From 27 July to 10 August 2017, the airborne StratoClim mission took place in Kathmandu, Nepal, where eight mission flights were conducted with the M-55 Geophysica up to altitudes of 20 km. New particle formation (NPF) was identified by the abundant presence of nucleation-mode aerosols, with particle diameters d_p smaller than 15 nm, which were in-situ-detected by means of condensation nuclei (CN) counter techniques. NPF fields in clear skies as well as in the presence of cloud ice particles (d_p > 3 µm) were encountered at upper troposphere–lowermost stratosphere (UTLS) levels and within the Asian monsoon anticyclone (AMA). NPF-generated nucleation-mode particles in elevated concentrations (N_nm) were frequently found together with cloud ice (in number concentrations N_ice of up to 3 cm⁻³) at heights between ∼ 11 and 16 km. From a total measurement time of ∼ 22.5 h above 10 km altitude, in-cloud NPF was in sum detected over ∼ 1.3 h (∼ 50 % of all NPF records throughout StratoClim). Maximum N_nm of up to ∼ 11 000 cm⁻³ was detected coincidently with intermediate ice particle concentrations N_ice of 0.05–0.1 cm⁻³ at comparatively moderate carbon monoxide (CO) contents of ∼ 90–100 nmol mol⁻¹. Neither under clear-sky nor during in-cloud NPF do the highest N_nm concentrations correlate with the highest CO mixing ratios, suggesting that an elevated pollutant load is not a prerequisite for NPF. Under clear-air conditions, NPF with elevated N_nm (> 8000 cm⁻³) occurred slightly less often than within clouds. In the presence of cloud ice, NPF with N_nm between 1500–4000 cm⁻³ was observed about twice as often as under clear-air conditions. NPF was not found when ice water contents exceeded 1000 µmol mol⁻¹ in very cold air (< 195 K) at tropopause levels. This indicates a reduction in NPF once deep convection is prevalent together with the presence of mainly liquid-origin ice particles. Within in situ cirrus near the cold point tropopause, recent NPF or intense events with mixing ration n_nm larger than 5000 mg⁻¹ were observed only in about 6 % of the in-cloud NPF data. In determining whether the cloud-internal NPF is attenuated or prevented by the microphysical properties of cloud elements, the integral radius (IR) of the ice cloud population turned out to be indicative. Neither the number of ice particles nor the free distance between the ice particles is clearly related to the NPF rate detected. While the increase in ice particles' mass per time $\left(\frac{\mathrm{d}m}{\mathrm{d}t}\right)$ is proportional to the IR and mainly due to the condensation of water vapour, additional condensation of NPF precursors proceeds at the expense of the NPF rate as the precursor's saturation ratio declines. Numerical simulations show the impact of the IR on the supersaturation of a condensable vapour, such as sulfuric acid, and furthermore illustrate that the IR of the cloud ice determines the effective limitation of NPF rates.

中文翻译：

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2017 年亚洲季风反气旋热带对流层顶层新粒子形成 (NPF) 的原位观测——第 2 部分：冰云内的 NPF

2017 年 7 月 27 日至 8 月 10 日，机载 StratoClim 任务在尼泊尔加德满都进行，在那里使用 M-55 Geophysica进行了八次飞行任务，飞行高度高达 20 公里。新颗粒形成（NPF）通过成核模式气雾剂的丰富存在来鉴定，具有颗粒直径 d _p小于15纳米，这是由凝结核（CN）计数器技术的装置在原位检测。在晴朗的天空以及在云冰颗粒的存在NPF字段（d _p  >  3  μ米）在对流层上层-最下面平流层（UTLS）水平和亚洲季风反气旋（AMA）中遇到。NPF 产生的成核模式粒子浓度升高（N _nm ) 经常与云冰（ N_冰的数量浓度高达 3 cm ^-3）一起在约 11 至 16 公里的高度被发现。从 10 公里高度以上约22.5 小时的总测量时间开始，在约 1.3 小时（ 整个 StratoClim 中所有 NPF 记录的约50%）内总检测到云中 NPF。最大 N _nm高达~  11 000 cm ^-3与中等冰粒子浓度0.05–0.1 cm ^{-3 的}N_冰同时检测到，一氧化碳 (CO) 含量相对适中∼  90–100 nmol mol ^-1。无论是在晴空下还是在云中 NPF 期间，最高N _nm浓度都与最高的 CO 混合比相关，这表明污染物负荷升高并不是 NPF 的先决条件。在晴朗的空气条件下，具有升高的N _nm ( >  8000 cm ^-3 ) 的NPF发生的频率略低于云中。在有云冰的情况下，观察到N_纳米在 1500-4000 cm ^-3之间的NPF 的频率大约是晴空条件下的两倍。NPF未找到时冰水含量超过1000  μ摩尔摩尔^-1在非常冷的空气（<  195 K) 在对流层顶水平。这表明，一旦深对流普遍存在，并且主要是液态冰粒的存在，NPF 就会减少。在靠近冷点对流层顶的原位卷云内，仅在大约 6% 的云中 NPF 数据中观察到了最近的 NPF 或混合比n _nm大于 5000 mg ^{-1 的}强烈事件。在确定云内部 NPF 是否被云元素的微物理特性减弱或阻止时，冰云种群的积分半径 (IR) 具有指示性。冰粒的数量和冰粒之间的自由距离都与检测到的 NPF 率无关。而冰粒质量每增加一次$\left(\frac{\mathrm{d}米}{\mathrm{d}吨}\right)$与 IR 成正比，主要是由于水蒸气的冷凝，NPF 前体的额外冷凝以 NPF 速率为代价，因为前体的饱和比下降。数值模拟显示了 IR 对硫酸等可凝蒸气过饱和的影响，并进一步说明云冰的 IR 决定了 NPF 率的有效限制。