What is IAQ?
A single composite score that summarizes indoor air, calibrated to the same 0–500 scale as the U.S. EPA outdoor AQI.
Breathe Better. Live Smarter.®
Air quality reference.
Know what changed. Know what to do. Definitions, thresholds, sources, and recommended responses for every Terrestream reading.
- 207+
- plain-English guides
- 6
- status bands
- AI
- actionable insights
Device readings, weather, pollen, smoke, and source patterns are connected into practical responses instead of isolated numbers.
Start with what you noticed
What should I do about my air?
CO2 + ventilation
Stale air or sleep
Find closed-room buildup, overnight patterns, and recovery actions.
PM2.5 + PM10
Dust, smoke, or particles
Separate indoor sources from outdoor smoke, pollen, and resuspended dust.
Moisture + building context
Humidity or mold risk
See when comfort becomes condensation, dust-mite, or mold risk.
NOx + VOC + PM
Cooking or combustion
Understand gas stoves, garages, candles, and ventilation tradeoffs.
Indoor + Open-Meteo
Allergies or pollen
Connect outdoor pollen and weather to indoor particle changes.
AI recommendations
What action should I take?
Move from readings to source, confidence, and mitigation choices.
Near you
Relevant guides for Columbus, OH
Start with your question
Common air-quality questions, routed to the right guide.
What indoor air quality sensor should I buy?
Compare measured channels, interpretation, integrations, and limits before you buy.
Why is my bedroom stuffy?
Start with CO2 buildup, door closure, occupancy, and recovery time.
Is this wildfire smoke?
Use PM2.5, PM10, outdoor AQI, wind, and recovery patterns together.
Is cooking affecting my air?
Look for the PM, VOC Index, and NOx Index fingerprint of combustion and cooking.
Why is my room dusty?
Separate resuspended dust, pollen, outdoor particles, and filtration recovery.
What action should I take?
Move from readings to source likelihood, confidence, and mitigation choices.
Compare monitors
Buyer comparisons live in Learn.
These articles are dated and sourced so Terrestream can be compared against real devices without turning the product page into a wall of competitor copy.
Compare indoor air-quality monitors
A sourced buyer guide across the monitors people actually cross-shop.
Terrestream vs Awair Element
Five-factor score-driven monitor versus broader sensing and interpretation.
Terrestream vs Airthings View Plus
Radon-forward monitor versus broader day-to-day IAQ event interpretation.
Terrestream vs Aranet4 HOME
Portable CO2 awareness versus a stationary room IAQ system.
Terrestream vs IQAir AirVisual Pro
AQI-forward display versus multi-signal indoor source interpretation.
Terrestream vs AirGradient ONE
Open-home hardware comparison for sensing, dashboards, and interpretation.
Terrestream vs PurpleAir
Outdoor particle-network context versus indoor room decision support.
Sensor metrics
Carbon dioxide indoors
Every exhale adds CO₂ to the room. Past about 1,000 ppm, focus slips. Past 1,500, headaches.
PM2.5: the fine stuff
Particles smaller than 2.5 micrometers slip past your nose, lodge deep in the lungs, and cross into the bloodstream. They are the single most-studied air pollutant.
PM10: dust, pollen, and the coarse fraction
Larger particles that mostly get filtered in the upper airway, but they still matter for allergies, asthma, and visibility.
VOCs: the invisible smell
Volatile organic compounds are the carbon-based gases evaporating off everything: cooking, candles, paint, new furniture. Some are merely annoying. Some are not.
NOₓ: gas stoves, traffic, asthma
Nitrogen oxides come from combustion. Indoors, the main source is a gas stove. The health link with childhood asthma is robust.
Humidity: the 30 to 50 percent rule
Below 30%, your throat dries out and viruses last longer. Above 60%, mold and dust mites thrive.
Temperature: comfort, sleep, productivity
ASHRAE defines a comfort zone. The bedroom is its own special case: cooler is better.
Barometric pressure: weather, altitude, headaches
Pressure rarely changes how the air feels, but it changes how the body feels. It is also the most reliable indoor weather forecast you have.
Lux: light, circadian rhythm, and screen time
Light is information your body uses to set its clock. Most indoor environments give it the wrong information.
Formaldehyde (HCHO): why Terrestream does not measure it
Formaldehyde (HCHO) is the most asked-about specific VOC. The Terrestream SEN66 does not measure, report, or detect it - do not use the device to check for formaldehyde. If you suspect it, get a dedicated test or professional advice.
Benzene: why Terrestream does not measure it
Benzene (C₆H₆) is IARC Group 1, present in vape aerosol, traffic, attached garages, and wildfire smoke. The Terrestream SEN66 does not measure, report, or detect it - do not use the device to check for benzene. Only speciated lab testing can identify it; if you suspect benzene, seek professional testing or advice.
Ozone: an outdoor pollutant we read but cannot make
Ground-level ozone is the most consequential summertime air pollutant in much of North America. The sensor cannot detect it directly; the dashboard pulls it from Open-Meteo.
Outdoor & weather
AQI vs IAQ: the same scale, two contexts
Both numbers use the same 0–500 color band, but the math is different and so is the answer to "is it bad?"
