Title: Application of satellite observations and adjoint inverse modeling to intercontinental transport of ozone pollution
Description: The thesis investigates intercontinental transport of tropospheric ozone pollution and its implication on surface air quality, using satellite observations from TES and OMI and in situ measurements from the INTEX-B aircraft campaign. The observations are interpreted with the GEOS-Chem 3-D global chemical transport model (CTM) and its adjoint. Collocated nadir measurements of tropospheric ozone (O 3 ) and carbon monoxide (CO) from TES show significant O 3 -CO correlations downwind of polluted continents, providing a valuable test of the model to simulate intercontinental transport of ozone. OMI NO 2 observations indicate a factor of 2 increase of Asian anthropogenic NO x emissions from 2000 to 2006. Satellite observations of CO from AIRS and TES indicate two major events of Asian transpacific pollution during INTEX-B (April-May 2006). Correlation between TES CO and ozone observations provides evidence for transpacific ozone pollution. Transpacific pollution plumes tend to split over the Northeast Pacific; the northern branch circulates around the Aleutian Low and has little impact on North America, while the southern branch circulates around the Pacific High and impacts western North America. Sustained ozone production driven by peroxyacetylnitrate (PAN) decomposition in the southern branch roughly doubles the transpacific influence from ozone produced in the Asian boundary layer. Asian pollution enhanced surface ozone concentrations by 5-7 ppbv over western North America in spring 2006. The 2000-2006 rise in Asian anthropogenic emissions increased the influence by 1-2 ppbv.

The GEOS-Chem adjoint model is applied to quantify source contributions to ozone pollution at two adjacent sites on the U.S. west coast in spring 2006: Mt. Bachelor Observatory at 2.7 km altitude and Trinidad Head near sea level. The adjoint model computes the sensitivity of ozone concentrations at the receptor sites to ozone production rates at the resolution of underlying CTM over the history of air parcels reaching the site. Both sites show maximum intercontinental influences from northeast China and southern Japan, adding to a background production distributed over the extra-tropics. Three different methods for validating and intercomparing satellite measurements of atmospheric composition are analyzed, and illustrated with tropospheric ozone observations from TES and OMI. The first method uses in situ vertical profiles for absolute instrument validation; it is limited by the sparseness of in situ data. The second method involves smoothing the retrieved profile from one instrument with the averaging kernel matrix of the other; it provides a global intercomparison but dampens the actual difference between instruments. The third method uses a CTM as intercomparison platform; it closely reproduces the true differences and also provides a global intercomparison. Application to a full year of TES and OMI data shows mean positive biases of 5.4 ppbv for TES and 2.5 ppbv for OMI at 500 hPa relative to ozonesonde data. Differences between TES and OMI are generally within ±10 ppbv, indicating a good agreement between the two instruments and allowing a well-constrained model evaluation.
Subjects: Air, Pollution, Ozone