Urban Emissions of Nitrogen Oxides, Carbon Monoxide, and Methane Determined from Ground-Based Measurements in Philadelphia

• Published in: Environmental science & technology Vol. 55; no. 8; pp. 4532 - 4541
• Main Authors: Anderson, Daniel C, Lindsay, Andrew, DeCarlo, Peter F, Wood, Ezra C
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 20.04.2021
• Subjects: Air Pollutants - analysis; Air pollution; Air quality; Anthropogenic Impacts on the Atmosphere; Carbon dioxide; Carbon Dioxide - analysis; Carbon dioxide emissions; Carbon monoxide; Carbon Monoxide - analysis; Combustion; Emission inventories; Emission measurements; Emissions; Environmental Monitoring; Environmental protection; Fossil fuels; Fuel combustion; Greenhouse gases; Humans; Methane; Methane - analysis; Natural gas; Nitrogen oxides; Nitrogen Oxides - analysis; Philadelphia; Photochemicals; Photosynthesis; Pollutants; Roadsides; Urban areas; Philadelphia
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/acs.est.1c00294

Nitrogen oxides (NO X ) 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 NO X , CH4, CO, and CO2 made at Drexel University in Philadelphia along with NO X 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 NO X and CO, similar in some ways to how EFs are determined from tunnel studies. Comparison of the inferred NO X and CO fuel-based EF to the National Emissions Inventory (NEI) suggests errors in NEI emissions of either NO X , 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 NO X and CO.