.50) — plus control buttons. **Pause** freezes the animation so you can inspect the particle field, **Clear Particles** empties the domain, and the two presets, **Clear Day** and **Smog Event**, jump all three sliders to well-ventilated or trapping configurations respectively. There are no camera or orbit controls; the view is a fixed 2-D vertical slice of the near-surface air. ## Related microsims - Boundary layer — the planetary boundary layer whose depth is exactly the mixing height $H$ this sim caps - Aerosol — the suspended particulate matter being advected and trapped - Eddy (fluid dynamics) — turbulent eddies are the dispersal mechanism a strong inversion suppresses - Sensible heat — surface sensible-heat flux drives the lapse rate that builds or breaks the lid - [[Weather_forecasting]] — air-quality forecasts hinge on predicting inversion episodes - [[Stratosphere]] — Earth's permanent, planetary-scale inversion layer ## Links (Wikipedia order) <!-- injected from _registry/childlinks/Air_pollution.json (2026-07-30T02:09:12Z) --> `1948_Donora_smog` · `1982_Bukit_Merah_radioactive_pollution` · `1997_Indonesian_forest_fires` · `1997_Southeast_Asian_haze` · `2005_Malaysian_haze` · `2006_Southeast_Asian_haze` · `2009_Southeast_Asian_haze` · `2010_China_drought_and_dust_storms` · `2010_Southeast_Asian_haze` · `2013_Southeast_Asian_haze` · `2015_Southeast_Asian_haze` · `2016_Malaysian_haze` · `2016_Southeast_Asian_haze` · `2016_Vietnam_marine_life_disaster` · `2017_Southeast_Asian_haze` · `2019_Kim_Kim_River_toxic_pollution` · `2019_Southeast_Asian_haze` · `2019_Vietnam_forest_fires` · `ASEAN_Agreement_on_Transboundary_Haze_Pollution` · `Academic_Press` · `Acetone` · `Acid_rain` · `Actinides_in_the_environment` · `Acute_radiation_syndrome` · `Adaptive_management` · `Adult_mortality` · `Advertising_mail` · `Aerosol` · `Agbogbloshie` · `Agent_Orange` · `Agricultural_land` · `Agricultural_pollution` · `Agricultural_wastewater_treatment` · `Agriculture` · `Air_pollution_in_Armenia` · `Air_pollution_in_Canada` · `Air_pollution_in_Germany` · `Air_pollution_in_Hong_Kong` · `Air_pollution_in_India` · `Air_pollution_in_Iran` · `Air_pollution_in_Macau` · `Air_pollution_in_Malaysia` · `Air_pollution_in_Nigeria` · 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`List_of_accidents_and_disasters_by_death_toll` · `List_of_countries_by_air_pollution` · `List_of_environmental_degrees` · `List_of_environmental_journals` · `List_of_environmental_laws_by_country` · `List_of_environmental_research_institutes` · `List_of_epidemics_and_pandemics` · `List_of_international_environmental_agreements` · `List_of_most-polluted_cities_by_particulate_matter_concentration` · `List_of_national_public_health_agencies` · `List_of_notifiable_diseases` · `List_of_open-source_health_software` · `List_of_plants_used_in_herbalism` · `List_of_pollution-related_diseases` · `List_of_years_in_the_environment` · `Litter` · `Livestock` · `Low_birth_weight` · `Lower_respiratory_tract_infection` · `Lung_cancer` · `MIT_Press` · [[Magnesium]] · `Malaria` · `Management_of_depression` · `Manure` · `Manure_management` · `Marble` · `Margaret_Sanger` · `Marine_conservation` · `Marine_debris` · `Marine_mammals_and_sonar` · `Marine_pollution` · `Marine_resources` · `Mary_Mallon` · 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`Wildlife` · `Wildlife_conservation` · `Wildlife_management` · `Willingness_to_pay` · `Willow` · `Wind_power` · `Wood` · `Workers'_right_to_access_the_toilet` · `Working_memory` · `World_Health_Organization` · `World_Toilet_Organization` · `World_War_II` · `World_economy` · `World_energy_resources` · `Years_of_potential_life_lost` · `Yellow_fever` · `Z-test` · `Zero_waste` ## Overview Air pollution is the contamination of the atmosphere by gases and particulate matter