Abstract
Abstract. Capturing the vertical profiles and horizontal variations of atmospheric aerosols often requires accurate airborne measurements. With the advantage of avoiding health and safety concerns related to the use of butanol or other chemicals, water-based condensation particle counters have emerged to provide measurements under various environments. However, airborne deployments are relatively rare due to the lack of instrument characterization under reduced pressure at flight altitudes. This study investigates the performance of a commercial “versatile” water-based condensation particle counter (vWCPC, model 3789, TSI, Shoreview, MN, USA) under various ambient pressure conditions (500–920 hPa) with a wide range of particle total number concentrations (1500–70 000 cm−3). The effect of conditioner temperature on vWCPC 3789 performance at low pressure is examined through numerical simulation and laboratory experiments. We show that the default instrument temperature setting of 30 ∘C for the conditioner is not suitable for airborne measurement and that the optimal conditioner temperature for low-pressure operation is 27∘. Under the optimal conditioner temperature (27∘), the 7 nm cut-off size is also maintained. Additionally, we show that insufficient droplet growth becomes more significant under the low-pressure operation. The counting efficiency of the vWCPC 3789 can vary up to 20 % for particles of different chemical compositions (e.g., ammonium sulfate and sucrose particles). However, such variation is independent of pressure.
Highlights
Atmospheric aerosol particles are one of the key components of the atmosphere
The vWCPC 3789 counting efficiency was characterized as a function of operating pressure (500–920 hPa) for different conditioner temperatures (24– 33◦) with the factory settings for the initiator and moderator temperatures (59 and 10◦)
Under low-pressure conditions, the counting efficiency of the vWCPC 3789 operated with the factory settings decreased with the decrease in the operating pressure, especially when the operating pressure was below 700 hPa
Summary
The currently known ambient aerosol has a size range over several magnitudes and consists of complex chemical compositions, which vary with size, origin, age, and atmospheric processing. To understand the variation of atmospheric aerosol and its production, distribution, and evolution paths, Friedlander (1970, 1971) introduced a conceptual framework for characterizing instruments used for aerosol measurements Following this framework, the size distribution and number concentration of atmospheric aerosol particles are detected through electrostatic methods and condensational growth. The size distribution and number concentration of atmospheric aerosol particles are detected through electrostatic methods and condensational growth The latter approach is the only technique available for detecting uncharged sub-50 nm particles. It has become the dominant technique for assessing the integrated concentration of particles larger than a minimum size
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