CONTINUOUS AUTOMATED MEASUREMENT OF GASEOUS NITROUS AND NITRIC-ACIDS AND PARTICULATE NITRITE AND NITRATE

An automated measurement system for HONO(g) and HNO3(g) along with par ticulate nitrite and nitrate is described. The system alternately meas ures the gas phase and aerosol phase constituents. The gases are colle cted by a parallel plate wet denuder, and the effluent aerosol is coll ected by steam condensation, followed by impaction/thermophoresis. The fully automated instrument provides separate but quantitative collect ion of gases and particles at relatively high flow rates and displays very low interference from NO and NO2. Coupled to an anion chromatogra ph, the detection limit estimated for a signal equivalent to that of t h ree times the noise level of the blank is 110 parts per quadrillion (ppq, 10(-15) atm) and 230 ppq of gaseous HONO and HNO3, respectively, and 230 and 650 pg/m(3) aerosol nitrite and nitrate, respectively, fo r a 8-min integrated sample. The instrument operates over prolonged pe riods with minimal attention. Data are reported for outdoor ambient ai r measurements and for indoor air with kerosene-fueled space heaters i n operation.