||Ozone, Chlorine, INDOEX, PRIME, Peroxy Radicals, Halogens, Photochemistry, aerosols, warming rates, entrainment, troposphere, marine boundary layer
||This work describes in detail the photochemistry of ozone 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 :b:INDOEX:/b: campaign studied the chemistry of remote areas of the Indian Ocean and the influence of the outflow from the Indian subcontinent on these regions. Measurements of trace gases (NMHC, O3, RO2*, CO, HCHO, NO, O3 soundings, and satellite data of O3, HCHO, and NO2) and parameters (j(NO2), j(O(1D), and met. data) were performed and have been compared with the results of a model. The comparison between measurements and simulations revealed large discrepancies, which indicated the presence of significant levels of Cl (10:sup:4:/sup:-10:sup:5:/sup: 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 and therefore on the dynamics of the Earth. 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 :b:PRIME:/b: campaign took place near London, UK. Ambient measurements of trace gases (HO2, RO2*, NO2, NO, PAN, CO, CH3OOH, H2O2, OH) were carried out. 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 (5-10) was in total disagreement with the model results (1-2.3). The measured H2O2 mixing ratios are also in disagreement with the observed HO2 amounts. 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.