The reservoir of ozone in the boundary layer of the eastern United States and its potential impact on the global tropospheric ozone budget

An analysis of available ozone data in the eastern two-thirds of the United States indicates that a substantial reservoir of ozone is present in the summertime. Five-year mean concentrations range from 40 to 65 ppbv. The reservoir covered an area of several million square kilometers and extends vertically from the surface to 1 to 2 km. The vertical distribution of ozone in the reservoir during midday supports a transport of additional ozone from the boundary layer to the free troposphere. Data are presented demonstrating the potential effect of transport by convective clouds and by the sea breeze circulation - mechanisms by which ozone may be transported out of the boundary layer into the free troposphere. The potential impact of this reservoir on the tropospheric ozone budget is discussed. It is shown that if less than half of the ozone mass in this reservoir is transported to the free troposphere, then the amount of ozone transported out of the boundary layer approximates the amount of ozone transported downward during a tropopause fold event.