Data health & coverage

Most air-quality sites show you numbers; far fewer show you how healthy the data behind those numbers is. We think an honest air-quality service should be transparent about its own coverage — how many cities are reporting, where the gaps are, and how it handles them. This page explains how government air monitoring works, why coverage is never perfect, and the rules we follow so that a gap in the data never becomes a wrong number on your screen.

Why data transparency matters

Air quality only helps you if you can trust it on the day it matters, and trust depends on knowing what the service does when it cannot measure something. A site that quietly shows yesterday's value as today's, or fills an empty city with an estimate, looks more complete but is actively misleading. We take the opposite view: it is better to say "we don't have a fresh reading here right now" than to invent one. Being open about coverage is not an admission of weakness — it is what makes the numbers we do show worth believing, and it follows directly from our editorial standards.

How government air monitoring works

Air quality is measured by fixed, reference-grade monitoring stations operated by government agencies — in India, the Central Pollution Control Board network. Each station continuously samples the air and reports pollutant concentrations, which are published through open-data feeds. Because stations are physical installations, coverage is uneven: big cities may have several, smaller towns one, and many places none at all. This is simply the reality of how the ground truth is collected, and it shapes what any honest air-quality site can and cannot show.

What "reporting" means

On DailyAQI, a city counts as "reporting" when we have received a fresh reading — within the last few hours — from at least one particulate monitor, and have been able to compute its AQI. Particulate matter is the key because it almost always drives India's index, so a city without a working PM monitor cannot be given a reliable headline number. A "reporting" city is therefore one we can stand behind at this moment, not merely one that exists in the registry.

Why stations go quiet — and how we handle it

Monitors go offline for maintenance, feeds lag, and occasionally a whole city drops out of the data for a while. Our response is always the same, and it is the heart of this page: we never fill the gap with a guess. A city with no fresh reading keeps its page but displays "data updating" instead of a value, so it does not flicker in and out of existence, and it never shows a stale number dressed up as current. When fresh data returns, the reading reappears automatically on the next hourly refresh. You can read exactly how a reading is computed, and why we exclude carbon monoxide, in our methodology.

India and world coverage

Coverage differs by source. Indian data comes from CPCB and refreshes hourly, giving dense, frequent coverage across the country on the national scale. World data comes from OpenAQ, aggregating public monitors under a range of provider licences, and both coverage and freshness vary more from place to place. Because the two systems also use different scales — CPCB for India, US EPA for the world — we keep them clearly separated so a coverage gap in one is never masked by the other. The live counts of how many Indian and world cities are reporting are shown on this page rather than asserted here, because those numbers change every hour.

Sanity checks and exclusions

Coverage is about more than presence; it is about validity. Before a reading is published it passes basic checks, and impossible or negative values are discarded rather than shown, because a single corrupt figure can distort an index defined by its worst pollutant. Our exclusion of carbon monoxide belongs here too: rather than convert CO with a factor we cannot verify, we leave it out, which keeps our headline aligned with CPCB's own values. Every exclusion is a deliberate choice in favour of a number we can defend.

How this honesty helps you

The practical payoff of all this is simple. When DailyAQI shows a city's AQI, you can treat it as a real, recent measurement, not a placeholder; and when it shows "data updating," you know to check a nearby city instead rather than trusting a stale figure. That reliability is the entire point of publishing our own data health. If you ever want to sanity-check what you are seeing, the live homepage and the map reflect the same feed, so the picture is consistent across the whole site.

Key takeaways

• We publish our own data health because trustworthy numbers depend on being open about coverage.
• Air quality is measured by fixed government stations, so coverage is naturally uneven.
• "Reporting" means a fresh particulate-based reading we can compute an AQI from.
• When a station goes quiet we show "data updating" — never a stale or invented value.
• India (CPCB, hourly) and world (OpenAQ) coverage are kept separate, on their own scales, with live counts shown on the page.