Nitrogen Dioxide Content in Air

 

Independent Research Project

 

Ecology

 

November 4th, 1998

 

Marcie M. Fox

Abstract:

TNT containing explosives are one of the numerous modes by which free nitrogen can become a part of the earth’s atmosphere. If presented in high enough concentrations over a long period of time, the Nitrogen dioxide which is formed within the atmosphere as a result of these explosions can be very dangerous to the human respiratory system. I was particularly interested in this topic since I grew up in an area where there are numerous limestone quarries. My hypothesis going into this investigation was that atmospheric Nitrogen dioxide levels would be higher in an area where explosives are used than in an area where they are not. To test this hypothesis, I chose two different sites where measurements were taken, one being a limestone quarry where TNT explosives were regularly used, and the other a natural setting surrounding a pond where no explosives were used. In order to collect my data, I used the LaMOTTE Company Air Sampling Pump (Model BD, Code 1944) together with the accompanying Nitrogen Dioxide In Air Test Kit (Code 7690) made by the same company. Eight samples were collected at each site, and a statistical t-test was performed to determine whether or not Nitrogen dioxide concentrations were significantly different. The probability that the two sites had the same Nitrogen dioxide concentration was less than 0.05, . . . a statistic which supports the experimental hypothesis of this investigation.

Introduction:

Nitrogen dioxide can be formed by the natural atmospheric process of oxidation of nitric oxide or pure nitrogen gas (Bockris, 1978). There are numerous modes by which this reservoir of nitrogen may enter the atmosphere such as motor-vehicle exhaust, fertilizers, electrical storms, and explosives. It is the latter which I was interested in investigating in this project.

The molecular structure which is found on the cover of this report is that of perfectly symmetrical trinitrotoluene, otherwise known as TNT. Assembled of Carbon, Hydrogen, Oxygen, and Nitrogen, TNT is a very powerful explosive which begins as a compact solid. The individual molecules collapse when jolted, enabling the Oxygen atoms to combine with the Carbon and Hydrogen atoms to form Carbon Dioxide and Water Vapor respectively (Whitten, Gailey, and Davis, 1992). This collapse then frees the Nitrogen atoms which thereupon form Nitrogen gas. It is this Nitrogen gas that can then be broken down and oxidized to form Nitrogen dioxide through a series of atmospheric chemical reactions (Whitten, Gailey, and Davis, 1992):

N2(g) + O2(g) ® 2NO(g)

2NO(g) + O2(g) ® 2NO2(g)

I was particularly interested in this topic since I grew up in an area where there are numerous limestone quarries. TNT explosives are used within these quarries as the primary means of rock disruption. If presented in high enough concentrations over a long period of time, the Nitrogen dioxide which is formed within the atmosphere as a result of these explosions can be very dangerous to the human respiratory system. It can penetrate to the smaller airways and the alveoli where crucial gas exchange occurs (Bockris, 1978). Nitrogen Dioxide can significantly damage these airways, or even destroy, them by causing them to either collapse or fill with fluid (Bockris, 1978), leading to very serious respiratory and health problems.

Hypothesis:

My hypothesis for this investigation was that atmospheric Nitrogen dioxide levels would be higher in an area where explosives are used than in an area where they are not. To test this hypothesis, I chose two different sites where measurements were taken:

Site #1 - Halquist Stone Quarry

This is a limestone quarry in Sussex, WI where I grew up.

TNT explosives are used here as a means of rock disruption.

Site #2 - Hunter’s Ridge Pond

This is a small man-made pond located in the middle of the subdivision

where I currently live in Pewaukee, WI. It is a very open and natural

setting with very little traffic and no periodic use of explosives.

Methods:

The data for this investigation were collected on Tuesday October 20th, 1998 between the hours of 10:00 a.m. and 3:00 p.m.. I chose to collect all of my data on the same day so as to keep the investigation as controlled as possible. This way there would be no additional means of interference such as one set of data being collected on a clear day, and the other on a rainy day where Nitrogen dioxide levels may have been elevated due to the storm rather than the explosives. In order to collect my data, I used the LaMOTTE Company Air Sampling Pump (Model BD, Code 1944) together with the accompanying Nitrogen Dioxide In Air Test Kit (Code 7690) made by the same company.

I chose to collect eight measurements from each site so that statistical analysis of their differences was possible. Each sample was collected in the same manner as indicated in the LaMOTTE procedure, The Air Sampling Pump was allowed to bubble the atmospheric gas through 10 ml of Nitrogen Dioxide Absorbing Solution for 10 minutes at 0.2 Liters per minute (LaMOTTE, 1996).

