Laboratory and Field Evaluations of the GeoAir2 Air Quality Monitor for Use in Indoor Environments

Abstract

Low-cost aerosol sensors open routes to exposure assessment and air monitoring in various indoor and outdoor environments. This study evaluated the accuracy of GeoAir2--a recently developed low-cost particulate matter (PM) monitor--using two types of aerosols (salt and dust), and the effect of changes in relative humidity on its measurements in laboratory settings. For the accuracy experiments, 32 units of GeoAir2 were used, and for the humidity experiments, 3 units of GeoAir2 were used, alongside the OPC-N3 low-cost sensor and MiniWRAS reference instrument. The normal distribution of slopes between the salt and dust aerosols was compared for the accuracy experiments. In addition, the performance of GeoAir2 in indoor environments was evaluated compared to the pDR-1500 reference instrument by collocating GeoAir2 and pDR-1500 at three different homes for five days. For salt and dust aerosols smaller than 2.5 µm (PM2.5), both GeoAir2 (r = 0.96-0.99) and OPC-N3 (r = 0.98-0.99) were highly correlated with the MiniWRAS reference instrument. However, GeoAir2 was less influenced by changes in humidity than OPC-N3. While GeoAir2 reported an increase in mass concentrations ranging from 100% to 137% for low and high concentrations, an increase between 181% and 425% was observed for OPC-N3. The normal distribution of the slopes for the salt aerosols was narrower than dust aerosol, which shows closer slope similarities for salt aerosols. This study also found that GeoAir2 was highly correlated with the pDR-1500 reference instrument in indoor environments (r = 0.80-0.99). These results demonstrate potential for GeoAir2 for indoor air monitoring and exposure assessments.

Ambient characterisation of PurpleAir particulate matter monitors for measurements to be considered as indicative

“…Precision was determined for each system and campaign-wise by means of the coefficient of variation (CV, Sousan et al 2021, Streuber et al 2022:…”

“…Precision was determined for each system and campaign-wise by means of the coefficient of variation (CV): 43,44 CV = σ / μ where σ is the standard deviation and μ is the average of the coincident concentrations reported by both sensors within a system.…”

“…Precision and inter-channel QA/QC Precision was determined for each system and campaign-wise by means of the coefficient of variation (CV): 43,44 CV ¼ s/m…”

“…While such evaluations are both relevant and necessary to quantify performance, the results will not necessarily hold true for the same type of LCS used in a different context or across a set evaluated in parallel, leading to less precise measurements (Streuber et al 2022, Sousan et al 2021. This is largely owing to the difficulties in computing PM mass from particle counts (Williams et al 2019.…”

“…42 While such evaluations are both relevant and necessary to quantify performance, the results will not necessarily hold true for the same type of LCS used in a different context or across a set evaluated in parallel, leading to less precise measurements. 43,44 This is largely owing to the difficulties in computing the PM mass from particle counts. 45,46 In other words, the dimensions measured by using the LCS (six size bins, temperature, T, and relative humidity, RH, for the PurpleAir) are limited when providing the highdimensionality of the complex relationship between the PM number and dry mass.…”