Impacts on surface ozone by black carbon and boundary layer interaction in Nanjing,China

【摘要】：Black carbon(BC) is an important solar-radiation absorbing aerosol in atmosphere.The impacts of BC on surface ozone via influencing the photolysis rates have been found in previous studies.The BC-boundary layer(BL) interactions also influence the surface ozone.With simulation conducted by the online model system(WRF-Chem),changes of surface ozone caused by BC-BL interactions are demonstrated in Nanjing city in this study.Because of the absorption of incident solar radiation induced by BC,the air above BL was heated and then BL development was depressed.The weakened turbulence entrained less ozone from ozone-rich air above BL down to surface.While,with the BL depression,more ozone precursors(e.g.NO_2) were confined in lower BL which made the chemical process supply more ozone at the ground level before noon.As a result,surface ozone reduced before noon with the maximum reduction of 16.4 ppb,suggesting that the vertical mixing process played the most import role in influencing the surface ozone.In the afternoon,since the delay of BL development,the ozone is not mixed well in vertical and larger O_3-gradient existed at the top of BL.High concentration of ozone aloft can be entrained down to the surface offsetting the surface ozone reduction.By implementing the ozone tagging method into WRF-Chem,we found that ozone from Jiangsu(JS),Anhui(AH) and outside the model domain(O_3-INFLOW) decreased by about 2-4.5 ppb through BC-BL interactions.On the contrary,since the delayed development of BL,more ozone contribution from North China Plain(NCP)(5.6-11.2 ppb) in/above upper BL was entrained down and enhanced surface ozone in Nanjing in the afternoon.