Seasonal climatology of CO₂ across North America from aircraft measurements in the NOAA/ESRL Global Greenhouse Gas Reference Network

Abstract

Seasonal spatial and temporal gradients for the CO2 mole fraction over North America are examined by creating a climatology from data collected 2004–2013 by the NOAA/ESRL Global Greenhouse Gas Reference Network Aircraft Program relative to trends observed for CO2 at the Mauna Loa Observatory. The data analyzed are from measurements of air samples collected in specially fabricated flask packages at frequencies of days to months at 22 sites over continental North America and shipped back to Boulder, Colorado, for analysis. These measurements are calibrated relative to the CO2 World Meteorological Organization mole fraction scale. The climatologies of CO2 are compared to climatologies of CO, CH4, SF6, N2O (which are also measured from this sampling program), and winds to understand the dominant transport and chemical and biological processes driving changes in the spatial and temporal mole fractions of CO2 as air passes over continental North America. The measurements show that air masses coming off the Pacific on the west coast of North America are relatively homogeneous with altitude. As air masses flow eastward, the lower section from the surface to 4000 m above sea level (masl) becomes distinctly different from the 4000–8000 masl section of the column. This is due in part to the extent of the planetary boundary layer, which is directly impacted by continental sources and sinks, and to the vertical gradient in west‐to‐east wind speeds. The slowdown and southerly shift in winds at most sites during summer months amplify the summertime drawdown relative to what might be expected from local fluxes. This influence counteracts the dilution of summer time CO2 drawdown (known as the “rectifier effect”) as well as changes the surface influence “footprint” for each site. An early start to the summertime drawdown, a pronounced seasonal cycle in the column mean (500 to 8000 masl), and small vertical gradients in CO2, CO, CH4, SF6, and N2O at high‐latitude western sites such as Poker Flat, Alaska, suggest recent influence of transport from southern latitudes and not local processes. This transport pathway provides a significant contribution to the large seasonal cycle observed in the high latitudes at all altitudes sampled. A sampling analysis of the NOAA/ESRL CarbonTracker model suggests that the average sampling resolution of 22 days is sufficient to get a robust estimate of mean seasonal cycle of CO2 during this 10 year period but insufficient to detect interannual variability in emissions over North America.

Bias corrections of GOSAT SWIR XCO<sub>2</sub> and XCH<sub>4</sub> with TCCON data and their evaluation using aircraft measurement data

“…In order to test for remaining biases in the GOSAT data after applying the empirical correction developed using TCCON data, we use aircraft profile data provided by the Comprehensive Observation Network for TRace gases by AIrLiner (CONTRAIL) project (Machida et al, 2008), the NOAA Earth System Research Laboratory/Global Monitoring Division (ESRL/GMD; Xiong et al, 2008;Sweeney et al, 2015), the US Department of Energy (DOE; Biraud et al, 2013;Schmid et al, 2014), the National Institute for Environmental Studies (NIES; Machida et al, 2001), the Japan Meteorological Agency (JMA; Tsuboi et al, 2013), the HI-APER Pole-to-Pole Observations (HIPPO) project (Wofsy et al, 2011Kort et al, 2012;Santoni et al, 2014), and an aircraft measurement campaign by NIES and the Japan Aerospace Exploration Agency (JAXA) (Tanaka et al, 2012). To calculate aircraft-based XCO 2 and XCH 4 (as described in the next paragraph), we also used tower data from the Meteorological Research Institute (MRI) in Tsukuba (Inoue andMatsueda, 1996, 2001) and the NOAA ESRL/GMD tall tower network in Park Falls, WI and West Branch, IA .…”

Carbon Dioxide in the Free Troposphere and Boundary Layer at the Mt. Bachelor Observatory

“…The seasonal cycle at MBO shows a similar pattern compared with other mountain-top observatories (Mauna Loa Observatory (MLO) and Jungfraujoch (JFJ)). However, the data from MBO and JFJ are more similar in that both show an earlier summer CO 2 minimum compared with MLO (Sweeney et al, 2015). 3.…”

“…5 in Sweeney et al (2015). Within this figure, Sweeney et al (2015) shows annual climatological CO 2 vertical profiles from 16 sites in the NOAA/Earth System Research Laboratory (ESRL) Global Greenhouse Gas Reference Network Aircraft Program. We can compare specifically with the Trinidad Head (THD) site, which is nearest to MBO.…”

“…2 shows that the summer minimum of CO 2 is shifted earlier at MBO and JFJ compared with MLO. Sweeney et al (2015) discusses a significant temporal lag at MLO relative to BL observations in North America. This offset highlights an earlier summer CO 2 minimum for high latitude sites in North America compared with MLO.…”

“…Numerous types of sites have been used to measure atmospheric CO 2 , such as: surface observatories (Idso et al, 2001;Newman et al, 2008;Ramonet et al, 2010;Rice and Bostrom, 2011;Pérez et al, 2012), balloon soundings (Bischof et al, 1980;Li et al, 2014), aircraft measurements (Bischof et al, 1980;Lloyd et al, 2002;Machida et al, 2002;Sidorov et al, 2002;Gurk et al, 2008;Shashkov et al, 2011;Sun and De Wekker, 2011;Sweeney et al, 2015), tall towers (Bakwin et al, 1995;Haszpra et al, 2005;Haszpra et al, 2012), and mountain-top observatories (Goldman, 1974;Thoning et al, 1989;Sturm et al, 2005;De Wekker et al, 2009;Ramonet et al, 2010;Brooks et al, 2012). Even though there are numerous methodologies for the measurement of CO 2 and data on atmospheric CO 2 concentrations have been available since the late 1950s, atmospheric chemistry models still have difficulty estimating CO 2 concentrations in conditions other than in a well-mixed planetary boundary layer (Haszpra et al, 2012).…”