Methane Destruction Efficiency of Natural Gas Flares Associated with Shale Formation Wells

Flaring to dispose of natural gas has increased in the United States and is typically assumed to be 98% efficient, accounting for both incomplete combustion and venting during unintentional flame termination. However, no in situ measurements of flare emissions have been reported. We used an aircraft platform to sample 10 flares in North Dakota and 1 flare in Pennsylvania, measuring CO₂, CH₄, and meteorological data. Destruction removal efficiency (DRE) was calculated by assuming a flare natural gas input composition of 60–100% CH₄. In all cases flares were >99.80 efficient at the 25% quartile. Crosswinds up to 15 m/s were observed, but did not significantly adversely affect efficiency. During analysis unidentified peaks of CH₄, most likely from unknown venting practices, appeared much larger in magnitude than emissions from flaring practices. Our analysis suggests 98% efficiency for nonsputtering flares is a conservative estimate for incomplete combustion and that the unidentified venting is a greater contributor to CH₄ emissions

Emissions from South Asian Brick Production

Thirteen South Asian brick kilns were tested to quantify aerosol and gaseous pollutant emissions. Particulate matter (PM_2.5), carbon monoxide (CO), and optical scattering and absorption measurements in the exhaust of six kiln technologies demonstrate differences in overall emission profiles and relative climate warming resulting from kiln design and fuel choice. Emission factors differed between kiln types, in some cases by an order of magnitude. The kilns currently dominating the sector had the highest emission factors of PM_2.5 and light absorbing carbon, while improved Vertical Shaft and Tunnel kilns were lower emitters. An improved version of the most common technology in the region, the zig-zag kiln, was among the lowest emitting kilns in PM_2.5, CO, and light absorbing carbon. Emission factors measured here are lower than those currently used in emission inventories as inputs to global climate models; 85% lower (PM_2.5) and 35% lower for elemental carbon (EC) for the most common kiln in the region, yet the ratio of EC to total carbon was higher than previously estimated (0.96 compared to 0.47). Total annual estimated emissions from the brick industry are 120 Tg CO₂, 2.5 Tg CO, 0.19 Tg PM_2.5, and 0.12 Tg EC

Impact of Marcellus Shale Natural Gas Development in Southwest Pennsylvania on Volatile Organic Compound Emissions and Regional Air Quality

The Marcellus Shale is the largest natural gas deposit in the U.S. and rapid development of this resource has raised concerns about regional air pollution. A field campaign was conducted in the southwestern Pennsylvania region of the Marcellus Shale to investigate the impact of unconventional natural gas (UNG) production operations on regional air quality. Whole air samples were collected throughout an 8050 km² grid surrounding Pittsburgh and analyzed for methane, carbon dioxide, and C₁–C₁₀ volatile organic compounds (VOCs). Elevated mixing ratios of methane and C₂–C₈ alkanes were observed in areas with the highest density of UNG wells. Source apportionment was used to identify characteristic emission ratios for UNG sources, and results indicated that UNG emissions were responsible for the majority of mixing ratios of C₂–C₈ alkanes, but accounted for a small proportion of alkene and aromatic compounds. The VOC emissions from UNG operations accounted for 17 ± 19% of the regional kinetic hydroxyl radical reactivity of nonbiogenic VOCs suggesting that natural gas emissions may affect compliance with federal ozone standards. A first approximation of methane emissions from the study area of 10.0 ± 5.2 kg s^–1 provides a baseline for determining the efficacy of regulatory emission control efforts