Sulphite content of atmospheric aerosol particles.

The content of sulphite in atmospheric aerosol particles is investigated by filter and cascade impactor measurents. The role of atmosheric trace gases and meteorological conditions for the formation of sulphite in particles is discussed

Fog chemistry during EUMAC joint cases. Analysis of routine measurements in southern Germany and model calculations

The role of fog events for acid production and moist deposition in southern Germany during three EUMAC Joint Cases has been investigated by analysis of routine measurements and simulations with a one-dimensional fog-chemistry model. To identify the chemical and meteorological conditions, routine measurements by different institutions have been interpreted. The periods under consideration include a smog episode with low photooxidant concentrations during the 'Winter Case' in February 1982. The 'Wet Case' in spring 1986 represents a period with higher photooxidant concentrations. Conditions which are mostly characterized by low SO2 and oxidant concentrations and comparatively high pH-values in the fog are given during the 'SANA 1' case in autumn 1990. Fog mostly occurs as a subscale phenomenon, but sometimes it can also cover large areas and it can contribute significantly to moist deposition. The model results indicate that the liquid phase sulfate production in the fog layer may even e xceed the gas phase production during 24 hours within a layer of the same height occasionally. On the other hand, during the SANA 1 case the sulfate production in the fog was extremely low at night due to lack of oxidants and SO2. Depending on the dissipation time of the fog a remarkable effect on the photolysis rates is possible. Since a significant amount of particulate mass is lost by moist deposition during fog, it is evident that fog events can have a noticeable effect on some of the gas phase constituents which are easily soluble

On the relationship between the roughness length of a scalar quantity and the corresponding sublayer-Stanton number

Considering SHEPPARD'S effective diffusivity approach for the molecular-turbulent sublayer, the relationship between the roughness length of a scalar quantity, zp, and the corresponding sublayer-Stanton number, Bi, is re-formulated. This re-formulation leads to Bi(-1) = kappa(-1) ln (1 + zo/zp), where zo is the roughness length for momentum. Based on this equation, it is evident that (a) the relationship Bi(-1) = kappa(-1) ln (zo/zp) commonly used is a doubtful approximation for the interfacial sublayer, and (b) the sublayer-Stanton number is positive-definite even if zp >= zo > 0. This is in contrast to negative Bi(-1) values found in the literature. Moreover, it is shown that Bi(-1) values derived with SHEPPARD's approach are much smaller than those provided by the more adequate REICHARDT's approach

Determination and accuracy of VOC fluxes above a pine/oak forest at Castelporziano.

Concentrations of α-pinene, β-pinene and limonene were determined as two or three point profiles above the Mediterranean pine/oak forest at Castelporziano, Italy. Based on these, as well as on micrometecrological data, the fluxes of these compounds were estimated using the modified Bowen-ratio method and a log-profile fit. The accuracy of the calculated fluxes was estimated, resulting in errors around 50%, which were mainly produced by the relatively small concentration gradients observed. The dependence of emission fluxes on surface temperature was interpolated by three equations of the form F(T) = Fsexp(β·(T − TS)) for the three compounds. The three resulting temperature exponents β were significantly greater than the value for monoterpenes given by Guenther et al. (1993, J. Geophysical Research 18, 12,609–12,617). It is also greater than the corresponding value derived by Bertin et al. (1997, Atmospheric; Environment) from the isoprene model of Guenther et al. (1993, J. Geophysical Research 18, 12,609–12,617)

Intercomparison of different aethalometers with an absorption technique: Laboratory calibrations and field measurements.

The prototype of a new aethalometer was calibrated and tested in the laboratory by applying graphite, salt and iron oxide aerosol particles. It turned out that the response of the aethalometer was critical to the ratio of the mass of absorbing and non-absorbing materials. The aethalometer data from field measurements were compared with results gained by an optical absorption technique (Hanel's method). The correlations showed wide scattering, presumably due to different compositions of atmospheric particles. During field measurements the prototype was also compared with a commercial aethalometer of the 'Hansen-type'. The measured soot concentrations differed by about 50% on average. The results of the commercial aethalometer and the absorption technique agreed very well.The prototype of a new aethalometer was calibrated and tested in the laboratory by applying graphite, salt and iron oxide acrosol particles. It turned out that the response of the acthalometer was critical to the ratio of the mass of absorbing and non-absorbing materials. The aethalometer data from field measurements were compared with results gained by an optical absorption technique (Hanel's method). The correlations showed wide scattering, presumably due to different compositions of atmospheric particles. During field measurements the prototype was also compared with a commercial aethalometer of the 'Hansen-type'. The measured soot concentrations differed by about 50% on average. The results of the commercial aethalometer and the absorption technique agreed very well