Pollen and ozone: the outdoor numbers that change your indoor advice
When outdoor ozone or pollen is high, "open a window" stops being good advice.
Sulfur dioxide: the outdoor number for fuel and fire
SO₂ comes from burning sulfur-bearing fuels: coal, heavy oil, diesel ships, volcanic activity, and wildfires. The device does not measure it; the dashboard pulls it from Open-Meteo.
Why your reading differs from the nearest EPA monitor
Three reasons your number rarely matches the official outdoor AQI: hyperlocal variation, time resolution, and calibration class.
Dew point: the number that says it's sticky
Relative humidity is relative to temperature. Dew point is absolute. If you want to know whether the air is "muggy," dew point is the number.
Apparent temperature: what your body feels
The thermometer reading is just the air. Heat index and wind chill account for humidity and wind: closer to what your body experiences.
UV index: sunburn risk in a single number
The UV index condenses solar ultraviolet intensity into a 0–11+ scale. Above 6, take precautions. Above 8, every minute counts.
Wind and infiltration: how the outdoors gets in
Outdoor wind drives air through small cracks and gaps in your building. Higher wind = more outdoor air entering, whether you want it or not.
Pollen species: the six that matter most
Alder, birch, grass, mugwort, olive, ragweed. Open-Meteo reports each; the seasons are very different.
Precipitation: the great atmospheric scrubber
Rain removes particles from air. Snow does too, more slowly. The hours after a steady rain are some of the cleanest air you'll ever breathe outside.
Climate zone effects
The same reading means different things in cold-dry, hot-humid, and temperate climates. The interpretation adjusts.
Seasonal IAQ shifts
Winter, spring, summer, fall. The dominant indoor-air pressure changes with the calendar.
Canadian Air Quality Health Index
Canada uses a 0–10+ health-risk index instead of the US 0–500 AQI. Different math, different recommendations, same goal.
Aerosol Optical Depth
What satellites see when they look at our atmosphere. Aerosol Optical Depth quantifies how much sunlight gets scattered or absorbed by particles, and it lines up with ground-level PM in useful ways.
Mineral dust events
Saharan dust to the Caribbean and Texas, Asian dust to the Pacific Northwest. Distinct from wildfire smoke chemically, sometimes visually similar.
Visibility as air quality
How far you can see is a direct proxy for how much fine particulate is in the air. The relationship is well-quantified and useful.
Cloud cover and photochemistry
Cloudy days produce less outdoor ozone. Sunny days produce more. The dashboard uses cloud cover to predict tomorrow's ozone today.
Solar radiation and air chemistry
Direct radiation, diffuse radiation, shortwave total. The numbers behind outdoor ozone, indoor lux, and the circadian signal all come from the same place.
Snow depth and winter IAQ
Fresh snow scrubs particulates from outdoor air. Persistent snow traps cold air at the surface, sometimes for days, with all that implies for inversions.
Tree pollens, regional
A short list of headline genera covers the broad strokes, but tree pollens vary by region. Oak in the South, cedar in Texas, maple in the Northeast, birch in the North.
Mold spore forecasts
Outdoor mold spore counts are tracked alongside pollen by allergy services. Different biology, often confused, sometimes the actual culprit when pollen seems low.
Ammonia and agriculture: the rural PM2.5 story behind the outdoor card
NH₃ from livestock and fertilizer is a major PM2.5 precursor. The outdoor feed does not carry ammonia itself; what the dashboard shows is the resulting outdoor PM2.5 from the Google Air Quality API.
Pesticide drift: when farms are upwind
Pesticide drift is the rural-IAQ analog of wildfire smoke: outdoor-driven, episode-based, and worst during spraying seasons. The playbook is forecast, close, filter.
Air quality is not distributed equally, and the indoor sensor cannot fix that
Outdoor PM2.5 and NOx sit higher near highways, near ports, near industrial sites, and downwind of all three; those locations correlate with race and income in the United States and Canada in ways that are not accidents.
Your commute is part of your exposure, and Terrestream cannot measure it
A fixed indoor sensor cannot follow you into a car cabin, a bus, or a bike lane next to a highway. The exposure that happens on the way to work is real, and it belongs to a different category of instrument.
Sources & scenarios
Wildfire smoke: what is in it, what to do
A complex aerosol dominated by PM₂.₅, with VOCs, NOx, and dozens of trace species. Indoors, the right response is to seal up and filter, not ventilate.
Gas-stove cooking: the fingerprint
A pan on a gas burner produces a remarkably consistent multi-pollutant signature: NOx, ultrafine PM, VOCs, and humidity, all rising and falling together.
Candles and incense: small flame, big PM spike
A single candle can push a small room past 100 µg/m³ PM₂.₅ in under ten minutes. Incense is worse.
Cleaning products: the VOC spike you can smell
Pine, citrus, ammonia, bleach. Most cleaning products produce sharp VOC spikes; some combinations are acutely toxic.
New furniture and paint: the slow VOC bleed
Particleboard, foam, finishes, and many paints off-gas formaldehyde and other VOCs for weeks to months. A new sofa changes the room's baseline.
