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Nitrogen Dioxide (NO2) Concentrations in the Greater Pittsburgh Area

Kristina Marks

Advisor: Dr. Dan ShortRobert Morris University

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Abstract

A comprehensive assessment of levels of the pollutant gas nitrogen dioxide (NO2) in the atmosphere is required for developing effective strategies for air quality control methods. The Palmes diffusion tube method is an inexpensive and accurate method of measuring NO2. The Atmospheric Research Kit (ARK), which utilizes Palmes tubes, was developed as an educational tool for high school teachers and their students in Allegheny County. The ARK was used to measure NO2 concentrations at various sites in the Greater Pittsburgh Area for a six month period. Results from the Palmes method were standardized against the EPA’s approved chemiluminescence technique. The study recorded daily, weekly, monthly and annual variation in NO2, via chemiluminescence; with monthly NO2 PDT measurements at all 7 sites having close correlation with Allegheny Heath Department’s routine monitoring of both an urban and rural (background) sites. The study also investigated meteorological factors; finding a negative correlation between temperature and NO2 concentrations, and no correlation with snowfall and rainfall. The Palmes method average NO2 concentration of 15ppb RMU for the six month period was ±1 ppb from the chemiluminescence monitor average, indicating the reliability of the PDT method.

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1. INTRODUCTIONNitrogen dioxide (NO2) is a reddish-brown gas that belongs to a family of highly reactive

gases called nitrogen oxides (NOX). These gases form primarily when fuel is burned at high temperatures, and come principally from motor vehicle exhaust and other fuel combustion sources. NO2 plays major roles in the atmospheric reactions that produce ground-level ozone or smog and acid rain, which potentially causes human health concerns (Heal, 2002). In order to assess the potential effect of NO2, as well as develop strategies for effective control of NO2 pollution, monitoring of atmospheric gas pollutants must be accurate and reliable. There are two methods routinely used for the monitoring of atmospheric NO2; (i) chemiluminescence method, (ii) Palmes diffusion tube (PDT) method. Nitrogen dioxide is routinely monitored using fixed location chemiluminescence analyzers which require an on-site power source. Due to those requirements, extensive ground-based air quality monitoring over wide geographical areas presents serious difficulty and is no longer widely undertaken.

The Atmospheric Research Kit (ARK) was developed in order to engage school students (local) in the study of atmospheric pollutant gases, showcasing spectroscopic analysis as an important scientific technique; and to test the reliability of Palmes diffusion tubes against chemiluminescence monitors. The project was grant funded and lasted from September to March. The five other participating schools (West Mifflin, Hopewell, McGuffey, North Hills, and South Fayette) were involved in training days on June 16 and 17, 2014. The first training day included instruction of how to properly use an auto pipet and an overview of UV-Visible spectroscopy. The second training day was an overview of NO2 measurements and introduction to the Palmes diffusion tube method. The grant was sponsored by the Colcom Foundation, a local environmental foundation. Colcom provided the funds for the ARK kits and the installation of a chemiluminescent analyzer at Robert Morris University (RMU). Support is given by RMU in the form of laboratory space and supplies. The goal of the study was the compare and contrast measurements of nitrogen dioxide over a wide variety of locations in the Pittsburgh area and to use the project as a whole to help promote awareness of Pittsburgh’s air quality issues in the local community.

2. ENVIRONMENTAL IMPACTS OF NITROGEN DIOXIDENO2 is a major component in the atmospheric reaction that produces ground-level ozone,

and is also a strong oxidizing agent that reacts in the atmosphere to form nitric acid, a key component of acid rain/deposition. In addition to these negative effects on our atmosphere, the amounts of NO2 that are being produced today can have dire consequences on human respiratory health and so they must be monitored to ensure safe living conditions.

Photochemical smog is a unique type of air pollution which is caused by reactions between sunlight, nitrogen dioxide and hydrocarbons (HCs). Photochemical smog forms through a series of chemical reactions among those compounds in the atmosphere. When nitric oxide (NO), a component of the exhaust from cars and power plants, enters the atmosphere, it reacts with oxygen to produce NO2. The sun's UV rays then can break nitrogen dioxide down, which leads to the formation of low-level ozone (O3). Ozone's presence at the ground level is what poses a serious health risk.

