Abstract
We performed 7.5 weeks of path-integrated concentration measurements of CO2, CH4, H2O, and HDO over the city of Boulder, Colorado. An open-path dual-comb spectrometer simultaneously measured time-resolved data across a reference path, located near the mountains to the west of the city, and across an over-city path that intersected two-thirds of the city, including two major commuter arteries. By comparing the measured concentrations over the two paths when the wind is primarily out of the west, we observe daytime CO2 enhancements over the city. Given the warm weather and the measurement footprint, the dominant contribution to the CO2 enhancement is from city vehicle traffic. We use a Gaussian plume model combined with reported city traffic patterns to estimate city emissions of on-road CO2 as (6.2 ± 2.2) × 105 metric tons (t) CO2 yr−1 after correcting for non-traffic sources. Within the uncertainty, this value agrees with the city’s bottom-up greenhouse gas inventory for the on-road vehicle sector of 4.5 × 105 t CO2 yr−1. Finally, we discuss experimental modifications that could lead to improved estimates from our path-integrated measurements.
Highlights
Measurements of greenhouse gases, especially CO2 and CH4, are critical for monitoring, verification, and reporting as countries and cities work towards decreasing their carbon emissions
We demonstrate the use of an open-path dual frequency comb spectroscopy system for quantifying city emissions of carbon dioxide
We send light over two paths: a reference path that samples the concentration of gases entering the city from the west, and an over-city path that measures the concentrations of gases after the air mass has crossed approximately twothirds of the city, including two major commuter arteries
Summary
Measurements of greenhouse gases, especially CO2 and CH4, are critical for monitoring, verification, and reporting as countries and cities work towards decreasing their carbon emissions. Waxman et al.: Estimating vehicle carbon dioxide emissions from Boulder, Colorado (Shusterman et al, 2016), on the other hand, has a much lower cost per sensor It requires calibration for quantitative results, but the high density of the point sensors can provide lower sensitivity to systematics (Turner et al, 2016). As an alternative to these approaches, horizontal, kilometer-scale, open-path instruments could in principle be used to determine CO2 emissions from cities Such instruments are capable of continuous measurements over a large area with a single instrument (e.g., Wong et al, 2016; Dobler et al, 2017; Coburn et al, 2018). Dual-comb spectroscopy (DCS) is a high-resolution, broadband technique spanning hundreds of wave numbers but with a resolution that exceeds even highend Fourier transform infrared spectrometers (FTIRs) leading to a negligible instrument lineshape (Coddington et al, 2016) This allows for simultaneous measurements of multiple species and path-integrated temperature with low systematic uncertainty and without the need for instrument calibration. We discuss improvements to this estimate, which could be realized by more advantageous beam paths that sample a larger spatial and temporal fraction of the full city emissions and by a more detailed inventory model
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
