Evaluation of Atmospheric Condition of Ahmedabad, Gujarat, India

By Niki Gopani¹* and Dr. Akshey Bhargav²
May 2011

  1. Asst. Professor at Kalol Institute of Technology & Research Centre, Kalol, Gujarat, India
  2. Principal of Engineering, Kalol Institute of Technology & Research Centre, Kalol, Gujarat, India
Abstract
Understanding of the atmospheric conditions of a particular area is very important to assess the dispersion ability of pollutants from any source of air pollution. The wind rose diagrams are the important tools to represent graphically the percentage frequency distribution of wind speed and direction for a given period & location. Similarly, the atmospheric stability is an important parameter which determines the ability of pollutants to disperse in the atmosphere. The analysis of atmospheric conditions reveals that Ahmedabad region falls under highly unstable atmospheric stability class which may be considered good for dispersion of air pollutants. More ever, the plume rise from any elevated source would be relatively higher for effective dispersion of air pollutants resulting into less ground level concentration of air pollutants over a period of time and space.

Keywords: Wind rose, pollutants, air pollution, Atmospheric stability, plume rise

Present Study

An effort has been made in the present research work to prepare monthly, seasonal and annual wind roses and stability roses with a view to analyze the atmospheric conditions of Ahmedabad, Gujarat.

Applications of Wind Roses

The wind roses are the important tools for overall spatial planning and environmental policy parameter. It provides the overall scenario of sectoral winds along with their speeds to facilitate the planners to identify the locations or areas for residential colonies, commercial activities, and industrial areas & so on so forth.

These wind roses are prepared with the help of “wind rose plot view” software developed by Lakes Environmental by making use of 3 hourly wind speed and wind direction data in the prescribed format. The wind speed and wind direction data

In the present study has been obtained from the Indian Meteorological Department, Ahmedabad.

These roses have the following applications:

Similarly, the atmospheric stability roses represent graphically the % frequency distribution of different stability classes in different directions for a specified period and location. The application of stability roses are mainly in the air dispersion modeling which predict ground level air pollutant concentrations for a given air polluting source under different stability conditions.

Wind Roses Diagrams and their Analysis

Annual Wind Rose
Annual Wind Rose

Annual Wind Rose

The annual average wind rose tends to indicate predominant wind direction as SW with predominant south-westerly wind sector, followed by NW, NE & SE wind sectors.

The pre-dominant wind speed is in the range of 0.5 to 2.0 m/s followed by wind range of 2.0 to 3.0 m/s & 3.0 to 5.0 m/s. Majority of the winds have been observed below 5 m/s. The percentage of calm winds is also significant with 21.40%

Winter Wind Rose
Winter Wind Rose

Winter Wind Rose

Similarly, winter wind rose tends to indicate predominant wind direction blowing as NE along with predominant north-easterly wind sector followed by NW.

The pre-dominant wind speed is in the range of 0.5 to 2.0 m/s followed by wind range of 2.0 to 3.0 m/s & 3.0 to 5.0 m/s and > 6 m/s. Majority of the winds have been observed below 5 m/s. The percentage of calm winds is also significant with 29.38%

Summer Wind Rose
Summer Wind Rose

Summer Wind Rose

Moreover, summer wind rose tends to indicate predominant wind direction as SW along with predominant south-westerly wind sector followed by NW.

The pre-dominant wind speed is in the range of 0.5 to 2.0 m/s followed by wind range of 2.0 to 3.0 m/s & 3.0 to 5.0 m/s and > 6 m/s. Majority of the winds have been observed below 5 m/s. The percentage of calm winds is 11.1

Monsoon Wind Rose
Monsoon Wind Rose

Monsoon Wind Rose

Monsoon wind rose tends to indicate majority of predominant wind direction as SW along with predominant south westerly wind sector followed by NW.

The pre-dominant wind speed is in the range of 2.0 to 3.0 m/s followed by wind range of 0.5 to 2.0 m/s & 3.0 to 5.0 m/s and > 6 m/s. Majority of the winds have been observed below 5 m/s. The percentage of calm winds is 18.89.

Post Monsoon Wind Rose
Post Monsoon Wind Rose

Post Monsoon Windrose

Finally, post monsoon average wind rose tends to indicate predominant wind direction as NW along with predominant north-westerly wind sector followed by NE, SW & SE.
The pre-dominant wind speed is in the range of 0.5 to 2.0 m/s followed by wind range of 2.0 to 3.0 m/s & 3.0 to 5.0 m/s. Majority of the winds have been observed below 5 m/s. The percentage of calm winds are quite significant of the order of 38.31.

The analysis of seasonal wind roses would show that the predominant wind direction is SW during summer & monsoon where as NE during winter and NW in post monsoon. The pre-dominant wind speed is in the range of 0.5 to 2.0 m/s during summer, winter and post monsoon season for monsoon season pre-dominant wind speed is in the range of 2.0 to 3.0 m/s.

The analysis of Annual wind rose reveals the fact the predominant wind direction is SW with predominant south-westerly wind sector, followed by NW, NE & SE wind sectors and in all the cases the average wind speeds are less than 1m/s which can be classified as low wind speeds during 2009 for Ahmedabad city. The calm conditions during 2009 are of the order of around 21.40%.

Atmospheric Stability

The atmospheric stability is defined as the ability of the atmosphere for the dispersion of air pollutants released from various air polluting sources.

