Volatile organic compound measurements
(whole air) in selected urban areas
Prof. Donald R. Blake
Department of Chemistry
University of California, Irvine
Irvine, CA 92697
drblake@uci.edu
Mexico City, Mexico
Hong Kong
Makkah, Saudi Arabia
Volatile Organic Compounds in the atmosphere
O2 RO
2
VOCs
NO
RO
OH
HO2
NO2
VOCs
VOCs
NOx
O3
O2
Oxygenated VOCs
VOCs
NOx
SO2
O + O2
VOCs
NOx
Secondary organic aerosol (SOA)
VOC reactions lead to:
• Tropospheric ozone (O3)
• Secondary organic aerosol (SOA)
These products impact:
• Air quality, global climate, health
Some VOCs are toxic:
• e.g. Benzene is carcinogenic
After: www.chem.wisc.edu/users/keutch/ and
www.york.ac.uk/inst/sci/APS/backgrd_files/figure4.gif
Modeled surface ozone (O3)
Iran lies in a region that experiences severe O3 pollution
ppbv O3
Modeled mean surface O3 in excess of 40 ppbv
July-August 2006 (Lelieveld et al., ACP, 2009)
UC Irvine Rowland-Blake group
Measurements of volatile
organic compounds (VOCs)
in global ecosystems:
• Global background monitoring
» Pacific Basin
• Areas with special conditions
» Marine environments
» Agriculture
» Oil and natural gas
» Biomass burning, etc.
Pristine
• World’s cities/megacities
» Mecca, Saudi Arabia
» Guangzhou, China
» Karachi, Pakistan
» Mexico City, etc.
Polluted
UC Irvine air sampling technique
Air sampling canisters
• 2-L stainless steel
• Conditioned, evacuated
• Bellows valve
• Sampling period: 1‒2 minutes
Air sampling near Rabigh, Saudi Arabia
Air sampling at Canada’s oil sands mining sites
Laboratory analysis
Detectors:
• Flame Ionization Detection (FID)
» Sensitive to hydrocarbons
• Electron Capture Detection (ECD)
» Sensitive to halocarbons, alkyl nitrates
• Mass Spectrometer Detection (MSD)
» Unambiguous compound identification
Each sample of air is split and sent to 5
different column-detector combinations
Sample chromatogram
Compound
Ethane
Benzene
C2Cl4
LOD
Precision
3 pptv
1%
3 pptv
3%
0.01 pptv
5%
1 part per trillion by volume
(pptv or 10-12) is equivalent to
1 second in 320 centuries
Accuracy
5%
5%
10%
C9: 1,2,3-Trimethylbenzene
C8: n-Octane
C6: Methylcyclohexane
C6: Benzene
C4: i-Butane
C5: i-Pentane
C3: Propane
C3: Propene
0 min
Time (minutes)
16 min
Speciated measurements of >100 VOCs, CO
Alkanes
Alkenes
Aromatics
1. Methane
2. Ethane
3. Propane
4. i-Butane
5. n-Butane
6. i-Pentane
7. n-Pentane
8. n-Hexane
9. n-Heptane
10. n-Octane
11. n-Nonane
12. n-Decane
13. 2,2-Dimethylbutane
14. 2,3-Dimethylbutane
15. 2-Methylpentane
16. 3-Methylpentane
17. 2-Methylhexane
18. 3-Methylhexane
19. 2,3-Dimethylpentane
20. 2,2,4-Trimethylpentane
21. 2,3,4-Trimethylpentane
22. 2-Methylheptane
23. 3-Methylheptane
26. Ethene
27. Propene
28. 1-Butene
29. i-Butene
30. cis-2-Butene
31. trans-2-Butene
32. 1,3-Butadiene
33. 1-Pentene
34. cis-2-Pentene
35. trans-2-Pentene
36. 2-Methyl-1-Butene
37. 2-Methyl-2-Butene
38. 3-Methyl-1-Butene
39. 2-Methyl-1-Pentene
40. 4-Methyl-1-Pentene
41. Isoprene
42. α-Pinene
43. β-Pinene
52. Benzene
53. Toluene
54. Ethylbenzene
55. m-Xylene
56. o-Xylene
57. p-Xylene
58. Styrene
