Ozone Changes at the Surface and in the Free Troposphere

Abstract

Analysis of the available long-term ozone records of surface and ozonesonde observations from rural stations confirm the continuous increase of ozone concentration, by about 1% per year, during the last two decades. Although the data are very sparse and do not represent a global average, they reveal some interesting seasonal variations. It appears that the surface ozone during November-January is increasing at a greater rate than during May-October. This could be a confirmation to recent modelling studies highlighting the important combined effect of anthropogenic emissions and natural level of concentrations of NO_x, non-methane hydrocarbons (NMHC), as well as CO and CH₄, on the ozone production in the troposphere. The ozone in the upper part (500–300 hPa) of the troposphere usually shows a lower rate of increase than the ozone in the lower part (850–500 hPa). The monthly deviations from the mean of the lower stratospheric ozone compared with those of the surface ozone show some general concurrence of the shape of the long-term fluctuations, but also show some differences, which together with the opposite (by sign) trends of both series may indicate domination of processes affecting the surface ozone regime, other than solely the cross-tropopause transfer.