TEMPERATURE AND RELATIVE HUMIDITY FACTORS DURING FUMIGATION

It was noted that when the chamber was closed the temperature and relative humidity coditions inside and outside the chamber varied considerably and altered conditions prevailed for more than 3 hr (Figure 1.1). The conditions inside remained constant, while outside the chamber, that is in the laboratory, these varied as the day progressed. Such differences were natural between well-ventilated laboratory and a closed chamber. The relative humidity was invariably higher inside the chamber except towards the evening when outside conditions were more humid.

Since most of the fumigations were carried out from late morning onwards, efforts were made to modify the chamber conditions by creating better circulation inside the chamber. For this purpose, a series of minifans were installed taking care to see that the fans covered all parts of the chamber. This way, it was noticed thatthought the temperature remained high inside the chamber relative humidity could be maintained at a reasonable level (Figure 1.2). Some mild temperature fluctuations inside the chamber, however, were noticed, with corresponding changes in relative humidity. These were sought to be corrected with stabilizers for power supply since no other cause was thought possible.

After putting some plants inside the chamber, again the temperature and relative humidity went up inspite of the fans (Figure 1.3). Since the rise in temperature and relative humidity were within the range naturally occuring in the city, it was decided to proceed with the fumigation work, under the acknowledged static conditions of the chamber, wherein slightly higher temperature and relative humidity conditions prevailed for the duration of the experiment.

It is also to be remembered that with absorption of the pollutant gas, its net concentration inside the chamber would progressively diminish. However, this change was not expected to be a major one at sub-ppm level of concentration of the gas in a big chamber of the volume (5.44 cu m) constructed for this work, especially within a short duration of 3-4 hr; a duration selected on the consideration that in this city wind direction changes take place every 4 hr approximately.

EMISSION AND ESTIMATION OF GASEOUS AMMONIA INSIDE THE CHAMBER

At N. T. P., 17 gm of ammonia occupies 22,400 cc. Under laboratory conditions where the temperature was 27°C and pressure was 760mm Hg the volume occupied by 17 gm ammonia would be 24,640 cc. Accordingly, 11.5 ml of 1 M freshly prepared liquor ammonia becomes necessary for occupying a chamber of 5.44 cu m capacity at approximately 50 ppm concentration. A few sodium hydroxide pellets were added to hasten the evolution of ammonia gas. Five minifans were used for diffusion of the evolved gas within the chamber.

After 30 min of the evolution and diffusion of gas in the chamber, actual concentration of ammonia was estimated. The air from the chamber was sucke at the rate of 2 lit / min by adjusting a flowmeter, with the help of a pump, and passed through a bubbler containing 0.02 N H2S04, for 1 hr. After addition of the Nessler's Reagent, absorbance of the colour developed was read on Spectronic-20 photoelectro- colorimeter at 370 nm wave length. Calculations were done as per the following formula ( Leveggi et al., 1973 ):


Where A is absorbance at 370 nm, U. A. is unit absorbence, E is efficiency, F is flowrate, T is time, and D is dilution. It was found that at different times, the resultant concentration of ammonia in the chamber was around 30,000 ± 6,000 ug/m³, or 50±10ppm.

ACKNOWLEDGEMENT

The authors are thankful to Prof. B. C. Haldar, Director, The Institute of Science, Bombay for his help and keen interest in the work; to Dr. S. V. Soman and Mr. H. V. Rane of the Physical Chemistry Department of the Institute; and to Mr. T. N. Mahadevan of Air Monitoring Section of Bhabha Atomic Research Centre, Bombay for their suggestions.

REFERENCES

• Dennis, L. M. 1913. Gas Analysis. The Macmillan Co., N. Y. pp 273-276.
• Efremova, I. V., T. I. Duryba and V. E. Kozlova.1974. Sampling for the continuous determination of sulphuric acid and sulphur dioxide content in flue gases. Knim. Prom. Moscow. 3 : 232
• Leveggi,D. A., W. Siw and M. Feldstein. 1973.Nesslerization method of assimilation of ammonia. Air Poll. Cont. Assoc. J., 23 : 30.
• RaoRaRaoD. N. and D. Pal. 1975. A plant growth chamber for air pollution studies. Indian J. Environ, Health 17:105-110.
• Vogel, I. A. 1961. A text-book of quantitative inorganic analysis including elementary instrumental analysis. Language Book Soc. and Longman,London