The Aburrá Valley region in Colombia, with Medellín as its main city, is an urban centre with about three million people. An investigation was carried out to deter-mine a set of baseline concentrations for VOC compounds associated with diesel fuel and gasoline, as vehicular emission tracers in the region. The VOC measurement campaigns, based on TENAX tube sampling and analysis according to TO-17 EPA method, were done in areas of low and high vehicular flow as well as on-board measurements covering major Medellín road networks during 24 hours. The results showed that there was a relation between VOCs concentrations and vehicular activi-ty. The diesel fuel sulfur content was also found as an important factor on VOC hy-drocarbon formation.
VOCs tend to be polluting considering both their inhalation and contact effects and as a source of secondary pollutants. For the present study, they were classified into two (2) groups: poly-nuclear aromatic hydrocarbons (PAHs) and aliphatic hydrocarbons (AH). Table 1 shows the list of VOCs studied and some basic characteristics.
The studied VOCs behave differently, following the two main types (alkanes [AH], and PAH) and this has to do with their molecular weight, as shown in the behavior of their vapor pressure and boiling point, properties that have to do with their presence in the atmosphere (Figure 1 and Figure 2).
VOCs studied and their vapour pressures as related to molecular weight
VOCs studied and their boiling points as related to molecular weight
VOCs studie
Compound
Molecular weight
Vapor pressure at 25˚C, mm Hg
Boiling temperature at atm. pressure, ˚C
Nature
Formula
n-Nonane
128.3
4.45
150.6
AH
C9H20
n-Decane
142.3
1.43
174.2
AH
C10H22
n-Undecane
156.3
0.412
196.0
AH
C11H24
n-Dodecane
170.4
0.135
214.0
AH
C12H26
n-Tridecane
184.4
0.0560
232.0
AH
C13H28
n-Tetradecane
198.4
0.0116
253.0
AH
C14H30
n-Pentadecane
212.4
0.00310
268.0
AH
C15H32
Naphthalene
128.2
0.0850
218.0
PAH
C10H8
1-Methylnaphthalene
142.2
0.0670
240.0
PAH
C11H10
2-Methylnaphthalene
142.2
0.0550
241.0
PAH
C11H10
Phenanthrene
178.2
0.000121
332.0
PAH
C14H10
1-Methylphenanthrene
192.3
0.0000501
354.0
PAH
C15H12
2-Methylanthracene
192.3
0.0000727
353.5
PAH
C15H12
A review [1] [2] of the health impact and occupational limits of the studied VOCs is shown in Table 2.
In general, VOCs play an important role in environmental problems by their accumulation and persistence in the environment [3] . Some VOCs, especially those of high molecular weight, resist oxidation processes and become persistent, being adsorbed on particles and transported over long distances [4] , powering the global greenhouse effect.
So far no studies of these compounds have been done locally, so it is deemed important to carry out an exploratory work, in parallel with the fact that sulphur content of diesel fuel is undergoing changes at the time, from 2000 to 50 ppm and it is desired to correlate those changes with the said VOCs concentrations.
Alkanes tend to be emitted by vehicles, as they are components of fuels. Table 3 shows typical contents of studied VOCs in low sulfur diesel and gasoline [5] . The other studied PAHs come from oil and coal tars and incomplete combustion, including wood combustion; Phenanthrene is also associated with cigarette and marihuana smoke and charcoal broil.
Occupational data for some of the VOCs studied. studie
TEEL-0: Concentration below which people will experience no adverse health effects is 0.015 ppm (105 μg/m3)
n-Tridecane
24
Irritating to eyes and skin. Inhalation causes irritation of the lungs and respiratory system.
TLV Not established
n-Tetradecane
19.2
Irritation eyes, skin. Inhalation causes irritation of the lungs and respiratory system
TLV Not established
n-Pentadecane
17
No clear indication of risks
TLV Not established
Naphthalene
18
Irritating to skin and eyes
TWA 10 ppm (50 mg/m3)
1-Methylnaphthalene
7.3
Irritation. Toxic by all routes (i.e., ingestion, inhalation, and skin contact)
TLV = 0.5 ppm (2.9 mg/m3)
2-Methylnaphthalene
7.4
Irritating to skin
TLV = 0.5 ppm (2.9 mg/m3)
Phenanthrene
36 - 1570
A known irritant, photosensitizing skin to light. Potential occupational carcinogen
TWA = 0.028 ppm (0.2 mg/m3)
Typical contents of studied VOC in low sulfur diesel and gasolin
Compound
Type
% in typical diesel low S fuel
% in gasoline
n-Nonane
AH
0.84
0.24
n-Decane
AH
0.92
0.19
n-Undecane
AH
0.93
0.15
n-Dodecane
AH
1.01
0.11
n-Tridecane
AH
1.61
0.09
n-Tetradecane
AH
1.21
0.03
n-Pentadecane
AH
1.09
0.01
Total studied AH
AH
7.61
0.82
Naphthalene
PAH
0.36
0.30
2. Materials and Methods
The apparatus set up for the sampling is described in Figure 3.
