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List of Abstracts 95also from agriculture and biomass burning. In addition to pollutants which are directly emitted into theatmosphere such as NOx, SO2 or CO, other species including ozone and many VOCs are formed throughsecondary reactions. Changes in land use and agricultural practice as well as climate change can also affectemissions into the troposphere.In order to understand the changes induced by anthropogenic activities, measurements are needed of keyparameters in representative locations over long periods of time. These data sets can then be interpreteddirectly or used to validate atmospheric models and their predictions. In-situ measurements from the groundand from airborne platforms provide local data with high accuracy and temporal resolution but limitedcoverage. Satellite observations on the other hand provide the global view and are ideally suited forobservation of global change.In this contribution, long-term data sets derived from satellite observations performed by GOME,SCIAMACHY, and GOME-2 are used to investigate decadal changes in tropospheric composition. Fromthese measurements, tropospheric column amounts of NO 2 , SO 2 , HCHO, and glyoxal could be retrieved,providing a detailed picture of changes in atmospheric composition. Overall decreasing NO 2 levels in manyindustrialised countries are observed while at the same time NO 2 levels in China and many large citiesthroughout the world continue to increase. Sulphur dioxide levels have been increasing in China for manyyears but this trend was reversed recently while in the US SO 2 amounts have been clearly reduced since thefirst GOME observations in 1995. Both HCHO and glyoxal have mainly biogenic precursors with someanthropogenic contributions. Nevertheless, there is indication for increasing columns in Asia.P-Observations 1.18 ID:4589 15:35Why can we see near-surface tropospheric patterns in OMI and other UV O3 retrievals? How we canwe see these better?Robert Chatfield 1 , Xiong Liu 2 , Robert Esswein 31 NASA, Ames Research Center2 Harvard Smithsonian Astrophysical Observatory3 Bay Area Environmental Inst. & AmesContact: Robert.B.Chatfield@nasa.govAnalysis of tropospheric ozone soundings 2004-2006, primarily for North America, illustrates strongpatterns of correlation in the lower troposphere for some sites, mostly eastern and southern, and lowcorrelation for western sites like Trinidad Head, Richland, and Kelowna. Using the sondes, covariancesbetween an upper level that is theoretically well sampled in the UV, e.g., 750 hPa and near-surface ozoneyield linear relationships, O3_surface = a + b O3_aloft . Estimates based on "b" can be useful. Regions withrecirculation and convection allow modestly accurate estimates of O3_surface to be made, as we show withexamples. There are also varying of patterns of corrlation between different levels.We seek to improve estimation of lower-tropospheric and surface ozone by using the relatively strongcorrelation of theta (potential temperature) and chi (ozone mixing ratio). Both are conserved for periods oftime that regression estimates for chi may be obtained from UV and sonde records. We have found thattypically methods with little physical interpretation, neural nets or projection pursuit regression, providebetter estimates than geophysical estimates, e.g., based on theta-chi relationships. We will discuss our effortsso far to bridge toward more understandable geophysical statistical modeling.iCACGP-IGAC 2010 12 July, 2010