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Table 1

Summary of published literature addressing O&NG influences on air quality in Colorado. DOI: https://doi.org/10.1525/elementa.398.t1

YearAuthorsLead Author AffiliationTitleJournalPeer ReviewMethaneVOCsOzoneOtherMain Findings*

 
2008  Not specified CDPHE Denver Metropolitan Area and North Front Range 8-Hour Ozone State Implementation Plan State of Colorado Ozone
Implementation Plan 
    Transport from cool pool area of the Platte Valley in Weld County results in a mean daily maximum 8-hour ozone of 71 ppb at the four Front Range monitors considered. 
2009  Rodriguez et al. Colorado State Univ. Regional impacts of oil and gas development on ozone formation in the western United States JAWMA   Chemical and transport modeling A maximum MDA8 ozone enhancement of 9.6 ppb was estimated from O&NG emissions in southwestern Colorado. 
2012  McKenzie et al. Colorado School of Public Health Human health risk assessment of air emissions from development of unconventional natural gas resources Sci. Tot. Environ.   Health risk assessment Median concentrations of benzene, ethylbenzene, toluene, and m-xylene/p-xlyene were 2.7, 4.5, 4.3, and 9 times higher in the well completion samples than in other natural gas development samples, respectively. 
2012 Petron et al. NOAA/CIRES Hydrocarbon emissions characterization in the Colorado Front Range: A pilot study J. Geophys. Res.   Emissions of methane and light NMHC VOC are most likely underestimated in current inventories. 
2012  Levi Council on Foreign Relations Comment on “Hydrocarbon emissions characterization in the Colorado Front Range: A pilot study” by Pétron et al. J. Geophys. Res.    Consideration of previously unconsidered observations results in a new methane flux estimates that are consistent with current inventories, but inconsistent with the estimates in Petron et al. (2012). 
2013 Petron et al. NOAA/CIRES Reply to comment on “Hydrocarbon emissions characterization in the Colorado Front Range—A pilot study” by M.A. Levi J. Geophys. Res.   Flashing emission and regulatory modeled composition profiles for a limited number of condensate tanks probably do not represent the true range of these parameters for the thousands of such sources across the DJB in 2008. 
2013  Gilman et al. NOAA/CIRES Source signature of volatile organic compounds from oil and natural gas operations in northeastern Colorado Environ. Sci. Technol.   On average, 55 ± 18% of the VOC-OH reactivity was attributable to emissions from O&NG operations, indicating that these emissions are a significant source of ozone precursors. 
2013  Swarthout et al. Univ. of New Hampshire Volatile organic compound distributions during the NACHTT campaign at the Boulder Atmospheric Observatory: Influence of urban and natural gas sources J. Geophys. Res.   Natural gas associated emissions have the potential to impact downwind air quality as natural gas NMHCs comprised ≈24% of the calculated OH reactivity. 
2013  Brown et al. NOAA/CIRES Nitrogen, Aerosol Composition, and Halogens on a Tall Tower (NACHTT): Overview of a wintertime air chemistry field study in the front range urban corridor of Colorado J. Geophys. Res.   Halogens, NOx, NOy, aerosol Large observed mixing ratios of light alkanes, both in near-surface air and aloft, were attributable to local emissions from oil and gas activities. 
2013  LaFranchi et al. Lawrence Livermore National Laboratory Constraints on emissions of carbon monoxide, methane, and a suite of hydrocarbons in the Colorado Front Range using observations of 14CO2 Atmos. Chem. Phys.  CO, 14CO2 Enhanced concentrations of CH4 and C3-C5 alkanes were found in air influenced by emissions to the north and east of the Boulder Atmospheric Observatory (BAO) and were suggested to have been sourced from oil and gas fields located to the northeast. 
2014  Petron et al. NOAA/CIRES A new look at methane and nonmethane hydrocarbon emissions from oil and natural gas operations in the Colorado Denver-Julesburg Basin J. Geophys. Res.   Emission of methane, VOC, and benzene in the DJB were estimated to be 3 times, at least a factor of 2, and 7 times, respectively, larger than EPA and State inventories. 
2014  Kort et al. Univ. of Michigan Four corners: The largest US methane anomaly viewed from space Geophys. Res. Let.    Spaceborne remote sensing indicated large CH4 levels over the Four Corners region. Estimted emissions largely exceeded inventory estimates. 
2014  Thompson et al. Univ. of Colorado Influence of oil and gas emissions on ambient atmospheric non-methane hydrocarbons in residential areas of Northeastern Colorado Elementa    At residences near oil and gas operations, mean mole fractions of the C2-C5 alkanes were enhanced by a factor of 18–77 relative to the regional background, and present at higher levels than typically found in large urban centers. 
