Exceedances measure the number of days in the past 28 days for which daily pollutant levels have exceeded a minimum threshold for each location. The default view is EPA and the bar height shows the number of days that mean 24 hour levels have been above Moderate. The bars are further broken down so users can also see the number of days above the threshold for Unhealthy for sensitive groups, Unhealthy, Very unhealthy or Hazardous. In most cases values are above moderate for 28 the full 28 days.
To switch between WHO and AQI thresholds select the ellipsis / three dots (...) in the top right hand corner of the chart and select ‘Customize charts’. For WHO the chart shows the number of days in the past 28 days where the mean is above the WHO Air Quality Guideline of 25 μg/m3. In many cases NO2 levels are well below WHO and EPA levels so no values are visible.
Also, by clicking on the ellipsis (...) 3 dots in the top right hand corner of the chart, the charts can be printed, exported as a pdf, jpeg, or png. jpeg and png are most suitable for including in reports or social media.