Find the air that needs help — and fix yours tonight.
ActSmall · Air is a free, map-first air-quality portal. The map opens on a place where the air is hardest to breathe right now — and shows you, as a normal person, the single highest-leverage thing you can do for the air you live in. Tap any monitor for live PM2.5 readings against the WHO 2021 guideline, plus a curated list of citizen actions. No accounts. No tracking. Nothing for sale.
Information only.
This site is not medical advice, air-quality engineering certification, or first-aid guidance. For symptoms or any incident, ask qualified local people. Get help →
Build a $30 box-fan filter tonight
The headline action for almost every visitor is the same: assemble a Corsi-Rosenthal box. It is a 20-inch box fan with four MERV-13 furnace filters taped into a cube. The first peer-reviewed evaluation found it removes indoor PM2.5 with a clean-air delivery rate roughly comparable to commercial HEPA purifiers costing 5–10× as much. Background & build instructions on Wikipedia →
What you need
One 20" box fan, four 20"×20" MERV-13 furnace filters (or the closest local equivalent — the EU’s ISO 16890 ePM1 50–65% grade, or any “HEPA-grade for fine dust” furnace media), duct tape, a piece of cardboard for the bottom. Roughly US$30–60 in countries with cheap box fans (US, Canada, Australia); €40–80 in much of Europe; meaningfully more where fans are imported. Substitute a similar-CFM tower or pedestal fan with a single MERV-13/ePM1 wrap if box fans aren’t common where you are.
What it does
Pulls room air through four sides of filter media and exhausts cleaner air out the top. Indoor PM2.5 typically drops 50–80% within an hour in a small bedroom or classroom.
Where it helps most
Wildfire smoke days. Indoor cooking with gas. Diesel-heavy cities. Classrooms during respiratory virus season. Anywhere you spend the night.
What the map shows
Live PM2.5 (OpenAQ)
Every public ground-station that has reported PM2.5 in the last few hours, sourced from OpenAQ — an open archive of measurements from 100+ governmental and research networks worldwide.
WHO 2021 thresholds
Stations are coloured against the WHO Global Air Quality Guidelines: PM2.5 24-hour mean over 15 µg/m³ is "above guideline"; over 75 is "very unhealthy".
NO₂ and O₃
Where stations report nitrogen dioxide (traffic) or ground-level ozone (heat + sunlight + traffic), readings appear in the popup so you can see what kind of air it is, not just how dirty.
Country averages
Countries are shaded by their population-weighted PM2.5 from Our World in Data — useful when no station is right next to you.
Wildfire smoke (cross-link)
If a NASA FIRMS active fire is burning within ~300 km of a monitor, the popup links to the matching fire map entry so you can see why the air is bad.
Your own pins
Drop a pin on your home, your kid’s school, your bus stop. Saved only in your browser; nothing is uploaded.
From recognition to action, in one click
Every map click picks the single highest-leverage thing you can do for that monitor right now, based on the live data:
Build a Corsi-Rosenthal filter
If indoor air is the question (most days, most places), the headline action is the $30 box-fan filter described above. Cuts indoor PM2.5 by 50–80% within an hour.
Get N95 / KN95 masks
If a wildfire smoke event or AQI spike is currently active near the monitor, the action shifts to a properly fitted N95. CDC NIOSH approved respirators (CEL).
Fix gas-stove venting
If you cook indoors and PM2.5 spikes regularly, the action is range-hood or window-fan venting during cooking. Indoor NO₂ and PM2.5 from gas combustion is one of the most underrated household air-quality issues.
Find vetted clean-air operators
If structural pollution is the issue (refineries, ports, freight corridors), the recommender names long-running clean-air operators — Clean Air Task Force or your national air-quality network — so you know who already does the work. We surface the names; what you do next is your call.
Email a representative
Every primary action carries a one-click Email an MP / representative button with the country, the actual data point, and a short civil ask already written. You only have to pick the recipient and press send.
Tell two people
If nothing acute is signalled, the action becomes multiplication: forward the live view to two more people via your phone’s share sheet. The headline number travels with the link.
Below every primary action sit three small affordances: Mark done writes a private entry to your own action log so a one-shot intent becomes a habit you can see; 30-day reminder downloads a calendar event so the commitment outlives the moment; Tell two people uses your share sheet so reach multiplies without friction. The log lives only in your browser. Nothing is tracked, gamified, or sent anywhere.
How the data stays current
A small scheduled job pulls the OpenAQ public archive once a day for the latest PM2.5, NO₂, and O₃ measurements, normalizes each one against WHO 2021 thresholds, and serves the result to everyone who visits. Your browser only ever talks to our own server for the data layers. Result: same-day freshness, deliberately tiny running costs, and no upstream API gets polled more than its publication rhythm warrants.
Read more in methodology. Source code lives publicly — everything you see can be inspected.