Another problem associated with elevated levels of NO2 in the atmosphere is acid deposition. Acid deposition is formed primarily from sulfur oxides (SOX) and NOX reacting with water in the atmosphere to form sulfuric acid and nitric acid; its two major components. When

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the newly acidified precipitation reaches the ground it can have several negative effects on the local area. Perhaps one of the better known effects is acidification, a condition in which lakes and streams have a low pH level due to the acid deposition, resulting in the death of a variety of animal and plant life that cannot survive in the poor conditions. Soils are also affected by acid deposition, particularly in areas with highly siliceous bedrock (granite, gneisses, quartzite, and quartz sandstone) that is already partially acidic. When acid deposition occurs on acidic soils, important cations including potassium, calcium, magnesium, and sodium are readily leached out, making them unavailable to plants as nutrients. This occurrence, termed soil depletion, reduces the fertility of the soil. Similarly, in areas with old, highly leached soils, acid deposition depletes the small amounts of cations present, and the soil soon becomes unable to support plant life.

Elevated levels of NO2 in our atmosphere and environment has led to some major human health concerns. The health effects associated with breathing ground level ozone caused by photochemical smog. Studies have shown that O3 can cause negative pulmonary function responses and alterations in lung function and breathing patterns of otherwise healthy test subjects. These effects are compounded when suffering from a multitude of other respiratory issues (i.e., asthma, chronic obstructive pulmonary disease, etc.). Similar health problems exist when dealing with nitrogen dioxide by itself. For instance, studies have shown that bronchitis symptoms of children with asthma increase in association with annual NO2 concentration, and that reduced lung function growth in children is linked to elevated NO2 concentrations within communities already at current North American and European urban ambient air levels. Monitoring nitrogen dioxide is vital in understanding exposure patterns and to establish a link between exposure and health effects (Atkins, 1986).

3. SAMPLING PLAN, QUALITY CONTROL AND EXPERIMENTSThe Atmospheric Research Kits (ARK) of Palmes diffusion tubes were sent to five

different schools in the Pittsburgh area between May and June of 2014 (table 1).

School LocationRobert Morris University (RMU) Lat: 40˚31’14”N Long: 80˚12’39”WColfax Upper Elementary (CUE) Lat: 40˚32’29”N Long: 79˚46’56”WWest Mifflin (WMHS) Lat: 40˚22’40”N Long: 79˚52’80”WSouth Fayette (SFHS) Lat:40˚22’33”N Long: 80˚10’14”WMcGuffey (MHS) Lat: 40˚7’4”N Long: 80˚24’37”WHopewell (HHS) Lat: 40˚35’18”N Long: 80˚15’11”WNorth Hills (NHSHS) Lat: 40˚31’30”N Long: 80˚1’37”W

Table 1: Sampling sites

Since the participants at Colfax Upper Elementary (CUE) were not comfortable acting as analysts (due to the age of their students) their location was used both as a sampling site and inter-laboratory quality control. CUE provided tube samples to all six participating site for comparison. Training in the use of the devices for the schools was undertaken on June 16 and 17, 2014. Beginning in September 2014, the Palmes diffusion tubes were placed at designated sampling site at RMU along with CUE, North Hills Senior High School (NHHS), West Mifflin High School (WMHS), South Fayette High School (SFHS), McGuffey High School (MHS),

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Hopewell High School (HHS), Harrison Township (HT), and Lawrenceville. RMU is located in Moon Township, CUE in Springdale, HHS in Aliquippa, MHS in Claysville, NHHS north of Pittsburgh, SFHS in McDonald, and WMHS in West Mifflin (figure 1). At the beginning of September, twenty diffusion tubes were prepared with the three stainless steel screens coated with TEA solution. Those tubes were sealed and kept in a container away from outdoor air pollutants. Each month one stability tube was analyzed with the RMU and CUE diffusion tubes to test how long the prepared diffusion tubes can be used before contamination. The PDT concentrations were to be compared to two different chemiluminescent analyzers operated by the Allegheny County Health Department (ACHD) at fixed locations in Lawrenceville (LAW) and Harrison Township (HT). One location was in LAW for the comparison of the Pittsburgh high school PDT. A chemiluminescence monitor on the RMU campus was also used to compare the monthly concentration of the RMU PDT. The RMU PDT average monthly concentration was compared to the monthly average snowfall, temperature, and rainfall in order to determine the existence of any correlations.

Figure 1: Sampling locations: crosses denote ARK sites and asterisks denote chemiluminescent analyzer sites

Testing Period

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The deployment dates for RMU site and CUE were recorded by the inter lab personnel.

