Abstract
Abstract. The particle number size distribution is an important parameter to characterize the atmospheric aerosol and its influence on the Earth's climate. Here we describe a new optical particle size spectrometer (OPSS) for measurements of the accumulation mode particle number size distribution in the tropopause region on board a passenger aircraft (IAGOS-CARIBIC observatory: In-service Aircraft for a Global Observing System – Civil Aircraft for Regular Investigation of the Atmosphere Based on an Instrument Container). A modified KS93 particle sensor from RION Co., Ltd., together with a new airflow system and a dedicated data acquisition system, is the key component of the CARIBIC OPSS. The instrument records individual particle pulse signal curves in the particle size range 130–1110 nm diameter (for a particle refractive index of 1.47-i0.006) together with a time stamp and thus allows the post-flight choice of the time resolution and the size distribution bin width. The CARIBIC OPSS has a 50 % particle detection diameter of 152 nm and a maximum asymptotic counting efficiency of 98 %. The instrument's measurement performance shows no pressure dependency and no particle coincidence for free tropospheric conditions. The size response function of the CARIBIC OPSS was obtained by a polystyrene latex calibration in combination with model calculations. Particle number size distributions measured with the new OPSS in the lowermost stratosphere agreed within a factor of 2 in concentration with balloon-borne measurements over western North America. Since June 2010 the CARIBIC OPSS is deployed once per month in the IAGOS-CARIBIC observatory.
Highlights
The particle number size distribution is essential to describe the physical properties of the atmospheric aerosol and its influence on climate (Charlson et al, 1992; Mann et al, 2014)
The CARIBIC measurement container weighs 1.6 tons and is 3 m wide, the large number of on-board experiments forces a focus on small and light equipment with low power consumption. Besides these constraints we required an instrument with a lower size detection limit below 200 nm equivalent optical particle diameter. These requirements are fulfilled by the KS-93 particle sensor (RION CO., Ltd., Japan; www.rion.co.jp/english/, accessed 1 July 2015), an instrument developed for semiconductor manufacturing applications, which had not been applied to airborne atmospheric research before
For that purpose the number concentrations measured by the CARIBIC optical particle size spectrometer (OPSS) for 200 nm polystyrene latex (PSL) particles and corrected for the counting efficiency (Sect. 3.5) were compared to the number concentrations measured by the condensation particle counters (CPCs), corrected for coincidence
Summary
The particle number size distribution is essential to describe the physical properties of the atmospheric aerosol and its influence on climate (Charlson et al, 1992; Mann et al, 2014). The accumulation mode dominates the total particle mass concentration in air masses without coarse mode particles (particle diameter larger than 1.0 μm), for instance in the upper troposphere and lowermost stratosphere (UT/LMS). Aerosol particles in this region provide surface area for heterogeneous chemistry (Søvde et al, 2007) and influence the formation of ice clouds (Krämer et al, 2009) and thereby in-. In this study we present a new OPSS applied for regular measurements of the UT/LMS particle number size distribution on board a passenger aircraft. Examples of two flights provide an impression of the UT/LMS aerosol data obtained (Sect. 5)
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