• Asian Journal of Atmospheric Environment
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• v.8 no.4
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• pp.212-224
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• 2014

There are several studies on the effects of emissions of highly reactive volatile organic compounds (HRVOC) from the industrial sources in the Houston-Galveston-Brazoria (HGB) area on the high ozone events during the Texas Air Quality Study (TexAQS) in summer of 2000. They showed that the modeled atmosphere lacked reactivity to produce the observed high ozone event and suggested "imputation" of HRVOC emissions from the base inventory. Byun et al. (2007b) showed the imputed inventory leads to too high ethylene concentrations compared to the measurements at the chemical super sites but still too little aloft compared to the NOAA aircraft. The paper suggested that the lack of reactivity in the modeled Houston atmosphere must be corrected by targeted, and sometimes of episodic, increase of HRVOC emissions from the large sources such as flares in the Houston Ship Channel (HSC) distributed into the deeper level of the boundary layer. We performed retrospective meteorological and air quality modeling to achieve better air quality prediction of ozone by comparison with various chemical and meteorological measurements during the Texas Air Quality Study periods in August-September 2006 (TexA QS-II). After identifying several shortcomings of the forecast meteorological simulations and emissions inputs, we prepared new retrospective meteorological simulations and updated emissions inputs. We utilized assimilated MM5 inputs to achieve better meteorological simulations (detailed description of MM5 assimilation can be found in F. Ngan et al., 2012) and used them in this study for air quality simulations. Using the better predicted meteorological results, we focused on the emissions uncertainty in order to capture high peak ozone which occasionally happens in the HGB area. We described how the ozone predictions are affected by emissions uncertainty in the air quality simulations utilizing different emission inventories and adjustments.

• Journal of Korean Society for Atmospheric Environment
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• v.23 no.3
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• pp.297-310
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• 2007

Recent evidence has demonstrated that the pollutant recirculation can play an important role in leading to high ozone $(O_3)$ concentrations. In this study, the MM5-CAMx air quality modeling system was applied to simulate the pollutant recirculation and identify the transport of pollution during the high $O_3$ event (the maximum $O_3$ of 195 ppb) observed in the Greater Seoul Area (GSA) on $1{\sim}4$ June in 2004. The results showed a weak northeasterly synoptic wind during the night and early morning moved the air parcels containing the locally emitted urban pollution to the coast, which contributed to enhance $O_3$ formation in the southwest part of the GSA. As the sea breeze developed and started to penetrate inland in the late afternoon, the rapid build-up of $O_3$ concentration was found in the southwest coastal area due to the recirculation of the polluted air loaded with high level $O_3$. The simulated backward trajectories and observations at coastal sites confirmed the recirculation of pollutant with the late sea breeze is the dominant factor affecting the occurrence of high $O_3$ concentrations in the southwestern GSA.

• Journal of Korean Society for Atmospheric Environment
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• v.24 no.2
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• pp.196-205
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• 2008

Variability in vertical ozone and meteorological profiles was measured by 2Z electrochemical concentration cells (ECC) ozonesonde at Bangyi in Seoul ($37.52^{\circ}N$, $127.13^{\circ}E$) during June $6{\sim}9$, 2003 in odor to identify the vertical distribution of ozone and its relationship with the lower-atmospheric structure resulted in the high ozone concentrations near the surface. The eight profiles obtained in the early morning and the late afternoon during the study period clearly showed that the substantial change of ozone concentrations in lower atmosphere(${\sim}5\;km$), indicating that it is tightly coupled to the variation of the planetary boundary layer (PBL) structure as well as the background synoptic flow. All profiles observed early in the morning showed very low ozone concentrations near the surface with strong vertical gradients in the nocturnal stable boundary layer due to the photochemical ozone loss caused by surface NO titration under very weak vertical mixing. On the other hand, relatively uniform ozone profiles in the developed mixing layer and the ozone peaks in the upper PBL, were observed in the late afternoon. It was noted that a significant increase in ozone concentrations in the lower atmosphere occurred with the corresponding decrease of the mixing height in the late afternoon on June 8. Ozone in upper layer did not vertically vary much compared to that in PBL but changed significantly on June 6 that was closely associated with the variation of synoptic flows. Interestingly, heavily polluted ozone layers aloft (a maximum value of 115 ppb around 2 km) were formed early in the morning on 6 through 7 June under dominant westerly synoptic flows. This indicates the effects of the transport of pollutants on regional scale and consequently can give a rise to increase the surface ozone concentration by downward mixing processes enhanced in the afternoon.

• Journal of Korean Society for Atmospheric Environment
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• v.3 no.2
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• pp.27-32
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• 1987

As part of an air pollution epidemiological study of asthmatics residing in the Houston area, an air monitoring system provided data on the indoor and outdoor measurements of major pollutant gases sampled at selected residences during May ~ October 1981. Continuously monitored pollutant gases included sulfur dioxide ($SO_2$), nitrogen dioxide($NO_2$), nitric oxide(NO), carbon monoxide(CO), and ozone($O_3$). Outdoor levels for each pollutant were compared with their indoor levels(bedroom, kitchen, living room). Mean concentrations of each pollutant in the kitchen, and living room exceeded the mean levels outside except for ozone, while average bedroom levels for all gases except for $O_3$ and $NO_2$ were found higher than the corresponding outside levels. Indoor/ outdoor ratios for $SO_2$, NO, and CO were 1.8 ~ 2.7 times the outdoor levels, but indoor/ outdoor ratios for $NO_2$ and $O_3$ were 0.99 and 0.06, respectively. The impact of several important household characteristics (type of cooking fuel and cigarette smoking) on the indoor levels for these gases is evaluated.