Bedroom overnight: the CO₂ climb you sleep through
Two adults in a closed bedroom can push CO₂ past 2,000 ppm by 4 AM. The math is unforgiving.
Attached garages: the highest-risk source in most homes
A running engine ten feet from your living space. Cold-start emissions are the worst. Door seals matter more than you think.
Wood stoves and fireplaces
Solid-fuel combustion produces the largest, longest-lasting PM event most homes ever see indoors. Even a well-tended fire shifts the baseline for hours.
Vaping, smoking, and cannabis
Combustion and aerosolization indoors. Tobacco smoke, cannabis smoke, and vape aerosol all show on the sensor; the health profiles differ significantly.
Bathrooms and showers
A hot shower is a daily humidity event with a side of cleaning-product VOCs. Recognizable, mostly harmless, occasionally a mold-risk signal.
Moving into a new home
The first month is when off-gassing peaks, cleaning is heaviest, and the dashboard learns your normal. Expect noise; expect resolution.
Holiday and gathering patterns
Turkey day, parties, holiday candles, family visits. Combined source events look different from any single source.
Cooking fingerprints in depth
Gas, induction, electric, grilling, frying, roasting. Each cooking method has a distinct multi-parameter signature.
Evaporative coolers ("swamp coolers"): cool air, high humidity
Common in the desert Southwest, evaporative coolers add 20-40 grains of moisture to the air for every degree of cooling. Different dynamics than AC, and a different humidity playbook.
Post-renovation IAQ: bake out, clean up, then move back in
The first thirty days after renovation are the highest-emission window the building will ever see. The right protocol cuts months off the off-gas tail.
Basement IAQ: a different environment from the rest of the house
Basements run cooler, more humid, and lower-ventilated than the floors above. The HVAC lives down there, the water heater lives down there, and so do the paint cans, the radon, and most of the mold problems.
Apartment and condo IAQ: when the air problem is in the next unit
In a multi-unit building, your air is your neighbors' air. Cooking, smoking, cleaning chemicals, even fragrances migrate through shared HVAC, plumbing chases, and balcony paths. Here is how that happens and what can actually be done from inside one unit.
New-build vs old-house IAQ: two different problem sets
A tight 2020 build and a leaky 1925 farmhouse fail in opposite directions. The dashboard signatures are different, the priorities are different, and "better" depends on what you are trying to solve.
Microplastics in indoor air
Your clothes shed plastic. So does your carpet, your bedding, and your packaging. The dashboard's PM channels see the bigger fragments as a subset of total particles; the science on health impact is still arriving.
PFAS in indoor dust: the forever-chemical exposure route the dashboard does not see
PFAS exposure indoors is dominated by dust ingestion and dermal contact, not by inhalation. The SEN66 cannot detect them; reducing PFAS load is a housekeeping and procurement problem, not a sensor problem.
Mattress and bedroom off-gassing: the one room where it matters most
You spend a third of your life within a foot of a polyurethane foam slab. The "new mattress smell" is a measurable VOC emission curve, and it lasts longer than the marketing suggests.
Cannabis smoke indoors: a distinct profile from tobacco
Combustion is combustion: PM2.5, CO, PAHs, benzene. Cannabis adds THC and CBD aerosol and a different terpene signature. The dashboard sees it as a tobacco-shaped event with a longer VOC tail.
Humidifier bacterial risks: Legionella and the white-dust problem
A neglected ultrasonic humidifier aerosolizes whatever is in its reservoir, including bacteria. This is the one IAQ device where maintenance is a life-safety issue, not a comfort one.
Carpet versus hard floor, from an indoor-air-quality view
The blanket "carpet is always bad for IAQ" rule does not survive contact with the data. Quality, age, maintenance, and what is under the floor matter more than the category.
What a 3D printer is putting into your air
Hobby 3D printing emits ultrafine particles and VOCs that scale with filament chemistry and bed temperature. The dashboard sees it; here is what is happening and how to print without exposure.
Woodworking shop air quality at home
Sawdust from oak and walnut is an IARC Group 1 carcinogen for occupational woodworkers. The hobby shop in your garage deserves the same controls; the dashboard will tell you whether they are working.
Health & allergens
Ultrafine particles: what the sensor cannot see directly
Below 100 nanometers, particles get small enough to cross from lungs into bloodstream. The SEN66 sees PM₁ but stops there.
Mold: Terrestream is not a mold detector
Terrestream does not detect mold or count spores. It reports temperature, pressure, and relative humidity - conditions that are sometimes associated with mold. Mold can also grow in conditions and places the sensor never sees.
Dust mites: the bedroom ecosystem you cannot see
House dust mites need humidity to reproduce and warmth to thrive. The sensor reads both. Allergen is in the air whenever the bed gets disturbed.
Pet dander: what the PM₁₀ trace shows
Cat allergen is sticky and stays airborne for hours. Dog allergen settles faster. Both show up in PM₁₀ when pets move through a room.
Children: higher exposure, more vulnerable lungs
Kids breathe 50% more air per kg than adults, spend more time indoors, and have lungs that are still developing.
