Speciation of Volatile Organic Compounds (VOCs) in the atmosphere of O'Higgins’s region-Chile Extended Abstract # 276 Francisco Cereceda -Balic, Víctor Vidal, Juan L. Guevara, Jose L. Cayón, Claudio Saavedra. Laboratorio de Química Ambiental (LQA), Centro de Tecnologías Ambientales (CETAM), Universidad Técnica Federico Santa María (UTFSM), Avenida España 1680 Valparaíso, Chile.
[email protected]. Luis A. Díaz-Robles, Pablo Etcharren. Air Quality Unit, School of Environmental Engineering, Catholic University of Temuco. Manuel Montt 056, Casilla 15-D, Temuco, Chile.
[email protected]. Barbara Zielinska Desert Research Institute (DRI), Division of Atmospheric Sciences, 2215 Raggio Parkway, Reno, NV.
[email protected]
INTRODUCTION O'Higgins’s Region, located south of Santiago, has an area of 16,387 km ² and an estimated population of 849,120 inhabitants consisting of rural population dedicated to agriculture. The principle city of the region, located only 84 km south of Santiago, is Rancagua with a population of 206,971 inhabitants. Concentrations of tropospheric ozone (O3) that exceeds the 8 hour National Air Quality Standard of 120 g/m3, have been recorded in stations located at north part of the region. According to US-EPA, inhaling ground-level ozone can result in a number of health effects including induction of respiratory symptoms, such as decrements in lung function, inflammation of airways, among others.Thus, it is important to control and reduce O3 concentration in O´Higgins region. Ozone is a secondary pollutant produced photochemically in the atmosphere due to the interaction of NOx, OH and VOCs, in presence of solar radiation. It is well known that the control measures that are effective for ozone reduction have been NOx and VOCs emissions control 1. Volatile organic compounds (VOCs) constitute an important group of air pollutants as they contribute to serious air pollution problems like the formation of photochemical smog and ground-level ozone production. In addition several VOCs found in urban air are classified as carcinogenic compounds including 1, 3-butadiene and benzene. VOCs are emitted from anthropogenic sources, such as transportation, fossil fuel-burning, power plants, solid waste disposal, among others 2-3. In addition to the anthropogenic sources, many VOCs are produced naturally by vegetation. Biogenic emissions of VOCs are likely to exceed anthropogenic emissions in heavily vegetated and forested areas like O´Higgins region 2-4. Previous studies in O'Higgins’s region that were based on modeling and emissions inventories estimated the ambient VOCs concentration levels, but there is no records of ambient measurements of VOCs in this area to test the accuracy of the models.
This photochemical monitoring campaign measured ambient VOCs concentration levels in rural and urban areas of O´Higgins region in order to understand the phenomenon of the formation of photochemical pollutants in the study area.
EXPERIMENTAL METHODOLOGY An atmospheric monitoring campaign was carried out in the O´Higgins region, Chile, in summer 2008-2009 (December – January). Samples were taken at 3 monitoring stations located north of the region which correspond to “Rancagua” (Ra) urban station located 84 Km south of Santiago, “Codegua” (Co) rural station located 65 Km south of Santiago and “Casas de Peuco” (CP) rural station located 55 Km south of Santiago. Sampling was carried out simultaneously in the 3 monitoring stations between 11:00 hrs and 19:00 hrs (maximum solar radiation period). Air samples were taken using 2 type of sampling media at each station: (1) Thermal Desorption Tubes (ATD Tubes) packed with 180 mg of Tenax TA and 150 of mg Carbopack B were sampled at a flow rate of 25 mL/min and were analyzed for biogenic VOCs according to EPA method TO-17; (2) 6 L stainless steel SUMMA canisters were used to measure anthropogenic VOCs according to EPA method TO-15. ATD tubes sampler were equipped with a particulate matter filter (0.2 um pore diameter) and an ozone destroyer denuder prior to ATD tube, while Canister sampler where equipped with particulate matter filter (0.2 um pore diameter) prior to canister. After sampling, ATD tubes and Canisters were transported to the laboratory for analysis in seal and refrigerated (4ºC) containers. Analyses of ATD tubes were performed in Chile at the Environmental Chemistry Laboratory (LQA) of CETAMUTFSM using Thermal Desorption unit attached to gas chromatograph with mass spectrometer detector (ATD-GC-MS). A 2 stages thermal desorption unit Turbomatrix ATD, Perkin Elmer, USA were used. ATD was equipped with an autosampler carrousel with 50 tubes capacity, cryo-trap packed with Tenax TA, internal standard addition accessory and thermostatic transfer line. ATD was attached to a GC-MS Clarus 500, Perkin Elmer, USA equipped with a Supelco SPB 624 capillary column (60m x 0.25mm x 1,4 m), electronic ionization source and quadrupole mass spectrometer detector. Analyses were performed by the internal standard method using liquid -2 Carene (Sigma Aldrich, USA) as internal Standard. Canister Analyses were performed in USA at the Organic Analytical Laboratory of DRI using a 12 channel Canister analysis system (Lotus Consulting, USA) equipped with 5 types of cryo-traps, attached to a GC-MS Varian CP 3600 equipped with 2 capillary columns (a Plot-Alumina column attached to an FID detector for VOCs between C2 and C5; a Varian CP-Sil 5 column attached to a MS Detector for VOCs between C4 and C11). Canister analyses were performed by external calibration using certified VOCs Gas Standard mixtures (Scott specialty gases, USA).
