The Formation of Organic Compounds and Subsequent Emissions from Ventilation Filters

The objective of the study was to investigate the quality and quantity of emissions from used supply air filters by chemical and sensory methods. The effects of temperature, relative humidity (RH), and ozone on the pollutant emissions were examined. In addition, the contribution of diesel soot to the removal of ozone on filters was studied. The formation of organic emissions was investigated with laboratory and field tests. The sorption capacity of the filter dust was poor in tests made with model compounds at constant conditions. The specific surface area of the dust was also found to be low, which supports the results of the tests. Peak emissions of the model compounds and aromatic hydrocarbons were observed when RH was suddenly increased. In the thermodesorption tests of the filter dust, the compounds emitted included aldehydes, aliphatic and aromatic hydrocarbons, carboxylic acids, ketones, nitrogen-containing organics, and terpenes. Some emissions occurred already at room temperature, but the emissions increased substantially when temperature exceeded 100°C. Among the compounds emitted, aldehydes and carboxylic acids have low odor threshold values and they probably contribute to the perceived stuffy odor originated from the used filters. The supply air filters removed a fraction of ozone (O3). No removal of O3 was observed in clean pre-filters; however, some O3 was removed in unused fine filters. Dust which had accumulated on the filters increased the removal. The removal of O3 was highest at the start of exposure but then reached an almost steady state value within a few hours, typically 5-10% of the maximum removal. Ozone was removed effectively on sooty filters with simultaneous production of formaldehyde. The formation of acetaldehyde and some longer aldehydes was also observed during O3 exposure. With high RH of air, the removal of O3 increased on the filters. The pre-filter was the main odor source in air handling units. However, a sudden increase in the RH increased the odor emissions mainly from the fine filter. The effect of the elevated air humidity was again temporary and the intensity of the odor decreased to the initial value within 30 to 60 minutes. The sorption phenomenon is negligible at constant conditions in air handling unit. The formation of odorous compounds probably occurs mainly by oxidative processes. The chemical analyses suggest that aldehydes especially contribute to odor emission. The effect of RH on the emissions is short-term but it might lead to odor emissions when the weather changes. Removal of the O3 on ventilation filters is beneficial, since O3 has toxic effects. However, this benefit is at least partially lost due to the reactive and potentially harmful oxidation products formed in the reactions. Universal Decimal Classification: 628.8, 62-784.4, 697.942, 547-3, 628.511. 1 National Library of Medicine Classification: WA 754, WA 770 CAB Thesaurus: air quality; air pollution; air pollutants; buildings; ventilation; air filters; odours; dust; ozone; organic compounds; volatile compounds; temperature; relative humidity; sorption; desorption; oxidation; aldehydes; carboxylic acids