大气污染物跨境传输及其对青藏高原环境影响

The transboundary transport of air pollutants and their environmental impacts on Tibetan Plateau

青藏高原拥有独特的多圈层环境系统与生态类型,对我国乃至亚洲具有重要的生态安全屏障作用.在青藏高原开展污染物跨境传输的科学考察研究,既是地表多圈层相互作用研究的重要组成部分,也是支撑国家生态环境安全的战略需求.针对第二次青藏高原综合科学考察研究的'南亚通道'关键区,结合长期站点监测和短期强化观测,本文全面综述了青藏高原大气污染物时空分布、传输过程和机理,以及污染物对气候和生态系统影响方面的新认识.从历史趋势上看,青藏高原黑碳和汞等记录,自20世纪50年代以来呈现快速上升,反映了亚洲区域大气污染物排放的快速增多.从传输过程上看,跨越喜马拉雅山的高空环流以及局地的山谷风是大气污染物跨境传输的重要途径.大气气溶胶-雪冰辐射反馈效应对青藏高原的气候变化带来一定的影响,外源污染物对青藏高原生态系统的负面影响业已凸显.未来研究中,亟待精确量化跨境污染物的输送量和影响范围,预测未来情景下污染物排放与环境健康风险的变化趋势.

The Tibetan Plateau is the largest high altitude landform on Earth,with an area of over 2.5×106 km2 and an average elevation of^4000 m above sea level.With a unique multisphere environmental system,the Tibetan Plateau provides an important ecological sheltering function for China and other parts of Asia.The Tibetan Plateau is one of the world’s most pristine regions,benefiting from a sparse population with negligible local influence on its environment.However,it is surrounded by some of the most polluted areas in the world,such as South Asia,East Asia,and Southeast Asia.With the atmospheric circulation,such pollutants may impact the Tibetan Plateau through long-range transport.Clearly,the scientific research on the transboundary transport of pollutants is not only important for the understanding of multisphere interactions on the earth surface,but also could meet the national strategic needs for ecological and environmental protection.Long-term monitoring combined with short-term intensive observation campaigns,were used to comprehensively summarize the latest research progress regarding the spatial-temporal distribution and transport mechanism of air pollutants,as well as their climate and ecological impacts,which were achieved during the Second Tibetan Plateau Scientific Expedition.With respect of historical trends reconstructed from environmental archives,e.g.,glacial ice cores and lake sediments,the black carbon and heavy metals like mercury show a dramatic increase since 1950 s,which reflect the enhanced emission of air pollutants in Asia.On-line observation data and WRF-Chem modeling indicate that upper air circulation and local mountain-valley breeze system are the main drivers of trans Himalaya air pollution from South Asia.A regional climatechemistry model coupled with an aerosol-snow/ice feedback module was used to reveal the natural and anthropogenic light-absorbing aerosols’radiative effects over the Tibetan Plateau.Results indicated that the mineral dust both in the atmosphere and snow induced 0.1-0.5°C warming over the western Tibetan Plateau and Kunlun Mountains in spring.Meanwhile,dust aerosols caused snow water equivalent to decrease by 5-25 mm over the western TP,Himalayas and Pamir Mountains in winter and spring.The radiative effects of BC-in-snow induced surface temperature increased by 0.1-1.5°C and snow water equivalent decreased by 5-25 mm over the western Tibetan Plateau and Himalayas.According to the observations the black carbon and dust found in the snow and ice on the surfaces of glaciers were responsible for on average20%of the albedo reduction within the TP region.Those atmospherically transported pollutants also have obvious negative impacts on the ecosystem in Tibetan Plateau.For example,bioaccumulation of DDTs have been found in Tibetan terrestrial and aquatic food chains,and newly emerging compounds such as polyfluoroalkyl substances and hexabromocyclododecanes have been widely detected in wild fish species.Therefore,the corresponding ecological risks are of great concern.In the future,it is necessary to quantify the extent of atmospherically transported pollution and model the pollutant fate under the future environmental scenarios as well as establish environmental and health risk.