A comparative study of O₃ formation in the Houston urban and industrial plumes during the 2000 Texas Air Quality Study

Abstract

[1] Ozone formation in the Houston area during a period of high ozone concentrations that occurred on 29 August 2000 during the TexAQS 2000 study is examined to understand differences in the sources of O 3 precursors and the rate and efficiency of ozone formation over the city of Houston and the industrialized Ship Channel region to the east of Houston. From late morning through late afternoon on 29 August, a period of stagnation occurred, allowing accumulation of O 3 and product species separately over downtown Houston and the Houston Ship Channel. Three aircraft flights were made in the region, starting from about 0900 CST and extending to about 1700 CST. A localized plume of high O 3 ranging between 120 and 200 ppb was observed over the Ship Channel on all of these aircraft flights. Over the same time period, O 3 concentrations over the city were much lower ranging between 40 and 90 ppb. NO x concentrations measured in the two regions in the late morning were roughly the same, but hydrocarbon reactivities over the industrial area were much higher, by as much as a factor of 10. Photochemical box model calculations constrained by observations of NO x , hydrocarbons, O 3 , and other stable species indicated that the instantaneous ozone formation rate was much lower (3-18 ppb/h) over downtown Houston than it was over the Ship Channel (3-80 ppb/h). The much faster O 3 formation rates and higher concentrations observed over the Ship Channel are attributed to the much higher hydrocarbon reactivity, the majority of which was contributed by low molecular weight alkenes. These high hydrocarbon reactivities also caused O 3 over the Ship Channel to be produced with much higher efficiency than over urban Houston. Comparison of photochemical product distributions suggests that O 3 formation in the urban area is much more hydrocarbon limited than in the Ship Channel, consistent with the geographic distribution of major hydrocarbon sources in the area.

Nitrogen dioxide measurement by cavity attenuated phase shift spectroscopy (CAPS) and implications in ozone production efficiency and nitrate formation in Beijing, China

“…To further support this, we plot the daily OPE x versus the peak of NO x in early morning ([NO x ] 0 , a surrogate of NO x emissions from local traffic) in Figure 8. Similar to that reported by Chou et al [2009] Dommen et al, 1999;Ge et al, 2012;Kleinman et al, 2000;Nunnermacker et al, 1998;Olszyna et al, 1994] [Chou et al, 2009] and also in agreement with those at various urban sites, e.g., Houston and Tennessee, USA [Daum et al, 2003;Zaveri et al, 2003]. However, the correlation between OPE x and [NO z ]/[NO y ] is contrary to that observed at a rural site (SDZ) in Beijing, where~75% of O 3 pollution is from regional transport rather than local photochemical production [Ge et al, 2012].…”

Emissions from oil and gas operations in the United States and their air quality implications

“…Beginning with measurements done in 2000, it had been observed that ratios of hydrocarbons to NO x in industrial plumes were consistently factors of 2-15, and in some isolated instances even a factor of 50 or higher, than the ratios reported in the inventories (Daum et al, 2001). Ratios of hydrocarbon to NO x , higher than those in bottom-up emission inventories, were observed for alkanes, alkenes, and aromatics, but overall atmospheric reactivity was dominated by alkenes (Daum et al, 2003;Ryerson et al, 2003). These findings led to multiple years of efforts to identify the sources of the missing or underestimated emissions.…”

Formaldehyde and its relation to CO, PAN, and SO<sub>2</sub> in the Houston-Galveston airshed

“…Rapid ozone (O 3 ) formation processes are associated with releases of highly reactive volatile organic compounds (HRVOCs) from industrial facilities predominantly located in Houston's Ship Channel (HSC), which comprises large agglomerations of petrochemical industries (Kleinman et al, 2002;Daum et al, 2003Daum et al, , 2004Ryerson et al, 2003;Berkowitz et al, 2005); the impact of non methane hydrocarbons on downwind non-industrialized areas has been extensively studied . Among HRVOCs compounds that serve as radical sources are of particular concern.…”