Venzac Hervé, Sellegri Karine, Laj Paolo, Villani Paolo, Bonasoni Paolo, Marinoni Angela, Cristofanelli Paolo, Calzolari Francescopiero, Fuzzi Sandro, Decesari Stefano, Facchini Maria-Cristina, Vuillermoz Elisa, Verza Gian Pietro
Laboratoire de Météorologie Physique, Observatoire de Physique du Globe de Clermont-Ferrand, Université Blaise Pascal, 24 avenue des Landais, 63177 Aubière, France.
Proc Natl Acad Sci U S A. 2008 Oct 14;105(41):15666-71. doi: 10.1073/pnas.0801355105. Epub 2008 Oct 13.
Rising air pollution levels in South Asia will have worldwide environmental consequences. Transport of pollutants from the densely populated regions of India, Pakistan, China, and Nepal to the Himalayas may lead to substantial radiative forcing in South Asia with potential effects on the monsoon circulation and, hence, on regional climate and hydrological cycles, as well as to dramatic impacts on glacier retreat. An improved description of particulate sources is needed to constrain the simulation of future regional climate changes. Here, the first evidence of very frequent new particle formation events occurring up to high altitudes is presented. A 16-month record of aerosol size distribution from the Nepal Climate Observatory at Pyramid (Nepal, 5,079 m above sea level), the highest atmospheric research station, is shown. Aerosol concentrations are driven by intense ultrafine particle events occurring on >35% of the days at the interface between clean tropospheric air and the more polluted air rising from the valleys. During a pilot study, we observed a significant increase of ion cluster concentrations with the onset of new particle formation events. The ion clusters rapidly grew to a 10-nm size within a few hours, confirming, thus, that in situ nucleation takes place up to high altitudes. The initiation of the new particle events coincides with the shift from free tropospheric downslope winds to thermal upslope winds from the valley in the morning hours. The new particle formation events represent a very significant additional source of particles possibly injected into the free troposphere by thermal winds.
南亚地区不断上升的空气污染水平将产生全球性的环境后果。污染物从印度、巴基斯坦、中国和尼泊尔人口密集地区传输至喜马拉雅山脉，可能会在南亚地区导致显著的辐射强迫，对季风环流产生潜在影响，进而影响区域气候和水文循环，同时对冰川消退产生巨大影响。需要更准确地描述颗粒物来源，以限制对未来区域气候变化的模拟。在此，首次呈现了在高海拔地区频繁出现新粒子形成事件的证据。展示了位于海拔5079米的尼泊尔金字塔气候观测站（尼泊尔）这一最高大气研究站的16个月气溶胶粒径分布记录。气溶胶浓度受清洁对流层空气与从山谷上升的污染程度更高的空气界面处超35%的日子里发生的强烈超细粒子事件驱动。在一项初步研究中，我们观察到随着新粒子形成事件的开始，离子团簇浓度显著增加。离子团簇在数小时内迅速增长至10纳米大小，从而证实了在高海拔地区会发生原位成核。新粒子事件的开始与早晨时段从自由对流层下坡风转变为来自山谷的热上坡风同时发生。新粒子形成事件代表了一个非常重要的额外粒子源，可能会被热风吹入自由对流层。