Asthma triggers: the indoor list
Asthma is the most common chronic disease in children. Most of its triggers are things the sensor sees.
Cardiovascular disease and PM₂.₅
PM₂.₅ kills more people through hearts than through lungs. The mechanism is systemic inflammation, oxidative stress, and direct arterial effects.
Older adults and air quality
Cardiovascular sensitivity, frailty, medication interactions, and time-indoors all shift with age. The thresholds shift too.
COPD and air quality: tighter margins than asthma
Chronic obstructive pulmonary disease affects 16 million US adults. PM2.5 sensitivity is higher than asthma, exacerbations are more dangerous, and indoor recovery matters more.
Migraines and air quality: triggers the dashboard can show
VOC bursts, pressure drops, low CO₂-induced drowsiness preceding a migraine: the dashboard can document triggers a person knows but cannot prove.
Sleep apnea and air quality: humidity, mites, and overnight CO₂
OSA outcomes interact with bedroom-overnight conditions. The right humidity, low dust-mite allergen, and adequate ventilation can improve CPAP comfort and reduce AHI.
Mental health and air quality: an emerging literature
Recent research links chronic PM2.5, VOCs, and indoor CO₂ to depression, anxiety, and cognitive performance. The data is suggestive, not yet prescriptive.
Pets and air quality: birds, dogs, cats, and the rest
Pets share your indoor air. Birds are uniquely sensitive (the "canary in a coal mine" is literal); dogs and cats have their own profiles.
Infants and indoor air quality
A newborn breathes faster, has smaller airways, and spends almost every hour of every day in the same indoor environment. The standard adult guidelines were not written with that physiology in mind.
Using Terrestream
Where to put the sensor
Counter-height, away from vents and windows, in the room you actually use. The placement choice changes what you can interpret.
Open vs. closed windows
The single most consequential daily decision the dashboard helps you make. Six outdoor signals, three indoor signals, one answer.
How long until the air clears
CADR, room volume, air changes per hour. The math behind "the room should clear in about 20 minutes."
Reading the dashboard
What "elevated," "spike," "trend," "baseline," and "anomaly" mean. The vocabulary the AI uses.
A renter's guide to indoor air
You can't replace the HVAC, but you can do most of what matters. Eight interventions that need no landlord permission.
Multi-room comparison
Two sensors tell more than one twice. The difference between rooms is often where the real story is.
Circadian and ambient context
Why the dashboard shows sunrise, sunset, and moon phase alongside the air-quality data. Time of day is a meaningful signal.
Returning home: vacation recovery
A sealed empty home behaves predictably while you are gone. The first 24 hours back tells you what changed.
Outdoor air feeds: where the outside numbers come from
The dashboard's outdoor card layers several data streams: the Open-Meteo weather forecast, Google Air Quality for outdoor pollutants and the US EPA AQI, weather observations, and Google Pollen for pollen forecasts. Here is the pipeline.
Sensor drift over time: what to expect after year one
The SEN66's individual channels each drift differently. CO₂ self-calibrates against outdoor air, PM loses a few percent per year, VOC and NOₓ are relative baselines by design. Here is what changes and what does not.
When the data itself is unreliable
Sensors fail in a small set of recognizable ways. The dashboard flags the failures and the AI refuses to act on them. Here is how to tell a real spike from a glitch.
How the Terrestream sensors actually work
Three sensor packages, six sensing elements, twelve signals. Here is what is inside the device, what each part measures, and the physical reasons it can and cannot do what it does.
Should I bring a sensor to an Airbnb or VRBO?
Vacation rentals are someone else's indoor environment with someone else's cleaning routine, ventilation choices, and smoking history. A portable sensor turns that opacity into one hour of data.
Set up your Terrestream
A short first-run path: power the sensor, pair it, connect Wi-Fi, claim it to your account, then place it where the room air can circulate.
Pair with the app
Use the 6-digit passkey on the device screen to create an encrypted Bluetooth pairing, then finish the claim flow in the app.
Connect to Wi-Fi
Terrestream uses 2.4 GHz Wi-Fi. You can configure it from the app or use the temporary setup network when no Wi-Fi is saved.
The Tuesday-morning fan sound
A brief Tuesday fan sound is normally the SEN66 sensor self-clean cycle.
Quiet hours, brightness, and sound
Use Quiet Hours and device/app settings to reduce display, light, and sound behavior on a schedule.
Factory reset your device
Factory reset clears saved device configuration, claim, and account-linking information so the sensor can be paired again.
Before you sell or give away your device
Factory reset the sensor before another person receives it.
Privacy, data, and resale questions
Use the privacy portal and published Privacy Policy for binding answers about personal data, sharing, deletion, and export.
Compare monitors
Compare indoor air-quality monitors
A fair, sourced buyer guide to Terrestream, AirGradient ONE, Ruuvi Air, Awair Element, Airthings View Plus, Aranet4 HOME, Kaiterra Sensedge Mini, and IQAir AirVisual Pro.
