Aerosols of biogenic and anthropogenic origin affect the total radiative forcing of global climate. Poor knowledge of the pre-industrial aerosol concentration and composition, in particular of particles formed directly in the atmosphere from gaseous precursors, constitutes a large uncertainty in the anthropogenic radiative forcing. Investigations of new particle formation at pre-industrial-like conditions can contribute to the reduction of this uncertainty. Here we present observations taken at the remote Nepal Climate Observatory Pyramid station at 5,079 m above sea level, a few kilometres from the summit of Everest. We show that up-valley winds funnel gaseous aerosol precursors to higher altitudes. During this transport, these are oxidized into compounds of very low volatility, which rapidly form a large number of aerosol particles. These are then transported into the free troposphere, which suggests that the whole Himalayan region may act as an ‘aerosol factory’ and contribute substantially to the free tropospheric aerosol population. Aerosol production in this region occurs mainly via organic precursors of biogenic origin with little evidence of the involvement of anthropogenic pollutants. This process is therefore likely to be essentially unchanged since the pre-industrial period, and may have been one of the major sources that contributes to the upper tropospheric aerosol population during that time.

生源和人为来源的气溶胶影响全球气候的总辐射强迫。对工业化前气溶胶浓度和组成，特别是由气态前体直接在大气中直接形成的颗粒的了解不多，在人为辐射强迫方面存在很大的不确定性。在类似工业化前的条件下研究新颗粒的形成可以有助于减少这种不确定性。在这里，我们介绍了在距海拔珠穆朗玛峰顶数公里的海拔579 m处的偏远尼泊尔气候观测站金字塔站所进行的观测。我们显示，上谷风将气态气溶胶前体漏斗到更高的高度。在运输过程中，它们被氧化成挥发性极低的化合物，迅速形成大量的气溶胶颗粒。然后将它们运入对流层的自由空间，这表明整个喜马拉雅地区可能充当“气溶胶工厂”，并为自由对流层气溶胶种群做出实质性贡献。该地区的气溶胶生产主要通过生物成因的有机前体发生，几乎没有人为污染物参与的证据。因此，自工业化前以来，这一过程可能基本保持不变，并且可能是这段时期对流层上层气溶胶数量增加的主要来源之一。该地区的气溶胶生产主要通过生物成因的有机前体发生，几乎没有人为污染物参与的证据。因此，自工业化前以来，这一过程可能基本保持不变，并且可能是这段时期对流层上层气溶胶数量增加的主要来源之一。该地区的气溶胶生产主要通过生物成因的有机前体发生，几乎没有人为污染物参与的证据。因此，自工业化前以来，这一过程可能基本保持不变，并且可能是这段时期对流层上层气溶胶数量增加的主要来源之一。