Calculation of daily tropospheric ozone residuals using TOMS and empirically improved SBUV measurements: Application to an ozone pollution episode over the eastern United States

Abstract

A new technique for determining the integrated amount of ozone in the troposphere using concurrent observations from solar backscattered ultraviolet (SBUV) and Total Ozone Mapping Spectrometer (TOMS) data has been developed and is compared with various data sets. The technique makes use of the SBUV observations in the lowest three levels (1013‐63 mbar) of archived SBUV data to construct a climatology that is consistent with ozonesonde measurements. In the lowest layer (1013‐253 mbar), where ozone is almost always tropospheric, the SBUV measurements do not recreate the seasonality found in the ozonesonde data and consistently underestimate the amount of ozone at northern middle latitudes, the latitudes of interest for a later regional application. On the other hand, the key finding in this analysis shows that the integrated ozone amounts between 1013 and 63 mbar determined from SBUV are in good agreement with both the seasonality and the absolute ozone amount determined from the ozonesonde profiles. This result can then be used for determining a more accurate quantification of how much ozone is in both the troposphere and the stratosphere from any specific SBUV measurement. When used in conjunction with concurrent total ozone measurements from TOMS, we obtain better information about the distribution of ozone in the troposphere using the tropospheric ozone residual (TOR) technique. The TOR are then computed for the eastern United States during 1988 and compared to the ozonesonde measurements from Wallops Island during that year. The resultant comparison between the TOR and the Wallops Island measurements is considerably better using this technique when compared to calculated TOR values when the SBUV data are not corrected. The methodology is then applied to determine the large‐scale daily distribution of tropospheric ozone during times when surface concentrations of ozone were unusually high over vast regions on the eastern United States. These regional TOR patterns are analyzed in conjunction with various meteorological data sets and satellite imagery. Using such analyses, the relationship between the TOR distribution, meteorological processes in the lower troposphere, and the distribution of ozone at the surface during the 1988 episode is examined. This regional distribution of the TOR can be shown to be associated with the distribution of air masses that have evolved from the prevailing meteorological synoptic situation. The highest amounts of TOR are generally found off the coast of North Carolina and are consistent with the accumulation of ozone that had its origins over the northeastern United States and was subsequently advected southward off the North Carolina coast. The high TOR over the ocean is then caught in the persistent anticyclonic circulation where it becomes a source of ozone for the southeastern United States at a time when that region experiences numerous instances of surface ozone concentrations in violation of the Environmental Protection Agency hourly standards. When, over a period of several days, the dominating high‐pressure system over the eastern United States breaks down, TOR values decline, consistent with the fact that cleaner air of tropical origin is transported into the region.