The Influence Of Aerosol Feedback On Secondary Atmospheric Circulations And Vertical Exchange In The Atmospheric Boundary Layer

Aerosols have scattering and absorption effetts on atmospheric radiation.Since the energy of the Earth's atmospheric system is almost entirely from solar radiation.Increase of aerosols due to human activities,which can affect the energy and radiation balance of the atmospheric system to a certain extent,which in turn altersweather or climate system,especially in heavily polluted areas by atmospheric particles.Because the weather or climate system is an intricate system in which various processes are interrelated,two-ways feedback between aerosols and weather/climate systems occurs.To assess the impact of aerosol feedback radiation and weather and climate conditions based on atmospheric dynamics,the present study conducted extensive modeling investigations with multiple model scenarios.We select a heavily polluted area in China during the period of super-conventional emission reduction and compares the WRF-Chem modeling results in the"aerosol feedback"and"non-feedback"configurations.The results reveal that the aerosol feedback increases the concentrations of O₃,PM_2.5,and SO₂ in the atmospheric boundary layer(ABL)but weaken the strength of some meteorological variables,such as air temperature,the downward short-wave radiation near the surface,the ABL height,and the wind speed.The feedback simulations also forced the wind direction to the right,and enhanced the ground pressure.The magnitude of feedback influence is mainly related to the leves of particulate matters(PM).Higher PM concentration tends to reinforce the feedback effect.The results also found thatthe stronger radiation would cause stronger feedback effect,but the influence from radiation on the feedback is weaker than that from PM_2.5.The reponse of air pollutants and meteorological factors to the aerosol feedback influence is different.Air pollutants subject to the aerosol feedback influences vary locally.This feedback mechanisim force the changes in the meteorological factors on a relatively large scale,which are associated with atmospheric advection,background atmospheric circulation,and spatial-temporal changes in these meteorological factors themselves.The atmospheric circulation system on different scales are interacted each other and are constrainted by atmospheric dynamics and thermodynamics.The atmospheric system as a whole constrints the interations among different meteorological factors.Because the meteorological factors perturbated by aerosol feedback are subject to change,this change would alter an atmospheric circulation system,such as the secondary circulation.Hence,one of the focus in this Ph D study was on the influence of aerosol feedback on secondary circulation.The secondary circulation plays an important role in the vertical exchange between the ABL and the free atmosphere,such as momentum,air temperature,humidity,and air pollutants.This exchange might provide an effective route for the vertical mixing of air pollutants and other matters.Vertical exchange of air pollutants between the ABL and free atmosphere has been a challenge in of the transfer of air pollutants within the ABL or between the ABL and the free atmosphere.In the case of presence of hillside terrain,we investigate the effect of secondary circulation evolution on the changes in PM_2.5 in the ABL and examine the aerosol feedback impact on the reinforcement of secondary circulation subject to heavy,medium,and light PM_2.5 pollution episodes in Beijing and its surroundings in China.The results reveal that the presence of secondary circulation helps promote the vertical exchange of air pollutants between the ABL and the free atmosphere,weakens the atmospheric transport and diffusion capacity,which is conducive to the formation of heavy air pollutions.Overall,aerosol feedback reduces the wind speeds in the ABL and reinforces the secondary circulation.In addition to heavy pollution episode,such the reinforment by the aerosol feedback can be also observed in a medium PM_2.5 pollution episode.The reinforcement of the secondary circulation in the ABL facilitates the atmospheric transport of air pollutants and atmospheric variables inform the ABL to the free atmosphere.These results fill our knowledge gaps in the understanding of how and to what extent the aerosol feedback could contribute to the change in secondary circulation,in addition to meteorological factors,and provide a new knowledge in the two-ways feedback mechanisms and its impact on air pollutants in the atmosphere.