RMU CUESeptember 8/29/14 – 10/2/14 9/3/14 – 10/3/14

October 10/2/14 – 11/4/14 10/3/14 – 11/3/14November 11/5/14 – 12/8/14 11/3/14 – 12/3/14December 12/8/14 – 1/14/15 12/3/14 – 1/6/15January 1/17/15 – 2/17/15 1/3/15 – 2/3/15February 2/10/15 – 3/10/15 2/3/15 – 3/3/15

Table 2:RMU deployment dates compared to CUE

4. ANALYTICAL METHODSThe Allegheny County Health Department (ACHD) and the Environmental Protection

Agency (EPA) routinely monitors nitrogen dioxide using chemiluminescence fixed monitors and Palmes diffusion tubes.

4.1 Palmes Diffusion TubesPassive diffusion tubes (figure 2) are an acrylic tube, a removable cap, a fixed cap, and

three stainless steel screens coated with TEA – triethanolamine. Passive diffusion tubes were originally designed to be on-person samplers with a method developed for industrial environments (Palmes et al., 1976; and Shooter, 1993).

Figure 2: Palmes Diffusion Tube (PDT)

Over time, passive samplers were created for measuring NO2 in indoor (Spengler et al., 1983; Hoek et al., 1984; Noij et al., 1986; Colbeck, 1998) and outdoor environments. Atkins et al. (1986) has shown diffusion tubes used for experimental studies of numerous pollutants including SO2, CO, O3, and VOCs; as well as in multiple different countries. Passive samplers, developed by Palmes, Gunnison, DiMattio, and Tomczyk (1976), provide a convenient alternative for measuring NO2 in a highly inexpensive, accurate, and simple manner. The method has been thoroughly described by Shooter (1993). NO2 is absorbed onto TEA for a one month period. After that month, nitrite concentrations is measured by spectroscopy (figure 3) and converted into an NO2 concentration using Fick’s law of diffusion.

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Figure 3: Diagram of Beer-Lambert

Each individual piece of the Palmes diffusion tubes, along with the stainless steel screens are all placed in the sonicator. The sonicator is used as a mechanism to loosen up particles adhering to surfaces, such as the stainless steel and diffusion tubes, in ultrasonic cleaning. The components of the PDTs and stainless steel screens are placed in the drying oven in order to control for contamination and speed up the process. All glassware was acid washed to remove contamination.

The TEA – triethanolamine – solution was prepared with 50% deionized water and 50% solution to coat the screens for 10 minutes before being placed into each PDT for that particular month testing period. Once three screens are inserted into each of the three tubes, plus a method blank, the three samplers are positioned using mounting devices (figure 4). They are placed vertically at a height of 1.5–4 m from the ground surface (Palmes, 1976). The sample blank is retained with its cap intact, while the remaining tubes are exposed to the NO2 by removing their red cap (Aoyama and Yashiro, 1983). After exposure period, which in this experiment was typically 4 - 5 weeks, all samplers including the field blanks are collected and begin the process of chemical analysis.

Figure 4: sampling apparatus

AnalysisThe ARK kit used in the experiment provides enough materials for the preparation of a single

batch of reagents. These chemicals are stable for six months if stored in a sealed dark container and refrigerated. Storage containers should be covered with black paper or tape in order to preserve the light sensitive compounds.

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Standard PreparationPalmes diffusion tube NO2 concentrations are determined using a set of sodium nitrite

(NaNO2) calibration standards (figure 5). It is very important that the solutions are made up carefully, and accurately as the standards are used in the concentration calculation. The following steps were taken to prepare the standards:

STEP 1: A solution of 800 ppm NaNO2 is first prepared by adding 1.200 g of NaNO2 to 1 L of DI water in a volumetric flask. The flask should be capped and mixed thoroughly (50 inversions).

STEP 2: A working standard of 40 ppm NaNO2 is prepared by adding 5 mL of the 800 ppm solution to 100 mL of DI water in a volumetric flask. The flask should be capped and mixed thoroughly (50 inversions).

STEP 3: Calibration standards of 0, 0.5, 1, 2, and 4 ppm NO2- are made by adding 0, 1.25,

2.5, 5, and 10 mL of the 40 ppm solution to five 100 mL volumetric flasks. The flasks should be capped and mixed thoroughly (50 inversions).

Standards were to always be capped and never have a pipet or stirring rod placed in them. When using standards a sub sample was always removed for use to control external contamination. All of the above solutions were stored at 4 °C in appropriate containers and properly labeled with their makers name, contents, date of production and expiration date.

Figure 5: Standard Preparation

Reagent Preparation

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There are four reagents required. Reagents I and II are stable for six months if stored in a sealed dark container and refrigerated, while reagents III and IV have two week shelf lives. 4.2mL of reagent III is added to each PDT for spectroscopic analysis (figure 6).