2014 Colburn et al. The Endocrine Disruption Exchange An exploratory study of air quality near natural gas operations Human & Ecol. Risk Assess.   Health risk assessment The number of NMHCs and their concentrations were highest during the initial drilling phase and did not increase during hydraulic fracturing in a closed-loop system. 
2015  Richter et al. Univ. of Colorado Compact highly sensitive multi-species airborne mid-IR spectrometer Applied Physics   Formaldehyde Ethane was enhanced at least ten times above background levels in the DJB boundary layer. Regions with elevated ethane overlapped with elevated formaldehyde. 
2016  Townsend-Small et al. Univ. of Cincinnati Using stable isotopes of hydrogen to quantify biogenicand thermogenic atmospheric methane sources: A case study from the Colorado Front Range Geophys. Res. Lett.   Methane hydrogen and carbon stable isotopes analyses Biogenic CH4 comprised about 50% of total CH4 observed in the active oil and gas extraction region. 
2016  Franco et al. Univ. of Liege, Belgium Evaluating ethane and methane emissions associated with the development of oil and natural gas extraction in North America Environ. Res. Lett.    Between 2009–2015, Fourier Transform Infrared (FTIR) ethane column observations over Boulder show a 5.0% per year rate of increase. 
2016  Sullivan et al. NASA Goddart Quantifying the contribution of thermally driven recirculation to a high-ozone event along the Colorado Front Range using lidar J. Geophys. Res.   Air recirculation Complex meteorology in this region can significantly exacerbate pollution levels. A high summer 2014 surface ozone pollution event was associated with thermally driven upslope flow. 
2016  Reddy and Pfister NCAR Meteorological factors contributing to the interannual variability of midsummer surface ozone in Colorado, Utah, and other western U.S. states J. Geophys. Res.   Reanalysis of meteorology and regional chemistry modeling Significant correlations were found between July MDA8 O3 and meteorological variables. Increased 500 hPa heights lead to high July O3. particularly in areas of elevated terrain near urban sources of NO2 and other O3 precursors. 
2016  Vu et al. Univ. of California Riverside Impacts of the Denver Cyclone on regional air quality and aerosol formation in the Colorado Front Range during FRAPPE 2014 Atmos. Chem. Phys.  Peroxyacetyl Nitrate (PAN), CO, NH3, aerosol properties Meteorological patterns associated with the Denver Cyclone increased pollutant levels, including aerosol loadings in the Denver metropolitan area. Cyclone conditions promote transport of aerosol constituents from the NCFR into the Denver metropolitan area, increasing aerosol mass loadings and reducing visibility. 
2016  Halliday et al. Pennsylvania State Univ. Atmospheric benzene observations from oil and gas production in the Denver-Julesburg Basin in July and August 2014 J. Geophys. Res.    Unexpectedly high benzene mixing ratios were observed at a site near Platteville (maximum of 29.3 ppb), primarily at night, and assoicated to emissions from nearby O&NG operations. 
2016  Frankenberg et al. California Institute of Technology Airborne methane remote measurements reveal heavytail flux distribution in Four Corners region PNAS    In the Four Corners Region, methane sources include gas processing facilities, storage tanks, pipeline leaks, and well pads, and a coal mine; emissions ranged from 2 kg h–1 through ~5,000 kg h–1
2016  Dingle et al. Univ. of California Riverside Aerosol optical extinction during the Front Range Air Pollution and Photochemistry Éxperiment (FRAPPÉ) 2014 summertime field campaign, Colorado, USA Atmos. Chem. Phys.   Aerosol The light extinction coefficient best correlated with organic aerosols in O&NG emissions and with nitrate aerosols under O&NG and agriculture influences. 
2016  McDuffie et al. NOAA/CIRES Influence of oil and gas emissions on summertime ozone in the Colorado Northern Front Range J. Geophys. Res.   O&NG alkanes contribute over 80% to the observed carbon mixing ratio, roughly 50% to the regional VOC OH reactivity, and approximately 20% to regional photochemical O3 production. 
2017  Tzompa-Sosa et al. Colorado State Univ. Revisiting global fossil fuel and biofuel emissions of ethane J. Geophys. Res.   Over northeastern Colorado, year 2001 ethane inventory emissions had to be increased by more than 40% for modeled atmospheric mixing ratios to match observations. 
2017  Evans and Helmig Univ. of Colorado Investigation of the influence of transport from oil and natural gas regions on elevated ozone levels in the northern Colorado Front Range JAWMA    Transport from areas with O&NG operations accounted for on the order of 65% of 1-hr averaged elevated ozone levels at BAO and South Boulder, while the Denver urban corridor accounted for 9%. 
