In situ measurements of chlorine nitrate in the lower stratosphere

Inorganic chlorine compounds generated from the breakdown of anthropogenic halocarbons play pivotal roles in the photochemical destruction of stratospheric ozone. In order to understand the observed declines in global ozone columns over the last several decades as well as predict changes in ozone to perturbations from aircraft and a changing climate, we must quantitatively account for the total amount inorganic chlorine in the stratosphere and understand the mechanisms controlling its partitioning into the various chlorine species.;The lack of an in situ measurement of chlorine nitrate, one of the two main reservoirs of stratospheric inorganic chlorine, prevented closure on key questions concerning chlorine partitioning and the inorganic chlorine budget. The laboratory calibration and development of an instrument for the in situ measurement of chlorine nitrate in the lower stratosphere is described. The instrument was part of the payload for the POLARIS campaign of 1997. A description of the instrument as well as its mode of operation during POLARIS is also presented. Simultaneous measurements of ClO, ClONO;ER-2 data from 1991-1997 in combination with other measurements and studies of inorganic chlorine partitioning are investigated in order to determine the most likely cause of the 40% discrepancy in the inorganic chlorine budget seen in the ER-2 data from AASE-II and SPADE. It is concluded that a systematic error in the ALIAS measurements of HCl was the most likely cause of this discrepancy.