FAST TIME RESPONSE MEASUREMENTS OF HNO3 IN AIR WITH A CHEMICAL-IONIZATION MASS-SPECTROMETER

A chemical ionization mass spectrometer has been developed for fast ti me response measurements of HNO3 in ambient air. The apparatus was cha racterized in an informal intercomparison campaign at Green Mountain M esa in Boulder, Colorado. Nitric acid was measured over a wide range o f meteorological conditions. Detection limits of less than 15 pptv for a 1 s integration period were routinely obtained. The apparatus was s ufficiently sensitive to measure ambient levels of HNO3 for all condit ions except for periods of fog or heavy precipitation when HNO3 mixing ratios were less than 10 pptv.