The sampling method applied was EPA TO-17 using 90 mm length, 5 mm diameter stainless steel TENAX adsorption tubes filled with appropriate sorbent materials, prepared and supplied by the DRI (Desert Research Institute at Reno, Nevada, USA). The chemical analysis of the studied VOCs was also done at the DRI, using the Agilent Thermal Desorption-Gas Chromatograph/Mass Spectrometer (TD-GC/MS) system.
The environmental samples were taken in a measurement campaign conducted in three sites, two of them with heavy traffic, the other one with low or inexistent traffic, from July to August 2011, with sampling periods of 24 hours. Each zone was evaluated during a week.
Additional samples were taken in the discharge of a diesel motor working under standardized laboratory conditions with diesel fuel of variable sulfur content. Run cycles followed standard ECE-M2 at 2420 rpm. Figure 4 shows a scheme for the run cycle.
3. Methodology and Results3.1. Urban and Rural Sites
The VOC measurement campaign was conducted in three sites, two of them with heavy traffic (Poblado zone and Botanical Garden Park), the other one with low or inexistent traffic (Arví Park), from July to August 2010, with sampling periods of 24 hours. Each zone was evaluated during a week. Another sample was taken sampling during 24 hours continuously within a vehicle moving through designed zones in the city (On Board test). In the Figure 5, the sampling sites are located in the Aburrá Valley map. Table 4 shows the concentrations in the urban and rural zones, and in the on-board 24 hour samples. It is clear that rural areas have lower VOCs concentrations than urban ones.
Figure 6 compares the VOC concentrations found for the zones. It was found that the higher concentrations of the studied tracers correspond to pentadecane and naph-
Description apparatus for VOC measurement (left) and apparatus located in the sampling zone (right)
Concentrations in urban and rural zones, and in the on-board 24-hour samples studied
Compound
Poblado 05/08/10
Poblado 07/08/10
Poblado 10/08/10
Botanic Garden 20/08/10
Arvi Park 31/08/10
On-Board 02/09/10
Type of zone
urban
urban
urban
urban
rural
urban
n-Nonane
0.870
0.736
0.769
1.896
0.060
1.919
n-Decane
0.980
0.696
0.693
2.273
0.046
1.986
n-Undecane
0.668
0.473
0.467
1.417
0.038
1.728
n-Dodecane
0.389
0.301
0.324
0.685
0.025
0.564
n-Tridecane
0.274
0.237
0.237
0.516
0.031
0.730
n-Tetradecane
0.244
0.218
0.225
0.583
0.027
1.588
n-Pentadecane
0.241
0.190
0.207
0.986
0.057
6.379
Naphthalene
0.989
0.839
0.836
2.269
0.139
0.637
1-Methylnaphthalene
0.212
0.179
0.200
0.741
0.010
0.322
2-Methylnaphthalene
0.428
0.357
0.407
1.520
0.016
0.576
Phenanthrene
0.038
0.023
0.022
0.141
0.005
1.279
1-Metylphenanthrene
0.000
0.000
0.000
0.158
0.000
0.426
2-Methylanthracene
0.000
0.000
0.000
0.182
0.000
0.523
Total studied VOC
5.334
4.248
4.388
13.369
0.456
18.657
Total studied AH
3.666
2.851
2.922
8.357
0.286
14.894
Total estudied PAH
1.667
1.398
1.466
5.012
0.170
3.763
Run cycle scheme
Sampling sites (Google map image 2016)
thalene. The on-board sample shows higher VOC’s concentrations than the other sampling sites. Probably because the on board test environment was in continuous contact with mobile sources. Figure 7 shows comparative result for all the zones in terms of total VOCs.
