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?"
Guides & support
Find the right guide.
Set up your sensor, connect your home, and make sense of your air.
Tagged: Outdoor contextBrowse all guides
All guides
1–12 of 27 guides
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.
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.
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.
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: European pollen forecasts track each separately, and the seasons are very different. Terrestream's pollen levels come from Google.
Precipitation: the great atmospheric scrubber
Rain and snow wash particles out of the air, but not all sizes equally: pollen, dust and the tiniest particles go quickly, while most fine-particle mass lingers.
Open vs. closed windows
The single most consequential daily decision the dashboard helps you make. Six outdoor signals, three indoor signals, one answer.
Climate zone effects
The same reading means different things in cold-dry, hot-humid, and temperate climates. Knowing your zone tells you which problems to watch for.
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 rough but useful gauge of how much fine particulate is in the air, as long as the air is dry.
Cloud cover and photochemistry
Cloudy days produce less outdoor ozone. Sunny days produce more. Ozone forecasts build that in, and Terrestream reads the ozone forecast for your home's location.
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 or, when Google's reading is more than three hours old, from Open-Meteo.
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 air feeds: where the outside numbers come from
The dashboard's outdoor card layers several data streams: Open-Meteo for weather and modeled air quality, Google Air Quality for current pollutants and the US EPA AQI while its reading is under three hours old (Open-Meteo's values otherwise), and Google Pollen for pollen forecasts. Here is the pipeline.
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.
