{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,29]],"date-time":"2026-09-29T17:59:50Z","timestamp":1790704790119,"version":"4.1.0"},"reference-count":55,"publisher":"American Chemical Society (ACS)","issue":"8","license":[{"start":{"date-parts":[[2021,3,31]],"date-time":"2021-03-31T00:00:00Z","timestamp":1617148800000},"content-version":"stm-asf","delay-in-days":0,"URL":"https:\/\/doi.org\/10.15223\/policy-029"},{"start":{"date-parts":[[2021,3,31]],"date-time":"2021-03-31T00:00:00Z","timestamp":1617148800000},"content-version":"stm-asf","delay-in-days":0,"URL":"https:\/\/doi.org\/10.15223\/policy-037"},{"start":{"date-parts":[[2021,3,31]],"date-time":"2021-03-31T00:00:00Z","timestamp":1617148800000},"content-version":"stm-asf","delay-in-days":0,"URL":"https:\/\/doi.org\/10.15223\/policy-045"}],"funder":[{"DOI":"10.13039\/100000159","name":"Division of Atmospheric and Geospace Sciences","doi-asserted-by":"publisher","award":["AGS-179918"],"award-info":[{"award-number":["AGS-179918"]}],"id":[{"id":"10.13039\/100000159","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":[],"published-print":{"date-parts":[[2021,4,20]]},"abstract":"<jats:title>Abstract<\/jats:title>\n                  <jats:p>Nitrogen oxides (NOX) and methane impact air quality through the promotion of ozone formation, and methane is also a strong greenhouse gas. Despite the importance of these pollutants, emissions in urban areas are poorly quantified. We present measurements of NOX, CH4, CO, and CO2 made at Drexel University in Philadelphia along with NOX and CO observations at two roadside monitors. Because CO2 concentrations in the winter result almost entirely from combustion with negligible influence from photosynthesis and respiration, we are able to infer fleet-averaged fuel-based emission factors (EFs) for NOX and CO, similar in some ways to how EFs are determined from tunnel studies. Comparison of the inferred NOX and CO fuel-based EF to the National Emissions Inventory (NEI) suggests errors in NEI emissions of either NOX, CO, or both. From the measurements of CH4 and CO2, which are not emitted by the same sources, we infer the ratio of CH4 emissions (from leaks in the natural gas infrastructure) to CO2 emissions (from fossil fuel combustion) in Philadelphia. Comparison of the CH4\/CO2 emission ratios to emission inventories from the Environmental Protection Agency suggests underestimates in CH4 emissions by almost a factor of 4. These results demonstrate the need for the addition of long-term observations of CH4 and CO2 to existing monitoring networks in urban areas to better constrain emissions and complement existing measurements of NOX and CO.<\/jats:p>","DOI":"10.1021\/acs.est.1c00294","type":"journal-article","created":{"date-parts":[[2021,3,31]],"date-time":"2021-03-31T15:34:53Z","timestamp":1617204893000},"page":"4532-4541","source":"Crossref","is-referenced-by-count":22,"title":["Urban\nEmissions of Nitrogen Oxides, Carbon Monoxide,\nand Methane Determined from Ground-Based Measurements in Philadelphia"],"prefix":"10.1021","volume":"55","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-9826-9811","authenticated-orcid":true,"given":"Daniel\nC.","family":"Anderson","sequence":"first","affiliation":[{"name":"Drexel University , , , ,","place":["Philadelphia, Pennsylvania, United States, 19104"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Andrew","family":"Lindsay","sequence":"additional","affiliation":[{"name":"Drexel University , , , ,","place":["Philadelphia, Pennsylvania, United