Comparative results for VOC concentrations in all studied zones
Total VOC concentrations for the studied zones
It is clear in Figure 7 that the concentrations of VOCs in urban areas are clearly greater than the ones in rural areas. Urban total VOCs were about 25 times greater than the rural area. All concentrations, as expected, are clearly much lower than the reported occupational limits for the substances shown in Table 2.
3.2. A Review of VOC Concentrations in Urban and Rural Areas around the World
Following results reported elsewhere [2] [6] - [9] , Table 5 was prepared to compare values reported around the world with the ones found in the present study, in order to have a comparative measure of the magnitude of the problem in the Medellín region.
This analysis shows, in general, local values lower than the typical ones reported around the world. The typical values shown were chosen by the authors after elimination, at their own criteria, of extreme high values in the reported data.
VOC concentrations (range and typical) around the world and in this study
Concentrations in urban areas (μg/m3)
Concentrations in rural areas (μg/m3)
Compound
Range around the world
Typical around the world
Average of this study
Range around the world
Typical around the world
Average of this study
n-Nonane
0.07 - 467
5.06
1.24
0.0 - 58.2
4.067
0.060
n-Decane
0.16 - 1100
18.68
1.33
0.0 - 161.2
5.919
0.046
n-Undecane
0.15- 59
7.66
0.95
0.018 - 0.54
0.279
0.038
n-Dodecane
0.0 -160
0.97
0.45
0.0 - 0.25
0.044
0.025
n-Tridecane
0.18-2.7
0.93
0.40
0.01-0.12
0.066
0.031
n-Tetradecane
0.0 - 36
8.46
0.57
0.0 - 0.116
0.058
0.027
n-Pentadecane
0.19 - 158
15.47
1.60
0.01 -0.149
0.080
0.057
Naphthalene
0.0 - 77
2.27
1.11
-
-
0.139
1-Methylnaphthalene
0.00 - 5.1
0.59
0.33
-
-
0.010
2-Methylnaphthalene
0.00 - 1.1
0.39
0.66
-
-
0.016
Phenanthrene
0.01 - 129
1.08
0.30
0.0 -0.032
0.006
0.005
Total
61.58
8.94
10.52
0.456
3.3. Diesel Engine Exhaust Concentrations
At the time of the study, S content of diesel fuel used in the region was undergoing changes, from 2000 ppm to 50 ppm and it was desired to correlate those changes with VOCs concentrations in the exhaust gases coming from a diesel motor working under standardized laboratory conditions.
Table 6 shows the results, which show a clear effect of the sulfur content of the fuel on the emissions of the studied VOCs.
4. Conclusions
The region atmosphere shows presence of VOCs.
The concentrations in urban areas are clearly greater than the ones in rural area. In the average urban total VOCs are 27 times larger.
The values found in rural and urban areas tend to be smaller than the typical values reported, around the world, in the literature. Total VOCs show values around 15% of the reported typical values for urban areas and about 5% for rural areas.
The VOC concentrations are related to vehicle emissions, especially to diesel fuel vehicle emissions.
An initial baseline has been established which should be useful for future work and public policy in relationship to vehicle related pollution control.
Reducing S content on diesel fuel has been a beneficial step in this direction.
VOC concentrations in diesel fuel motor exhaust and sulfur content in diesel fuel
Compound
Fuel with sulfur at 50 ppm, µg/m3
Fuel with sulfur at 500 ppm, µg/m3
Fuel with sulfur at 2100 ppm, µg/m3
n-Nonane
177
62
160
n-Decane
407
153
528
n-Undecane
254
203
501
n-Dodecane
199
250
649
n-Tridecane
186
311
586
n-Tetradecane
111
311
450
n-Pentadecane
61
361
356
Naphthalene
179
140
141
1-Metylnaphthalene
87
134
176
2-Metylnaphthalene
170
218
317
Phenanthrene
1.43
12.83
5.60
Total studied VOC
1832
2155
3869
Total studied AH
1395
1650
3230
Total estudied PAH
437
505
639
Acknowledgements
This work was supported by POLITÉCNICO COLOMBIANO JAIME ISAZA CADAVID and ECOPETROL. We acknowledge the DRI Institute for the analytical and sampling assistance and the University of Antioquia, GIMEL group, for the work done in the laboratory motor testing.
Cite this paper
Posada, E., Gómez, M. and Monsalve, V. (2016) Assessment of Organic Compounds as Vehicular Emission Tracers in the Aburrá Valley Region of Colombia. Journal of Environmental Protection, 7, 1561-1570. http://dx.doi.org/10.4236/jep.2016.711129
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