Abstract: High humidity and fog water can affect the measurement results of atmospheric pollutants, or even damages the instruments. Therefore, it was necessary to dehumidify the sample air with specific drying techniques when sampling. This study tested and compared the dehumidification effectiveness and the influencing factors of four common drying devices, i.e., cyclone cutter, heating belt, Nafion drying tube, and silicone drying tube. The results showed that the cyclone cutter could effectively remove liquid water and it was suitable trace gases and fine particulate matters. The heating belt quickly reduced the relative humidity of the sample air; however, the relatively humidity exhibited large fluctuation. The average dehumidification efficiency was about 20%~40%. The heating belt was mainly suitable for the thermally stable pollutants. The dehumidification efficiency of Nafion drying tube was usually less than 20%, but it was suitable for all kinds of trace gases and particulate matters. The silica gel drying tube could quickly dry the sample air with stable and high efficiency of about 50% and it was mainly suitable for particulate matters. The use of the above drying techniques would cause a loss of trace gases in certain degree. Among them, the loss caused by heating was highest, about 10%. The loss caused by cyclone cutters and Nafion drying tubes was no more than 10% and even less than 5%. These drying devices had different applicability, advantages, and disadvantages, so it was necessary to take account into the measured component.

Key words: drying technology, dehumidifying device, dehumidification efficiency, loss, atmospheric sampling