| Abstract |
The increased aerosol concentration in the atmosphere contributes is highly affecting human health but mainly contributes in the reduction of temperature of planet, because of solar radiation reflection back to the space. The attendance rate of ions like SO42-, NO3-, NH4+ and Cl- to the total mass of particles was determined to be very high. For the previously mentioned ions as well for gases like SΟ2, ΗΝΟ3, ΝΗ3 and ΗCl, with which they are found in balance in the atmosphere, precise determinations are required. However it can be emphasised that this is a requirement that can be achieved through the development of proper methods that do not disturb their balance. The present work was mainly aimed in performing a comparison between different aerosol sampling techniques by using different filters in order to select a suitable method for the collection of specific gases or aerosol with less possible artefacts. Teflon and polycarbonate membrane, from fibres of glass (GFF) and cellulose, were used for the collection of particles meanwhile for the collection of gases different systems of filters and denuders were used. The samples were collected from two different locations. The first site is located in the centre of Heraklion, a region with high rates of pollution and the second in a remote region far from strong pollutants sources. The selected areas allowed us to exam the behaviour of the investigated sampling techniques (including filters type also) under different conditions of pollution. By performing experiments in three different periods of the year (i.e. spring, summer and winter) it was also possible to investigate if there is or not a meteorological influence on the results of each method. The main findings of the present work allow us to conclude that Teflon filters and polycarbonate membrane are the most suitable for particles collection. It has been found these two to behave the same during measurements without artefacts at the collection of particles. Amongst all investigated filters the GFF was found to behave in a different way because apart from the nitrate particles and nitric acid, they also collect unions of nitrogen we were not interested in species like nitric oxides (NOx=NO+NO2), nitrous acid (HNO2), peroxyacethylnitrate (PAN) and other organics. For ammonium GFF filter is not an appropriate one, as the concentration of this compound in particulate phase was determined to be under the detection limit of the instrumental methods used during analysis. Probably depending on the electrical charge which appears on the chloride particles, GFF filter can withhold part of the HCl gaseous form also. The behaviour of paper filters is not the same with that of the GFF. As for sulphurous species the investigated filters collected sulphate from particulate phase but also SO2 in the gaseous form and probably other unions of sulphur compounds. Most of the filters have been found to present positive artefacts during collection. In respect with nitrate particles the observed artefacts are probably due to detention of gaseous nitric acid but also of other nitrogen unions. At the collection of particulate ammonium by the paper filter, the positive artefact determined in the present work is mainly attributed to a partially ammonia absorption, which depends to a large extent upon the alkaline nature of the filters surface. The smallest positive artefact induced by filters is the one determined for sulphate particles (probably due to collection of small percentage of SO2). Except for the collection of nitric acid from the system of denuders and filters, where the results are different, for all other particles and gases their cross-correlation is satisfactory. The available published data regarding comparisons amongst different techniques of aerosol sampling are minimal but, in the last period, however, the scientific interest has been turned to this topic in order to reject those methods responsible of the main artefacts at the measurement of aerosols in the atmosphere, an observation that renders the present study as being important.
|
Αξιολόγηση δειγματοληπτικών τεχνικών για τη μέτρηση της ιοντικής σύστασης των αιωρούμενων σωματιδίων
