Atmospheric Mercury and Methane in the South-Central U.S.



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This study characterized temporal and spatial variations of atmospheric mercury and methane (CH4), and investigated their emission sources. Speciated atmospheric mercury observations collected over the period from 2008 to 2010 at the U.S. Atmospheric Mercury Network sites (AMNet) were analyzed. We found similar median levels of gaseous elemental mercury (GEM) as well as its seasonality at 11 sites. Seasonal and diurnal variations were also observed for gaseous oxidized mercury (GOM) and particulate bound mercury (PBM). This study also reports continuous measurements of total gaseous mercury (THg = GEM + GOM) for the first time in urban Houston area. We found that the median level of THg was consistent with the current global background level. A predominant feature of THg was the frequent occurrence of large THg spikes. Our measurements revealed that the variability of THg was primarily controlled by nearby mercury sources. Atmospheric mercury emissions in the Barnett Shale area were studied by employing both stationary measurements and mobile laboratory surveys. The influence of oil and natural gas (ONG) emissions was substantial in this area, as inferred from the i-pentane/n-pentane ratio (= 1.17). However, few THg plumes were captured in our extensive mobile laboratory surveys. Only one compressor station and one natural gas condensate processing facility were found to have significant THg emissions. Our results suggest that the majority of ONG facilities are not significant sources of THg; however, it is highly likely that a small number of these facilities contribute a relatively large amount of the emissions in the ONG sector. Atmospheric CH4 was also investigated to quantify emissions from ONG operations and landfills in the Barnett Shale area. The background CH4 level (10th percentile) was 1.89 ppmv, which was higher than the northern hemisphere background level. Emission rates were estimated using Inversed Dispersion Models. Model results show that well pad emissions were linearly correlated with gas production, yielding a total well pad emission rate of 1.44×105 kg CH4/hr in the Barnett Shale area. It was found that CH4 emissions from compressor stations and gas processing plants were substantial; several of them have similar emission rates as a major landfill.



Atmospheric mercury, Atmospheric methane, Air quality, Greenhouse gases, South-Central United States


Portions of this document appear in: Lan, X., R. Talbot, M. Castro, K. Perry, and W. Luke. "Seasonal and diurnal variations of atmospheric mercury across the US determined from AMNet monitoring data." Atmospheric Chemistry and Physics 12, no. 21 (2012): 10569. And in: Lan, Xin, Robert Talbot, Patrick Laine, Barry Lefer, James Flynn, and Azucena Torres. "Seasonal and diurnal variations of total gaseous mercury in urban Houston, TX, USA." Atmosphere 5, no. 2 (2014): 399-419. And in: Lan, Xin, Robert Talbot, Patrick Laine, Azucena Torres, Barry Lefer, and James Flynn. "Atmospheric mercury in the Barnett Shale area, Texas: Implications for emissions from oil and gas processing." Environmental science & technology 49, no. 17 (2015): 10692-10700. And in: Lan, Xin, Robert Talbot, Patrick Laine, and Azucena Torres. "Characterizing fugitive methane emissions in the Barnett Shale area using a mobile laboratory." Environmental science & technology 49, no. 13 (2015): 8139-8146.