Modelling of tropospheric ozone and radical chemistry

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This work describes in detail the photochemistry of O3 and radicals in both remote “clean air” and “heavily polluted” regions. The results of two field studies are presented: the Indian Ocean Experiment (INDOEX) and the Peroxy Radical Initiative for Measurements in the Environment (PRIME). The INDOEX campaign, an international research initiative, studied the chemistry of remote areas of the Indian Ocean and the influence of the outflow from the Indian subcontinent on these regions. Within the INDOEX campaign the first measurements of peroxy radicals were successfully performed above the Indian Ocean. These, together with other relevant trace gases (NMHC, O3, CO, HCHO, NO, O3 soundings, and satellite data of O3, HCHO, and NO2) and parameters (j(NO2), j(O( 1D), and meterological data) have been compared with the results of a 0-dimensional chemistry model. The comparison between measurements and simulations revealed large discrepancies, which indicated the presence of significant levels of Cl (10 4-105 molecule cm -3). In addition, a radiative transfer model has been modified and used to calculate the influence of highly absorbing aerosols on the energy budget of the Earth. The results of the RTM calculations of the warming rates caused by the aerosols’ absorption of solar radiation showed temperature increases up to 1 K. This temperature increase particularly above the MBL stabilised the atmosphere significantly. Therefore, the presence of aerosols in the layer above the MBL leads to enhanced stability during the day and less stability during the night. Satellite and sonde data were used for the investigation macro and mesoscale processes and for the identification of all relevant processes responsible for the amount of O3 present above the Indian Ocean. The combination of vertical profiles, satellite pictures of tropospheric columns of O3, NO2, HCHO, and meterological data, indicated that the amount of O3 resultant from the STE is the major source for tropospheric O3 in the SH Indian Ocean. The PRIME campaign took place during July and August 1999 near London, UK. Ambient measurements of trace gases (HO2, RO2*, NO2, NO, PAN, CO, CH3OOH, H2O2, OH) were carried out. During daylight the maximum RO2* mixing ratios varied between 15 and 70 pptv during “polluted episodes”. At night non negligible amounts of RO2* were observed, varying between 5 to 20 pptv. The comparison between simulated and measured daytime trace gas concentrations showed good agreement for RO2*, H2O2, OH and large discrepancies for HO2. The measured RO2* to HO2 ratio varied between 5 to 10, which is in total disagreement with the model results where this ratio varied between 1.1 and 2.3 even when the model was run with unrealistically high amounts of volatile organic compounds. The measured H2O2 mixing ratios are also in disagreement with the observed HO2 amounts assuming that H2O2 is exclusively produced via the HO2 self reaction. The actual measurements of RO2*, HO2, and NO taken during the early morning hours showed that these three species coexisted in high amounts. This cannot be explained by the known chemistry.