1. GEOS-CHEM Meeting 2005 Dylan Millet Variability of CH 2 O during ICARTT: Implications for GOME/OMI Dylan Millet GEOS-CHEM Users’ Meeting April 2005

2. GEOS-CHEM Meeting 2005 Dylan Millet Use ICARTT flight data to address: Satellite retrievals –Is GEOS-CHEM accurately representing the CH 2 O vertical profile (shape factor)? –What is the uncertainty/bias in the AMF? Variability in CH 2 O –What are the dominant sources of CH 2 O over N.A.? –Implications for satellite retrievals?

3. Air Mass Factor dd AMF G : Geometric factor w(  ): Scattering weights ~ -  (lnI B )/   S(  ):Shape factor Normalized vertical distribution From model AMF: Slant column / vertical column

4. GEOS-CHEM Meeting 2005 Dylan Millet All profiles E. U.S. Atlantic Vertical Profile Comparison

5. GEOS-CHEM Meeting 2005 Dylan Millet Clear Sky AMF Comparison - all profiles - Small negative bias (-6%) in modeled clear sky AMF

6. GEOS-CHEM Meeting 2005 Dylan Millet Continental profiles: -7% Oceanic profiles: +5%

7. GEOS-CHEM Meeting 2005 Dylan Millet Cloudy AMF Comparison Clouds: Can act to increase or decrease sensitivity of measurement

8. GEOS-CHEM Meeting 2005 Dylan Millet Cloudy AMF Comparison Actual cloud profile: Retrieved cloud:

9. GEOS-CHEM Meeting 2005 Dylan Millet Cloudy AMF Comparison Accounting for clouds: Small negative bias persists, larger spread

10. GEOS-CHEM Meeting 2005 Dylan Millet Continental profiles: -17% Oceanic profiles: +3%

11. GEOS-CHEM Meeting 2005 Dylan Millet CH 2 O Sources & Variability

12. GEOS-CHEM Meeting 2005 Dylan Millet CH 2 O Sources Importance of measured precursors to CH 2 O production:

13. GEOS-CHEM Meeting 2005 Dylan Millet CH 2 O Sources

14. GEOS-CHEM Meeting 2005 Dylan Millet CH 2 O Sources Continental boundary layer: Continental BL: P(isoprene) ~ 50% of P(total) on average OVOCs, methane important Variability in P(isoprene) > 10x P(others)

15. GEOS-CHEM Meeting 2005 Dylan Millet Conclusions Error in AMF: –Uncertainty of ±30% (2  ) for an individual clear-sky scene (higher for cloudy-sky) –Mean bias ~ -7% continental clear-sky; -17% continental cloudy-sky Sources of CH 2 O: –Isoprene, OVOC, methane dominant sources over N.A. –Variability in isoprene source > 10x that of other sources