REAGENT I: A 2 % solution of sulfanilamide is prepared by adding 20 g of sulfanilamide into 500 mL beaker, 100 mL DI water is added. 50 mL of 85 % ortho-phosphoric acid is slowly added. The solution is made up to 1 L with DI water and stored in an amber glass or dark colored bottle.(Note: Phosphoric acid is not included in the ARK kit.)

REAGENT II: 0.14 g of N-1-Napthyl-Ethylene-Diamine (NEDD) is added to a 100 mL volumetric flask. The solution is made up to 100 mL with DI water. Store in an amber glass or dark colored bottle.(Note: NEDD is not very soluble. Add approximately 50 mL DI water and shake vigorously to dissolve before making up to 100 mL.)

REAGENT III: In a 250 mL beaker mix 100 mL DI water, 100 mL of reagent I, and 10 mL of reagent II. Swirl to mix.

REAGENT IV: In a 250 mL beaker mix 100 mL of reagent I and 10 mL of reagent II. Swirl to mix. (Note: If reagents III and IV show any signs of a pink coloration they are contaminated and should be discarded and remade.)

Figure 6: Reagent PreparationChemistry of Reaction

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NO2 reacts with TEA to produce nitrosodiethanolamine (NDELA):

Figure 7: Reaction of TEA with NO2

The nitrosoamine is then hydrolyzed in presence of H3PO4 to form nitrite:(CH2CH2OH)2N.NO + H2O → (CH2CH2OH)2NH +HNO2

Nitrite reacts with sulfanilamide:

Figure 8: Chemistry of nitrite reacting with sulfanilamide

Diazonium salt couples with NEDD to form purple azo dye (chromophore):

Figure 9: Chemistry of NEDD reacting with diazonium salt

Calculation

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The equivalence between absorbed NO2 and nitrite ion is known as the Saltzman factor. Calibration exercises have confirmed that the factor is effectively 1.0. The rate of absorption is determined by the rate of diffusion of the gas along the tube. Fick’s law states that the rate of diffusion of a gas is proportional to the concentration gradient:

F = -D d C mol cm-2 s-1;dz

Where F is the flux of gas, D is the diffusion coefficient (cm2 s-1), C is the gas

concentration (mol cm-3) and z is the length of diffusion (cm).The quantity of gas Q (mols) transferred in t seconds for a cylinder radius r is:

Q = F(πr2)t

Thus Q = - D (C – C 0) π r 2 t mol (C0 = 0 with TEA)z

If r = 0.55 cm, D = 0.154 cm2 s-1, z = 7.1 cm then Q = -0.021Ct. In 1 hr the tube absorbs 74C mol NO2, or the NO2 in 74 cm3 of air (Boleij, 1986).

Spreadsheet CalculationsThe calculations and conversions of the absorption from the spectrometer to the

concentration of nitrogen dioxide in ppb are determined through the use of a spreadsheet. The spreadsheet (table 3) uses the calculated hours of the tubes outside for that month, the volume of the air, the slope of the linear regression from the monthly standards, and the absorption rate at 540nm.

Calculated Hours Out Abs.

Corrected Absorbance NO2

- on TEA NO2 in Air NO2 in Air NO2 in Air

(1 dec. pl.)     (ppm) (mg m-3) (ppm) (ppb)

672.0 0.137 0.137 0.274 0.0231 0.0120 12.0Table 3: Example PDT calculation

The calculations are as follows:Corrected Absorbance: Absorption - Absorption of Blank: 0.137 – 0 = 0.137; NO2 on TEA: Corrected Absorption/Slope from Standards: 0.137/2 = 0.274; NO2 in air (mg/m3): (NO2 on TEA*0.0042*1000000)/(Volume of air*hours outside): 0.274*0.0042*1000000 = 1150.8/(74)*(672) = 1150.8/49728 = 0.0231; NO2 in air (ppm): NO2 in air (mg/m3)*Avog. constant/molar mass of NO2:

0.0231*(6.022x1023)/46.0055 = 24/46.01 = 0.0120; and NO2 in air (ppb): NO2 in air (ppm)*1000: 0.0120*1000 = 12.0.

4.2 Chemiluminescence Analyzer

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NO2 is measured routinely by state and local agencies. Continuous measurement requires the use of expensive instrumental techniques such as chemiluminescence. These are usually located at fixed sites and do not provide spatial coverage. Chemiluminescence is a chemical technique which measures the intensity of light emission. NO is a relatively unstable molecule which will oxidize to NO2 (especially) in the presence of O3. The reaction of NO to NO2 through chemiluminescence is: NO + O3 ==> NO2+ O2 + hv. This reaction produces a quantity of light for each NO molecule which is reacted.

