Investigation of dust fall concentration and their heavy metal content in the ambient air of Tabriz- Iran

Abstract

Dustfall which having the particle size of more than 10 μm and its heavy metal content are one of the serious environmental hazards. Therefore, the study of the DF amount as well as composition, distribution, and sources of heavy metals is important from the aspects of air pollution and health effect. The aims of this study were (1) to investigate the spatial and temporal variation of dust deposition rates at the selected sampling sites at urban (Tabriz) and suburban regions (Aq Gonbad, Quri Gol, and Amand Dam); (2) to determine the monthly and spatial variability in the concentrations of the heavy metals (Al, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Se, Sr, Ti, V, Si, and Hg) associated with the DF; and (3) to identify the likely natural or anthropogenic sources of heavy metals in the DF. In this study, ASTM standard (ASTM, D1739-98,2004) was used to DF measurment. Samples were taken for a one-year period and sampling was performed monthly (48 samples per year). Total amount of DF was analyzed by ASTM method and amount of metals in DF was analyzed by acid digestion method and ICP reading. By determining the DF amount and its heavy metal contents, their relationship to temporal and spatial variability was determined using SPSS and Microsoft Excel softwares and analyzed (descriptive statistics (mean and standard deviation) and inferential statistics (Pearson correlation) by SPSS software). The obtained results of present study showed that the maximum average concentration of the DF belonged to Tabriz (7.98 ± 4.08 g/m². month), and the lowest average amount of the DF equal to 4.42 ± 2.1 g/m2.month was observed in the Ag Gonbad. Also, the DF amounts in compared with the standard 1929:2011 SANS D<18 was shown to be less than 18 g/m2.month at all the sites and months except the Ag Gonbad in May with the DF of 27.63 g/m2.month. The results of the first and second six-month comparisons that in warm seasons (first six months), compared to cold seasons (second six months), for reasons such as average environmental temperature and wind, and lower rainfall, the DF values is more. In the cold seasons, especially in urban areas (Tabriz region), the increased use of fossil fuels, especially the increase in domestic gas consumption, as well as air inversion and condensation of pollutants can play a significant role in increasing DF in these areas. The results showed that Fe and Al have the highest amount between the measured DF elements, respectively. Also, investigations showed that increasing or decreasing concentrations of studied metals can be due to seasonal changes, degradation or human activities. So that the concentration of metals measured in the study areas in cold seasons was more than the warm seasons. The results of statistical analysis to determine the contribution of various sources in the release of metals argued that most metals, in addition to natural origin, are also released through synthetic sources. In the cold seasons in urban areas, the share of emissions from artificial sources is much higher than in the warm seasons. The only metal that was released in this study through natural resources (the main element of the earth's crust), and the share of artificial sources in the release of this metal was too small, was aluminum metal. Other metals studied were mostly from artificial sources. Of course, some of these metals such as iron and manganese, which are considered as important soil elements, are also released through natural resources, but the role of artificial resources (due to the large number of industries, especially the metal industries) are more colorful and more contributing to the release of these metals.