Vertical Distribution Of Asian Dust In Springtime And Its Impacts On Ozone Over East Aisa

Mineral dust,as the largest contributor of aerosols in the global atmosphere,plays an important role in the whole earth system.Dust aerosols can influence the energy budget of the earth system directly by scattering and absorbing radiation,and indirectly by acting as cloud condensation nuclei?CCN?and ice nuclei?IN?.Asian dust from the Taklimakan Desert and the Gobi Desert is the second largest dust source on the earth.Asian dust aerosols can be raised up above the planetary boundary layer by cold fronts in spring,and then transported thousands of kilometers by the westerlies.Along the transport way,the vertical distribution of Asian dust may change,which not only impacts transport and deposition of dust itself,but also influences climate.Meanwhile,dust aerosols provide surfaces and alkalinity for potential reactions with air pollutants,many of which are acids.Those reactions can then modify physicochemical properties of dust particles,thereby changing the capability of dust particles as potential CCN and IN.Therefore,there is clearly a need for a better understanding of the vertical distribution of Asian dust in spring and its interactions with air pollutants.This study integrated multiple data sources,including satellite observations,ground monitoring observations,and meteorology reanalysis data to reveal key features associated with vertical distribution of Asian dust in spring and to quantify its impacts on surface ozone.First,CALIOP retrievals of dust extinction profiles were used to analyze vertical distribution of Asian dust over the source region,interannual variations of such distribution,and transport factors.Then,dust days and non-dust days were selected to investigate Asian dust impacts on surface ozone,based on the distribution of the coarse-mode particulate matter mass concentrations(PM_coarse)from the Ministry of Ecology and Environment,and then paired based on similar temperature?T?and relative humidity?RH?from ERA reanalysis data so as to minimize the effect of different meteorological conditions on the ozone difference between a dust day and its reference non-dust day.Lastly,quantitative statistics of surface ozone changes by dust events over northern China during spring 2015-2017 were derived and the factors affecting the magnitude of the ozone changes were analyzed.The results show that:?1?Taklimakan dust above 4 km is more related to dust transport in the upper dust layer?4-10 km?over downwind regions.Asian dust in the lower dust layer?0-4 km?is mixed with anthropogenic aerosols over East Asia during the transport in springtime.?2?There is significant interannual variation in the vertical distribution of dust extinction characteristics over the Taklimakan Desert?TD?,where seasonal and monthly dust extinction at 1-4 km is almost the same as that of dust AOD?R>0.99?but different from that at 4-6 km?R?0.42?.?3?The majority of the dust days shows lower surface O₃ concentrations compared to non-dust days both temporally and spatially over TD,the Gobi Desert?GD?and North China?NC?,with ozone reduction of-24.6%?-4.8% during spring 2015.In spite of higher or similar levels of primary pollutants,surface ozone concentrations are still lower during dust days over the three regions,supporting the mechanism of dust direct uptake of O₃.?5?During Asian dust events,more dust would lead to more ozone reductions at the surface,but the relationship is not linear and confounded by the complex effects of meteorological factors.