Tropical Tropospheric Ozone observed from GOME_2 and perspectives for TROPOMI

Abstract

Tropospheric Ozone is of particular interest not only because it is a greenhouse gas, but also because it directly affects human health and causes agricultural damage. There is still a large uncertainty about the global distribution of tropospheric ozone, because ozone sondes are sparce. Here global distribution patterns as observed from satellites are an excellent tool to increase our knowledge and understanding of the underlying processes. The presented data are based on the ozone Level 2 products from the GOME and GOME_2 measurements and retrieved by a convective cloud differential (CCD) algorithm. The stratospheric O3 column is estimated by vertical column above large convective clouds. The difference between the total column for cloud free observations and the stratospheric column equals the tropospheric column. One of the underlying assumption is that the stratospheric column does not vary with longitude for certain latitude bands. Due to this assumption this method can only be applied in the tropics (20°S to 20°N). The results compare well with the ozone soundings from the SHADOZ network. The average bias between the tropospheric columns from the GOME observations and the ozone is sondes is below 1 DU and the standard deviation is about 5 DU. For some stations the tropospheric columns deviated in the mean by less than 0.1 DU, only for the northern and southern most stations (Hanoi and Réunion island) average discrepancies of 5 DU and more were found. The CCD tropospheric ozone product shows similar distribution patterns as other tropospheric ozone products. In particular a comparison with the direct level 2 ozone profile retrieval from RAL proofs the good quality of both products. Currently the data are gridded on a grid of 2.5° longitudinal by 1.25° latitudinal and monthly averaged to get a reasonable signal to noise ratio. With the upcoming S5P missions the spatial and temporal resolution might be reduced.