The Download Data Files page has been refreshed with new data

The file download page has been refreshed with new data. Sorry for the delay, but many changes were being made to AQS that we needed to wait on.

First, 1/2 MDL values have been removed. Historically, as part of the data reduction process, AQS has replaced reported values that are below the Method Detection Limit (MDL) with 1/2 of the MDL for most pollutants. This was phased out for some pollutants beginning in 2013. This year, we completed the phase out for the remaining pollutants. Approximately 200 million values for 900 parameters had the 1/2 MDL substitution removed. Because values across all parameters, years, and summary levels were affected by this, all of the files on the page have been regenerated. (Previously summary values were based on the substituted values, now they are not.)

Second, the new ozone standard has not been fully implemented in AQS. Therefore the summary files do not contain information for the new ozone standard. However the AQI values have been updated.

Finally, a user reported an error in the 8-hour files. For files prior to 2008, the summary value excluding regionally concurred events is incorrect. This is a bug in our underlying database that could not be corrected before the files were generated. Rather than removing the 8-hour files, we are including them with this caveat. Other summary values are correct.