2017 Abeleira et al. Colorado State Univ. Source characterization of volatile organic compounds in the Colorado Northern Front Range metropolitan area during spring and summer 2015 J. Geophys. Res.   The NCFR is more strongly influenced by O&NG sources of VOCs than other urban and suburban regions in the U.S. 
2017  Cheadle et al. CIRES/NOAA Surface ozone in the Colorado northern Front Range and the influence of oil and gas development during FRAPPE/DISCOVER-AQ in summer 2014 Elementa  NOx Correlation analyses in case studies showed that oil and gas related activities are a NOx and O3 precursor source. 
2017 Pfister et al. NCAR Process-Based and Regional Source Impact Analysis for FRAPPÉ and DISCOVER-AQ 2014 Final Report to CDPHE   NOx Mobile sources and oil and gas related emissions are the largest contributors to local ozone production in the Northern Front Range Metro Area (NFRMA). 
2017  Baier et al. Pennsylvania State Univ. Higher measured than modeled ozone production at increased NOx levels in the Colorado Front Range Atmos. Chem. Phys.  Ozone production rate Ozone production rates peak during late morning. Rates predicted by three models were lower than direct observations. 
2017 Abeleira and Farmer Colorado State Univ. Summer ozone in the northern Front Range metropolitan area: weekend–weekday effects, temperature dependences, and the impact of drought Atmos. Chem. Phys.  NOx Ozone in the NCFR area was either stagnant or increasing between 2000 and 2015, likely because of decreasing NOx emissions in a NOx -saturated environment and increased anthropogenic VOC emissions. 
2017  Robertson et al. Univ. of Wyoming Variation in methane emission rates from well pads in four oil and gas basins with contrasting production volumes and compositions Environ. Sci. Technol.    In the DJB, ~70% of total methane emissions were from 20% of the well pads The total mass of methane emitted as a percent of gross methane produced was 2.1% (1.1–3.9%). 
2017  Kaser et al. NCAR The effect of entrainment through atmospheric boundary layer growth on observed and modeled surface ozone in the Colorado Front Range J. Geophys. Res.   Boundary layer growth, contribution of entrainment and synoptic transport to O3 A large day-to-day variability of ozone above the atmospheric boundaray layer was attributed to differing air mass origins. On average, morning boundary layer growth contributed 4.8 ppb hr–1 to the morning hour ozone increase. 
2017 Pfister et al. NCAR Using observations and source specific model tracers to characterize pollutant transport during FRAPPÉ and DISCOVER-AQ J. Geophys. Res.    Air flow characterization During upslope events, frequently, there is a separation of air masses that are heavily influenced by oil and gas emissions to the north and dominated by urban emissions to the south. NCFR pollution can “spillover” into the valleys to the west of the Continental Divide. 
2017  Yacovitch et al. Aerodyne Research Inc. Natural gas facility methane emissions: Measurements by tracer flux ratio in two US natural gas producing basins Elementa    Methane emission rates from DJB gathering stations (kg CH4 hr–1) were lower compared to results from other basins. 
2017  Zaragoza et al. Colorado State Univ. Observations of acyl peroxy nitrates during the Front Range Air Pollution and Photochemistry Experiment (FRAPPE) J. Geophys. Res.  PAN, Peroxyproply nitrate (PPN) Anthropogenic VOCs played a dominant role in PAN production during periods with high O3. The contribution of biogenic VOCs to local O3 production was relatively small. 
2017  Smith et al. Univ. of Michigan Airborne quantification of methane emissions over the Four Corners Region Environ. Sci. Technol.    Using five independent days of measurements, an average regional CH4 flux of 0.54 ± 0.20 Tg yr–1 was calulated, in close agreement with a space-based estimate for 2003–2009. 
2018  Bien and Helmig Univ. of Colorado Changes in summertime ozone in Colorado during 2000–2015 Elementa    Median and upper percentile surface O3 in the DMA has not declined at the rates seen in other western U.S. regions. 
2018  McKenzie et al. Univ. of Colorado Ambient nonmethane hydrocarbon levels along Colorado’s Northern Front Range: Acute and chronic health risks Environ. Sci. Technol.    O&NG air pollutant concentrations increased with proximity to an O&NG facility, as did health risks. 
2018  Peischl et al. NOAA/CIRES Quantifying methane and ethane emissions to the atmosphere from Central and Western U.S. oil and natural gas production regions J. Geophys. Res.   Total CH4 and C2H6 emissions attributed to O&NG operations in the Denver Basin region remained statistically unchanged between 2008 and March 2015. 
