DEVELOPMENT AND EVALUATION OF A PASSIVE SAMPLER TO COLLECT NITROUS-ACID AND SULFUR-DIOXIDE

A passive monitor for nitrous acid (HNO2) and sulfur dioxide (SO2), co nstructed from a 37 mm diameter polystyrene air sampling cassette, has been developed for use in an epidemiologic study of the respiratory e ffects of acid aerosols and vapors on infants and their mothers. It co nsists of a glass fiber filter coated with a 2% sodium carbonate solut ion and placed on the bottom of the cassette. The filter is held in pl ace by a polystyrene spacer whose lip has been removed and onto which a Gore-tex(R) convection barrier is glued. The exposed filter is extra cted and the aqueous extract is treated with hydrogen peroxide. It is analyzed by ion chromatography for nitrite and sulfate ions, which are used to determine HNO2 and SO2, respectively. The collection rate of the sampler is 100.4 mL/min (+/- 14.8) for HNO2 and 41.1 mL/min (+/- 3 .4) for SO2. The passive monitor was tested for the effects of humidit y over a range of HNO2 and SO2 concentrations and sampling times. The results indicated that the passive monitor can measure a wide range of HNO2 and SO2 concentrations and should be useful in characterizing ex posures in epidemiologic investigations and other studies.