New particle formation (NPF) in the tropical upper troposphere is a globally important source of atmospheric aerosols^1,2,3,4. It is known to occur over the Amazon basin, but the nucleation mechanism and chemical precursors have yet to be identified². Here we present comprehensive in situ aircraft measurements showing that extremely low-volatile oxidation products of isoprene, particularly certain organonitrates, drive NPF in the Amazonian upper troposphere. The organonitrates originate from OH-initiated oxidation of isoprene from forest emissions in the presence of nitrogen oxides from lightning. Nucleation bursts start about 2 h after sunrise in the outflow of nocturnal deep convection, producing high aerosol concentrations of more than 50,000 particles cm⁻³. We report measurements of characteristic diurnal cycles of precursor gases and particles. Our observations show that the interplay between biogenic isoprene, deep tropical convection with associated lightning, oxidation photochemistry and the low ambient temperature uniquely promotes NPF. The particles grow over time, undergo long-range transport and descend through subsidence to the lower troposphere, in which they can serve as cloud condensation nuclei (CCN) that influence the Earth’s hydrological cycle, radiation budget and climate^1,4,5,6,7,8.

热带对流层上层新颗粒形成 （NPF） 是全球大气气溶胶的重要来源^1,2,3,4。已知它发生在亚马逊盆地，但成核机制和化学前体尚未确定²。在这里，我们展示了全面的飞机原位测量，表明异戊二烯的极低挥发性氧化产物，特别是某些有机硝酸盐，驱动亚马逊对流层上部的 NPF。有机硝酸盐来源于 OH 在闪电产生的氮氧化物存在下对森林排放物中的异戊二烯进行氧化。成核爆发在日出后约 2 小时在夜间深对流的流出中开始，产生超过 50,000 个颗粒 ^cm-3 的高气溶胶浓度。我们报告了前体气体和颗粒的特征昼夜循环的测量值。我们的观察表明，生物异戊二烯、深热带对流与相关闪电、氧化光化学和低温环境温度之间的相互作用独特地促进了 NPF。这些颗粒随着时间的推移而增长，经过长距离传输，并通过沉降下降到对流层下层，在那里它们可以作为云凝结核 （CCN），影响地球的水文循环、辐射收支和气候^1,4,5,6,7,8。