5. RESULTS

LocationRobert Morris University

Time of the Year/Month

Sept 2014 Oct 2014 Nov 2014 Dec 2014 Jan 2015 Feb 2015RMU 1 0 17 16 12 11 26RMU 2 10 15 24 18 17 22RMU 3 1 12 18 13 14 28Average NO2 (ppb)

4 15 19 14 14 25

Std. Dev.

6 3 4 3 3 3

Table 4: RMU monthly NO2 concentration of PDT 1,2 and 3, and averages

Figure 10 shows the results of each month’s tubes from September 2014 through February 2015.

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Sept 2014 Oct 2014 Nov 2014 Dec 2014 Jan 2015 Feb 20150

5

10

15

20

25

30RMU 1

RMU 2

RMU 3

Month

NO

2 C

once

ntra

tion

(ppb

)

Figure 10: NO2 measured at RMU by Palmes Diffusion Tube method

WeatherTemperature

RMU NO2 (ppb) Average Temperature (˚F)Sept 2014 4 65Oct 2014 15 53Nov 2014 19 43Dec 2014 14 34Jan 2015 14 28Feb 2015 25 30

Table 5: RMU PDT average NO2 concentration and Moon Township (local weather station) average monthly temperature

Figure 11 compares the calculated Moon Township, PA, monthly average temperature with the Robert Morris University site monthly average nitrogen dioxide concentration (site: http://www.homefacts.com/weather/Pennsylvania/Allegheny-County/Moon-Township.html).

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Sept 2014

Oct 2014 Nov 2014

Dec 2014 Jan 2015 Feb 20150

10203040506070

RMU Average (ppb)Average Tem-perature (˚F)

Month

NO

2 C

once

ntra

tion

(ppb

)

Figure 11: RMU NO2 concentrations vs average monthly temperature

Snowfall

RMU NO2 (ppb) Average Snowfall (inches)Sept 2014 4 0Oct 2014 15 0.5Nov 2014 19 3.5Dec 2014 14 8Jan 2015 14 11.9Feb 2015 25 8.9

Table 6: RMU PDT NO2 concentration and Moon Township average monthly snowfall

Figure 12 displays the relationship between the monthly average snowfalls in Moon Township, PA, and the calculated nitrogen dioxide concentration average at the Robert Morris University site (site: http://www.homefacts.com/weather/Pennsylvania/Allegheny-County/Moon-Township.html).

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Figure 12: RMU NO2 concentrations vs monthly average snowfall

Rainfall

RMU NO2 (ppb) Average Rainfall (inches)Sept 2014 4 2.81Oct 2014 15 2.99Nov 2014 19 2.81Dec 2014 14 3.99Jan 2015 14 1.73Feb 2015 25 2.98

Table 7: RMU PDT NO2 concentration and Moon Township average monthly rainfall

Figure 13 displays the relationship between the monthly average rainfall in Moon Township, PA, and the calculated nitrogen dioxide concentration average at the Robert Morris University site (site: http://www.homefacts.com/weather/Pennsylvania/Allegheny-County/Moon-Township.html).

Sept 2014

Oct 2014 Nov 2014 Dec 2014 Jan 2015 Feb 20150

5

10

15

20

25

30

RMU Average (ppb)Average Snowfall (inches)

Month

NO

2 C

once

ntra

tion

(ppb

)

17

Sept 2014

Oct 2014

Nov 2014

Dec 2014

Jan 2015

Feb 2015

0

5

10

15

20

25

30

RMU Average (ppb)

Average Rainfall (inches)

Month

NO

2 C

once

ntra

tion

(ppb

)

Figure 13: RMU NO2 concentrations vs monthly average rainfall

Stability Tube

Sept 2014 Oct 2014 Nov 2014

Dec 2014 Jan 2015 Feb 2015

RMU NO2 Average (ppb)

4 15 19 14 14 25

Stability tube NO2 (ppb)

0 0 0 0 0 1

Table 8: RMU PDT average concentration vs concentration of RMU stability tube

Figure 14 shows the stability of the Palmes diffusion tubes after preparation over a certain period of time.