2018  Fann et al. US EPA Research Triangle Park Assessing human health PM2.5 and ozone impacts from U.S. oil and natural gas sector emissions in 2025 Environ. Sci. Technol.  PM2.5 Under current growth projections O&NG emissions are predicted to cause 37 and 34 annual premature deaths from the added PM2.5 and ozone production, respectively, in Colorado by 2025. 
2018  McMullin et al. CDPHE Exposures and health risks from volatile organic compounds in communities located near oil and gas exploration and production activities in Colorado (U.S.A.) Int. J. Environ. Res. & Public Health   Health effects 56 VOCs emitted from O&NG operations in Colorado were identified. Further characterization of primary and secondary VOCs emitted from O&NG sites during different phases of operations is needed to address the community health relevance. 
2018  Benedict et al. Colorado State Univ. Impact of Front Range sources on reactive nitrogen concentrations and deposition in Rocky Mountain National Park PeerJ   NOx, NOy, ammonia Elevated concentrations of reactive nitrogen were associated with emissions from oil and gas operations, which are frequently co-located with agricultural production and livestock feeding areas in the region, and from urban areas. 
2018  Abdi-Oskouei et al. Univ. of Iowa Impacts of physical parameterization on prediction of ethane concentrations for oil and gas emissions in WRF-Chem Atmos. Chem. Phys.   EPA emission inventory Comparison between airborne measurements and WRF-Chem model simulations indicated a low bias of ethane in the NFRMA close to O&NG activities, suggesting underestimation of O&NG emissions in the 2011 National Emissions Inventory (NEI). 
2018  Bahreini et al. Univ. of California Riverside Sources and characteristics of summertime organic aerosol in the Colorado Front Range: Perspective from measurements and WRF-Chem modeling Atmos. Chem. Phys.    Aerosol characterization It was estimated that the O&NG sector contributed to <5% of total organic aerosol, but up to 38% of anthropogenic secondary organic aerosol in the NCFR. 
2019  Oltmans et al. NOAA Boundary layer ozone in the Northern Colorado Front Range in July-August 2014 during FRAPPE and DISCOVER-AQ from vertical profile measurements Elementa    The association of high O3 days at BAO with transport from O&NG sectors suggested that O&NG emissions were an important source of O3 precursors and are crucial in producing peak O3 events. Exposure of populations in the Foothills area is not captured by the current regulatory network, and likely underestimated. 
2019 Tsompa-Soza et al. Colorado State Univ. Atmospheric implications of large C2-C5 alkane emissions from the U.S. oil and gas industry J. Geophys. Res.    Of four regions analyzed, Boulder showed the highest percentage contribution from the oil and gas sector to total abundances of C2-C5 alkanes throughout the troposphere. 
2019  Lindaas et al. Colorado State Univ. Acyl peroxy nitrates link oil and natural gas emissions to high ozone abundances in the Colorado Front Range during summer 2015 J. Geophys. Res. Acyl peroxy nitrates (APNs), photochemical modeling Anthropogenic VOC precursors dominated APNs production when O3 was most elevated in the NCFR in summer 2015. Propane and n-pentane, primarily from O&NG emissions, drive elevated PPN/PAN ratios during high O3 events. Emissions from the O&NG sector contribute to O3 production on high O3 days. 
2019  Kille et al. Univ. of Colorado Separation of methane emissions from agricultural and natural gas sources in the Colorado Front Range Geophys. Res. Let.  Ammonia Natural gas methane sources dominate over agricultural and other sources, but the latter are relatively more important when excess CH4 is smaller than 5 ppb. 
2019  Benedict et al. Colorado State Univ. Volatile organic compounds and ozone in Rocky Mountain National Park during FRAPPÉ Atmos. Chem. Phys.   The study estimated that for that high ozone events associated with O&NG signatures, NCFR sources contributed ≈20 ppb of additional ozone. 
YearAuthorsLead Author AffiliationTitleJournalPeer ReviewMethaneVOCsOzoneOtherMain Findings*

 
2008  Not specified CDPHE Denver Metropolitan Area and North Front Range 8-Hour Ozone State Implementation Plan State of Colorado Ozone
Implementation Plan 
    Transport from cool pool area of the Platte Valley in Weld County results in a mean daily maximum 8-hour ozone of 71 ppb at the four Front Range monitors considered. 
2009  Rodriguez et al. Colorado State Univ. Regional impacts of oil and gas development on ozone formation in the western United States JAWMA   Chemical and transport modeling A maximum MDA8 ozone enhancement of 9.6 ppb was estimated from O&NG emissions in southwestern Colorado. 
