Seasonal dependence of peroxy radical concentrations at a Northern hemisphere marine boundary layer site during summer and winter: evidence for radical activity in winter

摘要

Peroxy radicals (HO+Σ RO) were measured at theWeybourne Atmospheric Observatory (52° N, 1° E), Norfolkusing a PEroxy Radical Chemical Amplifier (PERCA) during the winterand summer of 2002. The peroxy radical diurnal cycles showed amarked difference between the winter and summer campaigns withmaximum concentrations of 12 pptv at midday in the summer andmaximum concentrations as high as 30 pptv (10 min averages) inwinter at night. The corresponding nighttime peroxy radicalconcentrations were not as high in summer (3 pptv). The peroxyradical concentration shows a distinct anti-correlation withincreasing NO during the daylight hours. At night, peroxyradicals increase with increasing NO indicative of the role ofNO chemistry. The average diurnal cycles for net ozoneproduction, N(O) show a large variability in ozone production,P(O), and a large ozone loss, L(O) in summer relative towinter. For a daylight average, net ozone production in summer washigher than winter (1.51±0.5 ppbv h and 1.11±0.47 ppbv h, respectively). The variability in NO concentrationhas a much larger effect on N(O) than the peroxy radicalconcentrations. Photostationary state (PSS) calculations show anNO lifetime of 5 min in summer and 21 minutes in thewinter, implying that steady-state NO-NO ratios are not alwaysattained during the winter months. The results show an active peroxyradical chemistry at night and that significant oxidant levels aresustained in winter. The net effect of this with respect toproduction of ozone in winter is unclear owing to the breakdown inthe photostationary state.