RESULTS AND DISCUSSIONS Figure 1 shows the total VOC concentrations by monitoring day at each monitoring station
80
Figure 1. Total Anthropogenic of VOCs concentration by Monitoring Station
g/m3
60 40 20 0 Dec 30 2008 Jan 06 2009 Jan 09 2009 Jan 14 2009 Jan 16 2009 Jan 21 2009 Jan 27 2009 Jan 28 2009
Codegua
Casas de Peuco
Rancagua
Total VOCs concentration is the sum of concentrations of compounds listed in Table 1. Table 1 also shows the mean concentrations of each anthropogenic VOC analyzed at O´Higgins Region. Table 1. Anthropogenic VOCs analyzed and mean concentration for sampling period VOC
Mean Conc. (µg/m3) n=8
ethene
1,10±0,16
1-pentene
0,74±0,14
2-methyl-1-pentene
0,07±0,03
Toluene
1,95±0,56
ethane
1,26±0,24
pentane
0,83±0,13
hexane
0,61±0,34
heptane
0,16±0,05
acetilene
0,95±0,18
isoprene
1,76±0,16
t-2-hexene
0,01±0,001
2,2,4-trimethyl-pentane
0,04±0,01
propene
0,56±0,13
trans-pentene
0,08±0,02
c-2-hexene
0,07±0,03
2,3,4-trimethyl- pentane
0,05±0,01
propane
2,45±0,81
cis-pentene
0,03±0,01
methyl-cyclo-pentane
0,30±0,12
2-methyl-heptane
0,08±0,06
1,3-butadiene
0,02±0,001
2-methyl-2-butene
0,13±0,03
benzene
0,77±0,12
4-methyl-heptane
0,10±0,04
n-butane
1,58±0,16
cyclo-pentene
0,03±0,01
cyclo-hexane
2,05±0,16
3-methyl-heptane
0,04±0,01
i-butane
2,32±0,42
cyclo-pentane
0,06±0,01
2,4-dimethyl-pentane
0,03±0,01
n-octane
0,15±0,03
trans-butene
0,18±0,16
2-methyl-pentane
0,15±0,03
2-methyl-hexane
0,26±0,05
ethylbenzene
0,31±0,07
i-butene
0,25±0,05
2,3-dimethy-butane
0,07±0,04
2,3-dimethyl-pentane
0,08±0,05
m&p-xylene
0,93±0,21
cis-butene
0,09±0,05
2-metilpentano
1,00±0,17
3-methyl-hexane
0,25±0,08
styrene
1,28±0,34
i-pentane
2,31±0,34
3-methyl-pentane
0,30±0,09
methyl-cyclo-hexane
0,07±0,02
o-xylene
0,44±0,09
nonane
0,22±0,05
VOC
Mean Conc. (µg/m3) n=8
VOC
Mean Conc. (µg/m3) n=8
VOC
Mean Conc. (µg/m3) n=8
Figure 1 clearly shows that Ra has higher concentration of anthropogenic VOCs than Co and CP which was expected since Ra is the only urban station monitored. Wind direction during the sampling period was mainly to north-east towards Co and CP stations, indicating that Ra is an emission site while Co and CP are receptor sites. To confirm this hypothesis, concentration ratios of some anthropogenic hydrocarbons were calculated for each monitoring station studied. Toluene and benzene are anthropogenic VOCs emitted mainly by mobile sources and their atmospheric concentration ratio is determined by their photochemical reaction rates. Both toluene and benzene react with OH radical in presence of solar radiation, but toluene react significantly faster than benzene, which results in toluene/benzene ratio of 2.5 – 3 for samples taken near emission sources. A ratio near 1 is obtained in background sites which indicate that lower ratios are characteristic for locations farther away from
emission sources 5. The same situation is observed for m&p xylene / ethylbenzene ratio which is 3.5 near emission sources 6. Table 2 shows these concentration ratios calculated at each monitoring station. Table 2. Mean concentration ratios calculated for each monitoring station studied
Toluene/Benzene m&p Xylene / Ethylbenzene
Ra
Co
CP
3:1 3.3:1
2.4:1 2,9:1
2.0:1 2,5:1
Theoretical near emission source 2.5:1 – 3:1 3.5:1
