Surface observations for monitoring urban fossil fuel CO₂ emissions: Minimum site location requirements for the Los Angeles megacity

Abstract

[1] The contemporary global carbon cycle is dominated by perturbations from anthropogenic CO 2 emissions. One approach to identify, quantify, and monitor anthropogenic emissions is to focus on intensely emitting urban areas. In this study, we compare the ability of different CO 2 observing systems to constrain anthropogenic flux estimates in the Los Angeles megacity. We consider different observing system configurations based on existing observations and realistic near-term extensions of the current ad hoc network. We use a high-resolution regional model (Stochastic TimeInverted Lagrangian Transport-Weather Research and Forecasting) to simulate different observations and observational network designs within and downwind of the Los Angeles (LA) basin. A Bayesian inverse method is employed to quantify the relative ability of each network to improve constraints on flux estimates. Ground-based column CO 2 observations provide useful complementary information to surface observations due to lower sensitivity to localized dynamics, but column CO 2 observations from a single site do not appear to provide sensitivity to emissions from the entire LA megacity. Surface observations from remote, downwind sites contain weak, sporadic urban signals and are complicated by other source/sink impacts, limiting their usefulness for quantifying urban fluxes in LA. We find a network of eight optimally located in-city surface observation sites provides the minimum sampling required for accurate monitoring of CO 2 emissions in LA, and present a recommended baseline network design. We estimate that this network can distinguish fluxes on 8 week time scales and 10 km spatial scales to within~12 g C m -2 d -1 (~10% of average peak fossil CO 2 flux in the LA domain).Citation: Kort, E. A., W. M. Angevine, R. Duren, and C. E. Miller (2013), Surface observations for monitoring urban fossil fuel CO 2 emissions: Minimum site location requirements for the Los Angeles megacity,

The BErkeley Atmospheric CO<sub>2</sub> Observation Network: initial evaluation

“…In an initial effort in this regard, Turner et al (2016) constructed and applied a WRF-STILT inverse model to synthetic observations with density similar to BEACO 2 N. For an area source the size of the Oakland metropolitan area, emissions were estimated to within 18 % accuracy; for a freeway-sized line source to within 36 %; and to within 60 % for the sum of six industrial point sources -consistently outperforming a smaller hypothetical network (three sites) with significantly better precision. Using week-long averages, the BEACO 2 Nlike network was able to further reduce the uncertainty in the integrated urban area source to < 2 %, a significant improvement over the citywide emissions estimates provided by real and proposed ∼ 10 site sensor networks described by Lauvaux et al (2016) (25 % uncertainty in five day averages), Kort et al (2013) (> 10 % uncertainty in monthly averages), and Wu et al (2016) (11 % uncertainty in monthly totals). These other studies use more conservative estimates of the combined instrument, model, and representativeness error (≥ 3 ppm, as opposed to ±1 ppm).…”

“…For example, Ehleringer et al (2008) maintain a CO 2 monitoring network in the Salt Lake City metropolitan area, the INFLUX network measures CO 2 , 14 CO 2 , and total column CO 2 across the city of Indianapolis (Turnbull et al, 2015), and NASA's Megacities Carbon Project has established sensor networks in the pilot cities of Los Angeles (Kort et al, 2013) and Paris (Bréon et al, 2015). These ground-based monitoring efforts are complemented by space-based observations from SCHIAMACY ( Burrows et al, 1995), GOSAT (Yokota et al, 2009), and most recently the Orbiting Carbon Observatory-2 (OCO-2), launched in July 2014, which provides total column CO 2 measurements over 1.29 by 2.25 km footprints once every 16 days (Eldering et al, 2012).…”

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“…based on gas mole fraction measurements, atmospheric transport modelling and statistical inference) is a relatively new scientific endeavour Kort et al, 2013;Bréon et al, 2015;Henne et al, 2016;Staufer et al, 2016). Instruments to measure urban GHG concentrations have been placed on tall masts or towers (at more than 50 m above the ground level, m a.g.l.)…”

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“…One of the most difficult aspects of measuring CO2 in urban areas is the collocated nature of anthropogenic and biogenic 25 sources and sinks, and difficulty in isolating these components (Verhulst et al, 2016, Hutyra et al, 2014, Kort et al, 2013.…”