Terrestream vs Awair Element
Awair Element is a compact five-factor monitor; Terrestream adds broader particulate sizing, NOx, pressure, light, and deeper interpretation.
Terrestream vs Airthings View Plus
Airthings View Plus is compelling when radon is central; Terrestream emphasizes multi-signal indoor behavior and local-friendly workflows.
Terrestream vs Aranet4 HOME
Aranet4 HOME is a focused portable CO2 monitor; Terrestream is a broader room air-quality system.
Terrestream vs IQAir AirVisual Pro
IQAir AirVisual Pro emphasizes PM2.5, CO2, AQI, and a large color display; Terrestream adds more indoor channels and source interpretation.
Terrestream vs AirGradient ONE
AirGradient ONE is an open-home indoor monitor with strong local-home appeal; Terrestream emphasizes polished room interpretation, commercial evidence, and buyer-ready guidance.
Terrestream vs Ruuvi Air
Ruuvi Air is a credible open-friendly SEN66 monitor; Terrestream emphasizes Wi-Fi-direct operation, a touchscreen display, outdoor-data fusion, and US buyer readiness.
Terrestream vs PurpleAir
PurpleAir is strongest as a particle and outdoor-map ecosystem; Terrestream is built for indoor room decisions across particles, gases, comfort, context, and recommendations.
Terrestream vs Apollo AIR-1
Apollo AIR-1 is a compact ESPHome/Home Assistant monitor with strong local-control appeal; Terrestream emphasizes a finished room device, broader buyer guidance, and included cloud intelligence.
Workplaces & schools
Central-dashboard monitoring for schools, offices, and industry
Many sensors across a building or campus, one dashboard, notifications when something looks unusual. A B2B contract unlocks the multi-site management plane and rule-based notifications keyed to your organization's hours, occupancy, and standards.
Meeting rooms and CO₂
Eight people in a 6×8 m room with the door closed will hit 2,000 ppm in under an hour. The cognitive cost is real and measurable.
Demand-controlled ventilation
Run the HVAC harder when people are in the room, less when they aren't. CO₂ sensors are how it knows.
Productivity and air quality
Decisions get worse, errors rise, and absences increase as air quality drops. The literature quantifies it; the dashboard surfaces it.
Sick building syndrome
A cluster of complaints, no single identifiable cause. The diagnosis has fallen out of fashion; the underlying problems haven't.
Classroom CO₂ and learning
Test scores correlate with ventilation rates. Attendance correlates with ventilation rates. The literature is unusually consistent.
EPA IAQ Tools for Schools
The U.S. EPA's structured framework for school IAQ management. Free, well-documented, widely adopted.
Schools and wildfire smoke
Close, mask, or shelter-in-place? AQI thresholds, building envelope, and student-population considerations.
Office IAQ: the 4 p.m. conference-room problem
A typical office starts at outdoor CO₂ baseline and ends the day at 1,200 ppm in the meeting rooms. Plus VOCs from cleaning and new furniture, plus whatever the outdoor air brings in.
School IAQ: where children spend a third of their day
Classrooms exceed CO₂ targets routinely, locker rooms add cleaning-product VOCs, older buildings have mold, and the school bus idles ten feet from the intake. A separate environment from home, with its own problems.
When the homework gets harder at 4 PM, check the CO₂
Closed door, one kid, two or three hours of after-school homework in a small bedroom. The cognitive-science literature predicts exactly the focus collapse parents see, and the dashboard usually shows the cause.
RESET, WELL, Title 24, and air monitoring
Sensor selection can be relevant to standards-aligned workflows, but device parts alone do not confer certification, accreditation, or code compliance.
Commercial IAQ monitoring for schools
Schools need room-level evidence: CO₂ for ventilation, PM recovery for filtration, humidity for comfort and building risk, and source patterns that facilities teams can act on.
Commercial IAQ monitoring for offices
Office IAQ monitoring turns meeting-room CO₂, filtration recovery, cleaning VOC events, and HVAC patterns into decisions facilities teams can defend.
Factory and light-industrial IAQ monitoring
Light-industrial spaces need pattern visibility around dust, combustion, solvents, ventilation, and maintenance. IAQ monitors support triage; they do not replace occupational hygiene instruments.
How interpretation works
What the AI can and cannot tell you
The dashboard interprets your air. It does not diagnose you, replace your doctor, or detect things the sensor cannot measure.
Dashboard vocabulary
The small set of words the dashboard uses with specific, defined meanings. Precision in the vocabulary lets the AI and the reader stay aligned.
Recovery curves
Each pollutant decays with its own characteristic shape. The shape is how the AI tells one event from another.
Time scales of air quality
Minutes to seasons. Knowing which time scale a parameter lives on is half of interpreting it correctly.
How parameters interact
Air-quality parameters do not change in isolation. Humidity pushes the VOC index. Ozone reacts with limonene to make formaldehyde. Knowing the interactions is how the AI avoids false alarms.
Cumulative vs acute exposure
A bad afternoon and a bad decade are different problems. The literature is clear about which matters more for what.
Benchmarking your home
Is your air normal? Population-level studies and the dashboard's own data let you compare to typical homes.
