Abstract
Abstract. Ice-nucleating particles (INPs) affect cloud development, lifetime, and radiative properties, hence it is important to know the abundance of INPs throughout the atmosphere. A critical factor in determining the lifetime and transport of INPs is their size; however very little size-resolved atmospheric INP concentration information exists. Here we present the development and application of a radio-controlled payload capable of collecting size-resolved aerosol from a tethered balloon for the primary purpose of offline INP analysis. This payload, known as the SHARK (Selective Height Aerosol Research Kit), consists of two complementary cascade impactors for aerosol size-segregation from 0.25 to 10 µm, with an after-filter and top stage to collect particles below and above this range at flow rates of up to 100 L min−1. The SHARK also contains an optical particle counter to quantify aerosol size distribution between 0.38 and 10 µm, and a radiosonde for the measurement of temperature, pressure, GPS altitude, and relative humidity. This is all housed within a weatherproof box, can be run from batteries for up to 11 h, and has a total weight of 9 kg. The radio control and live data link with the radiosonde allow the user to start and stop sampling depending on meteorological conditions and height, which can, for example, allow the user to avoid sampling in very humid or cloudy air, even when the SHARK is out of sight. While the collected aerosol could, in principle, be studied with an array of analytical techniques, this study demonstrates that the collected aerosol can be analysed with an offline droplet freezing instrument to determine size-resolved INP concentrations, activated fractions, and active site densities, producing similar results to those obtained using a standard PM10 aerosol sampler when summed over the appropriate size range. Test data, where the SHARK was sampling near ground level or suspended from a tethered balloon at 20 m altitude, are presented from four contrasting locations having very different size-resolved INP spectra: Hyytiälä (southern Finland), Leeds (northern England), Longyearbyen (Svalbard), and Cardington (southern England).
Highlights
Atmospheric ice-nucleating particles (INPs) are not well understood, with knowledge of their concentration, sources, temporal variability, transport, and size in its infancy (Kanji et al, 2017; Murray et al, 2012)
We present the results for this set of four Selective Height Aerosol Research Kit (SHARK) deployments to illustrate the capabilities of the SHARK for quantifying ice-nucleating particle spectra as well as demonstrating that the technique is consistent with more established methods
The relative humidity (RH) during the flight was monitored to ensure the SHARK did not sample in humidity approaching saturation; the impactor and optical particle counter (OPC) manufacturers’ specified threshold for the components is 95 % RH, but we aim to only sample with the RH below this value (∼ 80 %) in order to reduce the influence of hygroscopic growth on aerosol size
Summary
Atmospheric ice-nucleating particles (INPs) are not well understood, with knowledge of their concentration, sources, temporal variability, transport, and size in its infancy (Kanji et al, 2017; Murray et al, 2012). This is of importance because clouds between 0 and around −35 ◦C can exist in a supercooled liquid, mixed-phase (ice and water), or glaciated (ice only) state depending in part on the presence or absence of INPs (Kanitz et al, 2011; Vergara-Temprado et al, 2018). Porter et al.: Resolving the size of ice-nucleating particles
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