Tropospheric Ozone Trends In Nonurban Troposphere

The global distribution of tropospheric ozone shown in Figure 1 illustrates its wide range (more than a factor of 3) of abundance. Therefore, unlike trace gases such as chlorofluorocarbons, nitrous oxide, or carbon dioxide, which exhibit very small spatial gradients, an assessment of the global rate of increase of tropospheric ozone is difficult to determine from measurements at only a few locations. Outside of urban areas, only a few stations around the world have continuous long-term measurements of tropospheric ozone. Among these stations are the ones set up by the U.S. National Oceanographic and Atmospheric Administration (NOAA), which has maintained a carefully calibrated monitoring program at a number of stations around the world since the early 1970s (Oltmans and Levy, 1994). The monthly mean concentrations from Barrow and Mauna Loa are shown on the left side of Figure 2a. The linear least-squares fit illustrating the trend between 1973 and 1992 for these two data sets is also plotted on these figures. Even though both of these stations show a significant increase over this period, the measurements at Barrow

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