Bekö G, Halás O, Clausen G, Weschler C J
International Centre for Indoor Environment and Energy, Technical University of Denmark, Lyngby, Denmark.
Indoor Air. 2006 Feb;16(1):56-64. doi: 10.1111/j.1600-0668.2005.00401.x.
Used filters can be a strong sensory pollutant source. Oxidation processes, especially those initiated by ozone, may contribute to the pollutants emitted from such filters. In the present study, ozone was added to the airstream passing through used ventilation filters. Two flow rates were examined. While the upstream ozone concentration was approximately 75 ppb, the concentrations downstream of the filter were initially 35-50% lower. However, within an hour downstream concentrations were only 5-10% lower than those upstream. These filter samples were then placed for 48 h in nitrogen, ambient air containing less than 5 ppb ozone, or ambient air at an elevated temperature. This resulted in partial regeneration of the ozone removal capability of the filter. In analogous experiments, lower ozone removal occurred when the filter samples were first ventilated for 24 h with ozone-free air before making the measurements. Samples from a new filter removed <10% of the ozone in the airstream, and removal remained relatively constant over time. In companion studies, human subjects assessed the air passing through various used filter samples. In the initial evaluation each of the four filter samples, taken from the same filter and ventilated for 24 h, were assessed to be equivalent. The next evaluation was immediately after the samples had been kept for 24 h in either nitrogen, air, air at an elevated temperature or ozone. The nitrogen-treated filter was assessed to be best, while the ozone-treated filter was assessed to be the worst. The final evaluation occurred after ambient air had passed through the 'treated' filters for 2 h. All such ventilated filters were assessed to be more acceptable than immediately after the 24-h treatments; the ozonized and air-treated filters were the most polluting of the four. Practical Implications The present paper supports previous findings that loaded ventilation filters can be significant sources of sensory pollution. Replacing a loaded filter with a new filter temporarily removes this source of pollution. However, the present study does not provide an answer to how frequently changes are needed under different conditions. The results indicate that in cases of intermittent operation of ventilation systems, the airflow through the polluted filters should be restarted in sufficient time prior to occupancy to purge odorous pollutants that have accumulated on the filter surface. Removal of ozone upstream of the particle filters may further improve perceived air quality in the space downstream of the filter bank. Future efforts related to the development and application of low-polluting filtration systems are warranted.
用过的过滤器可能是一种强大的感官污染源。氧化过程，尤其是由臭氧引发的那些过程，可能会导致此类过滤器排放污染物。在本研究中，将臭氧添加到通过用过的通风过滤器的气流中。考察了两种流速。虽然上游臭氧浓度约为75 ppb，但过滤器下游的浓度最初要低35 - 50%。然而，在一小时内，下游浓度仅比上游低5 - 10%。然后将这些过滤器样品在氮气、臭氧含量低于5 ppb的环境空气中或高温环境空气中放置48小时。这导致过滤器的臭氧去除能力部分恢复。在类似实验中，在进行测量之前先用无臭氧空气对过滤器样品通风24小时，臭氧去除率较低。新过滤器的样品去除了气流中<10%的臭氧，并且去除率随时间保持相对稳定。在相关研究中，人类受试者对通过各种用过的过滤器样品的空气进行了评估。在初始评估中，取自同一过滤器并通风24小时的四个过滤器样品中的每一个都被评估为等效。下一次评估是在样品在氮气、空气、高温空气或臭氧中保存24小时之后立即进行。经氮气处理的过滤器被评估为最佳，而经臭氧处理的过滤器被评估为最差。最后一次评估是在环境空气通过“处理过的”过滤器2小时之后进行。所有此类通风后的过滤器被评估为比24小时处理后立即使用时更可接受；在这四个过滤器中，经臭氧处理和空气处理的过滤器污染最严重。实际意义 本文支持了之前的研究结果，即负载的通风过滤器可能是感官污染的重要来源。用新过滤器替换负载的过滤器可暂时消除这种污染源。然而，本研究并未回答在不同条件下需要多频繁地更换过滤器。结果表明，在通风系统间歇运行的情况下，应在入住前足够的时间重新启动通过污染过滤器的气流，以清除积聚在过滤器表面的有气味污染物。在颗粒过滤器上游去除臭氧可能会进一步改善过滤器组下游空间的空气质量感知。未来有必要在低污染过滤系统的开发和应用方面做出努力。
