Atmospheric Particulate Characterization,Concentration,and Size Distribution Over The Ngari Region Of The Tibetan Plateau

Known as“the roof of the world,”“the Asian Water Tower,”and“the Third Pole,”the Tibetan Plateau has a crucial role in climate change in Asia and even the world.Due to the significant impact of global warming,regional climate research has become a hot topic in scientific research.Although the Tibetan Plateau has been less affected by human activities,temperature warming is still happening on the plateau.The reason is not only greenhouse gases but also atmospheric particulates.As an ecologically sensitive region,the rise of atmospheric particulates can easily affect atmospheric circulation as well as ice and snow ablation over the Tibetan Plateau.Therefore,understanding the dynamics of the atmospheric environs on the Tibetan Plateau is crucial to providing references for the formulation of atmospheric environmental protection guidelines and policies in China and even around the world.In addition,brown clouds generated in the South Asian atmosphere will carry significant amounts of industrial pollution and biomass burning emissions from the Indo-Gangetic Plain to the inner regions of the plateau,seriously compromising the region’s ecological environment.In this context,a deep understanding of the remote sources and transport mechanisms of atmospheric particles in the plateau region is necessary.This article used ground monitoring data,satellite data,and reanalysis data to evaluate the concentration level,particle size distribution characteristics,and potential source areas of atmospheric particulates at Ngari Station,whilst also analysing the differential effects of an atmospheric brown cloud phenomenon on particulate matter over the Tibetan Plateau.During the study period,the PM₁₀,PM_2.5 and PM₁ concentrations at Ngari Station were low at 10.51μg·m^-3,4.05μg·m^-3 and 2.47μg·m^-3,respectively.Concentrations of PM₁₀ and PM_2.5 were lower than the primary standards of PM₁₀(40μg·m^-3)and PM_2.5(15μg·m^-3)annual mean particulate matter concentration（GB 3095—2012）and WHO（World Health Organisation）annual target value,indicating that Ngari Station has clean atmospheric properties.For example,the daily average concentration of0.25～32μm particles at Ngari Station is 26.91 per cm³,whereas the daily average surface area concentration of particulate matter is 17.88μm^2·cm^-3,and the daily average volume concentration of particulate matter is 15.41μm³·cm^-3.The mass concentration of atmospheric particulate matter at Ngari Station shows apparent seasonal variations,significantly higher in winter and pre-monsoon than in post-monsoon and monsoon seasons.In winter and pre-monsoon seasons,the temperature and height of the atmospheric boundary layer are low,while the atmospheric pollutant volume capacity is small.In the winter and pre-monsoon seasons,vegetation coverage is very low,and floating dust is frequent.Therefore,particulate matter concentration is higher during the winter and pre-monsoon seasons than in other seasons.During the monsoon season,wind speed is low and particle carrying capacity is weak.In addition,there is more precipitation and the humidity is high,resulting in high vegetation coverage and the lowest atmospheric particle mass concentration.A Spearman correlation analysis of the mass concentration of particulate matter and meteorological factors at Ngari Station showed that,except for wind speed,temperature,humidity,and boundary layer height were negatively correlated with mass concentration.Wind rose chart indicators show that the main direction of atmospheric particulates is the southwest.The potential source areas of atmospheric particulate matter at Qomolangma Station and Ngari Station are in the south of the Himalayan Mountains.At the same time,the potential source areas of atmospheric particulates at Ngari Station are mostly in the south of Kashmir and northern India,whereas the potential source areas of atmospheric particulate matter at Qomolangma Station are mostly in Nepal and its neighbouring areas.In 2019,an analysis of the continued excessive PM_2.5 levels at the Qomolangma Station from May 8 to May 11 showed that a high pollution event was caused by biomass burning on the Indo-Gangetic Plain.Due to differences in air mass sources,wind speed,and direction during the pollution period,air pollution from the Indo-Gangetic Plain affected Ngari Station and Qomolangma Station to different degrees.From May 8 to May 11,2019,the particulate matter concentration at Qomolangma Station was much higher than at Ngari Station.