1. Study on NO x lifetime in chemistry transport model Ran Yin

2. Motivation Nitrogen oxides plays an important role in tropospheric chemistry Discrepancy between the model simulation and satellite-retrieved tropospheric NO2 columns: Why?? How to optimize emission inventory using space-borne column: the NOx lifetime is a critical parameter in the inversion, especially in higher resolution. simulated NO2 column (10 15 moles/cm 2 ) OMI NO2 column (10 15 moles/cm 2 )

3. Motivation (con’t) GOME2 observes up to 100% higher than OMI. Can we explain the observed decrease in NO 2 column by a diurnal cycle of NO x lifetime? GOME2 OMI (10 15 moles/cm 2 )

4. Background Information How is NO2 column measured by satellite? SOLAR BACKSCATTER MEASUREMENTS Scattering by Earth surface and by atmosphere NO2 : wavelength region 420-450 nm Top-down Information from Satellite: GOME 1995-2003 SCIAMACHY 2002-present OMI 2004-present GOME-2 2006-present Solar I o Backscattered intensity I B Albedo A

5. Background Information (con’t) Emission NO NO 2 HNO 3 lifetime NITROGEN OXIDES (NO x ) Tropospheric NO 2 column ~ E NOx NOx = NO + NO 2 Map Surface NO x Emissions Wind smears the local relationship between column and emission Do we need to worry about the transport between grid boxes?

6. Method E: emission P: production L: loss D: deposition F in : Flux-in F out : Flux-out Chemistry: principle daytime removal path for NOx is Comparison between two kind of lifetime: Loss by reaction and deposition Loss by horizontal transport to other gridbox Simplify Eq.1: Eq.1 Solve continuity equation: emission chemistry transport flux = k -1 Using a regional chemistry transport model (REAM) :

7. Result: Chemistry lifetime In every time-step (1 hr): lifetime [hour] [hour] determined by oxidation rate and dry deposition OH depletion 100 % difference between GOME2 overpass and OMI overpass

8. Result: Integrated Lifetime Set F in = 0, between each time-step lifetime [hour] [hour] much smaller difference, insufficient to explain the difference between two satellite

9. Result: Transport lifetime lifetime [hour] [hour]

10. Result: Comparison between two lifetime Red region: chemistry lifetime > transport time GOME2 overpassOMI overpass nighttime

11. Conclusion By comparison between chemistry lifetime and transport lifetime, the model with a horizontal resolution of 36 km is sensitive to NO 2 signal in summer daytime Although chemical loss rate much higher at OMI overpass, the discrepancy between GOME2 and OMI can not be explained by the overall lifetime of NO x at different time of the day