[摘要] Continuous measurements of concentrations of reactive gases, radiation, andmeteorological parameters are carried out at the Meteorological ObservatoryHohenpeissenberg (MOHp) as part of the Global Atmosphere Watch (GAW)Program. NO, NO
2, O
3 and J
NO2 data from a four-year period(March 1999-December 2002) are evaluated for consistency withphotochemical steady state (PSS, Φ=1) conditions. The extentof deviation from PSS reveals a strong dependence on wind direction at thestation. Median values of Φ in the south sector are in the range of2.5-5.7 and show a high variability. In contrast, values for the otherdirections show a relatively low variability around a median level of 2.When taking into account peroxy radical concentrations (Φ
ext=1)PSS was reached in 13-32% of all cases for the years 1999-2002.
The differences in wind sectors can be explained by local effects. It isshown that the height of the sample inlet line, its distance to the forestand the surrounding topography has a strong impact on both the absolute andrelative deviations from PSS. Global irradiance and thus, photolysis ofNO2 is reduced within the dense forest. Since the reaction of NO withO3 is still proceeding under these conditions, increased NO2/NOratios are produced locally in air which is transported through the forestand advected to the MOHp site.Estimates of the peroxy radical concentration (RO2) inferred from PSSare compared with peroxy radical measurements made at the site in June 2000during a three-week campaign. The PSS derived RO2 levels were higherthan corresponding measured levels by at least a factor of 2-3. Thisanalysis was made for a wind sector with minimal local effects on PSS. Thusthe corresponding Φ median of 2 can be regarded as an upper limit fora deviation from PSS due to chemical reactions, i.e. by peroxy radicals andpossible other oxidants converting additional NO to NO2.
