Regional research views
Compare city and state station observations with periods, sources, station coverage, eligibility and scan limitations clearly distinguished.
A practical data glossary
Source references explain the underlying index and model service; they do not endorse this Observatory. Use the source, timestamp and stated limitations together when interpreting a reading.
- AQI and concentration
- AQI is an index, not a pollutant concentration. India's National AQI summarises air-quality categories using pollutant sub-indices. A concentration is an amount of a named pollutant in air; µg/m³ means micrograms per cubic metre, while ppb means parts per billion. Do not read a concentration as an AQI score or compare different index systems as if they were the same.
- Averaging window
- The averaging window is the period represented by a value, such as an hour or a day. It is not the same as the time the page loaded. Read the unit and averaging period beside each pollutant. Unknown windows limit interpretation; an hourly value and a daily value are not interchangeable.
- Observation, publication, retrieval and refresh
- Observation time describes when the source says the measurement applies. Publication time, when supplied, is when the source released it. Retrieval time is when this service obtained it. Page refresh only rechecks what is stored and may return the same reading. Station timestamps and local-time date controls use your browser's time zone, not necessarily Indian Standard Time. Where a view explicitly shows another zone, use that label.
- Model time and display expiry
- Google's model time describes its estimated conditions at a city-centre grid point. Retrieved tells you when the estimate was obtained; shown until is its display limit, not a forecast or a promise of accuracy until that time. Estimates have separate availability and request limits, are not used to fill station-history gaps and do not automatically poll every five minutes.
- Fresh, stale, offline and missing
- Freshness labels describe the age of an observation using the source's configured cutoffs, not how healthy the air is. Stale or offline means a current reading is not available under those rules; it does not establish a hardware failure. No data can also mean incomplete coverage, a disabled source or an observation not accepted for publication.
- Coverage and comparison
- The directory and counts cover records available to this Observatory, not all monitoring in India. Search results do not guarantee readings exist. Load more where offered and check period and pollutant filters. A station near you may be in different conditions; the nearest-station search radius is an operational limit, not an exposure model.
What recorded history can tell you
Select a period and inspect the recorded points or their table. Gaps mean no eligible stored observation is available, not zero pollution. A location history collects station observations for that place; it is not a representative city trend. Compare individual stations with matching pollutant, units and averaging windows. Different coverage and reporting patterns limit comparisons; these plots do not establish causes or policy impact.
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