{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,5,6]],"date-time":"2026-05-06T00:57:56Z","timestamp":1778029076881,"version":"3.51.4"},"reference-count":51,"publisher":"MDPI AG","issue":"12","license":[{"start":{"date-parts":[[2018,12,9]],"date-time":"2018-12-09T00:00:00Z","timestamp":1544313600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100008433","name":"Consejer\u00eda de Educaci\u00f3n, Juventud y Deporte, Comunidad de Madrid","doi-asserted-by":"publisher","award":["2016-T1\/AMB-1695"],"award-info":[{"award-number":["2016-T1\/AMB-1695"]}],"id":[{"id":"10.13039\/501100008433","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>Schools are amongst the most densely occupied indoor areas and at the same time children and young adults are the most vulnerable group with respect to adverse health effects as a result of poor environmental conditions. Health, performance and well-being of pupils crucially depend on indoor environmental quality (IEQ) of which air quality and thermal comfort are central pillars. This makes the monitoring and control of environmental parameters in classes important. At the same time most school buildings do neither feature automated, intelligent heating, ventilation, and air conditioning (HVAC) systems nor suitable IEQ monitoring systems. In this contribution, we therefore investigate the capabilities of a novel wireless gas sensor network to determine carbon dioxide concentrations, along with temperature and humidity. The use of a photoacoustic detector enables the construction of long-term stable, miniaturized, LED-based non-dispersive infrared absorption spectrometers without the use of a reference channel. The data of the sensor nodes is transmitted via a Z-Wave protocol to a central gateway, which in turn sends the data to a web-based platform for online analysis. The results show that it is difficult to maintain adequate IEQ levels in class rooms even when ventilating frequently and that individual monitoring and control of rooms is necessary to combine energy savings and good IEQ.<\/jats:p>","DOI":"10.3390\/s18124345","type":"journal-article","created":{"date-parts":[[2018,12,10]],"date-time":"2018-12-10T03:36:41Z","timestamp":1544413001000},"page":"4345","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":63,"title":["A Wireless Gas Sensor Network to Monitor Indoor Environmental Quality in Schools"],"prefix":"10.3390","volume":"18","author":[{"given":"Alvaro","family":"Ortiz Perez","sequence":"first","affiliation":[{"name":"Laboratory for Gas Sensors, Department of Microsystems Engineering, University of Freiburg, Georges-K\u00f6hler-Allee 102, 79110 Freiburg, Germany"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-0392-4044","authenticated-orcid":false,"given":"Benedikt","family":"Bierer","sequence":"additional","affiliation":[{"name":"Laboratory for Gas Sensors, Department of Microsystems Engineering, University of Freiburg, Georges-K\u00f6hler-Allee 102, 79110 Freiburg, Germany"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Louisa","family":"Scholz","sequence":"additional","affiliation":[{"name":"Laboratory for Gas Sensors, Department of Microsystems Engineering, University of Freiburg, Georges-K\u00f6hler-Allee 102, 79110 Freiburg, Germany"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"J\u00fcrgen","family":"W\u00f6llenstein","sequence":"additional","affiliation":[{"name":"Laboratory for Gas Sensors, Department of Microsystems Engineering, University of Freiburg, Georges-K\u00f6hler-Allee 102, 79110 Freiburg, Germany"},{"name":"Fraunhofer Institute for Physical Measurement Techniques (IPM), Heidenhofstra\u00dfe 8, 79110 Freiburg, Germany"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-2109-1936","authenticated-orcid":false,"given":"Stefan","family":"Palzer","sequence":"additional","affiliation":[{"name":"Department