harmful to health and ecosystems. Crucially, ground-level concentration depends not only on how much is emitted but on the atmosphere's capacity to dilute it, which is set by wind and vertical stability. Temperature inversions are the classic meteorological trigger of severe episodes: the Great Smog of London (1952), Donora, Pennsylvania (1948), and persistent Los Angeles photochemical smog all formed when a warm lid capped a shallow, stagnant layer of city air. ## The science Normally temperature falls with height at the environmental lapse rate, on average $\Gamma \approx 6.5\ \text{°C/km}$. A rising dry parcel cools at the dry adiabatic lapse rate $\Gamma_d = \frac{g}{c_p} \approx \frac{9.81}{1004} \approx 9.8\ \text{°C/km}.$ Comparing the environment to the parcel sets stability: | Lapse condition | Stability | Vertical mixing | |---|---|---| | $\Gamma > \Gamma_d$ | Unstable | Vigorous | | $\Gamma = \Gamma_d$ | Neutral | Moderate | | $0 < \Gamma < \Gamma_d$ | Stable | Weak | | $\Gamma < 0$ (inversion) | Very stable | Suppressed | Stability is quantified by the Brunt–Väisälä frequency $N^2 = \frac{g}{\theta}\frac{d\theta}{dz}$; an inversion makes $N^2$ large and positive, so buoyancy strongly resists uplift and the mixing height $H$ shrinks. A steady-state "box" (ventilation) model then captures the dilution: the near-surface concentration scales as $C \propto \frac{Q}{u\,H},$ where $Q$ is the emission rate, $u$ the wind speed, and $H$ the mixing height. Concentration falls as $1/u$ and $1/H$ — halve the wind or the lid height and the haze roughly doubles. The Inversion Strength slider lowers $H$, Wind Speed sets $u$, and Emission Rate sets $Q$. ## Controls -> what each maps to | Control | Maps to | Range / values | Meaning | |---|---|---|---| | Wind Speed | Advection / ventilation velocity $u$ | 0–10 m/s (default 3.0) | Faster wind sweeps particles downwind and dilutes; $C \propto 1/u$ | | Emission Rate | Source strength $Q$ | 0–80 particles/s (default 35) | Particles released each second from the ground source | | Inversion Strength | Lid stability / inverse mixing height | 0–1 (default 0.50) | Higher values lower $H$ and cap vertical dispersion | | Pause | Simulation clock | button | Freeze or resume particle motion | | Clear Particles | Particle buffer | button | Remove all particles to reset the haze | | Preset: Clear Day | Slider bundle | button | Low emission, weak inversion, brisk wind — particles disperse | | Preset: Smog Event | Slider bundle | button | High emission, strong inversion, light wind — haze accumulates | ## Learning objective Understand that ground-level pollution is governed as much by atmospheric stability and wind-driven dilution as by the emission rate itself. ## Limits and connections The box model assumes instant horizontal mixing and treats particles as passive and conserved — it ignores photochemistry, deposition, and buoyant plume rise, and the inversion here is a single sharp lid rather than a gradual profile. Even so, the $C \propto Q/(uH)$ scaling explains why calm, clear winter nights so reliably produce the worst air. ## Poster & source <div class="microsim-fallback"> <!-- poster image pending backfill --> <p><em>Live microsim · <a href="https://wikitube-3d-microsims.netlify.app/Air_pollution.html">open full</a> · source: Microsims for Dissemination/COSMOS_microsims/Air_pollution.html</em></p> </div> <!-- CRAFT-LINK:START g12 --> *Built to the [[WT!Three_js_Microsim_Master_Class|three.js Master Class]].* <!-- CRAFT-LINK:END --> ## Wikipedia : Wikitube **Strict pair:** [Wikipedia](https://en.wikipedia.org/wiki/Air_pollution) : [Wikitube](https://en.wikitube.io/wiki/Air_pollution) ## Previous hub tags Tree parent: [[Oxygen]]. Legacy hubs: `COSMOS`. --- *Sources: 1 legacy note. Minted wave 1, 2026-07-30 (v1.6 order).*