Humidity, density and inlet aspiration efficiency correction improve accuracy of a low-cost sensor during field calibration at a suburban site in the north-western Indo-Gangetic Plain (NW-IGP)

Low-cost particulate matter (PM) sensors are now widely used by concerned citizens to monitor PM exposure despite poor validation under field conditions. Here, we report the field calibration of a modified version of the Laser Egg (LE), against Class III US EPA Federal Equivalent Method PM₁₀ and PM_2.5 β-attenuation analyzers. The calibration was performed at a site in the north-western Indo-Gangetic Plain from April 27, 2016 to July 25, 2016. At ambient PM mass loadings ranging from <1-838 µg m⁻³ and <1-228 µg m⁻³ for PM₁₀ and PM_2.5, respectively, measurements of PM₁₀, PM_2.5 from the LE were precise, with a Pearson correlation coefficient (r) > 0.9 and a percentage coefficient of variance (CV) < 12%. The original Mean Bias Error (MBE) of ∼ -90 µg m⁻³ decreased to -30.9 µg m⁻³ (Sensor 1) and -23.2 µg m⁻³ (Sensor 2) during the summer period (April 27 - June 15, 2016) after correcting for particle density and aspiration losses. During the monsoon period (June 16 - July 25, 2016) the MBE of the PM_2.5 measurements decreased from 19.1 µg m⁻³ to 8.7 µg m⁻³ and from 28.3 µg m⁻³ to 16.5 µg m⁻³ for Sensor 1 and Sensor 2 respectively after correcting for particle density and hygroscopic growth. The corrections reduced the overall MBE to <20 µg m⁻³ for PM₁₀ and <3 µg m⁻³ for PM_2.5, indicating that modified version of the LE could be used for ambient PM monitoring with appropriate correction and meteorological observations. However, users of the original product may underestimate their PM₁₀ exposure.