Luftdaten Air Quality

Hi All
I thought a new thread for Luftdaten users might be handy to discuss experiences.
I have found mine over states PM10 in misty weather (I believe it is a characteristic). I am trying a possible solution. As it happens I used a 8mm tube which I heated and stretched to reduce the diameter for the sensor inlet. The tube is big enough to insert a strip of hard polystyrene (recycling number 6) which is supposed to be hygroscopic - attracting surface water. The idea is to condense mist particles which hopefully will then drip out. We will see.
Regards
Alan

Hi
I see the Sunwharf (Suggestions) has the AQI showing on his website graph - I’d like to do the same but could not find the gif.
Regards
Alan

Webfiles folder
Aqi.gif
Aqichart.gif

Thanks - I have those. Sunwharf has the aqi on the main screen graph so it is interesting to be able to see the wind direction just above.
Regards
Alan

I realise now he has uploaded the whole main screen - that’s what I can’t find as a gif
Alan

Found the switch in webfiles/webpage set up
Alan

Hi All
Looking around the Luftdaten map it seems many of the humidity figures are almost always 99.90%.
I wonder if the DHT22 is not getting a chance to register a reading when the sensor is only activated intermittently,
Does anyone have experience of the BME280 sensor.
Regards
Alan

You think it might be that.
Mine is at 99.9% for some time now too.
It did work after the install.
I think it is broken.
I am reading posts the dht22 sensor is of a very poor quality.
Some people have replaced the sensor 2 to 3 times already.
They like to install the bme280 sensor also, just like you.
The SHT31 sensor seems to be of a better quality but isn’t supported by luftdaten.
Just reading this stuff, I have no experience.
I have 2 new dht22 sensors lying here.
I will replace the sensor soon and see if it’s actually broken.

Hi
I read somewhere that the Luftdaten team are hoping to add a correction for the known issue of the SDS011 sensor giving poor readings in high RH. That is not going to work if the humidity is reported wrongly. I have tried using the contact form to report the problem but I don’t get a reply. I don’t speak German so find it hard to find any useful information. The temperature is reported accurately so I also wonder if the pipe enclosure is not properly ventilated and retains a high RH - that might explain why your system did work for a time. At this time of year we have few days with very low RH to dry things out.
Regards
Alan

Hi
I have now changed the temp/humidity sensor for a BME280 and the humidity looks much more sensible.
Brian - is there any way of deleting erroneous luftdaten readings. While testing the new sensor I got some very high readings (I really should give up my cigars).
Regards
Alan

Hi Brian
Sorry I missed the download.
I installed the zip of the new exe etc and the new boxes were there. I’m not sure if the BME280 has a separate id (it does as far as Luftdaten is concerned) or I have not found it yet. There is no clue in airquality2.txt . I do have indoor temp / humidity so I guess it does need the override.
Best wishes for Christmas and the New Year
Alan

I’m using the SDS011 sensor connected to my RPi and then to WD. It’s not the “official” Luftdaten package). What I’m seeing is that sometimes the values are relatively high. It’s interesting how the values change, as shown in attached figure. It drops almost discretely just after 2:32 and then also around 5:00. Has anyone observed such behaviour? The air is calm, no winds, but just high humidity over several days already. It’s few degrees above 0 degC so not freezing.
Is it possible high humidity causes such response?


aqichart.gif

Hi
I understand it is a known problem with high humidities. It seems particularly bad (no pun intended) in foggy situations.
My system has shown some enormous figures (400-500 on PM10) which are quite unrealistic for a small rural hamlet about 8K from the nearest (small) town.
I have tried inserting a strip of hard polystyrene into the air tube. The idea is that the surface is supposed to be hygroscopic (not absorbing but attracting) so that water particles might condense. It does not appear to work.
I think the Luftdaten team are trying to find an algorithm to compensate.
Incidentally the BME280 temp/humid sensor is so far performing much better than the SHT22 which stuck at 99.90%.
regards
Alan

I should have said DHT22 9I’m looking at the SHT series for something else
Alan

I don’t know what you mean by BME280 - is this sensor used with the SDS011? I have one connected nearby and could correct the PM values but would need to know the correction algorithm. Maybe the sensor needs just a little heating?

High RH is rare here but we have had a couple of fine rain or foggy days recently with the RH sitting in the very high 90’s. I have not seen the extreme particulate values that previous posts have suggested. My sensor is a PM-5003 connected wirelessly to a linux PC. There is some elevation of particulate values but I would expect that with the concurrent stagnant air conditions here at the end of the valley which trap woodfire smoke and other pollution.

I think it is the SDS011 that is mainly affected. In answer to Mihec the BME280 is an alternative T/H (and pressure) sensor. On opensensemap a lot of the humidity readings are stuck at 99.90% which is what my previous DHT22 t/h sensor always showed. If you use the T/H option I would recommend the BME sensor.
My site is at the far south western tip of the UK with very few pollution sources between me and the North Atlantic. With a west wind of about 10 knots currently I would expect quite low particle counts but actually they are all over the place so I strongly suspect the present fine particle fog we have. You can see what I mean on the Luftdaten map site. If the wind is in the right quarter (and light) I can pretty well tell when my neighbours light their woodburners. The SDS011 may not be the most accurate but is affordable and simple enough to allow a lot of users to participate so it is enough to show general pollution trends over a wide area.
Regards
Alan

In the last half hour it has started raining and cleared to fog - reading now more normal - does rather confirm the fog affect. You can also see what I mean on my site www.greatbosullow.net
Alan

That’s very interesting, on my sensor I don’t believe I have ever seen such a huge difference between PM 10 and the others 8O

Strangely a couple stations in the far west of France and another UK station to the NW of me sometimes show high readings with a west wind - with the proximity to the Atlantic I wonder if the humidity can contain dissolved salt.
Alan