Peroxy radical chemistry and the control of ozone photochemistry at Mace Head, Ireland during the summer of 2002

[摘要] Peroxy radical (HO₂+ΣRO₂) measurements, using thePEroxy Radical Chemical Amplification (PERCA) technique at the NorthAtlantic Marine Boundary Layer EXperiment (NAMBLEX) at Mace Head insummer 2002, are presented and put into the context of marine,boundary-layer chemistry. A suite of other chemical parameters (NO,NO₂, NO₃, CO, CH₄, O₃, VOCs, peroxides),photolysis frequencies and meteorological measurements, are used topresent a detailed analysis of the role of peroxy radicals intropospheric oxidation cycles and ozone formation. Under the rangeof conditions encountered the peroxy radical daily maxima variedfrom 10 to 40 pptv. The diurnal cycles showed an asymmetric shapetypically shifted to the afternoon. Using a box model based on themaster chemical mechanism the average model measurement agreementwas 2.5 across the campaign. The addition of halogen oxides to themodel increases the level of model/measurement agreement, apparentlyby respeciation of HO_x. A good correlation exists betweenj(HCHO).[HCHO] and the peroxy radicals indicative of theimportance of HCHO in the remote atmosphere as a HO_x source,particularly in the afternoon. The peroxy radicals showed a strongdependence on [NO₂] with a break point at 0.1 ppbv, where theradicals increased concomitantly with the reactive VOC loading, thisis a lower value than seen at representative urban campaigns.TheHO₂/(HO₂+ΣRO₂) ratios are dependent on[NO_x] ranging between 0.2 and 0.6, with the ratio increasinglinearly with NO_x. Significant night-time levels of peroxyradicals were measured up to 25 pptv. The contribution ofozone-alkenes and NO₃-alkene chemistry to night-time peroxyradical production was shown to be on average 59 and 41%. Thecampaign mean net ozone production rate was 0.11±0.3 ppbvh^-1. The ozone production rate was strongly dependent on [NO]having linear sensitivity (dln(P(O₃))/dln(NO)=1.0). Theresults imply that the N(O₃) (the in-situ netphotochemical rate of ozone production/destruction) will be stronglysensitive in the marine boundary layer to small changes in [NO]which has ramifications for changing NO_x loadings in theEuropean continental boundary layer.

[学科分类] 大气科学