States, 19104"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-6385-7149","authenticated-orcid":true,"given":"Peter F.","family":"DeCarlo","sequence":"additional","affiliation":[{"name":"Johns Hopkins University , , , ,","place":["Baltimore, Maryland, United States, 21218"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-9533-215X","authenticated-orcid":true,"given":"Ezra C.","family":"Wood","sequence":"additional","affiliation":[{"name":"Drexel University , , , ,","place":["Philadelphia, Pennsylvania, United States, 19104"]}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"316","published-online":{"date-parts":[[2021,3,31]]},"reference":[{"key":"2026081711232043700_cit1","doi-asserted-by":"publisher","first-page":"362","DOI":"10.1016\/j.envpol.2007.06.012","article-title":"Human health effects\nof air pollution","volume":"151","author":"Kampa","year":"2008","journal-title":"Environ. Pollut."},{"key":"2026081711232043700_cit2","doi-asserted-by":"publisher","first-page":"2845","DOI":"10.5194\/acp-19-2845-2019","article-title":"Characterization of ozone production\nin San Antonio,\nTexas, using measurements of total peroxy radicals","volume":"19","author":"Anderson","year":"2019","journal-title":"Atmos. Chem. Phys."},{"key":"2026081711232043700_cit3","doi-asserted-by":"publisher","first-page":"2063","DOI":"10.1016\/s1352-2310(99)00460-4","article-title":"Atmospheric\nchemistry of VOCs and NOx","volume":"34","author":"Atkinson","year":"2000","journal-title":"Atmos. Environ."},{"key":"2026081711232043700_cit4","doi-asserted-by":"publisher","first-page":"2597","DOI":"10.5194\/acp-16-2597-2016","article-title":"Formaldehyde production\nfrom isoprene oxidation across\nNOx regimes","volume":"16","author":"Wolfe","year":"2016","journal-title":"Atmos. Chem. Phys."},{"key":"2026081711232043700_cit5","doi-asserted-by":"publisher","first-page":"3823","DOI":"10.5194\/acp-7-3823-2007","article-title":"The global lightning-induced nitrogen\noxides source","volume":"7","author":"Schumann","year":"2007","journal-title":"Atmos. Chem. Phys."},{"key":"2026081711232043700_cit6","doi-asserted-by":"publisher","first-page":"1669","DOI":"10.1126\/science.250.4988.1669","article-title":"Biomass Burning in the Tropics: Impact\non Atmospheric\nChemistry and Biogeochemical Cycles","volume":"250","author":"Crutzen","year":"1990","journal-title":"Science"},{"key":"2026081711232043700_cit7","doi-asserted-by":"publisher","first-page":"37","DOI":"10.1023\/a:1009738715891","article-title":"A global inventory\nof nitric oxide emissions from soils","volume":"48","author":"Davidson","year":"1997","journal-title":"Nutrient\nCycl. Agroecosyst."},{"key":"2026081711232043700_cit8","doi-asserted-by":"publisher","first-page":"407","DOI":"10.1039\/b502128f","article-title":"Global partitioning\nof NOx sources using satellite observations: Relative roles of fossil\nfuel combustion, biomass burning and soil emissions","volume":"130","author":"Jaegle\u0301","year":"2005","journal-title":"Faraday Discuss."},{"key":"2026081711232043700_cit9","doi-asserted-by":"publisher","first-page":"130","DOI":"10.1016\/j.atmosenv.2015.03.055","article-title":"U.S. NO2 trends\n(2005-2013): EPA\nAir Quality System (AQS) data versus improved observations from the\nOzone Monitoring Instrument (OMI)","volume":"110","author":"Lamsal","year":"2015","journal-title":"Atmos. Environ."