Relative Contribution of Different Source Categories to Ozone Exceedances in the Houston-Galveston-Brazoria Area
Ozone concentrations at a particular
location depend on a number of variables such as quantity of emissions, types
of source categories, meteorology, and land use. Ozone
formation in the Houston-Galveston-Brazoria (HGB) area is associated with
emissions from on- and off-road vehicles, power plants and biogenic sources.
However, the extensive petrochemical industry that contributes both reactive
VOCs and NOx to the pollutant mix and ozone formation makes it a
unique region. In this study, the authors aimed to analyze the
relative contribution of different emission source categories to ozone in the HGB
area of Texas.
Emission Processing
System (EPS3) was used to prepare the emission files for five different source
combination cases (Base case, Biogenic, Area + Biogenic, Mobile + Biogenic,
Low-level Point + Biogenic). These emission files were used to perform
photochemical modeling with Comprehensive Air Quality Model with Extensions
(CAMx), and the results were analyzed with Visual Environment for Rich Data
Interpretation (VERDI) tool. The daily maximum ozone concentrations and
individual contributions of the source categories were analyzed over a 15-day
study period between June 1-15, 2012, at three locations (University of
Houston-Sugarland, Bayland Park and Conroe).
The results showed
that Isoprene emissions in the region, and transport of
biogenic VOCs from northeast Houston played a significant role at all three
locations, as evidenced by an average contribution of 49.7% ± 12.8%, 43.1% ±
12.0%, and 39.9% ± 9.28% from biogenic sources toward daily maximum ozone
concentrations, at Sugarland, Bayland Park and Conroe sites respectively. The
relative contribution Mobile + Biogenic source category was the primary factor
in this region, indicating the dominance of mobile source NOX
emissions in determining peak ozone exceedances. Conroe site had lower
deviations in the diurnal variations of ozone and lower peak concentrations as
compared to Sugarland and Bayland park sites, due to the location being distant
from the city center and the Houston ship channel. The remoteness of this site
is also evidenced by the relatively lower contribution of LPt + Biogenic source
category. The overall importance of emission source categories that need to be
targeted for regulatory control in the HGB area were observed to be in the
following sequence Mobile > Point > Area sources.
Article by Raghava
R. Kommalapati, et al, from Prairie View A & M University, Prairie View,
USA.
Full access: http://mrw.so/518LE3
Image by Morten, from Flickr-cc.
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