Abstract
AGI-30 impingers are widely applied for the efficient collection of bioaerosols. However, these glass vessels are not protected against solar radiation and changing ambient temperature during sampling, which may impair the sampling efficiency by too high or low temperatures of the sampling liquid leading to early proliferation of microorganisms or ice formation. In order to reduce such disadvantages, an impinger holder was developed and tested under laboratory and field conditions, which insulates and controls the temperature of the impinger and the sampling liquid by means of a Peltier element. The influence of various ambient temperatures and relative humidities on the temperatures of tempered and untempered impinger liquids such as mineral oil, peptone water, and phosphate-buffered saline (PBS) during sampling periods of 30 min was investigated and compared. The type of sampling liquid greatly influenced the amount of residual liquid after sampling and the temperature in both the tempered and untempered impingers depended on the type of sample liquid, ambient temperature, and humidity. Mineral oil showed the lowest losses, followed by PBS and peptone water. Tempering of the impingers had some influence on the amount of losses. Tempering also strongly influenced the number of culturable bacteria (colony-forming unit [CFU]) in the sampling liquids. In the tempered impingers, three times higher CFU/m3 were found than in the untempered impingers. A great advantage of tempering was that sampling at ambient temperatures as low as −5°C was possible. However, in spite of insulation and tempering the impinger to a fixed value, the variance was rather high due to varying ambient temperature and relative humidity, which always have a strong influence on condensation and evaporation and therefore on the amount of sample liquid and the resulting number of CFU. Nevertheless, the temperature-controlled AGI-30 impinger is a step forward to more stable results.
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