Characterization of a modified printed optical particle spectrometer for aerosol sampling systems.

The printed optical particle spectrometer (POPS) is a light-weight, low-cost instrument for aerosol number concentrations and size distributions measurements. Here we report on modifications of the POPS (Handix Scientific) to facilitate its use in multi-instrument aerosol sampling systems. The flow system is modified by replacing the internal pump with a needle valve and a vacuum pump. The instrument is integrated into closed flow systems by routing the sheath flow from filtered inlet air. A high-precision multichannel analyzer card (MCA) is added to sample the analog pulse signal. The MCA card is polled at 10 Hz frequency using an external data acquisition system and removes the count rate limitation of 10000 particles s^-1 associated with the POPS internal system. The MCA card enables integration of the POPS into larger setups that require precise time stamping and clock synchronization, especially in field. The 90/10 rise and fall times were measured to be 0.17 s and 0.41 s at 5 cm^-3 s^-1 and provide a sampling frequency of ~1-2 Hz below which the amplitude of measured fluctuations is captured with > 70% efficiency. We also integrated the POPS into the dual tandem DMA system, which generates dimer particles. We anticipate that this version will extend utilization of the POPS.