Theoretical Background 1:1 1:1
Values shown in Table 2 together with the predominant wind direction indicate that Ra is the emission site while Co and CP receive the emissions of anthropogenic VOCs from Rancagua. This means that control measures to reduce VOCs emissions must be focused on Rancagua, which is the largest city of the region. Figure 2 shows mean concentration of each biogenic VOC analyzed between December 2008 and January 2009 (n=8) by monitoring stations Figure 2. Period mean Concentration of Biogenic VOCs at each studied monitoring station 120 100
g/m3
80 60 40 20 0 a -pinene -pinene
b-pinene -pinene
D-3-carene -3-carene
Co
CP
limonene
Isoprene
Ra
Figure 2 shows that -pinene is the most abundant biogenic VOC observed followed by limonene. -Pinene is a terpene that is principally emitted by sclerophyllous trees and its emissions are higher in high temperatures 7. In O´Higgins region 80% of native forest correspond to sclerophyllous trees and during sampling period ambient temperatures exceeded 30ºC which indicates that this could be the principle source of -pinene in the region. The highest levels of biogenic VOCs are observed in Ra monitoring station (6.5 times anthropogenic VOCs concentration). Rancagua is the place with highest concentration of sclerophyllous vegetation with a forest surface of 3.975 Ha followed by CP with 2.545Ha and Co with 1.685Ha. Table 3 shows the hydrocarbon classes distribution in each studied monitoring station. Table 3 shows that alkanes show highest concentration in each monitoring station studied followed by aromatics, alkenes, isoprene and alkynes. Similar behavior is observed in Santiago (2002) except for the distribution of alkynes and isoprene. Higher proportion of alkynes could be due to the fact that isoprene is a biogenic VOC
produced in higher temperatures, and Santiago samples were taken in spring time with lower temperatures than samples collected in O´Higgins region Table 3. VOCs families distribution in O´Higgins region compared with Santiago Ra Co CP Parque O´Higgins Santiago 2002 5 Las Condes Santiago 2002 5
Alkanes 60.9% 54.2% 59.4%
Alkenes 10.7% 10.9% 9.6%
Alkynes 3.6% 4.0% 3.2%
Isoprene 5.7% 8.6% 7.0%
Aromatics 19.1% 22.3% 20.9%
59.8%
14.9%
8.1%
0.9%
16.3%
57.2%
14.6%
8.9%
0.6%
18.8%
SUMMARY Monitoring campaign in O´Higgins region allowed for a characterization of VOCs atmospheric concentrations and estimation of their sources. Results indicate that antrophogenic VOCs are mainly emitted in Rancagua and travel north in direction of Codegua and Casas de Peuco. Thus, in order to reduce ozone level in O´Higgins region, VOCs emissions must be controlled mainly in Rancagua. Higher biogenic than anthropogenic VOCs concentrations were observed mainly in native forest where the emissions of -pinene are the highest, followed by limonene.
ACKNOWLEDGMENTS The authors thank FONDECYT projects 1070500 and FONDEF D05-I-10054, and both CONAMA and Regional Government VI Region for the financial support. Also, we would like to acknowledge the DIUCT Project Convenio de Desempeño number 2006-2-03 for providing the cluster Santa.
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KEYWORDS Volatile Organic Compounds, Photochemical Pollution, VOCs, Monitoring Campaign
