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Karl Andre
,
Ralph Dlugi
, and
Gottfried Schnatz

Abstract

Light absorption by samples of atmospheric aerosol particles as a function of size was studied using the integrating sphere method. In addition, the optical properties of fog and cloud-water residues were determined. The samples were taken at two locations in West Germany: one fairly remote from pollution sources, the other near the industrial area of Frankfurt. The results show that particles <0.4 μm volume equivalent radius significantly alter the values of the absorption coefficient σA. The absorption index k of atmospheric aerosol particles, in general, cannot be considered a property of the sample material. The absorption of light by samples of large particles from background areas exposed to urban influences can be explained quantitatively by the presence of soot particles. The soot content of samples of large particles is ∼−10% of the total particle number. The number of soot particles in samples of giant particles is very small. Starting with the highest absorption of solar radiation the following sequence was found: non-activated particles, large particles, giant particles, cloud-and fog-droplet residues and, finally, rainwater residues.

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Maria G. Inclán
,
Jan Schween
, and
Ralph Dlugi

Abstract

The prognostic one-dimensional Forest–Land–Atmosphere Model (FLAME) has been further extended to simulate diurnal cycles of volatile organic compound (VOC) fluxes inside and above an idealized mixed forest mainly composed of oaks and pines. The tree height is 12 m and the leaf area index is 4. The canopy crown is divided into five layers of equal leaf area increment. The algorithms developed by Guenther et al. are applied to predict the monoterpene emission from leaves in each canopy layer. The value of photosynthetic active radiation (PAR) and foliage temperature (T leaf) required by these algorithms are provided by FLAME. The modeled PAR and T leaf are used for different leaf angle classes i from sun to shaded leaves within each layer j in the canopy.

In the present study the authors examine the VOC fluxes modeled at a reference level above the forest for two cases, A and B, for which the modeled canopy temperature T c reaches a maximum of approximately 21° and 31°C, respectively. It is supposed that VOC fluxes above the canopy are related to T c by a function of the form F(T c ) = F s exp[β c (T c T S )]. The authors intend to study the temperature exponent at canopy level β c by deriving best-fit slopes.

The resulting mean values of β c = 0.125 ± 0.002 K−1 for the morning VOC fluxes, and β c = 0.267 ± 0.004 K−1 for the afternoon, are larger than those used to calculate the emission on leaf scale from cuvette data (β 1 = 0.124 K−1 and β 2 = 0.09 K−1 for oaks and pines, respectively). A sensitivity study was carried out using the modeled mean values of T leaf and PAR in a canopy layer instead of the angle dependence to simulate measurements by an infrared radiation thermometer. The authors also tested the importance of the basal emission rate E s on the total VOC fluxes and β c above the canopy.

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