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Sept 2014

Oct 2014 Nov 2014 Dec 2014 Jan 2015 Feb 20150

5

10

15

20

25

30

RMU AverageStability of sealed tube

Month

NO

2 C

once

ntra

tion

(ppb

)

Figure 14: RMU NO2 concentration vs RMU stability tube concentration

High School Comparison

Hopewell West Mifflin McGuffey South Fayette North HillsSept 2014 15±9 6±1 17±5Oct 2014 5±2Nov 2014 12Dec 2014 23±25 14±2 15±5Jan 2015 20±8 11±2 5±1 14±1Feb 2015 8±1 12±1 13±4March 2015 13±2

Table 9: Monthly PDT average concentration of Hopewell, West Mifflin, McGuffey, South Fayette, and North Hills with standard deviation

Figure 15 shows the comparison of NO2 PDT monthly concentration between Hopewell, West Mifflin, McGufey, and South Fayette High School. Not every school gathered sufficient results each month; therefore, concentrations for few of the months are missing.

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Sept 2014 Oct 2014 Nov 2014 Dec 2014 Jan 2015 Feb 2015 March 2015

0

5

10

15

20

25

HopewellWest MifflinMcGuffeySouth FayetteNorth Hills

Month

NO

2 co

ncen

trati

on (p

pb)

Figure 15: HHS, WMHS, MHS, NHSHS and SFHS monthly NO2 concentration

Colfax Upper Elementary

Sept 2014 Oct 2014 Nov 2014

Dec 2014 Jan 2015 Feb 2015

RMU NO2 (ppb)

4 15 19 14 14 25

CUE NO2 (ppb) 7 6 10 15 23 30

Table 10: RMU PDT average vs CUE PDT average

Figure 16 compares the calculated Colfax Upper Elementary site monthly average concentration with that of the calculated monthly average concentration at the Robert Morris University site.

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Sept 2014 Oct 2014 Nov 2014 Dec 2014 Jan 2015 Feb 20150

5

10

15

20

25

30

35

RMU AverageCUE Average

Month

NO

2 Co

ncen

trati

on (p

pb)

Figure 16: RMU NO2 average concentration vs CUE NO2 average concentration

RMU - CUE West Mifflin McGuffeySept 2014 7 7Oct 2014 6 12 22Nov 2014 10 15Dec 2014 15Jan 2015 23Feb 2015 30

Table 11: comparison of CUE NO2 concentration between Hopewell, West Mifflin and McGuffey, and the inter-laboratory CUE from RMU

Chemiluminescence Monitor

RMU Chemiluminescence

Sept 2014 Oct 2014 Nov 2014 Dec 2014 Jan 2015 Feb 2015RMU PDT Average 4 15 19 14 14 25RMU Chemiluminescence

5.6 5.2 7.5 15.3 59.5 10.5

Table 12: RMU PDT monthly average concentration vs RMU Chemiluminescence monthly average concentration

Figure 17 shows the comparison between the chemiluminescence fixed monitor at RMU versus the use of the Palmes diffusion tubes at RMU.

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Septem

ber

Octobe

r

November

Decembe

r

Janua

ry

Februa

ry0.0

10.020.030.040.050.060.070.0

Chemil. @ RMUPDT @ RMU

Month

NO

2 C

once

ntra

tion

(ppb

)

Figure 17: RMU NO2 PDT average concentration vs RMU NO2 Chemiluminescence average concentration

Figure 18 shows the correlation between the RMU Chemiluminescence monitor concentrations to the RMU PDT concentrations. The January 2015 concentrations were removed as outliers due to the extensive construction work going on at the same time. The R2 value is 0.7 showing a good correlation.

0 5 10 15 20 25 300

2

4

6

8

10

12

R² = 0.651664899824287

NO2 via PDT (ppb)

NO

2 vi

a C

hem

ilum

ines

cenc

e (p

pb)

Figure 18: RMU NO2 PDT average concentration correlated to RMU Chemiluminescence concentration

Harrison Township & Lawrenceville Chemiluminescence NO2 concentration

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Month RMU (ppb) Lawrenceville (ppb) Harrison Twp (ppb)Feb 2014 9 20 14Mar 2014 7 14 5April 2014 6 12 5May 2014 5 9 4June 2014 4 8 6July 2014 4 7 4Aug 2014 4 7 4Sept 2014 6 9 5Oct 2014 5 11 7Nov 2014 8 14 9Dec 2014 9 14 5Jan 2015 60 15 7Feb 2015 11 15 10Mar 2015 10 16 7April 2015 5 11 4

Table 13: Comparison between RMU, Lawrenceville, and Harrison Township monthly chemiluminescence averages in ppb

Figure 19 shows the comparison between the RMU, Harrison Twp and Lawrenceville Chemiluminescence NO2 monthly concentrations.