},{"key":"2026081711232043700_cit10","doi-asserted-by":"publisher","first-page":"6269","DOI":"10.5194\/acp-19-6269-2019","article-title":"Trends\nand trend reversal detection in 2 decades of tropospheric NO2 satellite\nobservations","volume":"19","author":"Georgoulias","year":"2019","journal-title":"Atmos. Chem. Phys."},{"key":"2026081711232043700_cit11","doi-asserted-by":"publisher","first-page":"L22812","DOI":"10.1029\/2006gl027749","article-title":"Satellite-observed U.S. power plant\nNOxemission reductions\nand their impact on air quality","volume":"33","author":"Kim","year":"2006","journal-title":"Geophys. Res.\nLett."},{"key":"2026081711232043700_cit12","doi-asserted-by":"publisher","first-page":"75","DOI":"10.1002\/2013ef000196","article-title":"Reduced emissions\nof CO2, NOx, and SO2from U.S. power plants owing to switch from coal\nto natural gas with combined cycle technology","volume":"2","author":"de\nGouw","year":"2014","journal-title":"Earth\u2019s Future"},{"key":"2026081711232043700_cit13","doi-asserted-by":"publisher","DOI":"10.1029\/2012jd018304","article-title":"Long-term trends\nin nitrogen oxide emissions from motor vehicles at national, state,\nand air basin scales","volume":"117","author":"McDonald","year":"2012","journal-title":"J. Geophys. Res.: Atmos."},{"key":"2026081711232043700_cit14","doi-asserted-by":"publisher","first-page":"7360","DOI":"10.1021\/acs.est.8b00778","article-title":"Modeling Ozone in the\nEastern U.S. using a Fuel-Based\nMobile Source Emissions Inventory","volume":"52","author":"McDonald","year":"2018","journal-title":"Environ.\nSci. Technol."},{"key":"2026081711232043700_cit15","doi-asserted-by":"publisher","first-page":"D16303","DOI":"10.1029\/2009jd013527","article-title":"A top-down\nanalysis of emissions\nfrom selected Texas power plants during TexAQS 2000 and 2006","volume":"115","author":"Peischl","year":"2010","journal-title":"J. Geophys. Res.: Atmos."},{"key":"2026081711232043700_cit16","doi-asserted-by":"publisher","first-page":"78","DOI":"10.1016\/j.atmosenv.2014.07.004","article-title":"Measured\nand modeled CO and NO y in DISCOVER-AQ: An evaluation of emissions\nand chemistry over the eastern US","volume":"96","author":"Anderson","year":"2014","journal-title":"Atmos. Environ."},{"key":"2026081711232043700_cit17","doi-asserted-by":"publisher","first-page":"13561","DOI":"10.5194\/acp-16-13561-2016","article-title":"Why do models overestimate surface ozone in the Southeast United\nStates?","volume":"16","author":"Travis","year":"2016","journal-title":"Atmos. Chem. Phys."},{"key":"2026081711232043700_cit18","doi-asserted-by":"publisher","first-page":"371","DOI":"10.1016\/j.atmosenv.2016.02.020","article-title":"Constraining NOx emissions using\nsatellite NO2 measurements during 2013 DISCOVER-AQ Texas campaign","volume":"131","author":"Souri","year":"2016","journal-title":"Atmos. Environ."},{"key":"2026081711232043700_cit19","doi-asserted-by":"crossref","first-page":"7705","DOI":"10.1029\/2018JD028539","article-title":"Top-Down\nEstimates of NOx and CO Emissions From Washington, D.C.-Baltimore\nDuring the WINTER Campaign","volume":"123","author":"Salmon","year":"2018","journal-title":"J. Geophys. Res.:\nAtmos."},{"key":"2026081711232043700_cit20","doi-asserted-by":"publisher","first-page":"12368","DOI":"10.1029\/2018jd029133","article-title":"Nitrogen Oxides Emissions, Chemistry, Deposition, and\nExport Over the Northeast United States During the WINTER Aircraft\nCampaign","volume":"123","author":"Jaegle\u0301","year":"2018","journal-title":"J. Geophys. Res.: Atmos."