Spatial Analysis of Environmental Hazards

Spatial Analysis of Environmental Hazards

Evaluation of air pollution in Tehran city by Hefter's critical Inversion method

Authors
mostafa karampour 1
mohammad saligheh 2
meysam toulabi nejad 3
zahra zarei choghabaki 3
1 assistant prof. of climatology
2 Associate Profe of climatology
3 PHD student of climatology
10.18869/acadpub.jsaeh.3.1.51
Abstract
In issues related to air pollution, the thickness of the boundary layer is known as the depth of the mixed layer because the pollution on the ground surface is mixed in this entire layer through turbulence processes. In most cases, the boundary of the area is clearly visible on big industrial cities. The depth of the mixed layer has an important effect in the concentration of air pollution which is dependent on the intensity and duration of solar radiation and wind speed. Usually after 2 to 3 hours from the time of maximum solar radiation, air temperature near the earth's surface reaches its maximum value. At this time convection of heat is formed in the air near the earth surface and transfers the heat from the surface to higher altitudes. These vertical movements will cause atmospheric turbulence and increase in instability. This is when the growth of the mixed layer reaches to its highest level. After sunset, night temperature inversion occurs near the surface. This temperature inversion is due to the rapid cooling of the Earth's surface. In such condition, the cold air layer is near the earth's surface and the warm air layer sits on top of it and air is in a stable condition. As a result, the accumulation of contamination, if there are sources of pollutants, will increase in the earth's near-surface layer. If the conditions remain steady during the day, the mixed layer will not have much growth and as a result, contamination in the shallow layer near the surface of the Earth reduces solar radiation.

Each year, thousands of gaseous pollutants and particulate matter are emitted in the metropolitan area of Tehran and due to the geographical and climatic conditions of Tehran, temperature inversion phenomenon is not something unexpected. By formation of the inversion layer, these pollutants will remain near the earth's surface for a long time which in turn will be the cause of a lot of heart and respiratory problems. Therefore, identifying the characteristics of this layer on polluted days is of particular importance to the health of the residents of this city.

In this research, the study area is Tehran which is in the foothills of the southern Alborz and between longitudes 51 ° 2 'to 51 degrees 36' east and latitude 35 degrees 34 minutes and 35 degrees 50 minutes northern. The height of the northernmost point of this city is 1800 and up to 1200 meters in the center and 1050 meters in the south.

To conduct this research, inversion data including temperature, wind, atmospheric pressure and humidity and vertical navigation radiosonde data at the Mehrabad weather station from January to 29 December 2013, were taken from the Meteorological Organization of country. Then the statistics of daily vertical scroll of atmosphere above the Mehrabad synoptic station was received from the University of Wyoming. Also, the hourly data of air pollutants including gaseous pollutants CO, N2O, O3, SO2 and particulate matter (PM10) were prepared from the air quality control center (AQCC) for the stations Aghdasiyeh, Geophysics, Poonak, Rey and District 11.


After receiving information about the vertical scroll of the atmosphere in Mehrabad station, in order to have a closer examination of the vertical profiles of potential temperature changes in the lower atmosphere, using daily data from the radiosonde to obtain potential temperature changes in height were measured. Then, in order to identify the days with high pollution levels (the unhealthy condition for sensitive groups) and days with good conditions, so that all stations under study were the same, based on a standard index of air pollution Table 1 was developed. In the end, 4 days with critical inversion of potential temperature, including two polluted days (February 6th and August 16th) and two clean days (9 February and 5 June) were detected. Then according to the proposed method of Hefter, the approximate height of the boundary layer was calculated for these 4 days.


In this study, it was observed that the boundary layer height in contaminated cold season of the year reached 1,200 meters in the morning hours while in the afternoon in the cold samples, it grew to 1900 meters. In the warmer months based on the height of critical inversion layer in the selected days it reached more than 6,000 meters. In pure samples of warm and cold seasons, the boundary layer height had significant growth to the extent that in the cold sample of the year it reached to 2,100 meters in the morning and 2,600 meters in the afternoon. On June 5, which is intended to represent the clean and pure heating season, boundary layer height was of 5300 meters in the morning hours which shows a 4,000-meters increase in comparison to its polluted counterpart. The point to be noted is that since the active track of potential temperature can be considered as a measure of air stability, in the critical inversion, for the case of polluted samples of morning hours that were irradiated with inversion, active track of the potential temperature was very high in them. Thus on days with radiated inversion (polluted days) we can say that border of boundary layer was based on the inverted layer. Also the methods used in these types of inversions are more efficient for the determining height of the boundary layer.
Keywords
Air pollution
inversion
potential temperature
boundary layer
chart Skew-T
Deardroff, J.W .1974. Three dimensional numerical study of the height and mean structure of heated planetary boundary layer , Boundary-Layer Meteorology, 7: 81-106. DOI:10.1007/BF00224974.
Finardi, S; Pellegini, U .2002. Systematic snalysis of meteorological conditions causing severe urban air pollution episodes in the central PO Valley ,ARIANET,viaGilino 9,20128 Milano,Italia.
Heffter,J.L .1980. Transport Layer Depth Calculations, Second Joint Conference on Applications of Air pollution Meteorology,NewOrleans,LA.
Hurley, P .2007. Modelling mean and turbulence fields in the dry convective boundary layer with the eddy-diffusivity/mass-flux approach, Boundary-Layer Meteorol, 125:525–536. DOI:10.1007/s10546-007-9203-8.
Lin, J.; Michael B. M .2010. Impacts of boundary layer mixing on pollutant vertical profiles in the lower troposphere: Implications to satellite remote sensing, Atmospheric Environment, 44: 1726–1739. DOI: 10.1016/j.atmosenv.2010.02.009.
Panofsky H.A., Dutton J A. 1984. Atmospheric eturbulence, NewYourk,Willey&Sons,Inc ,397 pp.
Pesenson, I .2002. Implementation and evaluation of the Heffter Method to calculate the height of the planetary boundary layer above a southern Great Plains site, http://escholarship.org/uc/item/6pp1d93m.
Stull,R, B. 1993. An Introduction to Boundary Layer Meteology,Kluwer Academic publishers .
Stull,R, B .1988. An Introduction to Boundary Layer Meteorology.Dordrecht, Kluwer Academic publishers.p670.
Wyngaard, D. A.; Kaimal, J. C.; Haugen, O. R.; Coté, Y.; Izumi, S. J.; Caughey, and C. J. Readings .1976. Turbulence Structure in the Convective Boundary Layer, Journal of the atmospheric sciences, 33, 2152–2169. DOI: 10.1175/1520-0469(1976)0332.0.CO;2
Wyngaard, J; Richard B .1983. Top-down and bottom-up Diffusion of a scalar in the convective boundary layer, Journal of the atmospheric sciences. 41: 102–112.
DOI: 10.1175/1520-0469(1984)0412.0.CO;2.
USPEA,1998,Guidelin for Reporting of Daily Air Quality-Pollutant Standards Index –(PSI) Environmental Protection Agency,Washangton, DC.
Vardoulakis, S.; Kassomenos, P. 2008. Sources and factors affecting PM10 levels in two European cities: Implications for local air quality management, Atmospheric Environment, 42 (17): 3949-3963, DOI: 10.1016/j.atmosenv.2006.12.021.
Yin, S.; Shen, Z.; Zhou, P.; Zou, X.; Che, S.; Wang, W .2011. Quantifying air pollution attenuation within urban parks: An experimental approach in Shanghai, China, Environmental Pollution, 159(8-9): 2155-2163, DOI: 10.1016/j.envpol.2011.03.009.