Urban air pollution has been a global challenge world-wide. While urban vegetation or forest modelling can be useful in reducing the toxicities of the atmospheric gases by their absorption, the surge in gaseous pollutants negatively affects plant growth, thereby altering photosynthetic efficiency and harvest index. The present review analyses our current understanding of the toxic and beneficial effects of atmospheric nitrogen oxides (NOx), hydrogen sulphide (H2S) and carbon monoxide (CO) on plant growth and metabolism. The atmospheric levels of these gases vary considerably due to urbanization, automobile emission, volcanic eruptions, agricultural practices and other anthropological activities. These gaseous pollutants prevalent in the atmosphere are known for their dual action (toxic or beneficiary) on plant growth, development and metabolism. NO seems to exert a specialized impact by upregulating nitrogen metabolism and reducing tropospheric ozone. High H2S emission in specific areas of geothermal plants, fumarolic soils and wetlands can be a limitation to air quality control. Certain shortcomings associated with the designing of field experiments, sensitivity of detection methods and simulation development are yet to be overcome to analyze the precise levels of NO, H2S and CO in the rhizosphere of diverse agro-climatic regions. Several laboratory-based investigations have been undertaken to assess the roles of atmospheric gases, namely NOx, CO, H2S, and particulate matter (PM). However, in order to enable natural and sustainable mitigation, it is essential to increase the number of field experiments in order to identify the pollutant-tolerant plants and study their interactive impact on plant growth and agriculture.

Mt. Everest (Qomolangma or Sagarmatha), the highest mount on Earth and located in the central Himalayas between China and Nepal, is characterized by highly concentrated glaciers and diverse landscapes, and is considered to be one of the most sensitive area to climate change. In this paper, we comprehensively synthesized the climate and environmental changes in the Mt. Everest region, including changes in air temperature, precipitation, glaciers and glacial lakes, atmospheric environment, river and lake water quality, and vegetation phenology. Historical temperature reconstruction from ice cores and tree rings revealed the distinct features of 20th century warming in the Mt. Everest region. Meteorological observations further proved that the Mt. Everest region has been experiencing significant warming (approximately 0.33 degrees C/decade) but relatively stable precipitation during 1961-2018 AD. Projected results (during 2006-2099 AD) under different representative concentration pathway scenarios showed a general warming trend in the region, with larger warming occurring in winter than in summer. Meanwhile, the precipitation projections varied spatially with no significant trends over the region. Intensive glacier shrinkage was characterized by decreasing glacier areas, while glacier-fed river runoff increased. Glacial lakes expanded with increasing glacial lake areas and numbers. These findings indicated a clear regional hydrological response to climate warming. Owing to the remote location of Mt. Everest, the present atmospheric environment remained relatively clean; however, long-range transport of atmospheric pollutants from South Asia and West Asia may have substantially influenced the Mt. Everest region, resulting in increasing concentrations of pollutants since the Industrial Revolution. Anthropogenic activities have been shown to influence river and lake water quality in this remote region, especially in the downstream. The end of the vegetation growing season advanced in the northern slope and did not change in southern slope region of the Mt. Everest, and there was no significant change in start date of the growing season in the region. This review will enhance our understanding of climate and environmental changes in the Mt. Everest region under global warming.

The Tibetan Plateau is the largest high altitude landform on Earth, with an area of over 2.5x10(6) km(2) and an average elevation of similar to 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 1950s, 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 climate-chemistry 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 degrees 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 degrees 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 average 20% 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 hexabromocyclodo-decanes 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.