A tall tower flux measurement setup was established in metropolitan Houston, Texas, to
measure trace gas fluxes from both anthropogenic and biogenic emission sources in the
urban surface layer. We describe a new relaxed eddy accumulation system combined
with a dual-channel gas chromatography - flame ionization detection used for volatile
organic compound (VOC) flux measurements in the urban area, focusing on the results
of selected anthropogenic VOCs, including benzene, toluene, ethylbenzene and xylenes
(BTEX), and biogenic VOCs including isoprene and its oxidation products, methacrolein
(MACR) and methyl vinyl ketone (MVK). We present diurnal variations of
concentrations and fluxes of BTEX, and isoprene and its oxidation products during
summer time (May 22 - July 22, 2008) and winter time (January 1 - February 28). The
measured BTEX values exhibited diurnal cycles with a morning peak during weekdays
related to rush-hour traffic and additional workday daytime flux maxima for toluene and
xylenes in summer time. However, in winter time there was no additional workday
daytime peaks due mainly to the different flux footprints between the two seasons. A comparison with different EPA National Emission Inventories (NEI) with our summer
time flux data suggests potential underestimates in the NEI by a factor of 3 to 5.
The mixing ratios and fluxes of isoprene, MACR and MVK were measured during the
same time period in summer 2008. The presented results show that the isoprene was
affected by both tail-pipe emission sources during the morning rush hours and biogenic
emission sources in daytime. The observed daytime mixing ratios of isoprene were much
lower than over forested areas, caused by a comparatively low density of isoprene
emitters in the tower's footprint area. The average daytime isoprene flux agreed well
with emission rates predicted by a temperature and light only emission model (Guenther
et al., 1993). Our investigation of isoprene's oxidation products MACR and MVK
showed that both anthropogenic and biogenic emission sources exist for MACR, while
MVK was strongly dominated by a biogenic source, likely the isoprene oxidation
between the emission and sampling points.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2010-05-7960 |
| Date | 2010 May 1900 |
| Creators | Park, Chang Hyoun |
| Contributors | Schade, Gunnar W. |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | thesis, text |
| Format | application/pdf |
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