Detection Efficiency of a Water Condensation Particle Counter Using Electrically Neutral Sulfuric Acid and Sulfuric Acid-Dimethylamine Clusters
Darren Cheng, Joy Kiguru, COTY JEN,
Carnegie Mellon University Abstract Number: 6
Working Group: Instrumentation and Methods
AbstractAccurately quantifying atmospheric new particle formation (NPF) rates has pushed the development of condensation particle counters (CPCs) to detect smaller and smaller particles. Currently, CPC detection efficiencies are determined by comparing measured concentrations of size-selected ions with an aerosol electrometer. However, neutrally charged particles represent over 90% of particles formed during new particle formation events and may differ in detection efficiency compared to charged particles. Furthermore, detection efficiency experiments typically use charger ions, ammonium sulfate, sodium chloride, or silver ion particles that each display different detection efficiencies. These compositions differ from particles formed via previously observed atmospheric nucleation of SA and dimethylamine. This study presents a novel method to characterize the detection efficiency of electrically neutral sulfuric acid (SA) vapor and SA-dimethylamine (DMA) particles <1.5 nm in mobility diameter. The detection efficiency was inverted from measured water condensation particle counter (wCPC) concentrations and predicted concentrations of SA-DMA clusters produced by nucleating known concentrations of SA and DMA in a flow reactor. Detection efficiency was determined for a custom, three-stage wCPC. The wCPC was operated at seven different initiator temperatures (98, 91, 81, 71, 61, 51, and 41 °C), while the conditioner, moderator, and optics head were held constant at 1, 1, and 35 °C respectively. These conditioner-to-initiator temperature differences (ΔT) exhibited d50 between 1.8 to 2.6 nm, characterized by traditional ion calibration.