The　transformation　of　atmospheric　mercury　species　and　its　influencing　factors　are　a　prominent　subject　in　mercury　research.　However,limited　studies　have　examined　the　impacct　of　photochemical　processes　on　reactive　gaseous　mercury(RGM),particularly　in　the　lower　troposphere.　This　study　developed　a　dual-channel　atmospheric　mercury　monitoring　system　by　combining　a　two-stage　cation　exchange　membrane(CEM)sampler　with　a　Tekran　2537　analyzer.　Using　this　method,we　investigated　the　atmospheric　gaseous　mercury　concentration　in　Xiamen,a　coastal　city,from　May　to　September　2023.　Throughout　the　observation　period,the　average　concentrations　of　gaseous　elemental　mercury(GEM)and　reactive　gaseous　mercury(RGM)in　Xiamen　were(2.10±0.74)ng.m-3　and(218±131)pg.m-3,respectively.　RGM　concentrations　in　Xiamen　displayed　a　seasonal　variation　with　the　highest　levels　in　July,followed　by　August,June,September,and　May.　This　pattern　can　be　attributed　to　the　elevated　temperature　and　solar　radiation　in　summer,which　promote　the　conversion　of　GEM　to　RGM,while　the　high　temperature　hindered　the　distribution　of　RGM　from　the　gas　phase　to　the　particulate　phase.　Notably,higher　concentrations　of　GEM　were　observed　from　July　to　August,potentially　due　to　the　influence　of　typhoons.　In　terms　of　diurnal　patterns,both　GEM　and　RGM　concentrations　in　Xiamen　reached　their　peaks　in　the　early　morning　and　decreased　to　a　minimum　in　the　evening,　likely　influenced　by　changes　in　boundary　layer　height.　High　concentrations　of　RGM　were　frequently　detected　during　the　study,with　some　lasting　for　several　days.　A　chemical　box　model　F0AM　simulation　showed　that　during　high　RGM　concentration　events,the　influence　of　local　or　transported　photochemical　oxidations　on　RGM　was　more　significant　than　that　of　atmospheric　transport　and　anthropogenic　emissions.　©　2024　Science　Press.　All　rights　reserved.