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| Titel |
Comparison of aromatic hydrocarbon measurements made by PTR-MS, DOAS and GC-FID during the MCMA 2003 Field Experiment |
| VerfasserIn |
B. T. Jobson, R. A. Volkamer, E. Velasco, G. Allwine, H. Westberg, B. K. Lamb, M. L. Alexander, C. M. Berkowitz, L. T. Molina |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 10, no. 4 ; Nr. 10, no. 4 (2010-02-19), S.1989-2005 |
| Datensatznummer |
250008129
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| Publikation (Nr.) |
 copernicus.org/acp-10-1989-2010.pdf |
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| Zusammenfassung |
| A comparison of aromatic hydrocarbon measurements is reported for
the CENICA supersite in the district of Iztapalapa during the Mexico
City Metropolitan Area field experiment in April 2003 (MCMA 2003).
Data from three different measurement methods were compared: a
Proton Transfer Reaction Mass Spectrometer (PTR-MS), long path
measurements using a UV Differential Optical Absorption Spectrometer
(DOAS), and Gas Chromatography-Flame Ionization analysis (GC-FID)
of canister samples. The principle focus was on the comparison
between PTR-MS and DOAS data. Lab tests established that the PTR-MS
and DOAS calibrations were consistent for a suite of aromatic
compounds including benzene, toluene, p-xylene, ethylbenzene,
1,2,4-trimethylbenzene, phenol and styrene. The point sampling
measurements by the PTR-MS and GC-FID showed good correlations
(r=0.6), and were in reasonable agreement for toluene,
C2-alkylbenzenes and C3-alkylbenzenes. The PTR-MS benzene data were
consistently high, indicating interference from ethylbenzene
fragmentation for the 145 Td drift field intensity used in the
experiment. Correlations between the open-path data measured at 16-m
height over a 860-m path length (retroreflector in 430 m distance),
and the point measurements collected at 37-m sampling height were
best for benzene (r=0.61), and reasonably good for toluene,
C2-alkylbenzenes, naphthalene, styrene, cresols and phenol
(r>0.5). There was good agreement between DOAS and PTR-MS
measurements of benzene after correction for the PTR-MS ethylbenzene
interference. Mixing ratios measured by DOAS were on average a
factor of 1.7 times greater than the PTR-MS data for toluene,
C2-alkylbenzenes, naphthalene and styrene. The level of
agreement for the toluene data displayed a modest dependence on wind
direction, establishing that spatial gradients – horizontal,
vertical, or both – in toluene mixing ratios were significant, and
up to a factor of 2 despite the fact that all measurements were
conducted above roof level. Our analysis highlights a potential
problem in defining a VOC sampling strategy that is meaningful for
the comparison with photochemical transport models: meaningful
measurements require a spatial fetch that is comparable to the grid
cell size of models, which is typically a few 10 km2.
Long-path DOAS measurements inherently average over a larger spatial
scale than point measurements. The spatial representativeness can be
further increased if observations are conducted outside the surface
roughness sublayer, which might require measurements at altitudes as
high as 10 s of metres above roof level. |
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