Determining the Concentration of Heavy Metals at Urban Ambient Air (Case study: Rey City)

1. Environmental pollution to heavy metals is increasing every year and cause serious risks to human health, animals and plants. In terms of adverse effects on human health, particulate matter contains heavy metals are perhaps the most important air pollutants because of their non-biodegradable nature. They are released to the atmosphere via different processes and natural and man-made (anthropogenic) sources and enter body organs and tissues as a result of absorption through respiration of suspended particulate matter (SPM) which contains heavy metals and trace elements. Because of the risks posed by elements in Suspended Particulate Matter to human health and the ecosystem, it is important to develop effective control measure for air particulate emission. However, an important step in air pollution control program is the identification of pollutants, the contributing source and the relative contribution of each source. Elemental composition of SPM in ambient air of Rey city in Tehran has been investigated. Some of these pollutants, particularly the SPM and their elemental constituents are known to be hazardous to human health. It is therefore pertinent to investigate the activities of these industries. This has necessitated the present study to ascertain the degree of contamination of air in Rey City. Zone 20 of Tehran (Rey city) with an area of 176 square kilometer and population more than 370 thousand people is the most polluted area of Tehran due to the establishment of polluting industries such as cement factory, refinery, oil collection include pipelines, etc. The aim of this study is select the suitable sites in accordance with the US EPA standards to install air pollution monitoring station, investigate the change of metals concentrations as inorganic pollutants in ambient air and comparison with international standards and finally, their sources and anthropogenic contributions for the first time for this region.
2. There are different methods for sampling and determination of total suspended particulate matter in the atmosphere. This study has used the gravimetric techniques to sample and determine TSPM in Rey city according to the Standard Method, Compendium Method IO-3.1. In this method, the amount of particulate matter accumulated on the filter over a specified period of time is measured by weighing a pre-weighed filter after exposure. The flow rate of air sampled is measured over the test period. The result is expressed in terms of particulate mass collected (or loading) per unit volume of air sampled, usually as micrograms per cubic meter (μg/m3). The volume of air sampled is recorded by measurement of the device flow rate(s). Therefore, to achieve this purpose, 6 different stations were specified around this area according to the EPA standards included a residential, a traffic, two residential-industrial and two industrial stations.
High volume sampler, TCR TECORA model was used for the collection of the airborne particulate component of the atmosphere. The sample collection was carried out at 1394 in two seasons, summer and winter. Glass-fiber filter papers were dried and weighted before and after the sampling. So the daily concentrations of particulate matter with the size 3. The main purpose of this study is determination and monitoring some of heavy metals (such as Cr, Ni, Pb, Cd, Cu, Hg, Zn, Al and Fe) in ambient air in Rey city. So, 6 sampling stations were selected based on the effect of residential sources, mobile sources (vehicles) and stationary sources (industrial centers). Sampling of particulate matter in less than 10 micron diameter, were performed and the samples were analyzed to measure heavy metals according to the standard methods and EPA instructions. Analyzing the results of the measurements show that:  Annual concentration of chromium is higher than standard (0.01 μg/m3) at all sampling stations which shows the role of transportation (due to the corrosion of catalyst convertor and presence of asbestos in brake pad) and also industry, specially cement production in it’s emission to the ambient air. Chromium is naturally not an earth’s crust metal, so it increases at cold and rainy seasons and inversion.  Annual concentration of nickel is higher than standard (0.02 μg/m3), nearby different emission sources such as cement production, foundry and refinery which are the main emission sources of nickel in ambient air. Gradually, away from these sources and close to the residential zone, it will decrease.  Due to the production and distribution of lead-less gasoline since 1382, Lead pollution in ambient air which is most affected with traffic emissions, is lower than standard (0.5 μg/m3), but, it is higher than standard at stations locating near industrial zone, foundry, refinery and cement factory respectively.  Annual concentration of Cadmium is higher than standard (0.005 μg/m3) at all sampling stations. The most concentration is near industrial zone and then, cement factory which are the main emission sources. Analyzing the results shows that, the concentration of this metal increase in cold seasons due to the increasing of high temperature combustion processes.  All 6 stations show lower Mercury and Cupper emissions than standards (1 μg/m3). So, this area is in a satisfactory situation in terms of ambient emission of these parameters.  Regarding to the Zinc, Iron and Aluminum, no national or international standards is determined for ambient air emission, therefore, it is impossible to judge these metals emissions. However, the main sources of these metals in Rey city has been dust generated from calcareous soils (raw materials), cement clinker dust and metal smelting plants. These emissions are higher in summer than winter due to the less rain.
4. Airborne particulate matter (PM) emissions can be minimized by pollution prevention and emission control measures. Prevention, which is frequently more cost-effective than control, should be emphasized. Accordingly, some of the proposed measures to prevent or control their emissions include: 1. Management: Measures such as improved process design, operation, maintenance and other management practices, improving combustion efficiency, improving fuel injection zone configuration and combustion along with an adequate amount of excess air. 2. Choice of Cleaner Fuels: Such as natural gas, lighter distillate oil-based processes, low-ash fossil. 3. Fuel Cleaning: To reduce ash and sulfur content and/or co-firing of coal with higher and lower ash content, which can reduce ash content by up to 40%. 4. Choice of more efficient Technology and Processes: Advanced coal combustion technologies such as coal gasification and fluidized-bed combustion. 5. Select optimal particulate removal devices cyclones, wet scrubbers, electrostatic precipitators (ESPs) and bag-houses. ESPs are especially efficient in collecting fine particulates and can also capture trace emissions of some toxic metals with an efficiency of 99% and are the most cost effective according to the other equipments. Hence, continuity the monitoring and revision of filtration systems at pollutant zone are the main measures to eliminate the pollution. However, controlling emissions of many heavy metals, such as cadmium, lead, and mercury that are present as trace elements in fuels is a difficult and largely unsolved problem.