Reevaluating Ozone as a Tracer in the Moist Marine Troposphere

Previous studies have successfully used ozone as a conserved tracer for studying small-scale mixing However, there is evidence that ozone cannot be treated as a conserved tracer over periods of days when dealing with the ozone budgets in the moist marine troposphere. In this low NO[chi] environment the photochemical ozone decay rate is proportional to water vapor and ozone concentration, and ultraviolet radiation. For a moisture content of 10 g/kg, the photochemical decay is expected to be an order of magnitude more effective in removing ozone from the boundary layer than is deposition at the sea surface.

In the two Lagrangian experiments in ASTEX the ozone data collected from the NCAR Electra covered about one day, which is a rather short time for testing model results During the first experiment (June 13) the ozone concentration was low everywhere (about 20 ppbv), and no significant ozone loss was observed that could be distinguished from local fluctuations in ozone concentration. During the second Lagrangian experiment (June 19) ozone concentration in the boundary layer reached 50 ppbv, and ozone loss of about 5 ppbv was observed during the day. Preliminary results from numerical model calculations show somewhat lower values for ozone loss on this day.

In the past, the observation that ozone versus total-water mixing ratio (O₃-Q) mixing lines tend to be straight has been interpreted to imply that mixing is taking place between two conserved quantities. This interpretation is not necessarily correct. Calculations show that as ozone decays and mixing proceeds the O₃-Q mixing lines shift but remain nearly straight even after substantial ozone loss has taken place.