Using chemical ionization mass spectrometry for detection of HNO3, HCl, and ClONO2 in the atmosphere

Ion chemistry schemes involving three different reagent ions are described for measuring nitric acid (HNO3), hydrochloric acid (HCl), and chlorine nitrate (ClONO2) in the upper troposphere and lower stratosphere using chemical ionization mass spectrometry (CIMS). These schemes were evaluated in the laboratory for sensitivity and selectivity of the neutral species. The use of one scheme, based on the SF5− reagent ion, is described for airborne measurements. Initial atmospheric measurements show that HNO3, HCl, and ClONO2 can be measured using SF5− with high precision and accuracy.