In the space of ambient air quality monitoring, there are two basic and distinctive categories of professional air quality monitors; the High-End Professional and Low-Cost Professional monitors. I have been asked multiple times to recommend monitors for scientific studies and the deployment of them in cities.
It is very important to understand the strengths and weaknesses of both categories. It is also mandatory to recognize the fact that we will never get the exact same measurement from either category of sensors.
High-End Professional AQA
High-End Professional ambient air quality analyzers are used mostly by governments inside the air quality stations we have in most cities. Their strength is that they meet international standards for accuracy and they are certified by the EU (and similar bodies) to meet minimum performance requirements, in order to ensure that the measurement methods comply with the Data Quality Objectives set down in the Ambient Air Quality Directive (2008/50/EC) and in the amending Directive (EU) 2015/1480. Their weakness is that they require lots of energy to operate. In most cases, they are inside a fixed container with a refrigeration system to keep conditions stable. They are big and boxy in size and very expensive to purchase and operate. Additionally, they need constant maintenance by a technician. Another weakness is that in most cases these analyzers are not smart enough to broadcast measurement in real-time to the Cloud and they require other pieces of equipment to do that job, as a result, the cost of operation increases.
Depending on the pollutant we want to measure, High-End Professional ambient air quality analyzers use different measurement techniques. For example, UV absorption is used for the measurement of Ozone (O3). Chemiluminescence is used for the measurement of Nitrogen Oxides (NO/NO2). Tapered Element Oscillating Microbalance and/or Beta Attenuation monitor and/or Gravimetric monitor and/or Filter Dynamics Measurement System (FDMS) is used for the measurement of particulate matter (PM10 and PM2.5).
Low-Cost Professional AQM
Low-Cost Professional ambient air quality monitors are used in the cities or industrial sites to monitor air quality in a more flexible way because they have managed to fix some or most of the weaknesses of the High-End Professional ambient air quality analyzers. Their strengths are that they can broadcast measurements everywhere in the world in real-time as they are equipped with various communication wireless networks like WiFi, LTE, LoRa, SigFox, NB-IoT, etc. They are small and designed specifically to be mounted in traffic lights or city lights poles and similar. They require very little energy and can be operated on a single solar panel. They can be managed remotely and they need little maintenance. Most importantly one low-cost ambient AQ monitor can be +20 times less costly than a single government air quality station allowing us to have better spatio-temporal coverage of the air quality in a city. Their weakness is that they cannot measure pollutants as accurately as High-End Professional ambient air quality analyzers. However, they offer valuable information and trends of the conditions in the deployed area.
Low-cost sensors require better in situ calibration, and although some companies offer that service for their sensors, they also need to eventually meet some standards like the CEN/TC 264/WG.
Low-Cost Professional ambient air quality monitors use different measurement techniques to measure various pollutants. Electrochemical sensors are the most common method to measure gas pollutants like O3, NO2, NOx, SO2, etc. Optical light scattering is used for the measurement of particulate matter (PM10 and PM2.5).
Conclusion
All things considered, one cannot exist without the other as they complement each other. The population benefits a lot when cities invest in low-cost professional ambient air quality monitors as we are able to obtain a higher resolution of AQ data and inform the public in real-time of possible issues regarding the air we breathe. Having the high-end professional ambient air quality analyzers we make sure that there is accuracy across all monitors.
Some experts constantly debate about the accuracy of the low-cost monitors but we shouldn’t be obsessed with the exact values (ppm, ppb, μg/m3) between the high-end and the low-cost types of equipment but we should embrace the abilities they offer as and of course improve them over time as long as technology allows us to.
See The Air 
Great points. I often wonder what will happen with all of the luftDaten daten. It may only be used by a few people, but could be invaluable.
AQM are most relevant in areas where there are air problems. I live in an area where the sea breeze tends to blow particulate eastward – and the air is pretty clean. Downwind of a refinery, agriculture, or location with a lot of diesel trucks is another matter.
I think a good place for DIY AQM is around larger AQM systems to provide context and granularity. But the question remains, will anyone use the data? The US lags other countries, so we have to watch Europe to project our needs.
Best regards
Dave Clark
San Mateo (SF Bay Area)
California
Sotirios Papathanasiou posted: ” In the space of ambient air quality monitoring, there are two basic and distinctive categories of professional air quality monitors; the High-End Professional and Low-Cost Professional monitors. I have been asked multiple times to recommend monitors for “
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Unfortunately they aren’t used and still there isn’t a unified place where all DIY, low-cost Pro and government stations could report data for citizens to access them easily. There are a plethora of AQ platforms which make accessibility hard for the everyday dwellers to find info. OpenAQ has done a step towards unification but I only see PurpleAir and not Sensor Community (Luftdaten) data there. I will publish an article about it.
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Sotirios, many thanks for the time and effort you put into this excellent site. I have a couple of comments/questions regarding your post on High End vs Low Cost monitors. First, it seems to me that many applications for low cost sensors are simply to compare results on a relative basis. That is, to take readings at various places in a community or location, and then compare the data to discover where relatively high levels of, say, PM, are found. Then, with this data in hand, make some observations about why levels are high in the presence of certain polluters, like along highways or near factories, etc.
Given this, why so much emphasis on co-location with FRM and regulatory monitoring systems and generating complex (re) calibration schemes to keep these low-cost sensors aligned with the professional ones? I do agree that for use cases where the low-cost sensors are deployed to extend the reach of regulatory AQ then accuracy is paramount. But how often is this the case?
Second, and building on the first question, wouldn’t time and money be better spent on inter-calibration of a network of low-cost sensors so that they are calibrated relative to each other? This would make the investigative use case more robust and add rigor to the data.
Appreciate your thoughts.
– Drew
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Hi Drew,
Very good question.
To my understanding it has to do with the perception and what you can do with the low-cost monitor data.
For example, researchers need valid data for their papers so in most cases they insist in arguing that low-cost monitors are not good because some over or under estimate concentrations. I respect that.
Now, local authorities don’t want transparency so they use as an excuse the accuracy argument in their favor.
As you well said, you have to use low-cost monitor to lead you to the source of the problem (air pollution source) and not get fixated on the absolute value they give you. It is much more economic and they can offer better spatial-temporal models.
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