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I have an Atmotube Pro air quality sensor placed outside in a cup with a large bowl placed over the top of it to protect it from the wind and any rain but to allow air to filter through easily.

I'm trying to understand what might be the reason for the pattern of volatile organic compounds (VOCs) I am seeing.

The weather is partly cloudy today with some intermittant sunshine in my south of England city (the sun is not that strong with it being January). The monitor is placed on top of a 1st floor bay window. The wind is about 10mph NW and the temperature 6-7C. I live in a 250k populated densly packed city on a quiet road 150m from a couple of 30kmh limit busy roads and junction.

I have had similar patterns of high VOC levels in the past with them suddenly falling. I think it starts to rise when it gets sunny then falls as soon as the sun goes away.

What would be the most common reason for this pattern (sometimes the readings go to 2.0ppm)

VOCs emitted from roof when sun hits it (it is a lead roof)? Traffic building up? Pollution blown in from somewhere else? Fault with sensor? Traffic pollution turning into something else in the sunshine? Sudden changes in wind when it becomes cloudy?

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13:02 - 13:55 in one minute intervals, it is this difference in one minute that I am confused about 0.763, 0.37

0.356, 0.363, 0.373, 0.439, 0.507, 0.572, 0.622, 0.661, 0.763, 0.37, 0.356, 0.346, 0.334, 0.341, 0.354, 0.38, 0.347, 0.354, 0.333, 0.319, 0.323, 0.335, 0.35, 0.373, 0.477, 0.55, 0.35, 0.338, 0.341, 0.344, 0.345, 0.362, 0.333, 0.348, 0.364, 0.403, 0.519, 0.583, 0.624, 0.69, 0.66, 0.702

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  • $\begingroup$ can you post a longer series of readings 6-12hrs.any traffic lights close to where you live? $\endgroup$ – trond hansen Jan 10 at 13:52
  • $\begingroup$ Thanks for your input @trondhansen, I have added to the question. Yes, I am 150 meters away from two sets of traffic lights, one to the left of my house and one to the right. My house is on a road where there is almost no traffic but the busy road is just 150meters away. I have been thinking that the reason for the drop when it clouds over, could that be due to increase in wind when it clouds? $\endgroup$ – atreeon Jan 10 at 16:01
  • $\begingroup$ There are so many possible environment factors (human activity), close by and further away, that we can only speculate. You need to show that this is actually a long-time pattern that repeats and not just some random spikes. If a pattern, observations over a longer time will also show if there is a variation over a longer period, and if there is a relation with weather, which might give clues. Interesting hunt. $\endgroup$ – Jan Doggen Jan 10 at 16:22
  • $\begingroup$ I totally agree, it is a hunt! I will keep monitoring for a while and will update here after a week or two after suring up my observations. I feel I should need a weather station with wind, sun and temperature settings too. $\endgroup$ – atreeon Jan 10 at 17:10

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