2012  McKenzie et al. Colorado School of Public Health Human health risk assessment of air emissions from development of unconventional natural gas resources Sci. Tot. Environ.   Health risk assessment Median concentrations of benzene, ethylbenzene, toluene, and m-xylene/p-xlyene were 2.7, 4.5, 4.3, and 9 times higher in the well completion samples than in other natural gas development samples, respectively. 
2012 Petron et al. NOAA/CIRES Hydrocarbon emissions characterization in the Colorado Front Range: A pilot study J. Geophys. Res.   Emissions of methane and light NMHC VOC are most likely underestimated in current inventories. 
2012  Levi Council on Foreign Relations Comment on “Hydrocarbon emissions characterization in the Colorado Front Range: A pilot study” by Pétron et al. J. Geophys. Res.    Consideration of previously unconsidered observations results in a new methane flux estimates that are consistent with current inventories, but inconsistent with the estimates in Petron et al. (2012). 
2013 Petron et al. NOAA/CIRES Reply to comment on “Hydrocarbon emissions characterization in the Colorado Front Range—A pilot study” by M.A. Levi J. Geophys. Res.   Flashing emission and regulatory modeled composition profiles for a limited number of condensate tanks probably do not represent the true range of these parameters for the thousands of such sources across the DJB in 2008. 
2013  Gilman et al. NOAA/CIRES Source signature of volatile organic compounds from oil and natural gas operations in northeastern Colorado Environ. Sci. Technol.   On average, 55 ± 18% of the VOC-OH reactivity was attributable to emissions from O&NG operations, indicating that these emissions are a significant source of ozone precursors. 
2013  Swarthout et al. Univ. of New Hampshire Volatile organic compound distributions during the NACHTT campaign at the Boulder Atmospheric Observatory: Influence of urban and natural gas sources J. Geophys. Res.   Natural gas associated emissions have the potential to impact downwind air quality as natural gas NMHCs comprised ≈24% of the calculated OH reactivity. 
2013  Brown et al. NOAA/CIRES Nitrogen, Aerosol Composition, and Halogens on a Tall Tower (NACHTT): Overview of a wintertime air chemistry field study in the front range urban corridor of Colorado J. Geophys. Res.   Halogens, NOx, NOy, aerosol Large observed mixing ratios of light alkanes, both in near-surface air and aloft, were attributable to local emissions from oil and gas activities. 
2013  LaFranchi et al. Lawrence Livermore National Laboratory Constraints on emissions of carbon monoxide, methane, and a suite of hydrocarbons in the Colorado Front Range using observations of 14CO2 Atmos. Chem. Phys.  CO, 14CO2 Enhanced concentrations of CH4 and C3-C5 alkanes were found in air influenced by emissions to the north and east of the Boulder Atmospheric Observatory (BAO) and were suggested to have been sourced from oil and gas fields located to the northeast. 
2014  Petron et al. NOAA/CIRES A new look at methane and nonmethane hydrocarbon emissions from oil and natural gas operations in the Colorado Denver-Julesburg Basin J. Geophys. Res.   Emission of methane, VOC, and benzene in the DJB were estimated to be 3 times, at least a factor of 2, and 7 times, respectively, larger than EPA and State inventories. 
2014  Kort et al. Univ. of Michigan Four corners: The largest US methane anomaly viewed from space Geophys. Res. Let.    Spaceborne remote sensing indicated large CH4 levels over the Four Corners region. Estimted emissions largely exceeded inventory estimates. 
2014  Thompson et al. Univ. of Colorado Influence of oil and gas emissions on ambient atmospheric non-methane hydrocarbons in residential areas of Northeastern Colorado Elementa    At residences near oil and gas operations, mean mole fractions of the C2-C5 alkanes were enhanced by a factor of 18–77 relative to the regional background, and present at higher levels than typically found in large urban centers. 
2014 Colburn et al. The Endocrine Disruption Exchange An exploratory study of air quality near natural gas operations Human & Ecol. Risk Assess.   Health risk assessment The number of NMHCs and their concentrations were highest during the initial drilling phase and did not increase during hydraulic fracturing in a closed-loop system. 
2015  Richter et al. Univ. of Colorado Compact highly sensitive multi-species airborne mid-IR spectrometer Applied Physics   Formaldehyde Ethane was enhanced at least ten times above background levels in the DJB boundary layer. Regions with elevated ethane overlapped with elevated formaldehyde. 
2016  Townsend-Small et al. Univ. of Cincinnati Using stable isotopes of hydrogen to quantify biogenicand thermogenic atmospheric methane sources: A case study from the Colorado Front Range Geophys. Res. Lett.   Methane hydrogen and carbon stable isotopes analyses Biogenic CH4 comprised about 50% of total CH4 observed in the active oil and gas extraction region. 
