Measurement of airborne algal mortality rates due to heat shock treatment

• Published in: Building and environment Vol. 183; p. 107123
• Main Authors: Nakajima, Makiko, Masueda, Daisuke, Hokoi, Shuichi, Miyake, Chikahiro, Wada, Shinya, Takada, Satoru
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.10.2020; Elsevier BV
• Subjects: Airborne algae; Airborne sensing; Algae; Algal soiling; Chlorophyll; Chlorophyll fluorescence; Drought resistance; Fluorescence; Heat resistance; Heat shock; Heat treatment; Lichens; Moisture content; Mortality; Survival; Temperature; Temperature and humidity; Thermal resistance; Water content; Airborne algae; Chlorophyll fluorescence; Algal soiling; Temperature and humidity; Heat shock
• ISSN: 0360-1323; 1873-684X
• DOI: 10.1016/j.buildenv.2020.107123

Green and/or black soiling on building facades worldwide is caused by airborne algae, which has strong drought tolerance and grows in the atmosphere. Poikilohydric plants such as algae and lichens have high heat resistance under dry conditions and high thermo-sensitivity under wet conditions. However, there have been no studies of heat shock treatments against airborne algae adhering to surfaces. This study investigated the relationship between heat shock conditions (treatment temperature and duration and the water content of algae) and algal mortality. Algae collected from the exterior wall of a building were heat-treated in a laboratory, and their chlorophyll fluorescence intensity was measured. The following results were obtained: (a) higher treatment temperature and longer treatment time increased the rate of algal death, (b) the survival rate of heat-treated dry algae was higher than that of wet algae and recovered after the treatment, and (c) the effects of continuous and intermittent heat shock were similar, and algal mortality increased with the total treatment time. It was concluded that the airborne algae died after heat shock treatment at 35 °C for 24 h and at 40 °C after 6 h under wet conditions. Algae from an exterior concrete wall were heat-treated in a wet condition, and algal death was confirmed by the decrease in surface L* values and a color change from green to yellow. •Airborne algal death after heat shock evaluated by chlorophyll fluorescence.•Higher temperature and longer time increased the algal mortality rate.•Survivability of dry algae was higher than wet and recovered after heat shock.•Algal mortality increased with the total treatment time.•It was confirmed that algae on exterior wall died by heat shock due to color change.