The atmospheric stability is further classified under six categories starting from category A to category F. The atmospheric category A represents highly unstable atmosphere followed by B as unstable, C as slightly unstable, D as neutral, E as stable and F as highly stable. Highly unstable atmosphere is good for dispersion of air pollutants where as highly stable is known to have poor dispersion ability.

Atmospheric stability roses and their analysis

The atmospheric stability roses are defined as the graphical representation of the percentage frequency of different stability classes in different directions. These stability roses are primarily used in the air dispersion modeling for the prediction of air pollutant concentration over a period of time and space under different atmospheric stabilities.

The frequency distributions of different stability classes are done with the help of Pasquill Stability Classes table and the stability roses are prepared with the help of WRPROVIEW Software.

An effort has also been made to prepare Atmospheric stability roses with a view to assess the dispersion ability of the air pollutants in the atmosphere.

The seasonal & annual stability roses had been prepared and shown in figures, the details of which are given here under.

Annual Stability Roses
Annual Stability Roses

The Annual stability rose for 2009 as per figure above shows atmospheric stability “A” as predominant with 33.91% of occurrence with predominant wind direction SW followed by NW, NE & SE.

Winter Stability Roses
Winter Stability Roses

Similarly, the stability rose for the Season winter of 2009 as per above figure shows atmospheric stability “A” as predominant with 67.84% of occurrence with predominant wind direction NE which is followed by NW and N.

Summer Stability Roses
Summer Stability Roses

The stability rose for the Season Summer of 2009 as per figure above again shows atmospheric stability “A” as predominant with 30.12% of occurrence with predominant wind direction SW along with predominant south-westerly wind sector followed by NW

Monsoon Stability Roses
Monsoon Stability Roses

Similarly, the stability rose for the Season Monsoon of 2009 as per above figure shows atmospheric stability “B” as predominant with 31.9 % of occurrence with predominant wind direction SW along with predominant south westerly wind sector.

Post Monsoon Stability Roses

Post Monsoon Stability Roses
Post Monsoon Stability Roses

The stability rose for the Season Post Monsoon of 2009 as per figure above again shows atmospheric stability “A” as predominant with 38.3% of occurrence with predominant wind direction NW along with predominant north-westerly wind sector followed by NE, SW & SE.

Conclusions

The analysis of monthly stability roses reveals the fact that the atmospheric condition falls under category A which is classified as highly unstable. The % of occurrence under this category ranges from a minimum of 27.8% in the month of November 2009 whereas maximum of 48.66% in February 2009. The other atmospheric class “B” occurs in May, June, July and august month. The stability class B ranges from 33.46 to 37.90 %.

The predominant wind directions change monthly but having regard to seasonal months. For example, winter month (Nov. - Jan.) indicate NE as predominant wind directions, whereas, Feb to April shows NW, May to August SW as predominant wind directions. The months September and Octomber appears to be peculiar months which shows W and NW respectively as predominant wind direction.

Similarly, predominant wind speed range is 0.5 - 2 m/s during months September to April ( 8 months ) but 3 - 5 m/s shows in the months May and June, possibly due to summer months and turbulence created during these months. For July and Aug. months, the wind speed is predominant in the range of 2 - 3 m/s.

The seasonal wind direction have been found changing more as in all the seasons, the predominant atmospheric stability falls under class “A” except in monsoon season where it is under class “ B”.

The atmospheric conditions of Ahmedabad tends to indicate that the plume rise from any air polluting industry would relatively be higher resulting into less ground level concentration of air. This fact has been demonstrated in the research work being carried out by the author for Vehicular air pollution of Ahmedabad city. Moreover, according to Pasquill, the amount of turbulence in the ambient air has a major effect upon the rise and dispersion of air pollutant plumes. The amount of turbulence can be categorized into defined increments or "stability classes". According to him class A denotes the most unstable or most turbulent conditions and Class F denotes the most stable or least turbulent conditions.

Acknowledgement

I would like to express my deep and sincere gratitude to the institute, L. D. College of Engineering, Ahmedabad for providing me this opportunity. I am highly thankful to Prof. Dr. Akshey Bhargava, my guide, who has been Ex. Member Secretary, Rajasthan Pollution Control Board, Jaipur visiting Prof. L. D.College of Engg. and CEPT University and presently Principal, Kalol Institute of Technology and Research Centre. I also owe my gratitude to IMD (Indian Meteorology Department for providing me valuable inputs and data for this research work.

References

  1. "Air Pollution Meteorology", U.S.Dept. of Health, Education and Welfare, Washington DC, 1971.
  2. Magill, P.L., F.R. Holden and C. Acklay, "Air Pollution Handbook", McGraw-Hill Book Co., Inc., New York, 1956.
  3. Meteorological and Environmental System, Catalogue, CLIMATE Instruments Company, USA.
  4. Pasquill, F., "Atmospheric Diffusion", Van Nostrand and Co. Inc. USA, 1962.
  5. Perkins, H.C., "Air Pollution", McGraw-Hill Kogakusha Ltd., Tokyo, 1974.
  6. Stern, A.C. (Ed.), "Air Pollution", vol. 3, 2nd edn., Academic Press, New York, 1968.
  7. Strauss, W. (Ed.), "Air Pollution" Part-III, Wiley-Interscience, New York, 1978.

***

Copyright © 2011, ECO Services International