},{"key":"2026081711232043700_cit21","doi-asserted-by":"publisher","first-page":"25-1","DOI":"10.1029\/2002gl015601","article-title":"Linking ozone pollution and climate\nchange: The case for controlling\nmethane","volume":"29","author":"Fiore","year":"2002","journal-title":"Geophys. Res. Lett."},{"key":"2026081711232043700_cit22","doi-asserted-by":"publisher","first-page":"12614","DOI":"10.1002\/2016gl071930","article-title":"Radiative forcing\nof carbon dioxide, methane, and nitrous oxide: A significant revision\nof the methane radiative forcing","volume":"43","author":"Etminan","year":"2016","journal-title":"Geophys. Res.\nLett."},{"key":"2026081711232043700_cit23","doi-asserted-by":"publisher","first-page":"2058","DOI":"10.1098\/rsta.2010.0341","article-title":"Global atmospheric\nmethane: budget, changes and dangers","volume":"369","author":"Dlugokencky","year":"2011","journal-title":"Philos.\nTrans. R. 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U.S.A."},{"key":"2026081711232043700_cit26","doi-asserted-by":"publisher","first-page":"710","DOI":"10.1016\/j.envpol.2016.01.094","article-title":"Fugitive\nmethane emissions from leak-prone natural gas distribution infrastructure\nin urban environments","volume":"213","author":"Hendrick","year":"2016","journal-title":"Environ. Pollut."},{"key":"2026081711232043700_cit27","doi-asserted-by":"publisher","first-page":"6435","DOI":"10.1073\/pnas.1202407109","article-title":"Greater focus needed on methane leakage\nfrom natural\ngas infrastructure","volume":"109","author":"Alvarez","year":"2012","journal-title":"Proc. Natl. Acad. Sci. U.S.A."},{"key":"2026081711232043700_cit28","doi-asserted-by":"publisher","first-page":"183","DOI":"10.1126\/science.1210026","article-title":"Simultaneously mitigating near-term\nclimate change and improving human health and food security","volume":"335","author":"Shindell","year":"2012","journal-title":"Science"},{"key":"2026081711232043700_cit29","doi-asserted-by":"publisher","first-page":"318","DOI":"10.1029\/2018gb006009","article-title":"Very Strong Atmospheric Methane Growth\nin the 4 Years 2014-2017: Implications for the Paris Agreement","volume":"33","author":"Nisbet","year":"2019","journal-title":"Global Biogeochem. Cycles"},{"key":"2026081711232043700_cit30","doi-asserted-by":"publisher","first-page":"2805","DOI":"10.1073\/pnas.1814297116","article-title":"Interpreting contemporary trends\nin atmospheric methane","volume":"116","author":"Turner","year":"2019","journal-title":"Proc. Natl. Acad. Sci.\nU.S.A."},{"key":"2026081711232043700_cit31","doi-asserted-by":"crossref","first-page":"3227","DOI":"10.5194\/acp-16-3227-2016","article-title":"Contribution\nof oil and natural gas\nproduction to renewed increase in atmospheric methane (2007-2014):\ntop-down estimate from ethane and methane column observations","volume":"16","author":"Hausmann","year":"2016","journal-title":"Atmos. Chem. Phys."},{"key":"2026081711232043700_cit32","doi-asserted-by":"publisher","first-page":"2218","DOI":"10.1002\/2016gl067987","article-title":"A large increase\nin U.S. methane emissions over the past decade inferred from satellite\ndata and surface observations","volume":"43","author":"Turner","year":"2016","journal-title":"Geophys. Res.\nLett."},{"key":"2026081711232043700_cit33","doi-asserted-by":"publisher","first-page":"4991","DOI":"10.1029\/2018gl081731","article-title":"Long-Term\nMeasurements Show Little Evidence for Large Increases in Total U.S.\nMethane Emissions Over the Past Decade","volume":"46","author":"Lan","year":"2019","journal-title":"Geophys.