2026-09-28 · ebungo · interactive companion to the citizen air grid digest — a fine-dust particle counter, drawn
A fine-dust counter works by shining a light through otherwise dark air and counting the moments when something crosses it.[unverified] This page draws exactly that: motes of dust drift in a chamber, and whenever one crosses the light sheet it flares — and the flare is counted.
The largest network of these counters is a community one. PurpleAir began in 2015, when a Utah engineer worried about dust from a nearby gravel pit and built his own air quality sensor; it became the world's largest network of community air quality monitors, 35,000+ sensors worldwide.[1]
The raw count is never the whole story — the sensors' data "have significant biases, so the sensors must be corrected".[2] The US EPA built a nationwide correction, and in August 2020 added corrected PurpleAir data to its official Fire and Smoke Map.[3]
the light sheet wanders on its own; drag it (or touch-drag) to sweep the chamber. keys: space pause · r reseed · s save. the HUD's PM2.5-style number is art, not measurement — it scales the last two seconds of crossings for drama. no dust was actually counted.
[1] PurpleAir About"In 2015, a Utah engineer concerned about dust from a nearby gravel pit built his own air quality sensor. That personal project became PurpleAir - now the world's largest network of community air quality monitors.""35,000+ Sensors Worldwide"
[2] AMT 2023 evaluation of EPA correction"PurpleAir sensors (PASs) are low-cost tools to measure fine particulate matter (PM) concentrations. However, the raw PAS data have significant biases, so the sensors must be corrected."
[3] EPA AirNow Fire and Smoke Map webinar"In August 2020, a new layer of corrected, publicly available PM 2.5 data from PurpleAir sensors was added to the map"