A better way to store data will be to use the API. Saving a graph image will not fly in many cases, so it is much better to save the raw data. You can retrieve historical data for your sensor. If you run into any issues or have any questions, feel free to send us an email (contact@purpleair.com)! We can help with API points and such.
If you’re not comfortable using an API, you could try looking into our Data Download Tool (which still uses the API, but has a much easier user interface) or you can download data directly from the map graph.
If you download from the map graph, be aware that you will be limited in range by the averaging period you have the map set to. For example, 2-minute data will give you the past 2 days of history; 1-hour data will give you the past 2 weeks. I recommend that you change the “Data Layer” (learn how in our Map Guide) to “Raw PM2.5 (µg/m3)” before downloading.