| dct.abstract |
A wide variety of nitrogen-containing compounds present in the air can contribute to air pollution, which in turn affects both human health and the climate. In this thesis, the applicability of two miniaturized air sampling techniques, solid-phase microextraction (SPME) Arrow and in-tube extraction (ITEX) was studied, for the selective collection of nitrogen-containing compounds in air samples. Different types of sorbent materials, including Mobil Composition of Matter No. 41 (MCM-41), titanium hydrogen phosphate-modified MCM-41 (MCM-41-TP), and zinc oxide-modified mesoporous silica microspheres, were used as sorbent materials in the ITEX sampling system. The adsorption and desorption behavior of gaseous nitrogen-containing compounds in passive SPME-Arrow and active ITEX sampling systems, coated and packed with different sorbent materials, was investigated. In addition, saturation vapor pressures of atmospheric trace gases were experimentally and theoretically estimated. The sampling systems with selected sorbent materials were applied to the determination of nitrogen-containing compounds in boreal forest SMEAR II station, indoor air, and cigarette smoke.
Adsorbent and adsorbate properties, such as hydrophobicity and basicity, were the major factors that affected sorbent selectivity towards nitrogen-containing compounds. Moreover, the pore volume and pore sizes of the sorbents were essential parameters for the adsorption performance, especially in the SPME Arrow system. The ITEX packing and the SPME Arrow coatings were reproducible and reusable. Due to the active sampling principle, the ITEX sampler with higher adsorption and desorption rates provided better results for the analysis, especially when quick injection was needed in gas chromatography. The selectivity of the ITEX sampling system was increased with the trap accessory, but further study is needed to prevent the loss of the targeted compounds. Whereas the ITEX’s filter accessory was successfully employed to remove particles, enabling ITEX to collect only gas-phase samples. Vapor pressure results were achieved by laboratory experiments (by retention index approach) and by the COSMO-RS model.
An aerial drone was successfully employed as a platform to study vertical profiles of VOCs at high altitudes, from 50 to 400 m, for miniaturized SPME Arrow and ITEX atmospheric air sampling systems, along with portable devices for the real-time measurement of black carbon (BC) and total particle numbers. There was a clear distribution of the nitrogen-containing compounds collected at different altitudes at SMEAR II station, Finland, depending on their sources. In addition, other VOCs demonstrated the same trend. |
en |
