Abstract
Abstract. Earth's radiation budget is affected by new particle formation (NPF) and the growth of these nanometre-scale particles to larger sizes where they can directly scatter light or act as cloud condensation nuclei (CCN). Large uncertainties remain in the magnitude and spatiotemporal distribution of nucleation (less than 10 nm diameter) and Aitken (10–60 nm diameter) mode particles. Acquiring size-distribution measurements of these particles over large regions of the free troposphere is most easily accomplished with research aircraft. We report on the design and performance of an airborne instrument, the nucleation mode aerosol size spectrometer (NMASS), which provides size-selected aerosol concentration measurements that can be differenced to identify aerosol properties and processes or inverted to obtain a full size distribution between 3 and 60 nm. By maintaining constant downstream pressure the instrument operates reliably over a large range of ambient pressures and during rapid changes in altitude, making it ideal for aircraft measurements from the boundary layer to the stratosphere. We describe the modifications, operating principles, extensive calibrations, and laboratory and in-flight performance of two NMASS instruments operated in parallel as a 10-channel battery of condensation particle counters (CPCs) in the NASA Atmospheric Tomography Mission (ATom) to investigate NPF and growth to cloud-active sizes in the remote free troposphere. An inversion technique to obtain size distributions from the discrete concentrations of each NMASS channel is described and evaluated. Concentrations measured by the two NMASS instruments flying in parallel are self-consistent and also consistent with measurements made with an optical particle counter. Extensive laboratory calibrations with a range of particle sizes and compositions show repeatability of the response function of the instrument to within 5–8 % and no sensitivity in sizing performance to particle composition. Particle number, surface area, and volume concentrations from the data inversion are determined to better than 20 % for typical particle size distributions. The excellent performance of the NMASS systems provides a strong analytical foundation to explore NPF around the globe in the ATom dataset.
Highlights
Particles play important roles in chemical and physical processes in the atmosphere: they provide sites for heterogeneous reactions (Ravishankara, 1997), they serve as nuclei for the formation of clouds, and they directly and indirectly affect the Earth’s radiation budget (Solomon and IPCC Working Group Science, 2007)
We describe the modifications, operating principles, extensive calibrations, and laboratory and in-flight performance of two nucleation mode aerosol size spectrometer (NMASS) instruments operated in parallel as a 10channel battery of condensation particle counters (CPCs) in the NASA Atmospheric Tomography Mission (ATom) to investigate new particle formation (NPF) and growth to cloud-active sizes in the remote free troposphere
Comparisons of inverted size distributions from the scanning mobility particle spectrometers (SMPSs) and NMASS instruments are shown in Fig. 10, with a 20 nm peak selected by the DMA in the upper panel, and 32 nm in the lower panel
Summary
Particles play important roles in chemical and physical processes in the atmosphere: they provide sites for heterogeneous reactions (Ravishankara, 1997), they serve as nuclei for the formation of clouds, and they directly and indirectly affect the Earth’s radiation budget (Solomon and IPCC Working Group Science, 2007). C. Williamson et al.: Fast time response measurements of particle size distributions cles, those directly emitted into the atmosphere in the solid or liquid phase, affect the radiation budget by acting as cloud condensation nuclei (CCN) or directly scattering or absorbing sunlight. Williamson et al.: Fast time response measurements of particle size distributions cles, those directly emitted into the atmosphere in the solid or liquid phase, affect the radiation budget by acting as cloud condensation nuclei (CCN) or directly scattering or absorbing sunlight Secondary particles, those formed by nucleation from the gas phase in the atmosphere, often dominate both aerosol–cloud and aerosol–radiation interactions (Kulmala et al, 2004). The majority of the particles present in the troposphere in most environments have diameters < 100 nm, and substantial fractions of the total particle surface area and volume sometimes lie within this size range (Clarke and Kapustin, 2002)
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