VOC emissions uncertainty in the Houston-Galveston area is

large. It is suggested that alkene emissions in inventories

are significantly (factor of 3-10) lower than those inferred

from the aircraft measurements of formaldehyde

concentration during the TexAQS 2000. With such

emissions uncertainties, models will not accurately simulate

observations. Here we tested the emissions inventory

prepared by the Texas Commission for Environmental

Quality (TCEQ), who modified the olefin emissions from

several large point sources along the Houston Ship Channel

to have similar magnitudes as the NOx emissions.

CMAQ simulations including the CB-4 chemical mechanism

were performed for the episode August 23 – September 1,

2000 at 36-, 12-, and 4-km resolutions. Boundary condition

profiles were provided for 36-km runs, while boundary

conditions for the nested 12-km and 4-km runs were

provided from modeled results for the coarser domains. In

order to provide more realistic initial conditions for the

CMAQ runs, the model was allowed a spin-up time of two

days, then, restarted with initial conditions from hour 24 of

August 24, 2000. This procedure increased the reliability of

the modeled results for August 23-24, 2000.

Simulated ozone concentrations

54

Figure 9 provides daily maximum ozone concentration fields

from the simulation. The center of Houston and areas

downwind of the Ship Channel industrial areas show high

ozone concentrations. The highest value was 124 ppb, which

occurred around hour 20:00 UTC on August 31, 2000.

From the scatter diagram (Figure 10) comparing model

simulation with the continuous air monitoring site (CAMS)

data, we can identify the sites showing large discrepancies.

They are the industrial Houston Regional Monitoring Sites

7, 8 and 11 (EPA482010807, EPA482010808, and

EPA48710901, respectively) and the nearby Crawford

(EPA482011037) and Deer Park (EPA482011039) sites.

Time series plots for other sites show respectable simulation

results for most of the simulation days (see Figure 11)

except for the missed peak values on August 25 and 30. A

 

 

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