Predicted and actual air quality components for The Netherlands (RIVM).
Luchtmeetnet API is a free Environment API that requires no API key, is served over HTTPS and has unconfirmed CORS support.
The website Luchtmeetnet is an initiative of the Ministry of Infrastructure and the Environment, the National Institute of Public Health and the Environment (RIVM), GGD Amsterdam, EPA for the greater Rotterdam area (DCMR), the Province of Limburg, EPA's middle and western Brabant (OMWB) and EPA reg…
Details from api-docs.luchtmeetnet.nl.

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Corporate carbon emissions disclosures (scope 1, 2 and 3), company-reported and estimated
Open data from Great Britain’s Electricity System Operator
The Luchtmeetnet API is provided by Luchtmeetnet 2020 OpenAPI (api-docs.luchtmeetnet.nl). The website Luchtmeetnet is an initiative of the Ministry of Infrastructure and the Environment, the National Institute of Public Health and the Environment (RIVM), GGD Amsterdam, EPA for the greater Rotterdam area (DCMR), the Province of Limburg, EPA's middle and western Brabant (OMWB) and EPA reg…
Yes. The Luchtmeetnet API is listed in the Environment category of the public-apis directory, which only includes APIs that are free or have a free tier. Check its documentation for rate limits and paid plans.
No. The Luchtmeetnet API requires no authentication, so you can start making requests without signing up.
CORS support for the Luchtmeetnet API is unknown. Test a request from the browser, and fall back to a server-side call if it is blocked.
Yes. The Luchtmeetnet API is served over HTTPS, so it's safe to use in production.