I have a series of daily readings (NOx emissions) measured in parts per million.
I need to aggregate the daily readings into a monthly measure.
Clearly a sum operation will be incorrect (parts per million is a ratio).
Am I correct that aggregating samples in parts per million can be achieved with a simple mean operation?
e.g (if a month had 2 days).
100ppm (day1) + 500ppm (day2) = (100+500)/2 = 300ppm
What's the correct way to get the NOx in ppm over a whole month?