\nRes. Lett."},{"key":"2026081711232043700_cit34","doi-asserted-by":"publisher","first-page":"13123","DOI":"10.1021\/acs.est.6b02878","article-title":"Gridded\nNational\nInventory of U.S. Methane Emissions","volume":"50","author":"Maasakkers","year":"2016","journal-title":"Environ.\nSci. Technol."},{"key":"2026081711232043700_cit35","doi-asserted-by":"publisher","first-page":"8869","DOI":"10.1029\/2018jd028851","article-title":"Methane\nEmissions From the Baltimore-Washington Area\nBased on Airborne Observations: Comparison to Emissions Inventories","volume":"123","author":"Ren","year":"2018","journal-title":"J. Geophys. Res.: Atmos."},{"key":"2026081711232043700_cit36","doi-asserted-by":"publisher","first-page":"8500","DOI":"10.1029\/2019gl082635","article-title":"Large Fugitive Methane Emissions\nFrom Urban Centers Along the U.S. East Coast","volume":"46","author":"Plant","year":"2019","journal-title":"Geophys. Res. Lett."},{"key":"2026081711232043700_cit37","doi-asserted-by":"publisher","first-page":"9896","DOI":"10.1021\/acs.est.0c01175","article-title":"Toward Accurate, Policy-Relevant\nFossil Fuel CO2 Emission Landscapes","volume":"54","author":"Gurney","year":"2020","journal-title":"Environ.\nSci. Technol."},{"key":"2026081711232043700_cit38","doi-asserted-by":"publisher","first-page":"D16311","DOI":"10.1029\/2009jd013645","article-title":"Characterization\nof NOx, SO2, ethene, and propene from industrial emission sources\nin Houston, Texas","volume":"115","author":"Washenfelder","year":"2010","journal-title":"J. Geophys. Res.: Atmos."},{"key":"2026081711232043700_cit39","doi-asserted-by":"publisher","first-page":"3304","DOI":"10.1002\/2017jd027688","article-title":"Characterizing\nCO and NO y Sources and Relative Ambient Ratios in the Baltimore Area\nUsing Ambient Measurements and Source Attribution Modeling","volume":"123","author":"Simon","year":"2018","journal-title":"J. Geophys. Res.: Atmos."},{"key":"2026081711232043700_cit40","doi-asserted-by":"publisher","first-page":"287","DOI":"10.1021\/acs.est.8b05552","article-title":"Synthesis\nof Urban CO2 Emission Estimates from Multiple Methods from the Indianapolis\nFlux Project (INFLUX)","volume":"53","author":"Turnbull","year":"2019","journal-title":"Environ. Sci. Technol."},{"key":"2026081711232043700_cit41","doi-asserted-by":"publisher","first-page":"528","DOI":"10.1039\/c8em00471d","article-title":"Seasonal variation\nin aerosol composition\nand concentration upon transport from the outdoor to indoor environment","volume":"53","author":"Avery","year":"2019","journal-title":"Environ. Sci.: Processes Impacts"},{"key":"2026081711232043700_cit42","doi-asserted-by":"publisher","first-page":"367","DOI":"10.1119\/1.1632486","article-title":"Unified equations for the slope, intercept, and standard\nerrors of the best straight line","volume":"72","author":"York","year":"2004","journal-title":"Am. J. Phys."},{"key":"2026081711232043700_cit43","doi-asserted-by":"publisher","first-page":"220","DOI":"10.1016\/j.atmosenv.2007.09.049","article-title":"Long-term changes in emissions of nitrogen oxides and\nparticulate matter from on-road gasoline and diesel vehicles","volume":"42","author":"Ban-Weiss","year":"2008","journal-title":"Atmos. Environ."},{"key":"2026081711232043700_cit44","doi-asserted-by":"publisher","first-page":"125","DOI":"10.1016\/j.envpol.2012.01.019","article-title":"Methane\nand carbon dioxide fluxes\nand source partitioning in urban areas: The case study of Florence,\nItaly","volume":"164","author":"Gioli","year":"2012","journal-title":"Environ. Pollut."