59. i-Propylbenzene
60. n-Propylbenzene
61. 2-Ethyltoluene
62. 3-Ethyltoluene
63. 4-Ethyltoluene
64. 1,2,3-Trimethylbenzene
65. 1,2,4-Trimethylbenzene
66. 1,3,5-Trimethylbenzene
Alkynes
24. Ethyne
25. Propyne
Alkyl Nitrates
44. MeONO2
45. EtONO2
46. i-PrONO2
47. n-PrONO2
48. 2-BuONO2
49. 2-PeONO2
50. 3-PeONO2
51. 3-Methyl-2-BuONO2
Halocarbons
75. CFC-11
76. CFC-12
77. CFC-113
78. CFC-114
79. CCl4
80. CH3CCl3
81. HCFC-22
82. HCFC-124
83. HCFC-141b
84. HCFC-142b
85. HFC-134a
86. HFC-152a
87. H-1211
Cycloalkanes/alkenes
67. Cyclopentane
68. Methylcyclopentane
69. Cyclohexane
70. Methylcyclohexane
71. Cyclopentene
Sulfur Species
72. OCS
73. DMS
74. CS2
88. H-1301
89. H-2402
90. CH3Cl
91. CH3Br
92. CH3I
93. CH2Cl2
94. CHCl3
95. CHBr3
96. C2Cl4
97. CHBrCl2
98. CHBr2Cl
99. Ethylchloride
100. 1,2-DCE
High precision,
ultra-sensitive
measurements
of >100 C1-C10
volatile organic
compounds (VOCs)
Colman et al., An. Chem., 73, 3723-3731, 2001
Simpson et al., ACP, 10, 6445-6463, 2010
Volatile organic compound (VOC) sources
Biomass burning:
Fossil fuel combustion:
• Ethyne
• Benzene
• n-Butane
• Ethyne
• Benzene
• Ethene
Biogenic:
Natural gas leakage:
• Isoprene
• α-Pinene
• β-Pinene
• Methane
• Ethane
Industry:
• Propane
• i-Butane
• n-Butane
• C2Cl4
• HCFC-22
• HFC-134a
Liquefied petroleum gas:
Fossil fuel evaporation:
• i-Pentane
Cities studied by the Rowland-Blake group
City
Date
Publication
• Mexico City, Mexico
1993
Blake and Rowland (1995)
• Santiago, Chile
1996
Chen et al. (2001)
• Karachi, Pakistan
1998‒1999
Barletta et al. (2002)
• 28 U.S. cities
1999‒2005
Baker et al. (2008)
• 43 Chinese cities
2001
Barletta et al. (2005, 2006)
• Hong Kong/Guangzhou 2004‒present
Guo et al. (2004, 2006, 2007, 2009,
2012, 2013); Wang et al. (2005);
Barletta et al. (2008);
Jiang et al. (2010); Zhang et al. (2013)
• Beijing (Olympics), PRC 2008
Wang et al. (2010)
• Los Angeles, USA
2010‒present
Unpublished data
2007
Unpublished data
• Lahore, Pakistan
2012
Manuscript in preparation
• 3 Saudi Arabian cities
2012‒2013
Manuscripts in preparation
Basrah, Iraq
Cities studied by the Rowland-Blake group
1993‒present
Thousands of samples collected in more than 75 cities
Case study 1: Mexico City
What did we learn?
• High levels of propane,
i-butane and n-butane
» Up to 45‒200 ppbv
• Attributed to Liquefied
Petroleum Gas (LPG)
» Unburned leakage
» Incomplete combustion
• Significant contributor to O3
Recommendations to
improve air quality:
• Change LPG composition
• Lower LPG leakage rates
Mexico City, Mexico
Case study 2: Santiago, Chile
CO and tracers are good tracers for incomplete combustion
Both compounds were strongly enhanced by the morning commute
Case study 2: Santiago, Chile
Ethyne a good tracer for incomplete combustion
Propane is NOT enhanced by the morning commute
Case study 2: Santiago, Chile
Impact of the Leakage of Liquefied Petroleum Gas
(LPG) on Santiago Air Quality
Tai-Yih Chen1, Isobel J. Simpson, Donald R. Blake, and F. Sherwood Rowland
Department of Chemistry, University of California, Irvine
What did we learn?