Each of these samples was then treated with the Nitrogen dioxide reagents #2 and #3 and placed into the octet comparator. This device allowed for a concentration comparison based upon any apparent color change within the sample solutions after reagent treatment. Any color change was recorded in the data table as a comparator index number, which was then matched with a certain concentration of Nitrogen dioxide according to the following table:

NITROGEN DIOXIDE IN AIR CALIBRATION CHART

TIME COMPARATOR INDEX NUMBER

Minutes

1

2

3

4

5

6

7

8

1

0.00

2.8

7.0

14.0

21.0

28.0

42.0

56.0

5

0.00

0.56

1.40

2.80

4.20

5.60

8.40

11.20

10

0.00

0.28

0.70

1.40

2.10

2.80

4.20

5.60

15

0.00

0.19

0.47

0.93

1.40

1.87

2.80

3.74

20

0.00

0.14

0.35

0.70

1.05

1.40

2.10

2.80

values in ppm (LaMOTTE, 1996)

The actual measurements and index numbers for this investigation were as follows, and will be explained in greater detail later in this report:

DATA:

Nature

Quarry

Index Number

Concentration

Index Number

Concentration

Site #1

1

0.00 ppm

1

0.00 ppm

Site #2

1

0.00 ppm

1

0.00 ppm

Site #3

1

0.00 ppm

2

0.28 ppm

Site #4

1

0.00 ppm

1

0.00 ppm

Site #5

1

0.00 ppm

2

0.28 ppm

Site #6

1

0.00 ppm

1

0.00 ppm

Site #7

1

0.00 ppm

1

0.00 ppm

Site #8

1

0.00 ppm

2

0.28 ppm

 

 

Results:

The results for this investigation were obtained by statistical analysis of the differing Nitrogen dioxide concentration for the two sites. A statistical t-test was performed in order to determine whether or not the data sets were significantly different, which proceeded as follows:

Data

ppm Nitrogen dioxide in Air

(Natural Setting) 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

(Quarry Setting) 0.00 0.00 0.28 0.00 0.28 0.00 0.00 0.28

The null hypothesis is that both sites exhibited the same concentration of Nitrogen dioxide in the air, and the alternative hypothesis is that the Nitrogen dioxide concentration at the quarry is higher than that in the natural setting.

H0 : m N = m Q

Ha : m N < m Q

Statistics

S yN = 0.00 S yQ = 0.84

(S yN)2 = 0.00 (S yQ)2 = 0.71

S (yN2) = 0.00 S ( yQ2) = 0.24

yN = 0.00 yQ = 0.11

syN2 = 0.00 syQ2 = 0.021

sp = 0.10

t = -2.0

0.025 < P < 0.05

NOTE : Detailed calculations are attached at the end of the report.

Discussion:

Since a statistical analysis of the two sites indeed shows that the null hypothesis must be refuted in this investigation (probability that both sites have the same concentration of Nitrogen dioxide in the air is less than 0.05), it is safe to say that the initial experimental hypothesis has been supported by this data. There is indeed a statistically significant difference in Nitrogen dioxide concentration between the two sites, with a higher concentration being found at the Quarry. Based upon the design of this investigation it is also safe to say, though without absolute certainty, that the reason for this elevated concentration is the use of TNT explosives. There are a few circumstances which could be considered in further investigations, however,

My data was collected 11 days after a TNT detonation. Another investigation may look at the rate at which Nitrogen dioxide is removed from or dispersed throughout the atmosphere with regards to time. Nitrogen dioxide concentrations may be extremely high, for example, in the first two weeks of detonation, but taper off greatly after a month or two. The health standard for Nitrogen dioxide is 0.05 ppm over the course of a year (Whitten, Gailey, and Davis, 1992). Anything greater than that can be toxic and extremely dangerous to the human respiratory system. In comparison to the 0.05ppm standard, this investigation’s results were very high. In order to be justly investigated, however, Nitrogen dioxide levels should be measured over a longer period of time (six months to a year).

Another possibility for further investigation would simply by to modify the method of data collection. There were notes within the LaMOTTE procedure indicating that longer test periods, such as 15 or 20 minutes rather than the ten minutes which were used in this investigation, would lead to more accurate results if the majority of concentrations are very low. This leads me to believe that a longer test period may have shown some traces of Nitrogen dioxide even in the atmosphere of the natural pond setting which could then be compared to possibly even more accurate concentrations from the quarry. Lack of time and lack of resources prevented me from attempting this further investigation.

References

Bockris, J., O’M. 1978. Environmental Chemistry. Effects of Exhaust Pollutants. Pages 248 - 249.

LaMOTTE Company, Nitrogen Dioxide in Air Test Kit Procedure Sheet. 1996.

Whitten, K. W., Gailey, K. D., and Davis, R. E.. 1994. General Chemistry, Fourth Edition. Nitrogen Oxides and Photochemical Smog. Pages 914 - 916.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Nitrogen Content In Air

Author:

Marcie M. Fox

Date Data Collected:

October 20th, 1998

Variable Names:

Q = Quarry

N = Nature

Units of Measure:

ppm (parts per million)

ml (milliliter)

min (minute)

Lpm (liters per minute)

Methods:

a) Air sampling pump was allowed to run for 10 minutes at 0.2 Lpm

b) Solution was treated with two additional reagents

c) Color change was detected and compared within comparator

d) Resulting index number was matched to a concentration on table

 

 

 

 

 

DATA:

Nature

Quarry

Index Number

Concentration

Index Number

Concentration

Site #1

1

0.00 ppm

1

0.00 ppm

Site #2

1

0.00 ppm

1

0.00 ppm

Site #3

1

0.00 ppm

2

0.28 ppm

Site #4

1

0.00 ppm

1

0.00 ppm

Site #5

1

0.00 ppm

2

0.28 ppm

Site #6

1

0.00 ppm

1

0.00 ppm

Site #7

1

0.00 ppm

1

0.00 ppm

Site #8

1

0.00 ppm

2

0.28 ppm