of Computer Science, Universidad Aut\u00f3noma de Madrid, Francisco Tom\u00e1s y Valiente 11, 28049 Madrid, Spain"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2018,12,9]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"247","DOI":"10.1016\/j.ijheh.2005.03.003","article-title":"Daily time spent indoors in German homes\u2014Baseline data for the assessment of indoor exposure of German occupants","volume":"208","author":"Brasche","year":"2005","journal-title":"Int. J. Hyg. Environ. Health"},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"427","DOI":"10.1038\/sj.jea.7500244","article-title":"It\u2019s about time: A comparison of Canadian and American time-activity patterns","volume":"12","author":"Leech","year":"2002","journal-title":"J. Expo. Anal. Environ. Epidemiol."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"170","DOI":"10.1038\/sj.jes.7500490","article-title":"Indoor time-microenvironment-activity patterns in seven regions of Europe","volume":"17","author":"Schweizer","year":"2007","journal-title":"J. Expo. Sci. Environ. Epidemiol."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1016\/j.ijsbe.2016.03.006","article-title":"Impact of indoor environmental quality on occupant well-being and comfort: A review of the literature","volume":"5","author":"Arif","year":"2016","journal-title":"Int. J. Sustain. Built Environ."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"196","DOI":"10.1016\/j.envint.2016.05.009","article-title":"Children\u2019s well-being at schools: Impact of climatic conditions and air pollution","volume":"94","author":"Salthammer","year":"2016","journal-title":"Environ. Int."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"951","DOI":"10.1016\/j.buildenv.2005.10.027","article-title":"Perception of the thermal environment in high school and university classrooms: Subjective preferences and thermal comfort","volume":"42","author":"Corgnati","year":"2007","journal-title":"Build. Environ."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"997","DOI":"10.1080\/08958370050164626","article-title":"Elementary School Absenteeism and Air Pollution","volume":"12","author":"Chen","year":"2000","journal-title":"Inhal. Toxicol."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"2903","DOI":"10.1016\/0960-1686(90)90470-8","article-title":"The assessment of personal exposure to nitrogen dioxide in epidemiological studies","volume":"24","author":"Noy","year":"1990","journal-title":"Atmos. Environ. Part A Gen. Top."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"569","DOI":"10.1097\/01.HP.0000198787.93305.35","article-title":"Childhood leukemia incidence and exposure to indoor radon, terrestrial and cosmic gamma radiation","volume":"90","author":"Evrard","year":"2006","journal-title":"Health Phys."},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"31392","DOI":"10.3390\/s151229859","article-title":"A Survey of Wireless Sensor Network Based Air Pollution Monitoring Systems","volume":"15","author":"Yi","year":"2015","journal-title":"Sensors"},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"333","DOI":"10.1111\/j.1600-0668.2004.00251.x","article-title":"Associations between classroom CO2 concentrations and student attendance in Washington and Idaho","volume":"14","author":"Shendell","year":"2004","journal-title":"Indoor Air"},{"key":"ref_12","doi-asserted-by":"crossref","unstructured":"Batterman, S. (2017). Review and extension of CO2-based methods to determine ventilation rates with application to school classrooms. Int. J. Environ. Res. Public Health, 14.","DOI":"10.3390\/ijerph14020145"},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"569","DOI":"10.1111\/josh.12183","article-title":"Classroom carbon dioxide concentration, school attendance, and educational