20 Air Monitoring
Temperature Humidity/ precipitation Season Extreme Hot Hot
Dry Cold Changeable
Wet Wet
Changeable
Summer Summer Winter
few published results for entire AQ sensor system networks; Breathe London, a long running AQ network fi eld trial is the exception. The locations for sensor system fi eld trials have been in various climates: Finland, London, Delhi, Nairobi, Boston, Los Angeles, Belgium, Stuttgart, Beijing are just a few sites, each with their own climate and resultant environmental conditions. Results have been inconsistent for several reasons: different quality sensors, different sensor system constructions, various ML and regression analysis correction algorithms and different climates. The results are variable with the best performance from fi eld trials in mild climates during winter or summer months.
Concern about the data quality from low cost AQ sensor systems is driving standards committees to set Data Quality Objectives (DQOs) for these sensor systems. To achieve the DQO, sensor systems must be tested in the laboratory, in the fi eld, or in both environments. CEN standard committee TC264 WG42 has set two paths for DQO validation: either by extensive fi eld trials or by both shorter fi eld trials and laboratory testing (TS 17660-1:2021). This Technical Specifi cation demands fi eld trials in at least two sites (four sites for the extended fi eld trials) during two seasons, confronting this climate variation problem. ASTM D22.03 is writing a similar Practice Standard (WK64899), also demanding fi eld trials. However, neither document specifi es that sensors are tested in extreme climates, so the result is that sensor systems (not sensor networks) can be tested
Season Mild Classifi cation Extreme Classifi cation mild Summer Winter
Bwh Not summer Spring, Autumn Spring, Autumrn
Af, Aw Dfa
Am, Cfa
Csa, Bsh Cfa Dfb
Cfb, Dfb
in milder climates and manufacturers can claim they meet the DQO in all climates, although TS 17660 does warn about climate limitations.
Can we do better?
We can do better. It is assumed that if a sensor system passes in a climate with a certain temperature/ humidity regime, it will perform adequately when the temperature and humidity ranges in another climate are less extreme than the test site. Field trials in climates with severe temperature and humidity extremes during fi eld trials should qualify the sensor system for use in less severe climates.
We can view climates in the Köppen table more simply as mixtures of hot/ cold and wet/ dry. These can be combined to provide four climate scenarios: hot/ dry, hot/ wet, cold/ dry and cold/ wet. We consider cold/dry to not be as severe as cold/ wet, so three climate categories should be tested. In addition, rapid weather changes also stress test sensor system performance, so a fourth climate of changeable weather should be included. The above table lists possible extreme and mild climates in the four categories.
Discussions are beginning amongst certifying bodies, national laboratories and test houses to set up global test sites for validating sensor systems in different climates, ensuring they meet DQOs set by standards committees, following Directives
and legislation. VACUUMS, a European project, tested many systems; Marylebone in London has been a test site for various sensor systems; and the current AQ-SPEC program, operated by South Coast Air Quality Management Division (SCAQMD) in Los Angeles has tested many sensor systems, with all test results available on their website. Field trials can be run reliably in different climates, we need to expand to include test sites with more extreme climates.
Low cost AQ sensor systems and networks fulfi l a needed requirement to monitor our air pollution in all major urban centres globally. Commercial sensor systems are available from many manufacturers, we now need to build the trust that they can provide good quality data. The fi rst step is Test Specifi cations and Practice Standards from standards committees, the next step is globally recognised test sites that ensure data quality in all climates.
References 1
Nowack et al
Atmos.Meas.Tech.,14,5637–5655,2021 doi. org/10.5194/amt-14-5637-2021 2
Patra et al Building and Environment,
doi.org/10.1016/ buildenv.2020.107457 3
Popoola et al, Atmospheric Environment
doi.org/10/1016/j. atmosenv.2016.10.024 4
Rogulski et al, ACS Sensors 2016,22,3619
doi.org/10.3390/ s22103619 5
Hitchman, Saffell ACS Sensors 2021 6 (11), 3985-3993 doi. org/10.1021/1c01339 6
Ouyang, ACS Sensors 2020 5 (9), 2742-2746
doi.org/10.1021/ acssensors.0c01129 7
Han et al, ACS Sensors 2021,21,256
https://doi.org/10.3390/ s21010256
Author Contact Details Dr. John Saffell, CoGDEM • NosmoTech Ltd. Cambridge CB3 0AZ UK • Email:
jsaffell@btinternet.com • Web:
www.cogdem.org.uk Dr. John Saffell is Chairman of the Council for Gas Detection and Environmental Monitoring (CoGDEM) and a Director of NosmoTech Ltd. He was co-founder and Technical Director of Alphasense Ltd. and is a member of CEN TC216 and TC 264, BSI EH/2 and ASTM D22.
A simple and eff ective tool
for fi ghting radon contamination Over ten percent of cases of lung cancer are linked to an excess of exposure to radon, according to a report from the World Health Organisation.
Radon (Rn) is present from a wide variety of natural and man-made sources. This odourless, colourless radioactive gas is the immediate decay product of radium resulting from the radioactive decay of uranium that takes place naturally in rock and soil. Hence all people are exposed to Rn in varying degrees.
Most Rn in indoor air comes from soil and is proving to be more of a hazard than levels of Rn in the drinking water supply. The level of Rn inside a building is largely determined by its location and whether the ground on which it is located has signifi cant levels of uranium present to create the gas. Once Rn reaches the open air, it will rapidly dissolve to a relatively harmless, low concentration. However, if it rises in to a home or commercial property, it can be trapped and build up to dangerous levels for people inside the building. The radioactive decay will then create alpha particles, which in turn can cause permanent damage to lung tissue.
To combat this danger, Euro-Gas have developed the Radon SS, a unique, high performance phototransistor gas sensor capable of detecting a fi eld range of 0-65,000Bq/m3
technology can be easily integrated in portable and fi xed air quality and gas detection instruments and offers operators complete data for current and average Rn alpha particle concentration.
More information online:
ilmt.co/PL/o02B For More Info, email:
IET SEPTEMBER 2022 email: For More Info, email:
51267pr@reply-direct.com levels, with a standard range of 1750pCi/l Rn. This user-friendly
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92
