Determination of aerosol composition and growth rates

Atmospheric aerosol particles have a relevant impact on human lives. Human health is affected, because the aerosol particles enter the respiratory system and can settle there. This can subsequently lead to serious health problems. Furthermore, the aerosol particles influence through direct and indirect interactions with sunlight, directly and indirectly the Earth`s climate. Primary aerosol particles are emitted constantly into the atmosohere from various anthropogenic and natural sources. Secondary aerosol particles are formed by condensation of low-volatile gaseous compounds in the atmosphere spontaneously. This newly formed molecules can grow to larger particles and act subsequently as a cloud condensation nuclei, which then serve as the basis for cloud droplets. Model studies have shown that these freshly formed aerosol particles are responsible for about 50% of the global cloud condensation nuclei concentration. Intensive experimental and theoretical work have been performed in the past 20 years, to deepen the understanding of the mechanism underlying the formation processes. The project represents an experimental study of the chemical composition of atmospheric aerosol particles. The measurements are used to understand the physical and chemical properties of the newly formed aerosol particles. The development of measuring methods for the detection of the smallest aerosol particles has evolved rapidly in recent years. The chemical composition of the initial cluster structures can range in size up to about 2 nm (nm = nanometer = 2 * 10-9 meters) can be determined by high resolution mass spectrometry. Aerosol particles having a diameter greater than 10 nm can be chemically and physically analyzed with various methods. The proposed method is intended to close the gap in the size range of currently available instrumentation. The prioject aims at determining the chemical composition and also the particle growth rates in the 2-4 nm size range. The particle growth rates determine the climatic relevance of the newly formed particles, as they only serve as cloud condensation nuclei starting from a size of about 50-100 nm. The proposed methods combine electrical methods which are used to select the size of the measured aerosol particles and condensation methods by which the particles are counted. The condensation process allows to indirectly determine the chemical composition of the particles and the size selection of the particles allows the determination of their growth rates. The proposed project includes laboratory tests and field measurements at different locations (rural and urban areas) to evaluate the differences in particle characteristics between areas close to anthropogenic sources and more rural areas.

Aerosol particles are small airborne particles that affect us in many ways. Their size ranges from a few nm to around 100 micrometers. They are of natural and anthropogenic origin. A distinction is made between primary and secondary sources. Primary anthropogenic sources for aerosol particles are soot emissions or cigarette smoke. Primary natural sources are pollen, volcanic ash or sea spray. Secondary sources are a combination of natural and anthropogenic ones. Due to certain trace gases present in the atmosphere (sulfur, nitrogen oxides, organic components) in combination with other atmospheric conditions (solar radiation, temperature, relative humidity, etc.), spontaneous formation of new aerosol particles can occur. This process of spontaneous new formation could be observed everywhere in the atmosphere, with the exception of the Amazon region. If these newly formed aerosol particles continue to grow to larger sizes, they have a significant impact on cloud formation and, subsequently, on the climate and health. The investigation of the natural formation of the smallest aerosol particles and their growth up to cloud droplets is therefore of great interest. In my work, I examined the natural formation of the smallest aerosol particles in the Amazon region. This environment is one of the few regions on earth which is relatively unaffected by human influences. For the first time, spontaneous new formation of aerosol particles was observed on ground in the Amazon region. In order to examine these smallest aerosol particles more precisely, suitable measuring devices are required. The total concentration of the smallest aerosol particles is generally determined by condensational growth and further optical detection. In the course of an extensive laboratory study, different condensation particle counters using different methods to detect the particles present in the atmosphere were examined in the laboratory under well-defined conditions. One of the devices is a newly launched instrument that was used for the first time for such a rigorous investigation. The biggest difference in the methodology lies in the liquid used, which is brought into a defined saturation state in the device. Subsequently, the aerosols and the saturated vapor are mixed and the condensational growth of the aerosols is achieved by a temperature drop. Water, butanol and diethylene glycol are the liquids used in my study. The aim of the study was to investigate the influence of the chemical composition of the aerosol particles in connection with the condensation liquid used. An increased solubility due to chemical similarity between the condensing agent and the aerosol composition leads to a higher activation efficiency for smaller aerosol particles within the device. These findings further influence the results obtained from studies on the composition of the atmosphere, in particular the examination of the aerosol particles.