attainment","volume":"84","author":"Gaihre","year":"2014","journal-title":"J. Sch. Health"},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"157","DOI":"10.1111\/ina.12136","article-title":"Classroom conditions and CO2 concentrations and teacher health symptom reporting in 10 New York State Schools","volume":"25","author":"Muscatiello","year":"2015","journal-title":"Indoor Air"},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"228","DOI":"10.1080\/17508975.2012.725530","article-title":"What do we know about indoor air quality in school classrooms? A critical review of the literature","volume":"4","author":"Chatzidiakou","year":"2012","journal-title":"Intell. Build. Int."},{"key":"ref_16","doi-asserted-by":"crossref","unstructured":"Sandfort, V., Trabold, B., Abdolvand, A., Bolwien, C., Russell, P., W\u00f6llenstein, J., and Palzer, S. (2017). Monitoring the Wobbe Index of Natural Gas Using Fiber-Enhanced Raman Spectroscopy. Sensors, 17.","DOI":"10.3390\/s17122714"},{"key":"ref_17","doi-asserted-by":"crossref","unstructured":"Sandfort, V., Goldschmidt, J., W\u00f6llenstein, J., and Palzer, S. (2018). Cavity-enhanced raman spectroscopy for food chain management. Sensors, 18.","DOI":"10.3390\/s18030709"},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"982","DOI":"10.1021\/ac503450y","article-title":"Fast and Highly Sensitive Fiber-Enhanced Raman Spectroscopic Monitoring of Molecular H2 and CH4 for Point-of-Care Diagnosis of Malabsorption Disorders in Exhaled Human Breath","volume":"87","author":"Hanf","year":"2015","journal-title":"Anal. Chem."},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"5278","DOI":"10.1021\/ac404162w","article-title":"Fiber-Enhanced Raman Multigas Spectroscopy: A Versatile Tool for Environmental Gas Sensing and Breath Analysis","volume":"86","author":"Hanf","year":"2014","journal-title":"Anal. Chem."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"2004","DOI":"10.1364\/AO.16.002004","article-title":"Retroreflecting multipass cell for Raman scattering","volume":"16","author":"Hill","year":"1977","journal-title":"Appl. Opt."},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"7803","DOI":"10.1021\/acs.analchem.5b01462","article-title":"Cavity-Enhanced Raman Spectroscopy of Natural Gas with Optical Feedback cw-Diode Lasers","volume":"87","author":"Hippler","year":"2015","journal-title":"Anal. Chem."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"3193","DOI":"10.1364\/OL.41.003193","article-title":"Cavity-enhanced rotational Raman scattering in gases using a 20 mW near-infrared fiber laser","volume":"41","author":"Friss","year":"2016","journal-title":"Opt. Lett."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"351","DOI":"10.1006\/mchj.1994.1099","article-title":"A Review of the Applications of Tunable Diode Laser Spectroscopy at High Sensitivity","volume":"50","author":"Mantz","year":"1994","journal-title":"Microchem. J."},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"041102","DOI":"10.1063\/1.4959886","article-title":"Photoacoustic-based detector for infrared laser spectroscopy","volume":"109","author":"Scholz","year":"2016","journal-title":"Appl. Phys. Lett."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"529","DOI":"10.1016\/j.snb.2016.03.040","article-title":"A review on non-dispersive infrared gas sensors: Improvement of sensor detection limit and interference correction","volume":"231","author":"Dinh","year":"2016","journal-title":"Sens. Actuators B Chem."},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"954","DOI":"10.1016\/j.snb.2016.04.016","article-title":"A low cost MEMS based NDIR system for the monitoring of carbon dioxide in breath analysis at ppm levels","volume":"236","author":"Vincent","year":"2016","journal-title":"Sens. Actuators B Chem."