A Low-Cost Calibration Method for Temperature, Relative Humidity, and Carbon Dioxide Sensors Used in Air Quality Monitoring Systems

Abstract

Low-cost sensors provide an affordable alternative to monitor environmental parameters with acceptable performance. There is a substantial amount of literature where low-cost sensors are compared with high-end reference measurements. However, not all organizations have access to such reference infrastructure. We propose low-cost calibration methods for temperature, relative humidity, and CO2 to allow them to collect their own reliable data. These methods are based on simple techniques and procedures that allow temperature calibration to be achieved in the range of 0 to 50 °C, relative humidity from 0 to 90%, and CO2 between 0 and 1100 ppm. The materials used to create the calibration setups can be purchased online, at hardware stores, and in pharmacies. The reliability of the calibration methods was evaluated using several indicators, such as the airtightness of the calibration box, similarity with the factory calibration, similarity with the reference, similarity between different sensors, replicability of the calibration method, and the similarity with a golden standard. In addition, the results of the low-cost calibration methods were compared with the more advanced calibration methods. A short measurement campaign in the city of Santa Clara, Cuba, demonstrated that such calibrations transform in-house developed monitoring systems into valid low-cost scientific instruments for decision-making. This work creates opportunities for institutions and researchers hosted in low- and mid-income countries to build and validate their own equipment to reliably solve local problems.

A Smoke Chamber Study on Some Low-Cost Sensors for Monitoring Size-Segregated Aerosol and Microclimatic Parameters

“…Although the experimental arrangement with the smoke chamber provided relatively reliable values for PM x and microclimatic parameters, the accuracy of the data could be improved, for instance, with the application of lower volumes of the aerosol chamber, lower heating rates, and more sharply controlled RH conditions, e.g., by means of those reported in Ref. [41].…”

“…This is a definite disability of the measurement procedure/system at medium and high RH, which might be overcome by reducing the volume of the smoke chamber and/or utilizing a T-insulating medium inside, as suggested in Ref. [41]. Otherwise, this source of measurement error could be overcome with the use of the outer, moisturized air in the laboratory, which could make a better balance with the internal of the smoke chamber.…”

“…Additionally, LCSs demand more frequent calibration and comparison with reference methods, depending on several factors, such as the sampling site emission and the sampled aerosol type, for instance, by means of using research-grade instruments and/or data from official AQ stations [6][7][8][9][10][11][12]17]. Recently, it has been shown that LCSs can be calibrated with good accuracy using commercial, DIY-kit-like electrical/chemical apparatus, which are accessible to society at large [41]. Certainly, based on these principles, it would be easier to build up nodes for AQ monitoring, even a network over areas of different anthropogenic impacts, as was already demonstrated in the literature [45].…”

“…Besides these, a couple of ambient microclimatic parameters, such as air temperature (T a ) and relative humidity (RH), have been reported to influence the extent of bias for PM-mass/concentration readings, e.g., [8,17,27,34]. Further methodological improvements include the application of extended/refined calculation methods for PM mass [23], the use of deep-learning calibration techniques [40], and the application of various sets of internet of things (IoTs) accessible to society at large [41]. More details on the peculiarities of the application for LCSs can be found in extensive reviews [42][43][44].…”

Utilizing Low-Cost Sensors to Monitor Indoor Air Quality in Mongolian Gers

“…LCSs are sensitive and can be affected by changes in relative humidity, temperature, sensor aging, and changes in the composition of particulate matter [ 25 , 26 , 27 ]. LCSs can also suffer from a deviation of linearity at higher PM concentrations depending on their detection method.…”