2.3
Influence of vertical mixing on the distribution of trace gases during the 2006 TRAMP experiment in Houston, TX
Jochen Stutz, Univ. of California, Los Angeles, CA; and H. J. Oh, O. Pikelnaya, S. C. Hurlock, B. Lefer, J. Flynn, B. Rappenglueck, C. J. Flynn, W. Brune, J. E. Dibb, and R. Griffin
Vertical transport and mixing of
reactive trace gases in the boundary layer affect the chemistry of urban
pollutants. In the stable Nocturnal Boundary Layer (NBL), strong gradients of
ozone, nitrogen oxides and other species have been observed, making the
chemistry at night highly altitude dependent. Less pronounced gradients are
expected during the day. The vertical dependence of urban air chemistry
complicates the interpretation of ground observations of boundary layer
composition, as well as the quantification of urban pollution. The study of
this interaction both during the night and the day is therefore crucial to
improve our understanding of urban air quality and to further develop urban airshed
models.
Here we present data from the TRAMP
experiment held in August and September 2006 in Houston, TX. A long-path
Differential Optical Absorption Spectrometer (LP-DOAS) was set up at 70m
altitude on the roof of Moody tower on the University of Houston campus. Three retroreflector
arrays were mounted ~5km north – northwest in downtown Houston at altitudes of
20m, 130m, 300m. Concentrations of O3, NO2, SO2,
HCHO, HONO, and NO3 were retrieved in the altitude intervals between
20-70m, 70 – 130m, and 130 – 300m. Pronounced vertical gradients of all species
were observed during most nights. The upper interval was often probing the
residual layer, while the lower intervals were heavily influenced by ground
emissions. On a few occasions vertical gradients were also observed during the
day. A comparison with in-situ data showed that during the night the top of
Moody tower (70m agl) fluctuated between representing the lowest and the middle
LP-DOAS interval, showing the difficulty in interpreting nighttime data without
knowledge on the NBL properties. The impact of vertical mixing on urban air
chemistry is discussed based on various meteorological observations, including
those by a scanning aerosol LIDAR, and a 1D chemical transport model.
Particular attention is given to the chemistry of HONO, and its impact on
daytime OH levels, as well as the nocturnal NO3 radical chemistry,
and its impact on the NOx budget in Houston.
Session 2, Texas AQ2006 Field and Modeling Studies-II
Monday, 21 January 2008, 10:45 AM-11:45 AM, 230
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