document data available from Array of Things dataset

[artinthetrees]

• what is measured
• geographic and temporal granularity, including lat/long of each monitor by what it measures
• use the template in the data_sources.xlsx file (but feel free to extend it - e.g. by adding flags to indicate an item that is measured where a flag is not already included for that measure)
• first pass is that temporal granularity is high (less than hourly), and measures a wide array of air quality measures including ozone and no2, as well as temp and humidity