},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"580","DOI":"10.1016\/j.snb.2013.06.006","article-title":"Non-dispersive infra-red (NDIR) measurement of carbon dioxide at 4.2 \u03bcm in a compact and optically efficient sensor","volume":"186","author":"Hodgkinson","year":"2013","journal-title":"Sens. Actuators B Chem."},{"key":"ref_28","unstructured":"Lehrer, G., and Luft, K. (1938). Verfahren zur Bestimmung von Bestandteilen in Stoffgemischen mittels Strahlungsabsorption. (DE730478C), DE Patent."},{"key":"ref_29","doi-asserted-by":"crossref","unstructured":"Wittstock, V., Scholz, L., Bierer, B., Perez, A.O., W\u00f6llenstein, J., and Palzer, S. (2017). Design of a LED-based sensor for monitoring the lower explosion limit of methane. Sens. Actuators B Chem.","DOI":"10.1016\/j.snb.2017.03.086"},{"key":"ref_30","doi-asserted-by":"crossref","unstructured":"Scholz, L., Ortiz Perez, A., Bierer, B., Eaksen, P., W\u00f6llenstein, J., and Palzer, S. (2017). Miniature low-cost carbon dioxide sensor for mobile devices. IEEE Sens. J., 17.","DOI":"10.1109\/JSEN.2017.2682638"},{"key":"ref_31","first-page":"1","article-title":"Beat frequency quartz-enhanced photoacoustic spectroscopy for fast and calibration-free continuous trace-gas monitoring","volume":"8","author":"Wu","year":"2017","journal-title":"Nat. Commun."},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"161","DOI":"10.1016\/j.snb.2008.08.002","article-title":"New differential mode excitation photoacoustic scheme for near-infrared water vapour sensing","volume":"135","author":"Rey","year":"2008","journal-title":"Sens. Actuators B Chem."},{"key":"ref_33","doi-asserted-by":"crossref","first-page":"885","DOI":"10.1016\/j.snb.2016.03.022","article-title":"Low-cost gas sensing system for the reliable and precise measurement of methane, carbon dioxide and hydrogen sulfide in natural gas and biomethane","volume":"236","author":"Knobelspies","year":"2016","journal-title":"Sens. Actuators B Chem."},{"key":"ref_34","doi-asserted-by":"crossref","unstructured":"Bierer, B., N\u00e4gele, H.-J., Perez, A.O., W\u00f6llenstein, J., Kress, P., Lemmer, A., and Palzer, S. (2018). Real-Time Gas Quality Data for On-Demand Production of Biogas. Chem. Eng. Technol., 41.","DOI":"10.1002\/ceat.201700394"},{"key":"ref_35","doi-asserted-by":"crossref","first-page":"1957","DOI":"10.1080\/10473289.2000.10464225","article-title":"Investigation of the concentration of bacteria and their cell envelope components in indoor air in two elementary schools","volume":"50","author":"Liu","year":"2000","journal-title":"J. Air Waste Manag. Assoc."},{"key":"ref_36","doi-asserted-by":"crossref","first-page":"246","DOI":"10.1039\/b212341j","article-title":"Increased levels of bacterial markers and CO2 in occupied school rooms","volume":"5","author":"Fox","year":"2003","journal-title":"J. Environ. Monit."},{"key":"ref_37","doi-asserted-by":"crossref","first-page":"222","DOI":"10.1034\/j.1600-0668.2000.010004222.x","article-title":"The Effects of Outdoor Air Supply Rate in an Office on Perceived Air Quality, Sick Building Syndrome (SBS) Symptoms and Productivity","volume":"10","author":"Wargocki","year":"2000","journal-title":"Indoor Air"},{"key":"ref_38","doi-asserted-by":"crossref","first-page":"722","DOI":"10.1088\/0022-3727\/25\/4\/019","article-title":"Amplitude and phase study of the photoacoustic effect","volume":"25","author":"Papadopoulos","year":"1992","journal-title":"J. Phys. D Appl. Phys."},{"key":"ref_39","doi-asserted-by":"crossref","first-page":"34","DOI":"10.2307\/2310304","article-title":"An Algorithm for the Evaluation of Finite Trigonometric Series","volume":"65","author":"Goertzel","year":"1958","journal-title":"Am. Math. Mon."