The discrepancies between PurpleAir’s map and AirNow’s map are created and affected by a few things.
- Data reporting frequency
- Conversion rate of PM2.5 AQI
Data Reporting Frequency
The data from our sensors on AirNow’s map is reported once an hour. The number they report is based on the one-hour average we collected over the past 60 minutes.
The data on the PurpleAir map is reported on an average of 10 minutes by default.
For every single report that is shown from a PurpleAir sensor on AirNow, we show a minimum of 6 reports 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 a report of US EPA PM2.5.
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.”