Evaluating the performance of the low-cost black carbon sensor bcMeter at an urban background site

Black carbon (BC) in the atmosphere severely impacts human health and climate. Despite this, BC monitoring is often limited to a small number of locations. The emergence of low-cost sensors could facilitate coverage of black carbon measurements in urban and rural areas by increasing the spatial and temporal resolution of the data. In this perspective fits the bcMeter, a low-cost black carbon sensor operating with the same working principle as conventional aethalometers. In this work, two bcMeter were evaluated against a reference AE33 aethalometer (Aerosol Magee Scientific) at an urban background site in Mülheim-Styrum, Germany. Both bcMeter sensors were susceptible to frequent hardware and software problems, leading to shutdowns and significant data loss. Hourly averages showed high instrumental noise, resulting in scattered data with no meaningful interpretation. Reducing the temporal resolution to daily averages, both sensors followed the same trend in BC concentration as the reference aethalometer with acceptable correlation (R2 = 0.79 and R2 = 0.77, respectively) only after outlier removal. Both bcMeter showed a consistent underestimation of BC concentrations, traced to an incorrect inlet airflow reported by the internal flow sensors. A correction factor was calculated and applied to the BC calculation, effectively correcting the underestimation for bcMeter2 (slope = 1.02); for bcMeter1 the applied factor corrected the underestimation (slope = 0.94) after data cleaning. Overall, the bcMeter proved to be inadequate for short-term BC monitoring; nonetheless, the sensor showed promising results in correctly estimating BC concentrations over 24-hour and even 12-hour averages. These results showed how the bcMeter could be promising for future implementations in monitoring networks for orientation measurements, as particulate matter limit values are usually issued as a daily average as highest time resolution.