SOURCES OF HOX AND PRODUCTION OF OZONE IN THE UPPER TROPOSPHERE OVER THE UNITED-STATES

The sources of HOx (OH+peroxy radicals) and the associated production of ozone at 8-12 km over the United States are examined by modeling ob servations of OH, HO2, NO, and other species during the SUCCESS aircra ft campaign in April-May 1996, The HOx concentrations measured in SUCC ESS are up to a factor of 3 higher than can be calculated from oxidati on of water vapor and photolysis of acetone. The highest discrepancy w as seen in the outflow of a convective storm. We show that convective injection of peroxides (CH3OOH and H2O2) and formaldehyde (CH2O) from the boundary layer to the upper troposphere could resolve this discrep ancy. More generally, the data collected over the central United State s during SUCCESS suggest that local convection was a major source of H Ox and NOx to the upper troposphere. The OH and HO2 observations toget her with the observations of NO allow us to directly calculate the ozo ne production in the upper troposphere and its dependence on NOx. We f ind an average net ozone production of 2 ppbv day(-1) between 8 and 12 km over the continental United States in the spring. Ozone production was NOx-limited under essentially all the conditions encountered in S UCCESS. The high levels of HOx present in the upper troposphere stimul ate ozone production and increase the sensitivity of ozone to NOx emis sions from aircraft and other sources.