Risk vs hazard vs exposure
Three words public-health professionals use carefully. Loose usage in air-quality conversations causes most of the misinterpretation.
How anomaly detection works
When the data does not match any known pattern, the dashboard logs the event and asks for help interpreting it. That is by design.
Building type priors
Apartments, townhomes, detached single-family, and commercial buildings each have characteristic air-quality patterns. The AI uses the building type as a structural prior.
Where do the numbers come from?
Every reading on the dashboard has a source: a sensor on the device, a computation from sensor inputs, or an outdoor API. Knowing which is which is the first step in interpreting any of them.
The PM size cascade
PM10, PM2.5, PM1.0, ultrafines. Same physics, different particle-size buckets. The size determines where particles lodge in the body and what produced them.
Four air quality indices, compared
EPA AQI, WHO 2021 guidelines, Canadian AQHI, European CAQI. Four different ways to summarize the same air.
Filtration approaches, compared
HEPA, MERV, Corsi-Rosenthal. Three filtration paths to the same goal. Cost, performance, deployability differ in different directions.
Ventilation approaches, compared
Open windows, range hood, HRV/ERV, demand-controlled ventilation. Different ways to bring fresh air in and stale air out.
Combustion sources, an overview
Anything that burns indoors produces a multi-pollutant signature: NOx, fine particulates, VOCs, ultrafines, and (sometimes) CO. The dashboard has a shared interpretation framework for all of them.
Allergen sources, an overview
Mold, dust mites, pet dander, pollen, mold spores. Most household allergen exposure is one of these five. The dashboard groups them as a family.
The feel of air
Sometimes the air feels wrong even when all the numbers look normal. The dashboard integrates several parameters into a subjective-experience model that explains why.
Weekend vs weekday patterns
Most households run on a 5-and-2 schedule. The air does too, in ways the AI uses to set its baseline.
IAQ tradeoffs with energy: ventilation has a heating bill
Every cubic foot of outside air you bring in is air you have to heat or cool. In some climates "just open windows" is correct; in others it is the most expensive intervention you can pick.
CO₂ rebreathing detection: when a room is breathing itself
A near-linear CO₂ climb that does not decay is the signature of a room rebreathing its own air. The math is straightforward and the pattern is unmistakable on the dashboard.
Cognitive effects of CO₂: the Allen and Satish literature
Two landmark chamber studies (Satish 2012, Allen 2016) show executive function dropping monotonically as CO₂ rises from 550 to 1,400 ppm. The shape, the domains, and the mechanism candidates.
The indoor/outdoor ratio: one number that tells you what the envelope is doing
For most outdoor-driven pollutants, indoor concentration divided by outdoor concentration is the single most diagnostic number in the dashboard. It tells you whether your house is sealed, filtered, or leaking.
Using forecasts: how to act on tomorrow's air
Open-Meteo gives you hourly outdoor forecasts up to 7 days out. The dashboard uses them to suggest action before a problem arrives, not after. Here is how the forecast horizon maps to confidence.
Anticipating indoor events: outdoor current + forecast + indoor reading
Each of the three inputs is a signal. Combined, they let the AI predict whether an indoor event is about to happen, and recommend action before it does.
How confident the AI is when it makes a recommendation
The dashboard speaks in three voices: confident, cautious, and openly uncertain. Knowing which voice you are hearing is half the value.
The AI is an environmental advisor, not a medical one
The dashboard will tell you about your air. It will not diagnose, prescribe, or speculate about your health. The line between those two is bright and intentional.
How accurate is the reading, really?
Accuracy, precision, and drift are three different things, and consumer-grade sensors trade absolute accuracy for cost and form factor. Here is what the numbers on the dashboard actually mean.
Dose: why concentration times time is what your body sees
A short spike and a long low-level exposure can produce the same dose with completely different health implications. The dashboard tracks both because they answer different questions.
CO₂ as an airborne-pathogen proxy: what the ratio actually tells you
CO₂ does not measure pathogens. But CO₂ and exhaled pathogen droplets share a source (occupants) and a sink (ventilation), so the indoor-to-outdoor CO₂ ratio tracks the fraction of air in the room that other people have already breathed. This is why the Aranet model was widely adopted for ventilation monitoring during the pandemic.
SBS vs BRI vs MCS: three terms that are not interchangeable
"Sick building syndrome" gets used to mean three different things, and the difference matters because each leads to a different diagnostic path. Here is the disambiguation, with the room-by-room signatures the dashboard can and cannot help find.
Stack effect and pressure differentials: the building physics that moves your air
Warm air rises, cool air falls, and exhaust fans push the balance around. The result is that pollutants move through a building in predictable directions, the basement supplies the bedrooms more than you think, and a bath fan can backdraft a water heater. The dashboard makes the patterns visible.
Three mild elevations can outweigh one severe one
The body does not see pollutants one channel at a time. Mild PM2.5, mild NOx, mild humidity, and warm temperature can stack into a load that none of them would carry alone, and the dashboard reads them that way.
How air-quality sensors work
The Terrestream stack combines direct measurements, index outputs, context sensors, and interpretation. Those are different evidence classes, and the distinction matters.
