openaq-data-format

A description of the data format provided by the OpenAQ Platform.

Field	Type	Required	Description	Example
parameter	String	✓	The measured parameter; acceptable values are `pm25, pm10, co, bc, so2, no2, o3`	`"pm25"`
location	String	✓	Unique location name of the station	`"Escuela E-10"`
city	String		City (or regional approximation) containing location	`"Tocopilla"`
country	String	✓	Country containing location in two letter ISO format	`"CL"`
value	Number	✓	Recorded value	`10.2`
unit	String	✓	Unit of measurement, see note about units below; acceptable values are `µg/m³, ppm`	`"µg/m³"`
date	Object	✓	Time of measurement including both local time and UTC time. See note about dates.	`{"utc":"2015-10-26T17:00:00.000Z", "local": "2015-10-26T14:00:00-03:00"}`
sourceName	String	✓	ID to track measurement to source within the platform	`"Netherlands"`
sourceType	String	✓	The type of source; acceptable values are: `government, research, other`	`"government"`
mobile	Boolean	✓	Indicates whether the measuring station is stationary or mobile	`false`
coordinates	Object	✓	Location of measurement	`{"latitude": -22.087, "longitude": -70.193253}`
attribution	Array	✓	Data attribution in descending order of prominence	`[{"name": "TCEQ", "url":"http://www.tceq.state.tx.us"}, {"name": "City of Houston Health Department"}]`
averagingPeriod	Object	✓	Information about the time resolution of the measurement	`{"value": 1, "unit": "hours"}`

Formatted Data Object

The formatted data json object should look something like this:

{"date":{"utc":"2020-10-01T00:00:00.000Z","local":"2020-10-01T04:00:00+04:00"},
  "parameter":"pm25","value":20,"unit":"µg/m³",
  "averagingPeriod":{"value":1,"unit":"hours"},
  "location":"US Diplomatic Post: Abu Dhabi","city":"Abu Dhabi","country":"AE",
  "coordinates":{"latitude":24.424399,"longitude":54.433746},
  "attribution":[{"name":"EPA AirNow DOS","url":"http://airnow.gov/index.cfm?action=airnow.global_summary"}],
  "sourceName":"StateAir_AbuDhabi","sourceType":"government","mobile":false}

Dates and date ranges

Dates are stored as a javascript date containing both the local time and the UTC time.

"date": {
  "utc": "2015-07-16T20:30:00.000Z",
  "local": "2015-07-17T03:30:00.000+07:00"
}

The averages are always backward looking. That means that if a source reports a time range (3 - 4pm), then the latest time is picked (4pm).

Dealing with multiple measurements

It is possible that a station reports several measurements for the same pollutant per time period. When this occurs, the following measurement is stored:

the one with the shortest averaging period (1 hour average instead of 24 hour rolling average)
the one that reports the value in the pollutant's preferred unit

Preferred Units

OpenAQ only accepts measurements in µg/m³ and ppm. This means that volumetric concentrations reported in ppb are converted to ppm before being stored to the database. We do not convert between volumetric and mass concentrations (µg/m³ <-> ppm) to avoid making assumptions.

The platform also has a preferred unit of measurement per pollutant, but this is not strictly enforced. The Dutch locations, for example, report all their values in µg/m3.

Pollutant	Preferred unit
PM 2.5	µg/m³
PM 10	µg/m³
BC	µg/m³
CO	ppm
NO2	ppm
SO2	ppm
O3	ppm

Source types

Measurements can be provided by different types of sources:

government - Sensors that are deployed by or on behalf of governmental bodies.
research - Sensors that are deployed by researchers affiliated with universities and/or research organizations.
other - Sensors that are deployed by citizen scientists, often low-cost sensors.

openaq / openaq-data-format