Toward verifying fossil fuel CO₂ emissions with the CMAQ model: Motivation, model description and initial simulation

Figures & data

Table 1. CO₂ fluxes used in CMAQ simulations

Type of fluxes	Input data source	Total fluxes^a (Tg carbon month^−1)
Biosphere fluxes	(1) CT2011 optimized fluxes based on CASA (1˚ × 1˚; 3-hourly)	163.37 (96.79)
	(2) CASA (1˚ × 1˚; 3-hourly)	125.46 (72.22)
	(3) CLM4VIC (0.5˚ × 0.5˚; 3-hourly)	60.58 (6.74)
Fossil fuel fluxes	(1) VULCAN (2002; 10 km; hourly, United States only)	115.42 (115.42)
	(2) CDIAC (2007; 1˚ × 1˚; monthly)	132.42 (113.51)
Fire fluxes	GFED (0.5˚ × 0.5˚; monthly)	1.02 (0.79)
Ocean fluxes	CT2011 optimized fluxes	2.84 (0.00)

Note: ^aShown here are total fluxes over the whole CMAQ domain and within the contiguous United States (in parentheses), respectively.

Figure 1. Monthly mean NEE for October 2007 from (a) CT2011, (b) CASA (CT2011 prior), and (c) Community Land Model (CLM4VIC-BG1) in the model domain.

Table 2. List of model sensitivity experiments

Number	Notation^a	Meaning	Biosphere fluxes	Fossil fuel fluxes
1	VCT	Standard model configuration	CT2011	Vulcan and CDIAC^a
2	DCT	Replace Vulcan with CDIAC in the United States	CT2011	CDIAC
3	VCS	Replace CT2011 NEE with CASA	CASA	Vulcan and CDIAC^a
4	VCL	Replace CT2011 with Community land Model (v. 4)	CLM4VIC	Vulcan and CDIAC^a
5	BG	Background fossil fuel and biosphere sources outside the United States, no biosphere or fossil-fuel fluxes in the United States	CT2011(outside the U.S.)	CDIAC^b
6	BIO	Biosphere fluxes globally, no U.S. fossil-fuel emissions.	CT2011	CDIAC^b
7	FF	Fossil fuel emissions globally, no NEE in the United States	CT2011(outside the U.S.)	Vulcan and CDIAC^a

Notes: Key to model notation for simulations 1 to 4: A three-letter code is used, in which the first letter refers to the source of fossil fuel input in the United States (V for Vulcan, D for CDIAC). The next two letters refer to the source of NEE input (CT for carbon tracker, CS for CASA, CL for Community Land Model).

^aVulcan emissions are used for model grids within the United States, and CDIAC emissions are used for model grids outside the United States.

^bCDIAC emissions are used for model grids outside the United States only.

Figure 2. Monthly mean fossil-fuel CO₂ emissions for October 2007 from (a) Vulcan and (b) CDIAC in the model domain.

Figure 3. Sensitivity of monthly mean net CO₂ fluxes to choice of NEE, (a) CT2011 for VCT (“our standard model”), (b) CASA for VCS, and (c) Community Land Model 4VIC-BG1 for VCL. Fossil-fuel emissions (Vulcan inside the United States and CDIAC outside), fire emissions (GFED), and ocean fluxes (CT2011) are the same for the three model configurations.

Figure 4. Monthly mean CO₂ concentrations near the surface in October 2007 simulated by (a) CT2011, (b) DCT, and (c) VCT (“the standard run”).

Figure 5. Monthly mean CO₂ produced by (a) the background model (BG), (b) biospheric sources only in the United States (BIO-BG), and (c) fossil-fuel sources only in the U.S. (FF-BG) over the contiguous United States in October 2007. Note the scale change from (a) to (b) and (c).

Figure 6. Monthly mean CO₂ concentrations near the surface simulated for October 2007 by (a) VCT (b) VCS, and (c) VCL.

Figure 7. Monthly mean diurnal profiles of CO₂ in October 2007 observed at Boulder Atmospheric Observatory (BAO) (TOWER) and simulated by CT2011 and CMAQ with different configurations, DCT, VCT, VCS, and VCL.

Figure 8. Monthly mean concentrations of (a) CO₂, (b) NOx, (c) CO, and (d) SO₂ near the surface simulated by CMAQ for October 2007. CO₂ is simulated by VCT (our standard model).