| Popis: |
As a consequence of increased insulation levels, the growth of algae on facades has developed into a serious aesthetic problem over the past decade. Manufacturers of facade and coating materials are looking for strategies to avoid or at least delay the establishment of biofilms. Efficient product development, however, is complicated by the necessity of time-consuming free-weathering tests and a lack of objective measures to quantify the growth. In a two-year study the potential of pulse-amplitude modulation (PAM) fluorometry was tested for the quantification of algal growth on free-weathered specimens below the visual threshold. By using an imaging PAM in combination with a scanning device, surface colonization by algae was repeatedly visualized and analysed in detail. It was demonstrated that in the case of water saturation the resistance of a specific paint against algal growth can be quantified with sufficient accuracy by measuring the fluorescence yield after dark adaptation. The representative growth pattern identified, however, is not characterized by a linear accumulation of algal colonies but by a long phase of fluctuating biomass at a low level, followed by a steep increase. Only if the fluorescence yield rises significantly above the basic value does the specimen simultaneously show green discoloration. The duration of free-weathering tests, therefore, cannot be significantly shortened by using the more sensitive diagnostic tool. |
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