PM sensor accuracy and aerosols
Optical PM sensors estimate mass from scattered light. They are powerful for building telemetry, but aerosol chemistry and particle shape still matter.
VOC Index vs TVOC
VOC Index is a relative signal from a MOX gas sensor. TVOC is a concentration-style lab concept. They should not be collapsed into the same claim.
NOx Index vs NO₂
NOx Index is a combustion-pattern signal. It is not a regulatory NO₂ concentration measurement.
CO₂ sensor accuracy and ventilation
CO₂ is the clearest occupancy and ventilation signal in most rooms, but placement, calibration assumptions, and recovery time still shape the interpretation.
Pressure context and infiltration
Pressure is not an IAQ compliance channel. It is building-physics context that helps explain when outdoor air, weather, and HVAC operation are shaping indoor readings.
Lux and indoor-air context
Lux helps interpret placement, daylight, display behavior, and occupancy patterns. It is not proof of circadian lighting performance or WELL lighting compliance.
Sensor calibration, drift, and confidence
Good monitoring is not just a sensor spec. It is calibration evidence, drift expectations, placement discipline, and confidence-aware interpretation.
What to do
WHO vs EPA: two number systems, two philosophies
EPA NAAQS is regulatory. WHO 2021 is aspirational. The dashboard shows you both.
ASHRAE ventilation rates: the math behind "open a window"
ASHRAE 62.1 covers commercial; 62.2 covers homes. Both give you a number in CFM per person.
Health Canada residential guidelines
Canada publishes its own per-pollutant residential indoor-air guidelines. They are tighter than EPA on NO₂ and similar on PM₂.₅.
WELL, RESET, LEED: building-level certifications
For commercial buildings, three certifications dominate the indoor-air conversation. Each weights different things.
HEPA purifiers: the CADR math
A HEPA filter is the most effective single intervention for indoor particulates. Sizing it correctly is the part most people get wrong.
The Corsi-Rosenthal box-fan filter
A $50 box fan, four MERV-13 furnace filters, and twenty minutes of construction. CADR comparable to a $400 commercial unit.
HVAC MERV ratings: what your furnace filter actually does
MERV 8 catches dust. MERV 13 catches viruses. MERV 16 catches almost everything HEPA does. Most homes ship with MERV 6.
Range-hood venting: the single biggest cooking intervention
A properly vented hood at high speed captures 70-95% of cooktop emissions. A recirculating hood captures almost nothing.
How the sensor sees: optical CO₂ vs MOX
CO₂ is read by pulsing infrared light the gas absorbs and listening for the pressure wave. VOCs are read by watching a hot ceramic surface change conductance. Different physics, different limits.
Cross-sensitivities: what confuses each sensor
Every sensor has things it sees that it shouldn't. Knowing the cross-sensitivities is how the dashboard tells you the right story.
Co-movement patterns: the fingerprint catalog
A single metric tells you a number. Several metrics moving together tell you what happened.
What to do when PM is rising
A decision tree. Start with the source, end with the intervention. Each branch has a different right answer.
What to do when CO₂ stays high
Sustained CO₂ above 1,000 ppm means ventilation is not keeping up with occupancy. Four diagnostic paths.
What to do when VOC won't stabilize
Elevated VOC index for days or weeks. Five possible explanations, each with a different response.
What to do when humidity is stuck
Indoor humidity outside the 30-50% comfort and mold-safety range. Four diagnostic paths.
Plants as air purifiers: the NASA 1989 myth
A famous study tested potted plants in sealed chambers. Real-world rooms have orders of magnitude more air; the practical contribution is negligible. Have plants because you like them.
Reducing CO₂ indoors: the ventilation ladder
CO₂ is what people exhale. The only durable answer is moving more outside air in. Here is the cost-ordered ladder, from free to capital project.
Reducing NO₂ and NOₓ indoors: source elimination first
Indoor NOₓ comes from combustion. The intervention hierarchy starts with eliminating sources and ends with capture-and-exhaust for what remains.
Reducing PM2.5 indoors: filtration plus source control
Two levers: stop making fine particles, and remove them when they appear. CADR-sized HEPA in occupied rooms plus a MERV-13 HVAC filter does most of the work.
Reducing PM10 indoors: cleaning regime more than filtration
PM10 settles faster than PM2.5 and is more about deposited dust than airborne particles. Walk-off mats, damp methods, and HEPA-vacuuming carry most of the load.
Reducing VOCs indoors: substitution before mitigation
VOCs are easiest to manage by not introducing them. When you cannot avoid them, ventilation and bake-out are the durable tools.
Reducing indoor humidity: dehumidify, ventilate, repair
The 30-50% RH band is the IAQ sweet spot. Above 60% RH for sustained periods, mold and dust mites become a problem.
Raising indoor humidity: winter dryness and how to fix it
Cold outdoor air holds little water; once heated indoors, RH drops below 30%. Static, dry skin, respiratory symptoms, and infection-transmission risk all rise.
