Abstract
Abstract. Knowledge about the chemical composition of aerosol particles is essential to understand their formation and evolution in the atmosphere. Due to analytical limitations, however, relatively little information is available for sub-10 nm particles. We present the design of a nano-cloud condensation nuclei counter (nano-CCNC) for measuring size-resolved hygroscopicity and inferring chemical composition of sub-10 nm aerosol particles. We extend the use of counting efficiency spectra from a water-based condensation particle counter (CPC) and link it to the analysis of CCN activation spectra, which provides a theoretical basis for the application of a scanning supersaturation CPC (SS-CPC) as a nano-CCNC. Measurement procedures and data analysis methods are demonstrated through laboratory experiments with monodisperse particles of diameter down to 2.5 nm, where sodium chloride, ammonium sulfate, sucrose and tungsten oxide can be easily discriminated by different characteristic supersaturations of water droplet formation. A near-linear relationship between hygroscopicity parameter κ and organic mass fraction is also found for sucrose-ammonium sulfate mixtures. The design is not limited to the water CPC, but also applies to CPCs with other working fluids (e.g. butanol, perfluorotributylamine). We suggest that a combination of SS-CPCs with multiple working fluids may provide further insight into the chemical composition of nanoparticles and the role of organic and inorganic compounds in the initial steps of atmospheric new particle formation and growth.
Highlights
New particle formation (NPF) and subsequent growth have been intensively studied owning to their important roles in air pollution and climate (Kulmala et al, 2000, 2014; Kerminen et al, 2012; Zhang et al, 2012)
We present the concept of a nano-CCNC for measuring hygroscopicity and inferring chemical composition of nanoparticles in the diameter range of ∼ 2–10 nm
It comprises of a nano-differential mobility analyzer, a total particle counter and a nano-CCNC along with a neutralizer
Summary
New particle formation (NPF) and subsequent growth have been intensively studied owning to their important roles in air pollution and climate (Kulmala et al, 2000, 2014; Kerminen et al, 2012; Zhang et al, 2012). Chemical composition of the newly formed particles is key for understanding the production and transformation of atmospheric aerosol particles. Though sulfuric acid has been commonly recognized as a key species in NPF, it is not sufficient to explain the observed particle growth rate (Kulmala et al, 2013). Thermal desorption chemical ionization mass spectrometer (TDCIMS; Smith et al, 2004) and nano aerosol mass spectrometer (NAMS; Wang and Johnston, 2006) are commonly used at 10–30 nm particles. Direct chemical composition measurement of sub-10 nm particles is still difficult due to its rel-
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