Simulation And Quantification Of The Contribution Of Local Pollution Sources To Air Pollutants In Lhasa City

The remote location of the Tibetan Plateau,with little impact from human activities,has long been considered a world background station.Because of its sensitivity to climate change,it is considered an important response region for the northern hemisphere and even global climate.Therefore it is important to study the pollution status of this region.Although cities on the Tibetan Plateau are relatively clean compared to those in eastern China,surface observations in recent decades have shown that concentrations of air pollutants(CO,NO₂,SO₂,and PM_2.5)at urban sites on the Tibetan Plateau are comparable（on the order of magnitude）to those in areas with high anthropogenic emissions（e.g.,eastern China）.The contribution of local emissions（e.g.,biomass burning,religious activities）to air pollutants in the Tibetan Plateau cannot be ignored.A proper understanding of the impact of anthropogenic emissions on atmospheric chemistry and climate is crucial.In this study,the WRF-Chem model and observational dataset were used to assess the concentrations and sources of air pollutants in Lhasa city.The results show that the WRF-Chem model using standard emission inventories underestimates the surface concentrations of CO,SO₂,and PM_2.5in Lhasa by 59%,92%,and 79%,respectively.Possible reasons for the model underestimation of air pollutants on the Tibetan Plateau are（a）inadequate emission inventories on the Tibetan Plateau,（b）underestimation of long-range transport of pollutants from South Asia and eastern China,and（c）coarse spatial resolution of the model.Increasing the model resolution is beneficial to improve the simulation of NO₂,but only improves 6%and 8%for CO and SO₂.The sensitivity simulation experiments show that the long-range transport of air pollutants from eastern China and India contributes less than 10%to Lhasa.Insufficient emissions are considered to be the main reason why the model underestimates air pollutants in Lhasa.The results suggest that CO,SO₂,and PM_2.5 emissions in Lhasa may be underestimated by 85%,93%,and 88%,respectively,in August 2016.This study highlights the importance of local anthropogenic emissions on urban air quality in Lhasa on the Tibetan Plateau.