Monitoring urban air quality with a diffusion charger based electrical particle sensor

Urban air contains considerable amounts of harmful gaseous substances and aerosol particles. In this study, a recently introduced diffusion charger based PPS-M particle sensor (Pegasor Oy, Tampere, Finland) was evaluated for outdoor air quality measurements in urban environment. The PPS-M particle sensor was used in two stationary air quality measurement stations, one located in the roadside environment and the other in residential area, and in a mobile laboratory. The sampling of urban aerosol to the PPS-M sensor was performed without any pre-conditioning of aerosol. The sensor response to PM 2.5 varied between the measurements, being between 7 and 30 fA/(μg/m 3 ) depending on the aerosol source. The highest PM 2.5 response was observed in the roadside study for exhaust particles while the lowest PM 2.5 response was observed for large long range transported aerosol particles having relatively large mean particle size. The sensor signal was found to produce very linear response, with only minimal deviation, to the lung deposited particle surface area concentration (from 4.5 to 6 fA/(μm 2 /cm 3 )) and to the condensation sink of urban air particles (from 1.0 × 10 4 to 1.2 × 10 4 fA cm 3 ). The sensor response to particle number concentration was defined to be 0.0044 fA/(1/cm 3 ) in roadside environment. In this environment, the signal was found to correlate also with NO and NO 2 concentrations of roadside air due to the same origin of particulate and gaseous pollutants. Similar correlation between NO x and the PPS-M signal was not observed in residential area.