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The paper presents partial analytical solutions for equations describing variation in trace amounts of carbon dioxide in the atmosphere of habitable spaces within pressurized modules (PM) of a space station. The solutions may find practical application in calculations of concentrations for any contaminants, or for air flow through the purification system. It is shown that in a case where low-toxic contaminants are released into the PM atmosphere, it would be enough to cycle 3 volumes of the PM air through the purification system when the system operates without the breakthrough concentration (without the residual concentration of the contaminant at the outlet from the purification system), in order to achieve the 95% purification of the atmosphere. For highly toxic contaminants this value should be significantly increased depending on the maximum allowable concentration of the substance (47 volumes and more — up to 99.9% purification). The paper also considers variation in the concentration of the contaminant in the atmosphere during intermixing of atmospheres between PMs using intermodular ventilation. As a result, new analytical solutions were obtained for practical calculations which make it possible to determine gaseous contaminant concentration at any point in time and the time of the final equalization of the contaminant concentration in the space station atmosphere. It was determined that the time needed for complete mixing of gaseous contaminants through intermodular ventilation between two PMs does not depend on the initial concentrations of the contaminants (and only depends on the PM volumes and the intermodular ventilation flow rate). Key words: space station, pressurized module atmosphere, carbon dioxide, atmosphere purification, variation in concentration, air flow, atmosphere mixing.

Carbon dioxide (СО2) scrubbing from pressurized volumes of long-term space stations is one of the most critical aspects of crew life support, since each person, on average, releases 480 liters of СО2 (~ 1kg) per day. Meanwhile, СО2 is one of the gases required for human breathing, but at the same time its content in the atmosphere of the pressurized cabin must be kept below established standards, exceedance of which makes СО2 a contaminant harmful to humans. It should also be taken into account that at present the established standards for СО2 content in the space station atmosphere are not based on scientific research. The key parameter of the scrubbing system, which determines the СО2 content in the atmosphere of the space station pressurized cabin, is the effective flow rate of the scrubbed air through the system. It was established that in order to scrub the atmosphere, two requirements must be met: 1) supply the required air flow rate to the scrubbing system (this requirement applies to all types of the system), 2) provide the required efficiency of the scrubbing system for the contaminant removal. A formula has been derived for calculating the effective flow rate through the air scrubbing system, allowing not only to calculate the necessary charge through system of clearing, but also which makes it possible to compare performances of various types of systems. It was established that the most efficient system for scrubbing СО2 from the air is the sorption system, since it has the largest absorption surface, all other conditions being equal, and, therefore, it has the highest efficiency factor Key words Space station, carbon dioxide, air scrubbing, standards for СО2 content, effective airflow rate, calculation formula, efficiency factor, absorption system for scrubbing СО2 from air.