Quantification of CO<sub>2</sub> and CH<sub>4</sub> emissions over Sacramento, California, based on divergence theorem using aircraft measurements

Abstract

Abstract. Emission estimates of carbon dioxide (CO2) and methane (CH4) and the meteorological factors affecting them are investigated over Sacramento, California, using an aircraft equipped with a cavity ring-down greenhouse gas sensor as part of the Alpha Jet Atmospheric eXperiment (AJAX) project. To better constrain the emission fluxes, we designed flights in a cylindrical pattern and computed the emission fluxes from two flights using a kriging method and Gauss's divergence theorem. Differences in wind treatment and assumptions about background concentrations affect the emission estimates by a factor of 1.5 to 7. The uncertainty is also impacted by meteorological conditions and distance from the emission sources. The vertical layer averaging affects the flux estimate, but the choice of raw wind or mass-balanced wind is more important than the thickness of the vertical averaging for mass-balanced wind for both urban and local scales. The importance of vertical mass transfer for flux estimates is examined, and the difference in the total emission estimate with and without vertical mass transfer is found to be small, especially at the local scale. The total flux estimates accounting for the entire circumference are larger than those based solely on measurements made in the downwind region. This indicates that a closed-shape flight profile can better contain total emissions relative to a one-sided curtain flight because most cities have more than one point source and wind direction can change with time and altitude. To reduce the uncertainty of the emission estimate, it is important that the sampling strategy account not only for known source locations but also possible unidentified sources around the city. Our results highlight that aircraft-based measurements using a closed-shape flight pattern are an efficient and useful strategy for identifying emission sources and estimating local- and city-scale greenhouse gas emission fluxes.

Atmospheric Monitoring of Methane in Beijing Using a Mobile Observatory

“…Further attempts of CH 4 emission study by inverse modeling on a city scale would help understanding the observed signals. Similar studies report the quantification of CH 4 emission by mobile measurement platform such as airplanes [42,43].…”

“…Further attempts of CH4 emission study by inverse modeling on a city scale would help understanding the observed signals. Similar studies report the quantification of CH4 emission by mobile measurement platform such as airplanes [42,43]. The slope, the regression coefficient (r) and the confidence level (p), the number of observations (n), are also shown.…”

Estimating CH<sub>4</sub>, CO<sub>2</sub> and CO emissions from coal mining and industrial activities in the Upper Silesian Coal Basin using an aircraft-based mass balance approach

“…After a period of stable mole fractions since 2000, the atmospheric abundance of CH 4 has started to increase again in 2007, and after 2014 the increase intensified yet again (Nisbet et al, , 2016. The reason for this increased growth is currently investigated in several studies, which partly contradict each other by discussing biogenic sources, fossil fuel emissions and/or a decrease in the OH sink (Hausmann et al, 2016;Schaefer et al, 2016;Saunois et al, 2017;Turner et al, 2017;Worden et al, 2017;Nisbet et al, 2019).…”

“…A better understanding of vertical trace gas distribution is achieved by several transects at different heights but the same distance Karion et al, 2015;Pitt et al, 2019). Single point sources or small areas can be assessed by circular flight paths at different heights (Conley et al, 2017;Tadić et al, 2017;Ryoo et al, 2019). The airborne eddy covariance technique can directly infer vertical fluxes (Hiller et al, 2014;Yuan et al, 2015).…”

Estimating CH<sub>4</sub>, CO<sub>2</sub>, and CO emissions from coal mining and industrial activities in the Upper Silesian Coal Basin using an aircraft-based mass balance approach

“…A better understanding of vertical trace gas distribution is achieved by several transects at different heights but the same distance Karion et al, 2015;Pitt et al, 2019). Single point sources or small areas can be assessed by circular flight paths at different heights (Conley et al, 2017;Tadić et al, 2017;Ryoo et al, 2019). Using airborne eddy covariance technique, vertical fluxes can be inferred directly (Hiller et al, 2014;Yuan et al, 2015).…”