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 particulate nitrite and nitrate is described. The system alternately measures the gas phase and aerosol phase constituents. The gases are collected by a parallel plate wet denuder, and the effluent aerosol is collected by steam condensation, followed by impaction/thermophoresis. The fully automated instrument provides separate but quantitative collection of gases and particles at relatively high flow rates and displays very low interference from NO and NO2. Coupled to an anion chromatograph, the detection limit estimated for a signal equivalent to that of th 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, for a 8-min integrated sample. The instrument operates over prolonged periods with minimal attention. Data are reported for outdoor ambient air measurements and for indoor air with kerosene-fueled space heaters in operation.