Condensation Particle Counter

1. Condensation Particle Counter Content Expansion Chamber CPC Continuous Flow CPC Butanol CPC • TSI 3007 • TSI 3772 • TSI 3775 • TSI 3776 Water CPC • TSI 3786 Leibniz Institute for Tropospheric Research B2 Condensation Particle Counter University of Leipzig

2. Principle • Important instruments in aerosol technology are Condensation Particle Counters (CPC). • They are used to measure the particle number concentration down to the nanometer size range. • The lower detection efficiency is much lower than in optical particle counters. • The particles are enlarged due to supersaturation and a subsequent condensation of a condensable gas. The particles reach a size at which they can be optically detected. • The number concentration is measured for all particle larger than the lower detection diameter. Leibniz Institute for Tropospheric Research B2 Condensation Particle Counter University of Leipzig

3. CPCs are used to measure the number concentration in the submicrometer size range. • The lower detection diameter is determined by • the Kelvin diameter (supersaturation) • diffusion coefficient of the condensable gas • the particle material • The upper and lower detection limits are specific for each CPC type. • Following techniques were used in the past • microscope (particles collected on a plate) • picture (cloud chamber) • extinction • single particle in a continuous flow • Two types of CPCs • expansion chamber CPC (extinction) • continuous flow CPC (single particle) Leibniz Institute for Tropospheric Research B2 Condensation Particle Counter University of Leipzig

4. Expansion Chamber CPC • Pollak-Counter • The Pollak-Counter consists of a vertical pipe and porous ceramic wall • The porous wall is saturated with distilled water • A white light source and a photo detector are placed at the upper and lower end of the pipe, respectively • Principle • The aerosol is sucked into the pipe and the valves are closed • The pressure is increased by 200 mbar by a pump • The aerosol becomes saturated with water vapor • Now, the reference extinction is measured • The pipe is expanded to ambient pressure Leibniz Institute for Tropospheric Research B2 Condensation Particle Counter University of Leipzig

5. Due to adiabatic expansion, the water vapor becomes supersaturated and condenses on the particles. • The extinction is measured now again. • The ratio between the extinction measured after and before expansion is a measure of the particle number concentration • Remarks • The Pollak-Counter must be calibrated with monodisperse aerosols and a reference detector such as an aerosol electrometer • The lower detection diameter can be few nm and the lower concentration limit is approximately 100 particles cm-3 • The upper concentration limit is around 107particles cm-3 • The time resolution is several minutes • The Pollak Counter is not used anymore in science but still in operation at few monitoring stations Leibniz Institute for Tropospheric Research B2 Condensation Particle Counter University of Leipzig

6. Schematic Sketch of a Pollak-Counter Leibniz Institute for Tropospheric Research B2 Condensation Particle Counter University of Leipzig

7. Continuous Flow CPC • Modern CPCs operate with continuous aerosol flows and are able to count each single particle • Principle • The aerosol flow is saturated with butanol in a slightly heated saturator. • The the temperature of the butanol-aerosol mixture is decreased by 17-27°C in the condenser of the CPC • Here, the butanol become supersaturated and condenses onto the particles • The particles grow to droplets of several µm in diameter • The droplet flow is focused in a nozzle and introduced into a counting optic Leibniz Institute for Tropospheric Research B2 Condensation Particle Counter University of Leipzig

8. The droplets pass a laser beam, and each single particle creates a light pulse. • Pulses with an amplitude above a certain threshold are counted. • The particle number concentration can be calculated by knowing the aerosol flow rate. • Three commercially available CPCs are discussed in the following section. • TSI model: 3772, 3010 old • TSI model: 3775, 3022 old • TSI model: 3776, 3025 old Leibniz Institute for Tropospheric Research B2 Condensation Particle Counter University of Leipzig

9. CPC models TSI 3772 Leibniz Institute for Tropospheric Research B2 Condensation Particle Counter University of Leipzig

10. CPC model TSI 3775 Leibniz Institute for Tropospheric Research B2 Condensation Particle Counter University of Leipzig

11. CPC model TSI 3776 Leibniz Institute for Tropospheric Research B2 Condensation Particle Counter University of Leipzig

12. CPC model TSI 3007 Leibniz Institute for Tropospheric Research B2 Condensation Particle Counter University of Leipzig

13. Water CPC • Instead of alcohol, water is used for the measurement of sub-micrometer aerosol particles • Principle • The aerosol flow is saturated with water vapor and temperature equilibrated in a cooled saturator • Then the flow passes through a condenser with heated walls, which contain water. This produces an elevated vapor pressure • Evaporated water vapor diffuses faster to the center of the aerosol flow than the heat from the walls and thus supersaturates it • The particles act as condensation nuclei when they are larger than the activation size and grow quickly to droplets of a detectable size Leibniz Institute for Tropospheric Research B2 Condensation Particle Counter University of Leipzig

14. The droplet flow is focused in a nozzle and introduced into a counting optic • The droplets pass a laser beam, and each single particle creates a light pulse • Pulses with an amplitude above a certain threshold are counted • The particle number concentration can be calculated by knowing the aerosol flow rate Leibniz Institute for Tropospheric Research B2 Condensation Particle Counter University of Leipzig

15. CPC model TSI 3786 Leibniz Institute for Tropospheric Research B2 Condensation Particle Counter University of Leipzig