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A new high-transmission inlet for the Caltech nano-RDMA for size distribution measurements of sub-3 nm ions at ambient concentrations

机译:Caltech nano-RDMA的新型高传输入口,用于在环境浓度下测量亚3 nm离子的尺寸分布

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摘要

Reliable and reproducible measurements of atmospheric aerosol particle number size distributions below 10 nm require optimized classification instruments with high particle transmission efficiency. Almost all differential mobility analyzers (DMAs) have an unfavorable potential gradient at the outlet (e.g., long column, Vienna type) or at the inlet (nano-radial DMA), preventing them from achieving a good transmission efficiency for the smallest nanoparticles. We developed a new high-transmission inlet for the Caltech nano-radial DMA (nRDMA) that increases the transmission efficiency to 12 % for ions as small as 1.3 nm in Millikan–Fuchs mobility equivalent diameter, D_p (corresponding to 1.2  ×  10^(−4) m^2 V^(−1) s^(−1) in electrical mobility). We successfully deployed the nRDMA, equipped with the new inlet, in chamber measurements, using a particle size magnifier (PSM) and as a booster a condensation particle counter (CPC). With this setup, we were able to measure size distributions of ions within a mobility range from 1.2  ×  10^(−4) to 5.8  ×  10^(−6) m^2 V^(−1) s^(−1). The system was modeled, tested in the laboratory and used to measure negative ions at ambient concentrations in the CLOUD (Cosmics Leaving Outdoor Droplets) 7 measurement campaign at CERN. We achieved a higher size resolution (R  =  5.5 at D_p  =  1.47 nm) than techniques currently used in field measurements (e.g., Neutral cluster and Air Ion Spectrometer (NAIS), which has a R  ∼  2 at largest sizes, and R  ∼  1.8 at D_p  =  1.5 nm) and maintained a good total transmission efficiency (6.3 % at D_p  =  1.5 nm) at moderate inlet and sheath airflows (2.5 and 30 L min^(−1), respectively). In this paper, by measuring size distributions at high size resolution down to 1.3 nm, we extend the limit of the current technology. The current setup is limited to ion measurements. However, we envision that future research focused on the charging mechanisms could extend the technique to measure neutral aerosol particles as well, so that it will be possible to measure size distributions of ambient aerosols from 1 nm to 1 µm.
机译:可靠且可重现的10μnm以下大气气溶胶颗粒数尺寸分布的测量需要具有高颗粒传输效率的优化分类仪器。几乎所有的差分迁移率分析仪(DMA)的出口(例如长柱,Vienna型长柱)或入口(纳米径向DMA)都有不利的电势梯度,从而阻碍了它们对最小的纳米颗粒实现良好的传输效率。我们为Caltech纳米径向DMA(nRDMA)开发了一种新的高透射率入口,该离子将Millikan–Fuchs迁移率当量直径D_p(相当于1.2×10 ^(对应于1.3 nm)的离子的传输效率提高到12%。 -4)m ^ 2 V ^(-1)s ^(-1))。我们使用粒径放大仪(PSM)和凝结粒子计数器(CPC)作为助推器,成功地在腔室测量中部署了配备新进样口的nRDMA。使用此设置,我们能够测量迁移率范围为1.2×10 ^(− 4)到5.8×10 ^(− 6)m ^ 2 V ^(− 1)s ^(− 1)的离子的大小分布。该系统在实验室进行了建模,测试,并用于在CERN的CLOUD(宇宙离开室外液滴)7测量活动中测量环境浓度下的负离子。与目前在现场测量中使用的技术(例如,中性簇和空气离子光谱仪(NAIS),其最大尺寸为R〜2,R R〜1.8)相比,我们实现了更高的尺寸分辨率(D_p = 1.47 nm下R = 5.5)。在D_p = 1.5 nm时),并在中等进气和鞘气流(分别为2.5和30 L min ^(-1))下保持良好的总传输效率(D_p = 1.5 nm时为6.3%)。在本文中,通过在低至1.3µnm的高分辨率下测量尺寸分布,我们扩展了当前技术的极限。当前设置仅限于离子测量。但是,我们预想,将来着重于充电机制的研究也可以将技术扩展到测量中性气溶胶颗粒,从而有可能测量1μnm至1μm的环境气溶胶的尺寸分布。

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