Abstract
The Houston-Galveston-Brazoria (HGB) area of Texas has historically experienced severe air pollution events with high concentrations of ozone (O3) during the summer season. This study evaluates the contribution of different anthropogenic sources to ozone formation in the HGB area. The Emission Processing System (EPS3) is used to process emission files in four different scenarios (Base case as including All emission sources (BC), All sources— Area sources (AMA), All sources—Point sources (AMP), and All sources— Mobile sources (AMM). These files are used as input in photochemical modeling with the Comprehensive Air Quality Model with Extensions (CAMx) to simulate ozone formation. The data is analyzed for daily maximum ozone concentrations and contribution of source categories at three air quality monitoring locations (La Porte Sylvan beach-C556, Houston Texas avenue-C411, and Texas city in Galveston-C683) for a study period of June 1-June 30, 2012. The contribution of the point sources to ozone formation is dominated at all three locations, followed by mobile sources and area sources on high ozone days. The relative contributions of point sources are 27.51% ± 3.53%, 21.45% ± 7.36%, and 30.30% ± 9.36%; and mobile sources are 18.27% ± 2.22%, 20.60% ± 6.89%, and 18.61% ± 7.43%; and area sources were 4.2% ± 1.65%, 5.21% ± 1.59%, and 3.72% ± 1.52% at C556, C411, and C683, respectively. These results demonstrate the importance of regulatory focus on controlling point and mobile source emissions for NAAQS attainment in the study region.
Highlights
The air pollutant ozone refers to tropospheric or ground-level ozone
The relative contributions of point sources are 27.51% ± 3.53%, 21.45% ± 7.36%, and 30.30% ± 9.36%; and mobile sources are 18.27% ± 2.22%, 20.60% ± 6.89%, and 18.61% ± 7.43%; and area sources were 4.2% ± 1.65%, 5.21% ± 1.59%, and 3.72% ± 1.52% at C556, C411, and C683, respectively. These results demonstrate the importance of regulatory focus on controlling point and mobile source emissions for National Ambient Air Quality Standards (NAAQS) attainment in the study region
Our study reveals that the ozone exceedances in the study region in the June episode are greatly affected by point sources such as power plants, refineries, chemical manufacturing facilities, etc. followed by mobile sources, which include on-road, off-road, and non-road vehicles
Summary
The air pollutant ozone refers to tropospheric or ground-level ozone. Formation of peroxy radicals (RO2) is the major role of VOCs, which convert nitrogen monoxide (NO) back to nitrogen dioxide (NO2) without consuming O3 and reproduce hydroxyl radical (OH) to allow sustained net O3 formation [3] [4]. An early study explained ozone chemistry in the troposphere and the simplified photochemistry shown in chemical reactions Equations (1) to (4) where OH and HO2 are short-lived radicals and carbonyl compounds play role in further oxidation steps [3]. There are six criteria pollutants identified by the U.S Environmental Protection Agency (USEPA)
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