Development of analytical methodologies for the monitoring of the atmospheric particulate matter

The present research project focused on the development of analytical methodologies for the monitoring of the atmospheric Particulate Matter. Particulate matter (PM) is one of the main pollutants exceeding the ambient standards for air quality in Europe. In Italy, the mass concentration standards are overcome many times per year, mainly due to the unfavourable meteorological conditions (especially in the Po Valley regions) and to the transportation of the air masses coming from the Sahara Desert (Southern and Central regions). The direct and indirect influence of the PM on human health, global climate change and reduced visibility have led to numerous studies in the last past decades, focusing upon its complex composition, toxicology and the source attribution. The particulate matter is constituted by an heterogeneous mix of components, characterized by a variable chemical composition and different chemical-physical properties that greatly influence its deposition and distribution. For these reasons nowadays it is still very difficult to develop efficient abatement strategies to protect both human health and environment. To achieve these specific objectives it is necessary to focus on some issues that are still not resolved, by taking advantage of both the analytical chemistry and the statistical methods. One of the “open” issues is the determination of water content in PM. Water plays an important role in the formation of the secondary species starting from gaseous precursors. It is well known that these species undergo gas-particle equilibria influencing the sampling phase and altering the results of the monitoring campaigns but, given the great variability of the measured concentrations, to date, a clear interpretation of these processes has still not been found. More information could be obtained by determining the water content in PM. Moreover, the knowledge of the water amount sampled together with the atmospheric particles on appropriate media could be very useful to establish the water influence on the PM mass concentration as well. Till now, the water determination has been carried out mostly by indirect methods estimating the water adsorbed on not-sampled particles. During the present project a simple method to determine water in PM samples has been optimized and validated, based on the Karl-Fisher theory. The potentialities of the thermal desorption were also explored to study the different types of water linked to the particles. After the validation, this methodology has been then applied to real PM samples collected in geographical areas characterized by several emission sources (traffic, industries, etc.), demonstrating that water is a relevant component of the PM and it influences in a significant way the PM mass concentration especially in samples very rich of secondary inorganic compounds or natural sand. Moreover the type of water present in the atmospheric particles is strictly dependent on the PM chemical composition. The second part of this project concerned the measurements of the PM at high temporal resolution. Sampling and analysis of PM in real time at high time resolution allow to have some precious information about the temporal variability of the atmospheric pollutants’ concentration, that usually are lost with the 24-hours sampling time. Our attention was focused on a new device able to sample and analyze in real time the atmospheric inorganic ions, the Particle Into Liquid Sampler coupled with the Ion Chromatography (PILS-IC). The instrument in its original configuration is affected by some limits, the high detection limit values that make difficult to apply it in low polluted areas and the low time resolution due to the analysis of the solution contained in the chromatographic loop only at the injection time into the column. These limits were solved modifying the original instrumental configuration, inserting a pre-concentration system. The new optimized system was then validated and applied to a monitoring campaign. The results have been compared with those obtained by other analytical techniques aimed to measure the same species, showing good performance of the new system. The data obtained by using this system were also useful to understand the chemical form in which the ions were present in the atmosphere at the sampling time and allowed to isolate some hot spot pollution events. The last part of the present project has been carried out at the University of Birmingham (United Kingdom) under the kindly supervision of Prof. Roy M.Harrison and focused on the traceability of the PM emission sources. The knowledge of the emission sources is one of the main objectives in the PM studies, as it is necessary for developing efficient abatement strategies. The Source Apportion techniques are very helpful to reach this objective. In particular, the Positive Matrix Factorization receptor model (PMF) was applied to identify and quantify the PM sources at an industrial area of the Po Valley. This model is very useful to manage large databases coming from the chemical analysis of PM collected during long monitoring campaigns and is able to determine the main PM sources by looking at the correlation of the variables (measured species) at the monitored receptor sites. The variables to process by the model have been chosen with the support of a detailed chemical characterization of PM using a fractionation methodology based on the elemental solubility. The main PM sources in the Po Valley have been identified with the secondary nitrate and the biomass burning, although the industrial nature of the monitored area. Because of the wideness of the topics they will be treated in separated chapters.