## 1 Introduction  
At a time of increasing public awareness, migration of urban dwellers to rural areas, spatial development of cities bringing residential areas closer to industrial facilities, and rapid economic growth the presence of noxious odors has often been reported to environmental law monitoring and enforcement agencies. Irrespective of their origin, malodorous compounds may lead to psychological discomfort or, in extreme cases, to pathological symptoms, including headaches, vomiting, diarrhea, upper airway and eye irritation, and even depression [1; 2]. Due to the growing social awareness of the effects of air quality on human health and well-being, these issues have also become the subject of extensive research both in Poland and around the world [3; 4; 5]. Of particular note are studies on deodorization methods and evaluation tools measuring the performance of odor treatment systemsinvolving chemical (thermal and catalytic oxidation, ozonation), physical (condensation, adsorption, absorption), and biological (biofiliters, biosrcubbers, other bioreactors) technologies [6; 7; 8]. However, the available literature mostly concerns industrial applications, with no data on the sorption of volatile compounds by the flat filtration/adsorption media used in respiratory protective devices. Workplaces where the maximum allowable concentrations (MAC) of harmful substances are exceeded necessitate the use of gas filters and combined filters; otherwise, filtering facepiece respirators (FFRs) are worn to adsorb offensive odors. In addition to polymeric filtration layers, FFRs feature an activated carbon layer to reduce the amount of chemical compounds entering the breathing zone. In standard air-purifying respiratory protective equipment, air contaminated with volatile compounds flows through the sorption bed during inhalation, with the sorption capacity of that medium depending on the environmental conditions, airflow rate, and textural parameters of the material. Activated carbons used in adsorbers must meet a number of criteria, such as large adsorption capacity with respect to selected volatile compounds, low airflow resistance, low bulk density, large total micropore volume (to hold large amounts of adsorbed gases and vapors), and especially good adsorption kinetics and dynamics [9; 10]. Standardized test conditions for investigating the adsorption properties of gas filters are specified in the standard EN 14387:2004+A1:2008. Studies on the effects of textural properties of activated carbons on their capacity to adsorb volatile chemicals have been widely reported in the Polish and international literature [11; 12; 13; 14]. Due to the rising air pollution prevention requirements, researchers seek increasingly effective solutions that would be at once economical and ecologically safe. As a result, there has been a growing interest in zeolites-minerals which exhibit molecular-sieve, sorptive, and ion-exchange properties. Due to their widespread availability, low prices, and a suitable skeletal structure, they may be applied in broadly defined environmental technologies, from water and wastewater purification (removal of ammonium ions, radioactive elements, heavy metals, and petroleum hydrocarbon contaminants) to water and gas adsorption in agriculture and industry. While the international literature describes numerous zeolite applications in environmental engineering, and especially water and sewage treatment [15; 16], there have been no reports concerning the use of such materials in FFRs. Furthermore, no sorption capacity evaluation methods or measurements have been developed for volatile compounds found in the workplace at sub-MAC concentrations. The replacement of carbon sorbents with microporous zeolites or mesoporous silica materials may improve the effectiveness of odor abatement, thus reducing the hazards associated with work under conditions of exposure to offensive odorants adversely affecting human well-being.