• First use of a grid sampling
pattern to study VOCs in cities
• Liquefied petroleum gas (LPG)
» Major source of hydrocarbons,
even during heavy traffic
» Median propane up to 140 ppbv
• Unburned LPG leakage
» Leakage rate of 5%
» Contributes 15% to excess O3
Recommendations:
• Minimize LPG leakage
• Change LPG formulation
» Reduce alkene composition
Case study 3: Hong Kong, PRC
What have we learned?
• Full characterization of VOC sources
and concentrations over 10+ years
of monitoring
» Impact of vehicular sources, industry,
gasoline evaporation, solvent use
Mean sea level pressure and wind field on
1000 hPa between Oct 22 and Dec 1, 2007
• Impact of Asian monsoons on trace
gas concentrations:
» Winter maximum: continental influence
» Summer minimum: oceanic influence
• On-going VOC validation for Hong
Kong Environmental Protection
Department (HKEPD)
» Calibration and intercomparisons
» Expertise
Hong Kong, People’s Republic of China
H. Guo et al., AE, 2007
Case study 4: Karachi, Pakistan
What did we learn?
• Very high CH4 levels
» Compare: Background < 2 ppmv
» Significant natural gas leakage
• High levels of propane, butanes
» Liquefied petroleum gas
» Lower than in Mexico City
• High levels of benzene
» Up to 19 ppbv
» Concern for human health
• Importance of vehicle exhaust
Recommendations:
• Improved fuel quality
• Improved emission controls
Karachi, Pakistan
B. Barletta et al., AE, 2002
Case study 5: Mecca, Saudi Arabia
What have we learned?
• Very high CO and VOC levels
» Especially in tunnels
» Especially during Hajj
• Human health concerns
» Benzene: above 1-hr standards
» CO: above 30-min standards
• VOC sources include:
» Vehicle exhaust
» Gasoline evaporation
» Liquefied petroleum gas (LPG)
» Industry
Recommendations:
• Target aromatics, alkenes
• Improve air quality monitoring
Mecca, Saudi Arabia
Case study 5: Mecca, Saudi Arabia
Impact on O3 formation
• VOCs are an O3 precursor
• Potential for VOCs to form O3
is measured using hydroxyl
radical reactivity (kOH)
• Alkenes strongly contribute to
O3 formation in Mecca:
» Especially in tunnels
•A VOC’s potential to form O3 is a
function of its concentration
and reactivity towards its main
sink, OH:
𝑘OH =
Mecca, Saudi Arabia
(𝑘OH+VOCi VOC𝑖
+ 𝑘OH+CO CO
+
𝑘OH+NO NO + ⋯ )
VOC comparisons among megacities
City comparisons (no tunnels)
• VOC concentrations in cities
can range over many orders
of magnitude
» From near pristine levels to
extremely polluted
• Continuing emissions of CFCs
in many cities
• High levels of i-pentane,
especially in Mecca, indicate
gasoline evaporation
• High levels of benzene are a
concern in many cities
» Often related to traffic
» Sometimes exceed 1-hour air
quality standards of 150 ppbv
Conclusions and future directions
VOC measurements in selected
urban areas
• The Rowland-Blake group has
measured VOCs in urban areas
for more than 2 decades
Santiago, Chile
» Concentration assessments
» Source characterization
» Ozone formation potential
» Specific recommendations
• Our on-going work includes
collaborative studies in:
» Hong Kong, PR China
» Los Angeles, USA
» Cities in Saudi Arabia
• Our group has expertise and
equipment that could be used
to study air quality in Iran
Tehran, Iran
Acknowledgments