Statistical-Synoptic Analysis of CO pollutant Density according to wind direction and speed and its hazard in Tehran City

Document Type : Applied Article

Authors

1 Msc of Climatology, Faculty of Geographical Sciences, Kharazmi University

2 Assistant Professor of Climatology, Faculty of Geographical Sciences, Kharazmi University

3 Professor of Climatology, Faculty of Geographical Sciences, Kharazmi University,

4 PhD Student of Climatology, Faculty of Geographical Sciences, Kharazmi University

Abstract

Air pollution is one of the environmental hazards in metropolitans which made the life very expensive and even hazardous during last decades. The main aim of the present study is to determine the synoptic patterns which lead to formation and intensification of stable atmospheric conditions in cold seasons of year. The present study investigated the thermal and dynamic systems that lead to stable atmospheric conditions in Tehran in the cold season. In this study statistical, synoptic and Thermo-dynamic methods are used to achieve the objectives.The wind characteristics in all geographical directions (16 directions) were examined in a 10-year period in Tehran City. In order to calculate the correlation between CO and wind speed, Pearson Correlation Method and regression analysis were used in SPSS and MS Excell. The results showed a significant correlation between CO emissions and wind speed in all directions, but by separating all 16 wind directions, the highest correlation (significant at 99% confidence level) between the wind speed at the directions of NW ,SSE and W was observed which means that by increasing the wind speed, the density of CO emissions reduced (and vice versa). Another result from wind analysis is that there is a direct correlation between NE and ENE directions and CO pollutant which means that by increasing the wind speed in mentioned directions, the density of CO emissions increased as well. Also results showed that average wind speed in polluted days is 1.3 meter per second which is far less than the average of 2.5 meter per second in the period.
For synoptic analysis, 14 severe polluted days in cold seasons were selected during the period of 2002 to 2012. Maps of MSLP, 700 and 500 hpa and vorticity map in Grads software were drawn using ECMWF reanalysis data.
The results showed that most of the selected polluted days have followed the same synoptic pattern in which high pressure systems dominated and Tehran is located in the ridges axis and due to convergence in upper-air levels, subsidence had occurred near surface levels and the negative vorticity in the region intensified the air pollution. In Thermo-dynamic analysis, by drawing SkewT diagram in Raob software, the type and altitude of inversion, is determined. According to the results, The air pollution severity becomes very hazardous and critical at the times which radiational inversion occurs in altitudes less than 100 meters. Also results showed that in stable atmosphere, wind speed is very low from earth to mid levels of troposphere.
 
 

Keywords

References

 
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Environmental Management Hazards
Volume 2, Issue 4
January 2016
Pages 439-450

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