This ASHRAE research project carries forward two earlier ASHRAE-sponsored studies: RP-86,1 entitled "Field Study of Air Quality in Air Conditioned Spaces," was completed in 1970 and presented at the Society's Semiannual Meeting in January, 1971 (ASHRAE TRANSACTIONS 1971, 77, I); RP-112,2 "Ability of Air Conditioning Systems to Remove Pollutants under Controlled Conditions of Pollutant Level and Air Flow" was presented at the ASHRAE Fall Conference, October 1972 (TRANSACTIONS 1972,78,11). RP-86 was to determine the effectiveness of typical air conditioning systems in removing certain air pollutants from indoor air in office buildiilgs and similar· structures such as libraries and banks. The pollutants under investigation were particulate matter, sulfur dioxide and ozone. Results were most informative, but they also opened up .. many questions about the causes of the effects observed. Moreover, the test work was difficult to carry out because of ·the changeable levels of the pollutants. In order to overcome these difficulties, RP-112 was undertaken so that measurements of effectiveness could be made under controlled conditions of pollutant level and air flow. A, test area was established and a number of tests run. Since the effectiveness of washers or scrubbers in removing sulfur dioxide was of chief interest, it was decided that this and other means for the removal of sulfur dioxide should be subject for further investigation. RP-124, the project under discussion in this paper, represents a continuation of studies to determine the ability of air conditioning systems to remove pollutants. The work JR. Swanton, Jr. was Sr Staff Engr, Arthur D. Little, Inc, Cambridge MA and is now retired. This paper was prepared for presentation at the ASHRAE Spring Conference, Regina, Saskatchewan, Canada, May 16·18, 1973. The research project was sponsored by T.C. 2.3 (Air Contaminants: Gaseous & Particulate). 60 reported here includes, for the sake of clarity, material presented in the RP-112 report. In addition, a major effort is discussed devoted to the mechanism of removal of S02 by the use of scrlbbers, washers, charcoal and also with no removal equipment, starting with various measured concentrations delivered to the space or to the equipment. A few tests were undertaken with ozone, to determine what the problems'might be should a similar program be considered for this pollutant.