Feb 20

14

Mar 20

14

April 2

014

May 20

14

June 2

014

July 2

014

Aug 20

14

Sept 2

014

Oct 20

14

Nov 20

14

Dec 20

14

Jan 20

15

Feb 20

15

Mar 20

15

April 2

015

0

10

20

30

40

50

60

70

RMULawrencevilleHarrison Twp

Month

NO

2 C

once

ntra

tion

(ppb

)

Figure 19: RMU, Harrison Township, and Lawrenceville chemiluminescence monthly average NO2 Concentrations (ppb).

Figure 20 shows the correlation between the Lawrenceville location and the RMU chemiluminescence NO2 average. The January 2015 concentrations were removed as outliers

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due to the extensive construction work going on at the same time. The R2 value is 0.8 showing a significant correlation.

6 8 10 12 14 16 18 20 220

2

4

6

8

10

12

R² = 0.797144557188784

NO2 via PDT (ppb)

NO

2 vi

a C

hem

ilum

ines

cenc

e (p

pb)

Figure 20: Lawrenceville NO2 concentration vs RMU chemiluminescence NO2

concentration (ppb).

Figure 21 shows the NO2 concentration (ppb) from the RMU chemiluminescence fixed monitor each day from March 2014 to March 2015.

Jan-14 Mar-14 Apr-14 Jun-14 Jul-14 Sep-14 Nov-14 Dec-14 Feb-15 Apr-15 May-150

100

200

300

400

500

600

700

800

Time

NO

2 co

ncen

trati

on (

ppb)

Figure 21: RMU Chemiluminescence NO2 concentration (ppb) from March 2014 to March 2015.

6. DISCUSSIONThe data for the average of the Robert Morris University tubes show a significant leap from

September 2014 to October 2014 with an 11ppb difference. From October 2014 to January 2015

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each RMU tube is relatively close with the averages between 14ppb and 19 ppb. The average then increased up to 25 ppb in February 2015, which compares to the RMU fixed monitor concentration of 10ppb in February 2015. The average of the RMU chemiluminescence analyzer was 17 ppb compared to the RMU PDT average of 15 ppb. The RMU chemiluminescence was typically lower than the monthly average of the RMU PDT until January 2015 when the fixed monitor had a reading of 60 ppb.

When the monthly temperature in Moon Township was higher, the nitrogen dioxide concentration was lower, showing a negative correlation. However, in the comparison of average rainfall and snowfall in Moon Township and the average nitrogen dioxide concentration on the Robert Morris University campus, no correlation was found.

The results from the stability tube measurements showed that the concentration remained 0 ppb from September through January. As the concentration only rose to 1 ppb in February, overtime the concentration from the tested tubes could be affected if the prepared tubes are not placed out in reasonable time.

The average nitrogen dioxide concentration of WMHS over the six month time span was 12 ppb. MHS average concentration was calculated to be 14, with HHS average being 15, and SFHS slightly lower at 8 ppb. The inter-laboratory site with Colfax Upper Elementary site averaged to 15 ppb. The average standard deviation of each high school falls higher than the anticipated standard deviation of ±3 to ±5, which may have been the result of miscalculation from the ARK high school participants.

Harrison Township and RMU chemiluminescence averages were relatively the same due to the Harrison Township monitor placed for the comparison of city NO2. The overall Harrison Township average was 6 ppb, while RMU was 10 ppb and Lawrenceville was 12 ppb. The Lawrenceville average is higher since the location is a more polluted area, but the RMU average is higher again due to the 60 ppb January 2015 concentration.

7. CONCLUSIONThe differences in the RMU PDT average can be attributed to the beginning of construction

around the location of the tube’s testing site. As stated before, the majority of sources of nitrogen dioxide are man-made sources such as cars, trucks, heavy machinery, and coal-burning industries (Shooter, 1993). The monthly fluctuations in the PDT values follow a similar pattern to changes measured by the chemiluminescence analyzer. The 0.7 R2 value between the RMU PDT and RMU Chemiluminescence show good correlation, as well as the significant correlation between the Lawrenceville PDT and RMU Chemiluminescence at 0.8. The chemiluminescence measurements, however, are less time consuming to analyze, and has been adopted more often over the PDT method.

Chemical stability is the tendency to resist change due to internal reaction or action of outside factors, such as air and light. Our results have shown that the time frame of stability of TEA solution in a Palmes diffusion tube method atmospheric pollution test is roughly five months without any contamination.

