Comparisons of observed and modeled OH and HO 2 concentrations during the ambient measurement period of the HO x Comp field campaign

摘要: Abstract. A photochemical box model constrained by ancillary observations was used to simulate OH and HO2 concentrations for three days of ambient during the HOxComp field campaign held in Julich, Germany July 2005. Daytime levels observed four instruments were fairly well reproduced within 33% a base run (Regional Atmospheric Chemistry Mechanism with updated isoprene chemistry adapted from Master Chemical ver. 3.1) high R2 values (0.72–0.97) over range (0.3–2 ppb) NO (0.1–10 mixing ratios. HO2(*) levels, reconstructed results taking into account sensitivity toward speciated RO2 (organic peroxy) radicals, as recently reported one participating measurement mode, 93% higher than made single instrument. This also indicates an overprediction recycling. Together good model-measurement agreement OH, it implies missing source model. Modeled could only be matched addition strong unknown loss process that recycles at yield. Adding model, instead, proposed isomerization mechanism peroxy radicals (Peeters Muller, 2010) increased 28% 13% on average. Although these still 4% instruments, larger overestimations (42–70%) occurred respect other instruments. The overestimation diminished when reactive alkanes (HC8) solely introduced explain fraction reactivity. Moreover, became even case. These analyses imply rates are not readily supported ensemble radical observations. One characterized low (∼0.5 reactivity explained species, especially before noon. For this selected period, opposed general behavior, tended underestimate HO2(*). We found tendency is associated NOx concentrations, suggesting some production or regeneration processes under conditions being overlooked; might require revision ozone regimes.