In Situ Measurement of OH and (HO2 +RO2) during the 2003 and 2004 Summit, Greenland Campaigns

During the summer of 2003 and early spring of 2004 a Chemical Ionization Mass Spectrometer (CIMS) measured gas phase OH and (HO2 +RO2) in the boundary layer at Summit, Greenland. To measure HO2 +RO2, NO is added 3 minutes out of every 20. The addition of NO allows the HO2 +RO2 to be converted to the OH radical which then reacts with SO2 to form H2SO4. The H2SO4 is measured with the CIMS and the OH and HO2 +RO2 concentrations are inferred from the resultant [H2SO4]. The calculated sensitivity of HO2 +RO2 to the added NO of the sample is compared to observations. In addition to the response of the CIMS to the NO addition, the system field calibrations for both OH and HO2 are shown. The calibrations are performed in situ by photolyzing ambient H2O to form OH and HO2. Various aspects of the system performance such as detection limits and time response will be presented.