Reducing indoor ozone exposure: outdoor-driven, mostly avoidance
Indoor ozone comes mostly from outdoor infiltration on bad-air days. The playbook is window timing, building-envelope sealing, and avoidance of ozone-emitting devices.
Reducing SO₂ indoor impact: outdoor-driven, near industrial
SO₂ is almost entirely outdoor-driven from coal combustion, port shipping, oil refining, and volcanic emissions. The playbook overlaps PM2.5 plus SO₂ specifics.
Sealing and air tightness: the seal-then-ventilate sequence
A leaky house exchanges air the wrong way: cold drafts, dust infiltration, radon, outdoor ozone. Seal first, then add controlled ventilation. The order matters.
Spot ventilation: kitchen and bath exhaust done right
Task-specific exhaust handles the worst pollutant sources at their origin. Sized correctly and ducted to outdoors, it does more than whole-house ventilation can.
Low-VOC finish selection: reading the labels
Green Seal, GREENGUARD Gold, CARB Phase 2, FloorScore: which certifications actually mean low emission, which numbers matter, and where the labels do not help at all.
IAQ on a budget: best impact per dollar, in order
You do not need an HRV and three air purifiers to improve indoor air. The first $0 to $200 of effort delivers most of the gains. Here is the ladder, ordered by impact per dollar.
When to call a pro: the IAQ escalation triggers
Most IAQ problems are DIY. A handful are not. Here are the triggers that say "stop, hire a credentialed professional", and how to choose one.
Pet management for IAQ: managing the human side
You cannot get to zero dander or zero ammonia in a pet-containing home. Reducing exposure 50-80% is realistic, and the levers are mostly weekly habits rather than equipment purchases.
Wildfire season preparedness: what to do before the smoke arrives
A wildfire-smoke event runs better when the supplies are already on the shelf and the envelope is already tight. Here is the May-through-September checklist, sized to a typical western-US household.
Gas to electric: the IAQ side of home electrification
Replacing the gas stove with induction, the gas water heater with a heat pump, and the gas furnace with a heat pump removes the three largest indoor combustion sources at once. The IAQ delta is visible on the dashboard; the financial picture has shifted with new federal credits.
Working out at home: respiratory rate is the multiplier
During hard exercise you move three to ten times more air through your lungs than at rest. Whatever is in that air gets the same multiplier. Home gyms and yoga rooms deserve their own ventilation plan.
Cleaning up wildfire ash inside the home
Once the air clears outside, the ash that settled on every horizontal surface during the smoke event becomes the next problem. The cleanup protocol matters because dry sweeping puts everything you tried to keep out back into the air.
Mask selection: N95 vs KF94 vs surgical vs everything else
A particle-filtering respirator is the one piece of protection a HEPA at home cannot give you. Here is what each rating means and when each one is the right tool.
Safety
CO vs CO₂: we measure one, not the other
Carbon monoxide and carbon dioxide sound alike and the abbreviations look alike. They are completely different gases. Terrestream measures CO₂ only.
Smoke and fire: why we are not a smoke alarm
The particle sensor sees smoke once it fills a room. A UL 217 smoke alarm sees it in seconds and screams loud enough to wake a sleeping family. They are not substitutes.
Radon: an alpha-particle hazard we cannot detect
Radon is the second-leading cause of lung cancer in the US after smoking. It cannot be detected by any optical, NDIR, or MOX sensor; only alpha-particle counters can see it.
What Terrestream does not measure
Terrestream measures a specific set of air-quality parameters. There are many hazards it does not measure at all - here is a non-exhaustive list of common ones, and the dedicated detector or test to use instead.
Lead paint and renovation dust: a metal hazard we cannot see
Homes built before 1978 (US) and before 1992 (Canada) are likely to contain lead paint. Renovating without containment releases lead-laden dust that no air-quality sensor can identify.
Asbestos in older homes: a fiber hazard outside our envelope
Asbestos was used in insulation, popcorn ceilings, vinyl flooring, and roofing through the 1980s. Disturbing it releases microscopic fibers we cannot detect; mesothelioma latency is decades.
Smoke detector vs IAQ monitor: not the same instrument
A common confusion: the sensor on your wall reads PM2.5, and smoke is PM2.5, so it must be a smoke alarm too. It is not. The two devices answer different questions on different timescales with different consequences for being wrong.
Breathe Better. Live Smarter.
Turn air-quality knowledge into action.
One sensor. Twelve signals. Indoor readings connected to outdoor context and plain-English recommendations. Everything you just read can be measured live in your own home.
$249 USD one-time
Buy Terrestream Explore the sensor- No subscription required
- 30-day returns
- 1-year limited warranty
- Fast shipping via FedEx
Six sensors. Twelve signals.
Built on genuine Sensirion, Bosch, and Texas Instruments sensors.
- CO₂
- IAQ
- VOC
- NOₓ
- PM1
- PM2.5
- PM4
- PM10
- Temperature
- Humidity
- Pressure
- Light
Included
- In the box: the sensor, USB-C cable, power adapter, and printed field guide
- Dashboard and mobile app included
- Privacy-first air data
Works with
- Home Assistant
- MQTT
Home Assistant
MQTT