2016  Franco et al. Univ. of Liege, Belgium Evaluating ethane and methane emissions associated with the development of oil and natural gas extraction in North America Environ. Res. Lett.    Between 2009–2015, Fourier Transform Infrared (FTIR) ethane column observations over Boulder show a 5.0% per year rate of increase. 
2016  Sullivan et al. NASA Goddart Quantifying the contribution of thermally driven recirculation to a high-ozone event along the Colorado Front Range using lidar J. Geophys. Res.   Air recirculation Complex meteorology in this region can significantly exacerbate pollution levels. A high summer 2014 surface ozone pollution event was associated with thermally driven upslope flow. 
2016  Reddy and Pfister NCAR Meteorological factors contributing to the interannual variability of midsummer surface ozone in Colorado, Utah, and other western U.S. states J. Geophys. Res.   Reanalysis of meteorology and regional chemistry modeling Significant correlations were found between July MDA8 O3 and meteorological variables. Increased 500 hPa heights lead to high July O3. particularly in areas of elevated terrain near urban sources of NO2 and other O3 precursors. 
2016  Vu et al. Univ. of California Riverside Impacts of the Denver Cyclone on regional air quality and aerosol formation in the Colorado Front Range during FRAPPE 2014 Atmos. Chem. Phys.  Peroxyacetyl Nitrate (PAN), CO, NH3, aerosol properties Meteorological patterns associated with the Denver Cyclone increased pollutant levels, including aerosol loadings in the Denver metropolitan area. Cyclone conditions promote transport of aerosol constituents from the NCFR into the Denver metropolitan area, increasing aerosol mass loadings and reducing visibility. 
2016  Halliday et al. Pennsylvania State Univ. Atmospheric benzene observations from oil and gas production in the Denver-Julesburg Basin in July and August 2014 J. Geophys. Res.    Unexpectedly high benzene mixing ratios were observed at a site near Platteville (maximum of 29.3 ppb), primarily at night, and assoicated to emissions from nearby O&NG operations. 
2016  Frankenberg et al. California Institute of Technology Airborne methane remote measurements reveal heavytail flux distribution in Four Corners region PNAS    In the Four Corners Region, methane sources include gas processing facilities, storage tanks, pipeline leaks, and well pads, and a coal mine; emissions ranged from 2 kg h–1 through ~5,000 kg h–1
2016  Dingle et al. Univ. of California Riverside Aerosol optical extinction during the Front Range Air Pollution and Photochemistry Éxperiment (FRAPPÉ) 2014 summertime field campaign, Colorado, USA Atmos. Chem. Phys.   Aerosol The light extinction coefficient best correlated with organic aerosols in O&NG emissions and with nitrate aerosols under O&NG and agriculture influences. 
2016  McDuffie et al. NOAA/CIRES Influence of oil and gas emissions on summertime ozone in the Colorado Northern Front Range J. Geophys. Res.   O&NG alkanes contribute over 80% to the observed carbon mixing ratio, roughly 50% to the regional VOC OH reactivity, and approximately 20% to regional photochemical O3 production. 
2017  Tzompa-Sosa et al. Colorado State Univ. Revisiting global fossil fuel and biofuel emissions of ethane J. Geophys. Res.   Over northeastern Colorado, year 2001 ethane inventory emissions had to be increased by more than 40% for modeled atmospheric mixing ratios to match observations. 
2017  Evans and Helmig Univ. of Colorado Investigation of the influence of transport from oil and natural gas regions on elevated ozone levels in the northern Colorado Front Range JAWMA    Transport from areas with O&NG operations accounted for on the order of 65% of 1-hr averaged elevated ozone levels at BAO and South Boulder, while the Denver urban corridor accounted for 9%. 
2017 Abeleira et al. Colorado State Univ. Source characterization of volatile organic compounds in the Colorado Northern Front Range metropolitan area during spring and summer 2015 J. Geophys. Res.   The NCFR is more strongly influenced by O&NG sources of VOCs than other urban and suburban regions in the U.S. 
2017  Cheadle et al. CIRES/NOAA Surface ozone in the Colorado northern Front Range and the influence of oil and gas development during FRAPPE/DISCOVER-AQ in summer 2014 Elementa  NOx Correlation analyses in case studies showed that oil and gas related activities are a NOx and O3 precursor source. 
