A novel semi-direct method to measure OH reactivity by chemical ionization mass spectrometry (CIMS)

An operational chemical ionization mass spectrometer (CIMS) for hydroxyl radical (OH) and sulfuric acid (H.sub.2 SO.sub.4) concentration measurements was adapted to include observations of OH reactivity, which is the inverse of OH lifetime, for long-term monitoring at the Global Atmosphere Watch (GAW) site Hohenpeissenberg (MOHp), Germany. OH measurement using CIMS is achieved by reacting OH with SO.sub.2, leading to the production of H.sub.2 SO.sub.4, which is then detected. The adaptation for OH reactivity consists of the implementation of a second SO.sub.2 injection, at a fixed point further down flow in the sample tube to detect the OH decay caused by reactions with OH reactants present in the sample.