},{"key":"2026081711232043700_cit45","doi-asserted-by":"publisher","first-page":"10543","DOI":"10.5194\/acp-16-10543-2016","article-title":"Spatial and\ntemporal\nvariability of urban fluxes of methane, carbon monoxide and carbon\ndioxide above London, UK","volume":"16","author":"Helfter","year":"2016","journal-title":"Atmos. Chem. Phys."},{"key":"2026081711232043700_cit46","doi-asserted-by":"publisher","first-page":"117558","DOI":"10.1016\/j.atmosenv.2020.117558","article-title":"Using near-road\nobservations of CO, NOy, and CO2 to investigate emissions from vehicles:\nEvidence for an impact of ambient temperature and specific humidity","volume":"232","author":"Hall","year":"2020","journal-title":"Atmos. Environ."},{"key":"2026081711232043700_cit47","doi-asserted-by":"publisher","DOI":"10.1029\/2011JD016772","article-title":"Airborne and ground-based observations\nof a weekend effect in ozone, precursors, and oxidation products in\nthe California South Coast Air Basin","volume":"177","author":"Pollack","year":"2012","journal-title":"J. Geophys.\nRes.: Atmos."},{"key":"2026081711232043700_cit48","doi-asserted-by":"publisher","first-page":"143","DOI":"10.1016\/j.atmosenv.2018.01.019","article-title":"Characterization\nof air pollutant concentrations, fleet emission factors, and dispersion\nnear a North Carolina interstate freeway across two seasons","volume":"177","author":"Saha","year":"2018","journal-title":"Atmos. Environ."},{"key":"2026081711232043700_cit49","doi-asserted-by":"publisher","first-page":"1","DOI":"10.1016\/j.envpol.2012.11.003","article-title":"Mapping\nurban pipeline leaks: methane leaks across Boston","volume":"173","author":"Phillips","year":"2013","journal-title":"Environ. Pollut."},{"key":"2026081711232043700_cit50","doi-asserted-by":"publisher","first-page":"2005","DOI":"10.1021\/es034837g","article-title":"Methane\nEmissions from Vehicles","volume":"38","author":"Nam","year":"2004","journal-title":"Environ. Sci. Technol."},{"key":"2026081711232043700_cit51","doi-asserted-by":"publisher","first-page":"11242","DOI":"10.1002\/2017jd027359","article-title":"Large Uncetainties in Urban-Scale Carbon Emissions","volume":"122","author":"Gately","year":"2017","journal-title":"J. Geophys. Res. Atmos."},{"key":"2026081711232043700_cit52","doi-asserted-by":"publisher","first-page":"2961","DOI":"10.1021\/acs.est.8b02307","article-title":"Source Apportionment of Ambient Methane Enhancements\nin Los Angeles, California, To Evaluate Emission Inventory Estimates","volume":"53","author":"Kuwayama","year":"2019","journal-title":"Environ. Sci. Technol."},{"key":"2026081711232043700_cit53","doi-asserted-by":"publisher","first-page":"11285","DOI":"10.1021\/acs.est.9b02782","article-title":"Seasonally Resolved Excess Urban Methane Emissions from the Baltimore\/Washington,\nDC Metropolitan Region","volume":"53","author":"Huang","year":"2019","journal-title":"Environ. Sci. Technol."},{"key":"2026081711232043700_cit54","unstructured":"EPA\n          . Draft Inventory of US Greenhouse Gas Emissions\nand Sinks:\n1990\u20132019, 2021; pp 2\u20131\u20132-43."},{"key":"2026081711232043700_cit55","doi-asserted-by":"publisher","first-page":"5283","DOI":"10.1002\/2013jd021219","article-title":"High-resolution\nmapping of motor vehicle carbon dioxide emissions","volume":"119","author":"McDonald","year":"2014","journal-title":"J. Geophys. 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