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Volatile organic compound measurements (whole air) in selected urban areas
Prof. Donald R. Blake Department of Chemistry University of California, Irvine Irvine, CA 92697 [email protected]
Mexico City, Mexico
Hong Kong
Makkah, Saudi Arabia
Volatile Organic Compounds in the atmosphere
VOCs OH
HO2
NO
NO2 O + O2 O3
Oxygenated VOCs Secondary organic aerosol (SOA)
VOCs
After: www.chem.wisc.edu/users/keutch/ and www.york.ac.uk/inst/sci/APS/backgrd_files/figure4.gif
RO2
RO
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
O2
O2
VOCs NOx SO2
VOCs NOx
VOCs NOx
Modeled surface ozone (O3)
Modeled mean surface O3 in excess of 40 ppbv July-August 2006 (Lelieveld et al., ACP, 2009)
Iran lies in a region that experiences severe O3 pollution
ppbv O3
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.
• World’s cities/megacities
» Mecca, Saudi Arabia
» Guangzhou, China
» Karachi, Pakistan
» Mexico City, etc.
Pristine
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 LOD Precision Accuracy Ethane 3 pptv 1% 5% Benzene 3 pptv 3% 5% C2Cl4 0.01 pptv 5% 10%
1 part per trillion by volume (pptv or 10-12) is equivalent to
1 second in 320 centuries
C3: Propene
C3: Propane
C4: i-Butane
C8: n-Octane
C9: 1,2,3-Trimethylbenzene
C5: i-Pentane
C6: Benzene
C6: Methylcyclohexane
Time (minutes) 0 min 16 min
Speciated measurements of >100 VOCs, CO Alkanes 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
Alkynes 24. Ethyne 25. Propyne
Alkenes 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
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
Aromatics 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
Cycloalkanes/alkenes 67. Cyclopentane 68. Methylcyclopentane 69. Cyclohexane 70. Methylcyclohexane 71. Cyclopentene
Sulfur Species 72. OCS 73. DMS 74. CS2
Colman et al., An. Chem., 73, 3723-3731, 2001 Simpson et al., ACP, 10, 6445-6463, 2010
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
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
Halocarbons
High precision, ultra-sensitive measurements of >100 C1-C10
volatile organic compounds (VOCs)
Volatile organic compound (VOC) sources
Biogenic: • Isoprene
• α-Pinene
• β-Pinene
Biomass burning: • Ethyne
• Benzene
• n-Butane
Industry: • C2Cl4
• HCFC-22
• HFC-134a
Fossil fuel combustion: • Ethyne
• Benzene
• Ethene
Fossil fuel evaporation: • i-Pentane
Natural gas leakage: • Methane
• Ethane
Liquefied petroleum gas: • Propane
• i-Butane
• n-Butane
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
Basrah, Iraq 2007 Unpublished data
• Lahore, Pakistan 2012 Manuscript in preparation
• 3 Saudi Arabian cities 2012‒2013 Manuscripts in preparation
Cities studied by the Rowland-Blake group
1993‒present
Thousands of samples collected in more than 75 cities
Case study 1: Mexico City
Mexico City, Mexico
Recommendations to improve air quality:
• Change LPG composition
• Lower LPG leakage rates
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
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
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
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
Case study 3: Hong Kong, PRC
Hong Kong, People’s Republic of China
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
• 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
Mean sea level pressure and wind field on
1000 hPa between Oct 22 and Dec 1, 2007
H. Guo et al., AE, 2007
Case study 4: Karachi, Pakistan
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
B. Barletta et al., AE, 2002
Case study 5: Mecca, Saudi Arabia
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
Case study 5: Mecca, Saudi Arabia
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 = (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 » 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
Santiago, Chile