Time evolution of tropospheric ozone and its radiative forcing

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Abstract
Emission trends of ozone precursors have been estimated on the basis of CO2 emissions from use of fossil fuels and cement production (with regional emission indices), biomass burning estimates, use of fertilizers, and aircraft emissions. “Timeslice” calculations of changes in tropospheric ozone for 1850, 1900, 1950, 1960, 1970, 1980, and 1990 have been performed with the University of Oslo global three‐dimensional chemistry transport model (OsloCTM‐1). For surface ozone the regions of maximum growth are found to have shifted during the period. Up to 1950 the largest increase is found over central United States (+25–30 ppbv), while for the 1950–1970 period it occurs over southeastern Europe and northeastern Asia (+15–20 ppbv). For the last period (1970 to 1990) most of the growth is found over Asia (over the Persian Gulf, India, and northern China) reaching 15 to 20 ppbv. During the period up to 1970 the changes in the tropospheric ozone column are found to be most profound at northern high and midlatitudes (about 80% of the increase before 1970), while the increase at lower latitudes is found to accelerate in the 1970s and 1980s (60% of the increase before 1970). Radiative transfer models for thermal infrared radiation and shortwave radiation are used to calculate the time evolution of the radiative forcing. In 1950 the radiative forcing due to increase in tropospheric ozone since preindustrial times was about 1/3 of the present radiative forcing due tropospheric ozone. The present radiative forcing due to increase in tropospheric ozone since preindustrial times is estimated to 0.34 W m−2. Significant regional differences in the evolution of the radiative forcing is found due to the differences in ozone trends. The tropospheric ozone results are available at http://www.geofysikk.uio.no/data/ozone/trend.