My Maps don’t report the same values?

The quality of the air we breathe is important for everybody. This means that there are going to be multiple groups who also want to help keep people informed. PurpleAir is dedicated to reporting this important information, so we provide data to multiple providers for use in their studies, reporting, and resources.

Air Quality Indexing (AQI) is a medium by which agencies communicate to the public how polluted the air currently is. Air Quality Indexes are created through multiple scientific processes and are applied by multiple agencies worldwide. No AQI is singular, and all air quality indexes are valid in their reporting because there is no single way to interpret or display data.

The discrepancies between PurpleAir’s map and AirNow’s map are created and affected by a couple different factors.

  • Data reporting frequency
  • Conversion rate of PM2.5 AQI

Data Reporting Frequency

​The data from our sensors that displays on AirNow’s map is reported once an hour. The number they report is based on the one-hour average we collect over a 60 minute period.

​The data on the PurpleAir map reports a 10 minute average by default.

​Every time PurpleAir data is shown on the AirNow map, we report a minimum of 6 averages in the same time.

​The data will differ during this period, but we should show similar figures when the averaging period is set to one hour.

Conversion Rate

​The conversion rate on our map is set to “No” by default.

​The conversion rate applied to the data on the AirNow map is a conversion of PM2.5 through the US EPA conversion found here: The "Apply Conversion" Field.

​You can replicate this conversion in our map by navigating to the “Apply Conversion” field and selecting “US EPA.”

Using This Data

The reflection of data between sources assists everyone in making informed choices about the precautions that they take, and decisions they make when considering the air we breathe. We are grateful that organizations like AirNow trust our process and find use in our tools and reporting to help reach a wider population who are concerned about our air.