},{"key":"ref_40","doi-asserted-by":"crossref","unstructured":"Kneer, J., Eberhardt, A., Walden, P., Ortiz P\u00e9rez, A., W\u00f6llenstein, J., and Palzer, S. (2014). Apparatus to characterize gas sensor response under real-world conditions in the lab. Rev. Sci. Instrum., 85.","DOI":"10.1063\/1.4878717"},{"key":"ref_41","doi-asserted-by":"crossref","first-page":"140","DOI":"10.1016\/j.atmosenv.2013.07.056","article-title":"Characterization of traf fi c-related air pollutant metrics at four schools in El Paso, Texas, USA: Implications for exposure assessment and siting schools in urban areas","volume":"80","author":"Raysoni","year":"2013","journal-title":"Atmos. Environ."},{"key":"ref_42","unstructured":"(2001). VDI 4300 Blatt 7, Messen von Innenraumluftverunreinigungen\u2014Bestimmung der Luftwechselzahl in Innenr\u00e4umen, Beuth Verlag."},{"key":"ref_43","doi-asserted-by":"crossref","unstructured":"Mazzeo, N. (2011). Air Change Measurements Using Tracer Gases: Methods and Results. Significance of air change for indoor air quality. Chemistry, Emissin Control, Radioactive Pollution and Indoor Air Quality, InTech.","DOI":"10.5772\/1030"},{"key":"ref_44","doi-asserted-by":"crossref","first-page":"868","DOI":"10.1111\/ina.12383","article-title":"Carbon dioxide generation rates for building occupants","volume":"27","author":"Persily","year":"2017","journal-title":"Indoor Air"},{"key":"ref_45","doi-asserted-by":"crossref","first-page":"166","DOI":"10.1016\/j.enbuild.2012.06.022","article-title":"Naturally ventilated classrooms: An assessment of existing comfort models for predicting the thermal sensation and preference of primary school children","volume":"53","author":"Teli","year":"2012","journal-title":"Energy Build."},{"key":"ref_46","unstructured":"ASHRAE (1992). Standard 55, Thermal Environmental Conditions for Human Occupancy, ASHRAE Inc."},{"key":"ref_47","unstructured":"(2005). ISO\/TC 159\/SC 5. ISO 7730:2005:\u2014Ergonomics of the Thermal Environment\u2014Analytical Determination and Interpretation of Thermal Comfort Using Calculation of the PMV and PPD Indices and Local Thermal Comfort Criteria, ISO."},{"key":"ref_48","doi-asserted-by":"crossref","unstructured":"(2008). Umweltbundesamt. Gesundheitliche Bewertung von Kohlendioxid in der Innenraumluft, Bundesgesundheitsbl Gesundheitsforsch Gesundheitsschutz, 51, 1358\u20131369.","DOI":"10.1007\/s00103-008-0707-2"},{"key":"ref_49","doi-asserted-by":"crossref","first-page":"581","DOI":"10.1016\/j.buildenv.2012.10.007","article-title":"Providing better thermal and air quality conditions in school classrooms would be cost-effective","volume":"59","author":"Wargocki","year":"2013","journal-title":"Build. Environ."},{"key":"ref_50","doi-asserted-by":"crossref","first-page":"27","DOI":"10.1111\/j.1600-0668.2004.00320.x","article-title":"Do indoor pollutants and thermal conditions in schools influence student performance? A critical review of the literature","volume":"15","author":"Mendell","year":"2005","journal-title":"Indoor Air"},{"key":"ref_51","doi-asserted-by":"crossref","first-page":"535","DOI":"10.5194\/jsss-7-535-2018","article-title":"Gas sensors for climate research","volume":"7","author":"Scholz","year":"2018","journal-title":"J. Sens. Sens. Syst."}],"container-title":["Sensors"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1424-8220\/18\/12\/4345\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,4,4]],"date-time":"2026-04-04T10:51:46Z","timestamp":1775299906000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1424-8220\/18\/12\/4345"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2018,12,9]]},"references-count":51,"journal-issue":{"issue":"12","published-online":{"date-parts":[[2018,12]]}},"alternative-id":["s18124345"],"URL":"https:\/\/doi.org\/10.3390\/s18124345","relation":{},"ISSN":["1424-8220"],"issn-type":[{"value":"1424-8220","type":"electronic"}],"subject":[],"published":{"date-parts":[[2018,12,9]]}}}