Effect of an Aerosol Dryer on Ambient PM Measurements with SDS011 Low Cost Sensors during a Two-year Period in Duisburg, Germany

The performance of low-cost particulate matter (PM) sensors (NovaFitness SDS011) in connection with a self-developed aerosol dryer has been investigated in ambient air measurements over a two-year period by comparing the reported mass concentration of particulate matter (PM x ) with the results of a PM 10 reference filter sampler and two Tapered Element Oscillating Microbalances (TEOM), one for PM 10 and one for PM 2.5 . Special emphasis was put on the effect of relative air humidity on sensor readings. In total, four sensors were used per year in two pairs. For one pair, the aerosol was dried with a newly developed low-cost aerosol dryer, whereas the other pair measured the untreated aerosol. The results show that the 24 h average concentration reported by the sensor could be by a factor of up to 38 too high compared to the gravimetric measurement, if the aerosol was not dried, whereas the mismatch with a maximum factor of 5.4 was significantly lower when using the dryer. For the PM 10 concentration correction factors were determined from the ratios of the measured 24 h values of the sensors and the gravimetric reference. Corrected 24 h mean PM 10 concentrations with dryer agreed mostly within a factor of 2 with the gravimetric reference data from the filter sampler, whereas results from measurements without dryer agreed only within a factor of 5. The results further show that the sensors underestimate the mass concentrations in case of low relative humidity ( < 45%). Similar results are seen for the PM 2.5 data as well. Therefore, the use of a constant correction factor was checked. It is shown that an average correction factor of around 2.5 for the PM 10 and around 2.6 for the PM 2.5 readings could be a reasonable approach for all SDS011 sensors equipped with the newly developed aerosol dryer.