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Application of the Laser at measurement of particle size distribution in Tehran atmosphere (Iran)

Farah Halek , Ali Kavousi
Environmental Department,
Materials & Energy Research Center
Tehran, IRAN
Email: f-halek[at]merc.ac.ir  -  fhalek[at]yahoo.com
 

Tehran is located in a valley at the foot of the Alborz Mountains in northern Iran (35 degrees latitude north). Urban expansion in Tehran resulted from a high rate of population growth and rural-urban migration combined with a strong tradition of centralization in the capital. Much attention has been focused on particulate phase components of exhaust fumes due to possible acute and chronic respiratory effects. Tehran urban areas with poor ventilation, unfavorable geographical and meteorological conditions, and a high number of emission sources including motor vehicles experience air pollution problems especially suspended particles.

The ability of fast measurement of particulate materials including aerosols has consequences and impact on the environmental sciences, on human health, and on industrial process control. The first objective of this study was to measurement of PM in twenty sites in central areas in Tehran. Other objectives were to obtain detailed measurements of aerosol size distribution in Tehran's atmosphere during the 2006.

One of the most widely used method in sizing particulate materials is the laser diffraction (L.D). The Portable Aerosol Spectrometer model 1.108 GRIMM is capable of simultaneous measurement of inhalable, thoracic and respirable dust in different size ranges from 0.3 up to 20 μm. The model 1.108 uses a light scattering technology for single-particle counts, whereby a semiconductor-laser serves as the light-source. This spectrometer measures in real-time the particle size and mass distribution, generated through a scattering laser light, than permitting a validation/correlation by weighing the sampled dust collected on the integrated filter. It is capable to read EPA Environmental PM10, PM2.5 and PM1.0 values of 15 channels in real time and particle size distributions in count modes of 15 channels at same time simultaneously. To obtain the role of motor vehicles in particulate emissions, Hourly samplings were done for 10-12 hours (8:00 am to 18:00 – 20:00 pm).

In all samples the mean of PM10 and PM2.5 are high (77.53 µg/m3 and 19.32 µg/m3 respectively). The highest value of PM10 -average in sampling period- was found in Vali-Asre Square station 159.62 µg/m3 and the highest PM2.5 concentration is found 37.93 µg/m3 at the Enghelab Square station. Air pollution in Tehran atmosphere are higher than the U.S. National Ambient Air Quality Standards (NAAQS) for particulate matter less than 10 and 2.5 μm (PM 10 and PM2.5). In most stations mean of PM values were more than standards (annual standard 50 μg/m3 for PM10 and 15 μg/m3 for PM2.5).

The average of PM1.0 concentration was 11.72 μg/m3 and the highest PM1.0 were found 20.32 µg/m3 at the Enghelab Square.
 

 

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