1. Advisor: Michael McElroy
Emissions from China: Implications for the Regional and Global Environment
Yuxuan Wang
Advisor: Michael McElroy
Ph.D. Thesis Defense
January. 21, 2005

2. Surface Air Quality is not just a Regional Issue
“Optimistic” IPCC scenario: Asia UP by 50%; EU, U.S. down by 20%
[Introduction to atmospheric chemistry, Daniel Jacob, 1999]

3. Uncertainty in the Bottom-up Emissions
Bottom-up emissions ~ ( activity rate * emission factor)

4. Uncertainty in the Bottom-up Emissions
Bottom-up emissions ~ ( activity rate * emission factor) ?

5. Circulation Patterns and Implications for Air Quality
Winter Monsoon Conditions
Summer Monsoon Conditions
Depending on different time of the year, air quality over Hong Kong is subject to influences from Chinese mainland, Northeast Asia and Southeast Asia.

6. My Thesis Research
Development of a nested grid capacity in GEOS-CHEM model
Forward model analysis of aircraft and surface measurements of CO and NOy
Inverse model analysis to constrain Chinese emissions of CO and NOx
Food chain related emissions of N2O and NOx

7. GEOS-CHEM Global 3-D Model
Resolution: 4 x5 or 2 x2.5
Driven by assimilated meteorological fields
Coupled gas phase and aerosol simulations

8. Nested Grid Version of GEOS-CHEM
1 x1
4 x5

9. Heterogeneous Emission Patterns and Topography
CO Emissions over Southern China
Terrain Elevations

10. Aircraft and Chinese Stations Data
Time frame: Jan – Apr., 2001

11. Nested-grid model provides good agreement with observations

12. Model Underestimates Aircraft Observations of CO and NOy

13. Model Underestimates Surface MeasurementsCO
NOy

14. A priori Emissions of CO and NOx
Uncertainties: 154% for CO, 27% for NOx r
Source: Streets et al. [2003]

15. Forward Model Analysis
Observations
Emissions
GEOS-CHEM

16. Inverse Model Analysis
Forward
Observations
Inverse
Emissions
GEOS-CHEM

17. Tagged Tracer Simulation
Atmospheric “forward” model gives C = kE
Monitoring site measures concentration C

18. NOy Chemistry and Deposition Scheme
1. Model has no bias in simulating contributions of component NOy species to total NOy below 6km
 no systematic bias in NOy chemistry and relative deposition rate in the model
2. Linear relationship between NOx emissions and NOy concentrations can thus be adopted.

19. Inverse modeling
Bayesian approach to linear inversion with Gaussian statistics [Palmer et al., 2003]
a posteriori state vector
a posteriori error covariance matrix
The inversion is conducted independently for CO and NOy
Both aircraft (spatial coverage) and station data (temporal coverage) are used in the inverse analysis
The inverse model is not designed to constrain sinks of CO and NOy

22. CO
NOx

23. A posteriori Emissions Significantly Reduce Model Bias

24. A posteriori Emissions Significantly Reduce Model Bias

25. A posteriori Emissions Significantly Reduce Model Bias

26. Revising the ‘Bottom-up’ CO Emissions : Low Efficiency Industrial Processes
+34% higher (73% from industrial sector)
courtesy of Q. Zhang

27. ?

28. Microbial Sources of N2O and NOx
Nitrification: NH4+  NO2-  NO3-
Denitrification: NO3-  N2O  N2
The weight of the evidence suggests that nitrification provides the dominant source of N2O. O2
NH2OH
N2O, NO

29. Microbial Sources of N2O and NOx
Nitrification: NH4+  NO2-  NO3-
Denitrification: NO3-  N2O  N2
The weight of the evidence suggests that nitrification provides the dominant source of N2O. O2
NH2OH
Low levels of O2
Aerobic denitr.
N2O, NO
N2O, NO

30. Survey of Field and Laboratory Studies
Yield of N2O and NO increases with decreasing levels of O2
So does the NO / N2O ratio

31. Top-down Budget of N2O
Sink: photolytic process in the stratosphere  lifetime 120 yr
Pre-industrial concentration: 270 ppb  natural source of 10.9 TgN/yr
Current concentration (314ppb) and annual increase rate (0.8ppb)  current source of 16.6 TgN/yr
Anthropogenic source: 5.7 TgN/yr
Fossil fuel and industrial processes: 1.3 TgN/yr
Microbial sources: 4.4 TgN/yr

32. N Processed through the Agriculture/Animal/Human Food Chain
226

33. N Processed through the Agriculture/Animal/Human Food Chain
226
226 TgN/yr * 2% = 4.4 TgN-N2O /yr
NOx/N2O = 3 or 6% yield for NOx
Central China: 30% of Chinese N  0.9 TgN-NOx/yr

34. N Processed by Domestic Animals

35. Trends in N Processed through the Global Food Chain
Use the yield of 2% for N2O

36. Trends in Atmospheric N2O using a One-box Model
dC / dt = S / 4.8 – C/τ

37. Summary
The nested grid model provides an adequate account of the meteorological features in spring time over China [Wang et al., JGR, 2004a]
The current inventory underestimated Chinese emissions of CO and NOx [Wang et al., JGR, 2004b]
Biological emissions of N2O and NOx are significant for large developing countries [McElroy and Wang, GBC, 2005]

38. Acknowledgement Michael McElroy Daniel Jacob Steve Wofsy, Dan Schrag
Jennifer Logan, Chris Nielsen, Tao Wang, Paul Palmer
Atmospheric chemistry modeling group
HUCE China Project
EPS department
My family