2017 Pfister et al. NCAR Process-Based and Regional Source Impact Analysis for FRAPPÉ and DISCOVER-AQ 2014 Final Report to CDPHE   NOx Mobile sources and oil and gas related emissions are the largest contributors to local ozone production in the Northern Front Range Metro Area (NFRMA). 
2017  Baier et al. Pennsylvania State Univ. Higher measured than modeled ozone production at increased NOx levels in the Colorado Front Range Atmos. Chem. Phys.  Ozone production rate Ozone production rates peak during late morning. Rates predicted by three models were lower than direct observations. 
2017 Abeleira and Farmer Colorado State Univ. Summer ozone in the northern Front Range metropolitan area: weekend–weekday effects, temperature dependences, and the impact of drought Atmos. Chem. Phys.  NOx Ozone in the NCFR area was either stagnant or increasing between 2000 and 2015, likely because of decreasing NOx emissions in a NOx -saturated environment and increased anthropogenic VOC emissions. 
2017  Robertson et al. Univ. of Wyoming Variation in methane emission rates from well pads in four oil and gas basins with contrasting production volumes and compositions Environ. Sci. Technol.    In the DJB, ~70% of total methane emissions were from 20% of the well pads The total mass of methane emitted as a percent of gross methane produced was 2.1% (1.1–3.9%). 
2017  Kaser et al. NCAR The effect of entrainment through atmospheric boundary layer growth on observed and modeled surface ozone in the Colorado Front Range J. Geophys. Res.   Boundary layer growth, contribution of entrainment and synoptic transport to O3 A large day-to-day variability of ozone above the atmospheric boundaray layer was attributed to differing air mass origins. On average, morning boundary layer growth contributed 4.8 ppb hr–1 to the morning hour ozone increase. 
2017 Pfister et al. NCAR Using observations and source specific model tracers to characterize pollutant transport during FRAPPÉ and DISCOVER-AQ J. Geophys. Res.    Air flow characterization During upslope events, frequently, there is a separation of air masses that are heavily influenced by oil and gas emissions to the north and dominated by urban emissions to the south. NCFR pollution can “spillover” into the valleys to the west of the Continental Divide. 
2017  Yacovitch et al. Aerodyne Research Inc. Natural gas facility methane emissions: Measurements by tracer flux ratio in two US natural gas producing basins Elementa    Methane emission rates from DJB gathering stations (kg CH4 hr–1) were lower compared to results from other basins. 
2017  Zaragoza et al. Colorado State Univ. Observations of acyl peroxy nitrates during the Front Range Air Pollution and Photochemistry Experiment (FRAPPE) J. Geophys. Res.  PAN, Peroxyproply nitrate (PPN) Anthropogenic VOCs played a dominant role in PAN production during periods with high O3. The contribution of biogenic VOCs to local O3 production was relatively small. 
2017  Smith et al. Univ. of Michigan Airborne quantification of methane emissions over the Four Corners Region Environ. Sci. Technol.    Using five independent days of measurements, an average regional CH4 flux of 0.54 ± 0.20 Tg yr–1 was calulated, in close agreement with a space-based estimate for 2003–2009. 
2018  Bien and Helmig Univ. of Colorado Changes in summertime ozone in Colorado during 2000–2015 Elementa    Median and upper percentile surface O3 in the DMA has not declined at the rates seen in other western U.S. regions. 
2018  McKenzie et al. Univ. of Colorado Ambient nonmethane hydrocarbon levels along Colorado’s Northern Front Range: Acute and chronic health risks Environ. Sci. Technol.    O&NG air pollutant concentrations increased with proximity to an O&NG facility, as did health risks. 
2018  Peischl et al. NOAA/CIRES Quantifying methane and ethane emissions to the atmosphere from Central and Western U.S. oil and natural gas production regions J. Geophys. Res.   Total CH4 and C2H6 emissions attributed to O&NG operations in the Denver Basin region remained statistically unchanged between 2008 and March 2015. 
2018  Fann et al. US EPA Research Triangle Park Assessing human health PM2.5 and ozone impacts from U.S. oil and natural gas sector emissions in 2025 Environ. Sci. Technol.  PM2.5 Under current growth projections O&NG emissions are predicted to cause 37 and 34 annual premature deaths from the added PM2.5 and ozone production, respectively, in Colorado by 2025. 
2018  McMullin et al. CDPHE Exposures and health risks from volatile organic compounds in communities located near oil and gas exploration and production activities in Colorado (U.S.A.) Int. J. Environ. Res. & Public Health   Health effects 56 VOCs emitted from O&NG operations in Colorado were identified. Further characterization of primary and secondary VOCs emitted from O&NG sites during different phases of operations is needed to address the community health relevance. 