With the fixed monitor average of Pittsburgh being 14 ppb, the averages of the participating schools show no significant variation with location around the Greater Pittsburgh area with NO2 concentration. Pittsburgh’s average at 14 ppb, measured by the RMU chemiluminescence, is higher than the national average of 9 ppb, but significantly lower than the EPA national regulation for nitrogen dioxide at 53 ppb (EPA).

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Experimental studies by Glasius et al. (1999), Bush et al. (2001), and Hansen et al. (2001) have shown that over estimation by a passive sampler for NO2 above 15 ppb was less than 10 percent. Shown by Kirby et al. (2001), the accuracy of the passive sampler even for worst possible conditions is within the accuracy limit recommended by the European Union for analytical monitoring of ±25 percent.

The chemiluminescence fixed monitor at RMU calculated to have an average concentration of 16 ppb compared to the RMU PDT average of 15 ppb. With a difference of only 2 ppb and standard deviations of the participating schools ranging from ±1 to ±25, our current results show that the diffusion tube method is a reliable method for testing atmospheric gases, specifically nitrogen dioxide.

Future ResearchWith the temperature having a strong negative correlation on the nitrogen dioxide

concentration, a comparison of humidity and pollution concentration could be studied. Also, two different tests could have been completed at the RMU site to compare the effect of the heavy machinery from construction of a new building. Since construction began next to the testing site in October-November, a sub-site could have been placed across campus.

The overall involvement of the schools that were in the partnerships was not as dependable as needed for the study. With all schools, except for RMU and CUE, being responsible for their own analysis, the study relied on their consistency. MHS only had three reliable months, SFHS only had two, HHS had one reliable month, and data from NHHS was sent well after the study was completed. At SFHS, HHS and MHS, students involved either lacked desire to constantly continue the study for a full six month time span, or were not supervised and had error in the testing/analysis period. Not receiving data from NHHS until the report was written, and missing data from MHS, SFHS, and HHS could have a significant effect on the monthly and overall averages for each location. In future research, participation should be monitored more closely over the span of the study to ensure accurate and complete data.

Sources

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Aoyama, T. and Yashiro, T.: 1983, ‘Analytical Study of Low Concentration Gases, IV. Investigation of the Reaction by Trapping of Nitrogen Dioxide in Air Using the Triethanolamine Method,’ Journal of Chromatography 256, 69–78.

Atkins, D.H.F., Sandalls, J., Law, D.V., Hough, A.M. and Stevenson, K.: 1986, ‘The Measurement of Nitrogen Dioxide in the Outdoor Environment Using Passive Diffusion Tube Samplers,’ United Kingdom Atomic Energy Authority Report, AERE R-12133, Harwell Laboratory, Oxford shire.

Beer, R. (1992) Remote Sensing by Fourier Transform Spectroscopy, in the Chemical Analysis Series, Vol. 120, John Wiley & Sons, New York.

Boleij, J.S.M., Lebret, E., Hoek, F., Noy, D. and Brunekreff, B. (1986). The use of Palmes diffusion tubes for measuring NO2 in homes. Atmospheric Environment – Part A General Topics, Vol. 20 (No. 3), pp. 597-600.

Bush, T., Mooney, D., Stevenson, K.: 1999, ‘United Kingdom Nitrogen Dioxide Network, 1997,’ AEA Technology, NETCEN, Culham, ISBN 0-7058-1774-1.

Colbeck, I.: 1998, ‘Nitrogen Dioxide in the Workplace Environment’, Environmental Monitoring and Assessment 52, 123–130.

Glasius, M., Carlsen, M.F., Hansen, T.S. and Lohse, C.: 1999, ‘Measurements of Nitrogen Dioxide on Funen Using Diffusion Tubes,’ Atmospheric Environment 33, 1177–1185.

Hansen, T.S., Kruse, M., Nissen, H., Glasius, M. and Lohse, C.: 2001, ‘Measurements of Nitrogen Dioxide in Greenland Using Palmes Diffusion Tubes,’ Journal of Environmental Monitoring 3, 139–145.

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Indoor Nitrogen Dioxide Concentration Levels and Personal Exposure: A Pilot-Study,’ International Archives Occupational Environmental Health 55, 73–78.

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Noij, D., Lebret, E., Willers, H., Winkes, A., Boleij, J.S.M. and Brunekreef, B.: 1986, ‘Estimating Human Exposures to Nitrogen Dioxide: Results from a Personal Monitoring Study among Housewives,’ Environment International 12, 407–411.

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