1. Atmospheric C 2 H 2 and its relationship with CO as an indicator of air mass aging Xiao et al. [2007a] Fossil fuelauto BiofuelBiomass burning atmosphere CO ~2 mons C2H2C2H2 ~2 wks C 2 H 2 /CO

2. C 2 H 2 -CO correlation: a test of model transport and chemical processes Objective: to determine the information contained in C 2 H 2 -CO relationship for testing model emissions, transport, and OH levels

3. Atmospheric C 2 H 2 sources totalffbfbboceanic EDGAR 3.24.0 Gupta et al.[1998]3.1 Gautrois et al.[2003]8.8 Blake et al.[1996]2.1/2.8 Kanikiou et al.[1988]0.2~1.4 Plass et al.[1992]Negligibly small Plass-Dulmer et al.[1993] 0.16~0.54 This work6.61.73.31.6< 0.5 Asia Streets et al.[2003]0.9 Tg/year The model shows no significant bias in reproducing the major features of C 2 H 2 observed in atmosphere

4. C 2 H 2 /CO ratio: a tracer of air mass aging Observation (0-2 km): TRACE-P, PEM-Tropics B Model: averaged 0-2 km

5. C 2 H 2 /CO slope: not a robust tracer of air mass aging The variation of C 2 H 2 /CO slope reflects a combined influence of emission, transport, chemistry, and background. (1)(2)(3): TRACE-P, March (BL) (4)PEM-West A, September (UT) (5) PEM-Tropics B, March (BL) (6) PEM-Tropics A, September (FT) (7) TRACE-A, September (FT) (8) INTEX-A, Jul-Aug (BL) (3) (4) (1) (2) (7) (8) (5)(6) observations model (7) (3) (2) (1) (4) (8) CO C2H2C2H2

6. Interpretation of log[C 2 H 2 ]-log[CO] slope by Ehhalt et al. [1998] ~ 1.7-1.9 chemistry dominates dilution dominates β=1 β=β= β>β> dilution ~ chemistry chemistry dominates dilution dominates Narrow range!

7. Interpretation of log[C 2 H 2 ]-log[CO] slope by GEOS-Chem chemistry dominates dilution dominates Our model results are generally consistent with Ehhalt et al. [1998] ~ 1.7-1.9

8. INTEX-A (July-August, 2004) Persistent underestimate of C 2 H 6 emissions in the U.S. EPA National Emissions Inventories, including the latest NEI-99. Regional constraints on U.S. sources of ethane Xiao et al. [2007b]

9. Simulation of C 2 H 6 observations in INTEX-A (Jul-Aug,2004) EPA NEI-99 * 3.5 28% 47% Other Industrial (ngas/oil) Industrial solvent Biomass burning source of C 2 H 6 is minor compared to fossil fuel source Note different color scales!

10. Optimized C 2 H 6 emissions in the United States 1.6 0.7 1.3 Model [ NEI-99 * 3.5] / obs (< 2km) x7 in NEI-99 for the southern United States x1.8 in NEI-99 for the northern United States

11. Estimated CH 4 emission from natural gas/oil source in U.S. CH 4 /C 2 H 6 ER from fossil fuel 19 mol mol -1 C 2 H 6 emission in U.S 2.4 Tg yr -1 24 Tg yr -1 CH 4 fossil fuel emission in U.S. ground samples near natural gas/oil source region in south-central US [Katzenstein et al., 2003] as compared to: 10.5 Tg estimated by EIA (2005) 20 Tg by Wang et al. [2004] a major U.S. contribution to greenhouse warming is underestimated!