# Presentation: 513329

## Testing and improving OMI tropospheric NO2 using observations from the DANDELIONS and INTEX-B validation campaigns

- 1Jennifer Hains, 1Folkert Boersma, 1Mark Kroon, 2Hester Volten, 3Ronald Cohen, 3Anne Perring,1Ruud Dirksen, 1Pepijn Veefkind, 1Pieternel Levelt
- 1. KNMI, De Bilt, The Netherlands, contact:hains@knmi
- 2. RIVM, Bilthoven, The Netherlands
- 3. University of California, Berkley

**OMI tropospheric NO****2**** 2007-2005 annual average difference**

**Notes:**
Describe tropospheric NO2 observations during INTEX-B and DANDELIONS.
Compare campaign profiles with OMI  show improvements using version 3 instead of version 2.
Investigate influence of measurements on OMI tropospheric NO2 retrieval. 
Present tropospheric NO2 trends from OMI 

## March 2006

- Laser induced fluorescence (LIF) onboard aircraft sampled NO2 profiles
- March-June 2006
- Gulf of Mexico, Pacific, Honolulu , Anchorage
- Sample from 0.3-10km

## DANDELIONS 

**DANDELIONS**
- NO2 LIDAR and MAXDOAS sampled NO2.
- Nine clear sky days in September 2006.
- Cabauw, The Netherlands

- September 2006

## Conc. (7 altitudes) + 

**PBL**

**MAX DOAS**

**Lidar**

**Scattering**

- Conc. (7 altitudes) +
- PBL height (aerosol lidar)
-  VCpbl

**OMI  DOMINO**
- Tropospheric NO2
- vertical column (VCt)
- OMI pixel size 13x24 km2 (nadir).
- VCt = VCpbl + VCft

- Slant column + geo AMF  VCt

**Notes:**
Aircraft gets  the free trop but misses the lowest layer.
Lidar samples bl but misses the free trop.
MAXDOAS uses a geometric AMF to get the VCt

## DANDELIONS comparisons

**DANDELIONS comparisons**

**1:1**

**OMI V2**

- r = 0.53

- r = 0.76

**OMI V3**

- Brinksma et al. (2008) JGR

## INTEX-B Comparisons

**INTEX-B Comparisons**

**OMI V2**

- slope = 1.4
- r = 0.89

- slope = 1.2
- r = 0.87

**OMI V3**

**1:1**

- Boersma et al. (2008) AE

## Air Mass Factors 
What are they? A value that represents the solar optical light path from sun to detector incl. clouds, surface and aerosols present (VC=SC/AMF).
Calculated with radiative transfer models
When NO2 is close to the surface, the satellite is not sensitive to it and the air mass factor is small.
When NO2 moves up in the atmosphere, the satellite is more sensitive and the air mass factor increases.
Depends on a priori knowledge of clouds, albedo, and NO2 profile shape (from TM4).

**Air Mass Factors**
- What are they? A value that represents the solar optical light path from sun to detector incl. clouds, surface and aerosols present (VC=SC/AMF).
- Calculated with radiative transfer models
- When NO2 is close to the surface, the satellite is not sensitive to it and the air mass factor is small.
- When NO2 moves up in the atmosphere, the satellite is more sensitive and the air mass factor increases.
- Depends on a priori knowledge of clouds, albedo, and NO2 profile shape (from TM4).

**Slant column**

**Vertical column**

- Sensitivity

- Altitude

## Can we improve the algorithm ?

- Examine a-priori profile shape in TM4 model.
- Compare TM4 profile with campaign profiles.
- How does NO2 change with revised AMF.

## 17% change in NO2

- 17% change in NO2

## INTEX-B flight segments shown in white 

- Laser Induced Fluorescence (LIF) sampled NO2 profiles during INTEX-B
- Portion of flight segments below 600 m shown in grey.
- OMI pixels compared with INTEX-B NO2 profiles highlighted in black.

## 36% change

## Comparisons among DANDELIONS and OMI original and revised NO2

- Comparisons among DANDELIONS and OMI original and revised NO2

**1:1**

**1:1**

## Comparisons among INTEX-B and OMI original and revised NO2

**1:1**

**1:1**

- Comparisons among INTEX-B and OMI original and revised NO2

**Notes:**
Invite people to Kroon poster to learn more about validation needs

## OMI tropospheric NO2 2007-2005 

- Slide from Geert Vinken  (KNMI)

**OMI tropospheric ****NO****2**** 2007-2005 **
**annual average difference**

## 2008 Olympic Games

**2008 Olympic Games**

- EPA reports **7%** decrease in NOx emissions from 2005-2006
- OMI shows an average **10%** decrease in NO2 columns.

##     	2005	           2006                    2007	          2008 

-     	2005	           2006                    2007	          2008

##      	2005	                2006          	2007	          2008 

-      	2005	                2006          	2007	          2008

## Outline

**Outline**

- Describe tropospheric NO2 observations during INTEX-B and DANDELIONS.
- Compare campaign profiles with OMI  show improvements using version 3 instead of version 2.
- Investigate influence of measurements on OMI tropospheric NO2 retrieval.
- Present tropospheric NO2 trends from OMI

## Conclusions

- OMI tropospheric NO2 compares well with DANDELIONS and INTEX NO2 (r > 0.64).
- These results are fair weather biased.
- Including measured tropospheric NO2 profiles in the AMF calculation can change the AMF and OMI NO2 by up to 36%.
- This study supports the OMI validation need for more NO2 observations – see poster by Kroon et al.
- OMI shows NO2 decreases in Eastern US and NO2 increases in China.

## OMI DOMINO tropospheric NO2 algorithm

- Slant column NO2

- Stratospheric Slant column NO2

- Tropospheric Slant column NO2

- Stratospheric Vertical column NO2

- Tropospheric Vertical column NO2

- TM4-DOMINO

- AMF Strat

- AMF Trop

- TM4- global chemistry transport model run with assimilated OMI products
- TM4 produces NO2 profiles
- These NO2 profiles are used to calculate AMFs (air mass factors).

**OMI DOMINO tropospheric NO****2**** algorithm**

- TM4-DOMINO

- TM4-DOMINO

**Notes:**
Slant column is ingested into the TM4 model.
The AMF strat that is calculated is very close to the geometric amf.

## EXTRA

## The Site

**The Site**

- industry