2018  Benedict et al. Colorado State Univ. Impact of Front Range sources on reactive nitrogen concentrations and deposition in Rocky Mountain National Park PeerJ   NOx, NOy, ammonia Elevated concentrations of reactive nitrogen were associated with emissions from oil and gas operations, which are frequently co-located with agricultural production and livestock feeding areas in the region, and from urban areas. 
2018  Abdi-Oskouei et al. Univ. of Iowa Impacts of physical parameterization on prediction of ethane concentrations for oil and gas emissions in WRF-Chem Atmos. Chem. Phys.   EPA emission inventory Comparison between airborne measurements and WRF-Chem model simulations indicated a low bias of ethane in the NFRMA close to O&NG activities, suggesting underestimation of O&NG emissions in the 2011 National Emissions Inventory (NEI). 
2018  Bahreini et al. Univ. of California Riverside Sources and characteristics of summertime organic aerosol in the Colorado Front Range: Perspective from measurements and WRF-Chem modeling Atmos. Chem. Phys.    Aerosol characterization It was estimated that the O&NG sector contributed to <5% of total organic aerosol, but up to 38% of anthropogenic secondary organic aerosol in the NCFR. 
2019  Oltmans et al. NOAA Boundary layer ozone in the Northern Colorado Front Range in July-August 2014 during FRAPPE and DISCOVER-AQ from vertical profile measurements Elementa    The association of high O3 days at BAO with transport from O&NG sectors suggested that O&NG emissions were an important source of O3 precursors and are crucial in producing peak O3 events. Exposure of populations in the Foothills area is not captured by the current regulatory network, and likely underestimated. 
2019 Tsompa-Soza et al. Colorado State Univ. Atmospheric implications of large C2-C5 alkane emissions from the U.S. oil and gas industry J. Geophys. Res.    Of four regions analyzed, Boulder showed the highest percentage contribution from the oil and gas sector to total abundances of C2-C5 alkanes throughout the troposphere. 
2019  Lindaas et al. Colorado State Univ. Acyl peroxy nitrates link oil and natural gas emissions to high ozone abundances in the Colorado Front Range during summer 2015 J. Geophys. Res. Acyl peroxy nitrates (APNs), photochemical modeling Anthropogenic VOC precursors dominated APNs production when O3 was most elevated in the NCFR in summer 2015. Propane and n-pentane, primarily from O&NG emissions, drive elevated PPN/PAN ratios during high O3 events. Emissions from the O&NG sector contribute to O3 production on high O3 days. 
2019  Kille et al. Univ. of Colorado Separation of methane emissions from agricultural and natural gas sources in the Colorado Front Range Geophys. Res. Let.  Ammonia Natural gas methane sources dominate over agricultural and other sources, but the latter are relatively more important when excess CH4 is smaller than 5 ppb. 
2019  Benedict et al. Colorado State Univ. Volatile organic compounds and ozone in Rocky Mountain National Park during FRAPPÉ Atmos. Chem. Phys.   The study estimated that for that high ozone events associated with O&NG signatures, NCFR sources contributed ≈20 ppb of additional ozone. 

* Text in this column contains cited or partially shortened text from the listed articles.

Table references: [CDPHE, 2008; Rodriguez et al., 2009; Levi, 2012; McKenzie et al., 2012; Pétron et al., 2012; Brown et al., 2013; Gilman et al., 2013; LaFranchi et al., 2013; Pétron et al., 2013; Swarthout et al., 2013; Colborn et al., 2014; Kort et al., 2014; Petron et al., 2014; Thompson et al., 2014; Richter et al., 2015; Dingle et al., 2016; Franco et al., 2016; Frankenberg et al., 2016; Halliday et al., 2016; McDuffie et al., 2016; Reddy and Pfister, 2016; Sullivan et al., 2016; Townsend-Small et al., 2016; Vu et al., 2016; Abeleira et al., 2017; Abeleira and Farmer, 2017; Cheadle et al., 2017; Evans and Helmig, 2017; Kaser et al., 2017; Pfister et al., 2017a; Pfister et al., 2017b; Robertson et al., 2017; Smith et al., 2017; Tzompa-Sosa et al., 2017; Yacovitch et al., 2017; Zaragoza et al., 2017; Abdi-Oskouei et al., 2018; Bahreini et al., 2018; Benedict et al., 2018; Bien and Helmig, 2018; Fann et al., 2018; McKenzie et al., 2018; McMullin et al., 2018; Peischl et al., 2018; Yacovitch et al., 2018; Benedict et al., 2019; Kille et al., 2019; Lindaas et al., 2019; Oltmans et al., 2019; Tzompa-Sosa et al., 2019].

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