Large-scale land-sea interactions extend ozone pollution duration in coastal cities along northern China

Land-sea atmosphere interaction(LSAI)is one of the important processes affecting ozone(O_(3))pollution in coastal areas.The effects of small-scale LSAIs like sea-land breezes have been widely studied.However,it is not fully clear how and to what extent the large-scale LSAIs affect O_(3) pollution.Here we explored an O_(3) episode to illuminate the role of large-scale LSAIs in O_(3) pollution over the BohaieYellow Seas and adjacent areas through observations and model simulations.The results show that the northern Bohai Sea's coastal region,influenced by the Mongolian High,initially experienced a typical unimodal diurnal O_(3) variation for three days,when O_(3) precursors from BeijingeTianjineHebei,Shandong,and Northeast China were transported to the BohaieYellow Seas.Photochemical reactions generated O_(3) within marine air masses,causing higher O_(3) levels over the seas than coastal regions.As the Mongolian High shifted eastward and expanded,southerly winds on its western edge transported O_(3)-rich marine air masses toward the coast,prolonging pollution for an additional three days and weakening diurnal variations.Subsequently,emissions from the Korean Peninsula and marine shipping significantly affected O_(3) levels in the northern Bohai Sea(10.7%and 13.7%,respectively).Notably,Shandong's emissions played a substantial role in both phases(27.5%and 26.1%,respectively).These findings underscore the substantial impact of large-scale LSAIs driven by the Mongolian High on O_(3) formation and pollution duration in coastal cities.This insight helps understand and manage O_(3) pollution in northern Bohai Sea cities and broadly applies to temperate coastal cities worldwide.