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Simultaneous assimilation of satellite NO2, O-3, CO, and HNO3 data for the analysis of tropospheric chemical composition and emissions

by K Miyazaki, H J Eskes, K Sudo, M Takigawa, M van Weele, K F Boersma
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We have developed an advanced chemical data assimilation system to\ncombine observations of chemical compounds from multiple satellites.\nNO2, O-3, CO, and HNO3 measurements from the Ozone Monitoring Instrument\n(OMI), Tropospheric Emission Spectrometer (TES), Measurement of\nPollution in the Troposphere (MOPITT), and Microwave Limb Sounder (MLS)\nsatellite instruments are assimilated into the global chemical transport\nmodel CHASER for the years 2006-2007. The CHASER data assimilation\nsystem (CHASER-DAS), based on the local ensemble transform Kalman filter\ntechnique, simultaneously optimizes the chemical species, as well as the\nemissions of O-3 precursors, while taking their chemical feedbacks into\naccount. With the available datasets, an improved description of the\nchemical feedbacks can be obtained, especially related to the\nNOx-CO-OH-O-3 set of chemical reactions. Comparisons against independent\nsatellite, aircraft, and ozonesonde data show that the data assimilation\nresults in substantial improvements for various chemical compounds.\nThese improvements include a reduced negative tropospheric NO2 column\nbias (by 40-85%), a reduced negative CO bias in the Northern Hemisphere\n(by 40-90%), and a reduced positive O-3 bias in the middle and upper\ntroposphere (from 30-40% to within 10%). These changes are related to\nincreased tropospheric OH concentrations by 5-15% in the tropics and\nthe Southern Hemisphere in July. Observing System Experiments (OSEs)\nhave been conducted to quantify the relative importance of each data set\non constraining the emissions and concentrations. The OSEs confirm that\nthe assimilation of individual data sets results in a strong influence\non both assimilated and non-assimilated species through the\ninter-species error correlation and the chemical coupling described by\nthe model. The simultaneous adjustment of the emissions and\nconcentrations is a powerful approach to correcting the tropospheric\nozone budget and profile analyses.

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