Towards a better insight into the health effects of aerosol particle

Atmospheric aerosol exhibits a tremendous variety of characteristics, plays a decisive role in many atmospheric processes and is also known to have an impact on human health. Aerosol particles are composed of different inorganic compounds like sulfate, ammonium nitrate or graphite, but mainly consist of organic matter which comprises up to 70% of the particle mass. They can be introduced into the atmosphere as primary emissions from both anthropogenic as well as natural sources or by their formation through reactions within the atmosphere mainly from oxidation of volatile organic compounds (VOCs) to form secondary organic aerosol (SOA). SOA presumably provides the largest fraction to atmospheric aerosol and its organic matter consists of innumerable chemical compounds such as organic acids, aldehydes or organic peroxides. The formation of SOA has been studied in many environmental chamber experiments so far, but the formation, evolution and composition remains still unclear. Only a few studies have been performed to quantify peroxides in SOA, although model simulations indicated a very large contribution of these chemical species to SOA. In the atmosphere peroxides are mainly formed by the reaction of peroxy radicals (RO2) with HO2 radicals. RO2 originates from the reaction of VOCs with OH radicals in the presence of molecular oxygen (O2). Their fate in the atmosphere is dependent on the NOx concentration, because NO reacts competitively with RO2 to form alkoxy radicals (RO) and NO2. Different epidemiological studies could clearly show that elevated levels of particulate matter in the ambient air cause respiratory and cardio vascular diseases. Ultrafine particles (< 100 nm) are assumed to play an important role in these toxicological processes. In mechanistic laboratory studies the epidemiological findings could be supported but the interactions of ultrafine particles and lung cells in detail are still unclear. Peroxides are difficult to quantify because they exhibit low chemical stability. So far iodometry was used to investigate their contribution to SOA. Herein peroxides oxidize iodide ions (I) to molecular iodine (I2) which subsequently forms yellow colored triiodide ions (I3) with excessive I. I3 can be quantified by UV/VIS spectroscopy. However, low sensitivities using 1−cm cuvettes as well as the interference of O2 in the test reaction necessitated high aerosol concentrations and the resulting time resolution was very low (several hours). Here, an analytical setup was developed to quantify peroxides via iodometry combined with long path absorption spectroscopy where aerosol filter samples can be extracted and analyzed under anaerobic conditions. From blank measurements a detection limit of 0.1 μM or ______________________________________________________________________________________________________ ii 0.52 nmol m3 with respect to an aerosol sample volume of 500 L was calculated. Calibration experiments demonstrated that the reaction of I with all reactive peroxides, i.e., hydrogen peroxide (H2O2), peracids and peroxides with vicinal carbonyl groups (e.g., lauroyl peroxide) goes to completion and their sensitivity (slope of calibration curve) varies by only ±5%. However, very stable peroxides have a lower sensitivity. For instance tert-butyl hydroperoxide shows only 37% sensitivity compared to H2O2 after 1 h. The new instrument is called Peroxide-LOPAP in analogy to the original LOng Path Absorption Photometer (LOPAP) for HONO measurements. The Peroxide-LOPAP was used to measure time trends of the peroxide content in SOA from the ozonolysis and photo-oxidation of α-pinene in smog chamber experiments. Freshly generated SOA from α-pinene ozonolysis contained the highest amount of peroxides with 34% (assuming a molecular weight of 300 g mol1). In the photo-oxidation experiments peroxide contents decreased with increasing NO levels. A decrease of the peroxide content was observed with aging of the aerosol indicating a decomposition or reaction of peroxides in the particles. In another series of experiments five different anthropogenic SOA precursor sources have been investigated. Emissions from combustion processes were produced with a 2-stroke scooter, a EURO 2 diesel car and a modern wood stove. Additionally we included vegetable boiling and chicken frying as emission sources. SOA was generated by photo-oxidation with NOx. Peroxides in primary organic aerosol (POA) were at most 2.3% for all emission sources. In SOA peroxides up to 14.1% could be detected. SOA from combustion processes contained between 2 and 8% peroxides. Using the Peroxide-LOPAP as a UV/VIS-spectrometer, also the light-absorption of POA and SOA particle extracts were measured. Light-absorbing characteristics were presented as bulk organic matter mass absorption efficiency αOM,bulk(λ) and Ångström coefficient Åp. Extracts show a rapid decrease in absorption with increasing wavelength, as it is typical for brown carbon (BrC). The mass absorption efficiency at 365 nm of SOA from wood combustion was about two and a half times higher than from diesel emissions and at least 19 times higher than from scooter or cooking emissions. Compared to field measurements of aerosols with high levoglucosan content, a well known tracer for biomass burning, αOM,bulk(λ) of SOA from wood burning and diesel were 2-5 times higher. To classify the potential health risks of ambient particulate matter extensive investigations using suitable in-vitro systems to investigate the cell−particle interactions are essential. Therefore a new chamber for particle deposition studies was developed, characterized and used in cell experiments. The deposition chamber is equipped with a humidifier, suitable heater, insulation and an integrated system for electrostatic particle deposition, which is ______________________________________________________________________________________________________ iii used for a higher deposition efficiency. Moreover special manufactured 12-well plates are used to test 12 cell cultures in parallel. To mimic the physiological conditions of the lung the deposition chamber can be operated at constant 36-37 °C and 90-95% relative humidity. The particle deposition efficiency was quantified using a scanning mobility particle sizer (SMPS) and ion chromatography coupled to a mass spectrometer (IC/MS). Deposition in each well is uniform as well as in comparison to all 12 wells. Furthermore it is efficient and reproducible and thus the evaluation of dose–response relationships is possible. Therefore the deposition chamber is a suitable in-vitro system to test for realistic cell–particle interactions at physiological conditions minimizing any stress on the cell cultures other than from deposited nanoparticles. This chamber was used to investigate acute responses of airway epithelial cells and macrophages after exposure to POA and SOA from diesel and wood burning emissions. The emissions were fed into the PSI smog chamber and then photo-oxidized to generate SOA. The results demonstrate that a single, short-time exposure to these carbonaceous aerosols at ambient concentrations (10 particles cm3) leads to small, particle-specific cell responses. Moreover, the results indicate for cell-type specific effects in inflammatory mediator release. POA and SOA similarly affected macrophage phagocytic activity. But cell and tissue integrity remained unaffected as expected for ambient concentrations. The subtle, but distinct effects of carbonaceous aerosols on cells of the inner lung surface contribute to unraveling the basic mechanisms of epidemiologically observed health effects. ______________________________________________________________________________________________________ iv