Aircraft observations have revealed ubiquitous new particle formation in the tropical upper troposphere over the Amazon^1,2 and the Atlantic and Pacific oceans^3,4. Although the vapours involved remain unknown, recent satellite observations have revealed surprisingly high night-time isoprene mixing ratios of up to 1 part per billion by volume (ppbv) in the tropical upper troposphere⁵. Here, in experiments performed with the CERN CLOUD (Cosmics Leaving Outdoor Droplets) chamber, we report new particle formation initiated by the reaction of hydroxyl radicals with isoprene at upper-tropospheric temperatures of −30 °C and −50 °C. We find that isoprene-oxygenated organic molecules (IP-OOM) nucleate at concentrations found in the upper troposphere, without requiring any more vapours. Moreover, the nucleation rates are enhanced 100-fold by extremely low concentrations of sulfuric acid or iodine oxoacids above 10⁵ cm⁻³, reaching rates around 30 cm⁻³ s⁻¹ at acid concentrations of 10⁶ cm⁻³. Our measurements show that nucleation involves sequential addition of IP-OOM, together with zero or one acid molecule in the embryonic molecular clusters. IP-OOM also drive rapid particle growth at 3–60 nm h⁻¹. We find that rapid nucleation and growth rates persist in the presence of NO_x at upper-tropospheric concentrations from lightning. Our laboratory measurements show that isoprene emitted by rainforests may drive rapid new particle formation in extensive regions of the tropical upper troposphere^1,2, resulting in tens of thousands of particles per cubic centimetre.

飞机观测显示，在亚马逊 ^1,2 、大西洋和太平洋上空的热带对流层上层，无处不在的新粒子形成 ^3,4 。尽管所涉及的蒸气仍然未知，但最近的卫星观测显示，热带对流层 ⁵ 上层的夜间异戊二烯混合比高达十亿分之一 （ppbv）。在这里，在使用 CERN CLOUD（离开室外液滴的宇宙学）室进行的实验中，我们报道了羟基自由基与 -30 °C 和 -50 °C 的对流层上部温度下异戊二烯反应引发的新颗粒形成。 我们发现异戊二烯含氧有机分子 （IP-OOM） 以对流层上部发现的浓度成核，不需要更多的蒸汽。此外，100 ⁵ cm ⁻³ 以上的极低浓度硫酸或碘氧酸的成核速率提高了 10 倍，在 30 ⁶ cm 的酸浓度下达到 10 cm ^{−3 −3} 左右 ⁻¹ 的成核速率。我们的测量表明，成核涉及 IP-OOM 的连续添加，以及胚胎分子簇中的零个或一个酸分子。IP-OOM 还驱动颗粒在 3–60 nm h ⁻¹ 处快速生长。我们发现，在闪电产生的对流层上层浓度的 NO _x 存在下，快速成核和生长速率持续存在。我们的实验室测量表明，热带雨林排放的异戊二烯可能会推动热带对流层 ^1,2 上部的广泛区域迅速形成新的颗粒，导致每立方厘米产生数万个颗粒。