The budget and partitioning of stratospheric chlorine during the 1997 Arctic summer

Volume mixing ratio profiles of HCl, HOCl, ClNO3, CH3Cl, CFC-12, CFC-11, CC l4, HCFC-22, and CFC-113, were measured simultaneously from 9 to 38 km by t he Jet Propulsion Laboratory MkIV Fourier Transform Infrared solar absorpti on spectrometer during two balloon flights from Fairbanks, Alaska (64.8 deg rees N), on May 8 and July 8, 1997. The altitude variation of total organic chlorine (CCly), total inorganic chlorine (Cl-y), and the nearly constant value (3.7 +/- 0.2 ppbv) of their sum (Cl-TOT) demonstrates that the strato spheric chlorine species available to react with O-3 are supplied by the de composition of organic chlorinated compounds whose abundances are well quan tified. Measured profiles of HCL and ClNO3 agree well with profiles found b y photochemical model (differences < 10% for altitudes below 35 km) constra ined by various other constituents measured by MkIV. The production of HCl by ClO + OH plays a relatively small role in the partitioning of HCl and Cl NO3 for the sampled air masses. However, better agreement with the measured profiles of HCl and ClNO3 is obtained when this source of HCl is included in the model. Both the measured and calculated [ClNO3]/[HCl] ratios exhibit the expected near linear variation with [O-3](2)/[CH4] over a broad range of altitudes. MkIV measurements of HCl, ClNO3, and CCly agree well with ER- 2 in situ observations of these quantities for directly comparable air mass es. These results demonstrate good understanding of the budget of stratosph eric chlorine and that the partitioning of inorganic chlorine is accurately described by photochemical models that employ JPL97 reaction rates and pro duction of HCl from ClO + OH for the environmental conditions encountered: relatively warm temperatures, long periods of solar illumination, and relat ively low aerosol surface areas.