Hourly mean from real time download data

Data
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Calculating an hourly PM2.5 mean from real time download data, say 10.01-10.59 seems to give a different value than the hourly mean in downloaded hourly data. For example, 10.01-10.59/30 = 234 ((A+B)/2) but 10am is 183 in the hourly csv. Why is this?

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To clarify - this is using the EPA correction. The values agree as expected using the ALT cf=3 correction.

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Hi @LBHPA1, we’d like to see if we can replicate your results. Could you send us the following?

  • How this data was obtained. e.g., downloaded from the Map, the API, or locally from your sensor.
  • If this data was obtained from the API, please provide the API Queries you used (make sure you remove your API key). Alternatively, let us know if this data was downloaded from the map.
  • The sensor you were looking at. If publicly registered, you can reply with the sensor’s index. If privately registered, you can email us the index and read key.

Any other information you could provide to assist us with replicating your results would be appreciated.

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Hi Joshua

Thanks for following this up.

My query is from data downloaded from the map, the sensor is: 171999 LionFretsa-BXH (Bexley, London, UK)

I’ve attached a spreadsheet with hourly and real time PM2.5 data on 15/9 with the European AQI and EPA correction selected. I’ve added Alt CF for comparison. Low values do reconcile as expected but whilst mean hourly data for 10am gives 183, the mean of the real time values (10.01: 10.59/ 30) is 234. The values for Alt more or less reconcile – which suggest I’m not doing something stupid?

I’m gathering data on summer time outdoor burning so I’m interested in high values, I also wanted to present rolling hourly data – two hours >= 71ug/m3 being a trigger under the UK DAQI. I’m getting some academic interest in my results so I wanted to be able to explain this. But, I couldn’t find anything on it. It would be useful to know how accurate the real time data is – this suggests it over-estimates at high concentrations?

I’d appreciate any explanation if there is one.

Thanks.

Len Lucas

(Attachment bexley-reconciliation.xlsx is missing)

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Hi Joshua

Spreadsheet is here:

https://1drv.ms/x/s!AvEjY0UeNgpzg8sM_XfAr3cIPYD0lA?e=dvMNYP

Len Lucas