COMPARISON OF CALCULATED AND MEASURED PEROXIDE DATA COLLECTED IN MARINE AIR TO INVESTIGATE PROMINENT FEATURES OF THE ANNUAL CYCLE OF OZONE IN THE TROPOSPHERE

Large amounts of data on the concentration of peroxides have been coll ected in vertical profiles over the North Atlantic Ocean by a Hercules aircraft. The measured peroxide concentrations have been compared wit h concentrations calculated by a simple algorithm derived assuming tha t the standing peroxide concentration is in equilibrium with its produ ction and loss processes. In clean air where the peroxide and ozone co ncentrations are anticorrelated throughout the profile measured and ca lculated peroxide concentrations coincide, whereas in layers of pollut ed air within the profile, as determined from positive ozone peroxide correlations, calculated peroxide concentrations are greatly in excess of measured values. Using the degree of correlation between measured and calculated peroxide concentrations as a diagnostic, it is possible to show that many aspects of the seasonal cycle of ozone are caused b y in situ tropospheric chemistry. Thus the summer minimum in the seaso nal cycle of ozone, observed at clean marine ground-based sites such a s Mace Head, is due to photochemical destruction, and elevated levels of ozone are associated with the transport of polluted air, on occasio n over thousands of kilometers. Of particular interest if our analysis is correct, the broad maximum of ozone occurring between March and Ma y at ground-based sites has a large contribution from ozone formed by tropospheric as well as stratospheric chemistry.