State Air makes their data available under specific conditions and with limitations. Here is a listing from their website giving them:
State Air observational data are not fully verified or validated; these data are subject to change, error, and correction. The data and information are in no way official.
If observational data are used for analyses, displayed on web pages, or used for other programs or products, the analysis results, displays, or products must indicate that these data are not fully verified or validated.
Only validated data should be used for reports and data analysis whenever possible.
Publications, analyses, products, presentations, and/or derived information that rely on these data must give attribution to the U.S. Department of State.
Data and information reported by State Air are provided for the express purpose of providing U.S. citizens living and traveling abroad actionable health information related to air pollution.
There are some differences in the data between their site and mine. They have a good number of readings with negative concentration values, which cannot be correct. I have deleted those readings, rather than replace them with 0. There could also be import errors where my data differs from theirs, though I think I have caught most of those.