"Semivolatile Organic Compounds (SVOCs) play a crucial role in Secondary Organic Aerosol (SOA) formation, a major uncertainty in climate models. SVOCs are products of gas-phase oxidation of Volatile Organic Compounds (VOCs) in the troposphere, but they are very hard to measure in the gas phase. In the following proposed study, a new innovative method will be developed for the quantitative analysis of the burden of semivolatiles. The suitability of the denuders with different coatings will be identified for collecting SVOCs in the gas phase, and a modified Thermal-Desorption Proton-Transfer-Reaction Mass -Spectrometer (TD-PTR-MS) will be developed for measuring SVOCs in the gas and the particle phases. In addition, the selectivity of the TD-PTR-MS method will be increased for better identification of organonitrates, organosulfates, and organic halogen compounds. The enhanced TD-PTR-MS instrument will elucidate the role of SVOCs in SOA formation, thereby yielding a better understanding of aerosol formation, aerosol-climate effects, and the human interference with the hydrologic cycle. The instrument will be deployed at Cabauw Experimental Site for Atmospheric Research (CESAR) observatory to measure SVOCs from a rural area with urban and marine influences. This will give valuable insights into sources and the processing of SOAs, required for understanding the global SOA budget. These measurement data will be used to develop realistic parameterizations of the semivolatile burden of organics in the atmosphere under different meteorological conditions and pollution histories. The outcome of the project will be the development of a combined SVOC and organic aerosol measurement approach, the application of this new methodology in the field, and realistic parameterizations of SVOC budgets for use in climate models."