# Presentation: 537316

## Comparing old and new NO2 profiles and tropospheric AMFs for the OMI NO2 algorithm

**Comparing old and new NO****2**** profiles and tropospheric AMFs for the OMI NO****2**** ****algorithm**
**                ****Old Profile                                                                                         New Profiles**
**       ****(Current algorithm)****	****(Proposed algorithm)**
**_____________________________________________________________________**
**	****	**

**	****	**

**GEOS-Chem model profiles (v4.26) valid year 1997 at local time 0900-1200.**
**Profiles are geographically gridded **_**annual**_** means**
**Profiles truncated at ground level.**

**GMI model profiles (Aura4 run May 2008) valid year 2006 at local time 1300-1400.**
**Profiles are geographically gridded **_**monthly**_** means from GMI**
**Profiles shifted up so that profile bottoms are at local terrain height:**
**                  ****P   =   A   +   B ****· ****P****surf **** , **
**   ****where P is the GMI model pressure, A and B are constant vectors, and P****surf ****is the local surface pressure.**

**____________________________________________________________________**
**Clear-sky AMFs were computed for nadir viewing, using mean monthly SZAs and albedos at each location (averaged over same 2 ****x**** 2.5 deg****2**** grid cells as the GMI NO****2**** profiles).**
**____________________________________________________________________**
_**Results (new profiles relative to old):**_
**New AMFs (polluted regions) are 10-30% higher in summer, 5-15% lower in winter.**
**AMF differences in biomass burning areas are large (~100%).**
**Discrepancies are about twice as large with even small effective cloud fractions (~20%).**

## Comparison of tropospheric NO2 profiles and AMFs

**Comparison of tropospheric NO****2**** profiles and AMFs**

**Black line is GEOS-Chem annual mean profile from current algorithm.  Colored lines are the new GMI monthly mean profiles.  Dotted line is local terrain pressure.**

***Figure  1***

## AMF difference (new monthly vs old annual profiles)

**AMF difference (new monthly *****vs***** old annual profiles)**

***Figure  2***

**(a)  ****AMFs from GMI monthly mean profiles compared with AMFs from GEOS-Chem annual mean profiles.  SZAs and albedos are monthly means for each location.**

**(b)  ****Same as (a), but GMI monthly means are compared to GMI annual means. **

**(c)  ****Same as (b), but using fixed SZA = 45 deg, albedo = 0.05.**

## PDFs of tropospheric AMFs near Baltimore, MD

***Figure  9***

**PDFs of tropospheric AMFs near Baltimore, MD**
**(based on daily GMI NO****2**** profiles)**

**AMFs computed with monthly mean SZA and albedo. For each month, width of curve shows effect of daily variation in NO****2**** profile shape around the monthly mean. **
**Same as (a) ****except using fixed SZA = 45 deg and albedo = 0.05.**

## January difference in tropospheric AMFs

**       ****(a)**
**Monthly means based on GMI profiles, annual means from GEOS-Chem profiles. **
**(Monthly mean SZA, albedo and terrain pressure used at each grid location)**
**       ****(b) **
**Same as (a), except annual and monthly mean profiles are both from GMI.**

_**January**_** ****difference in tropospheric AMFs**
**Difference = (Monthly – Annual) / Annual**

***Figure  3***

## July difference in tropospheric AMFs

_**July**_** ****difference in tropospheric AMFs**
**Difference = (Monthly – Annual) / Annual**

***Figure  5***

**       ****(a)**
**Monthly means based on GMI profiles, annual means from GEOS-Chem profiles. **
**(****Monthly mean SZA, albedo and terrain pressure used at each grid location)**
**       ****(b) **
**Same as (a), except annual and monthly mean profiles are both from GMI.**

## NO2 AMF vs Surface Reflectivity

**NO2 AMF vs Surface Reflectivity**

## Annual Mean

- OMI (471nm, KNMI)

- MODIS (nadir refl at 470nm, BU)

- MODIS and OMI have similar spatial distributions
- GOME’s big pixel size (100km) makes its values much higher in tropic forests, mid to high lat regions due to cloud contamination, among others

- GOME (463nm, Koelemeijer)

## MODIS-based Product Comparison 

- MODIS-based Product Comparison

- Hsu’s LER (5-yr record, 3-season 0.1DEG)

- Standard product (2004 16-day 0.05DEG CMG, Col5)

- BU’s custom-made product (5-yr record, monthly 0.05DEG gap-filled CMG)

- Aeronet-used dataset (5-yr record, 16-day 0.005DEG, gap-filled)

**Notes:**
gap-filled vs. standard
5-yr vs. 1-yr

## Annual Mean Diff btw OMI & MODIS (BU)

- 0°

- Annual Mean Diff btw OMI & MODIS (BU)

- 30°

- 60°

- -30°

- -60°

- at 470nm

## OMI>MODIS

- OMI<MODIS

## Annual Variation: Peak-to-Trough

- MODIS 12 month nadir refls at 470nm (BU)

- Aeronet-used nadir refls (23 16-days) at 470nm

-  OMI 12 month LERs at 471nm

-       GOME 12 month LERs at 463nm

## April difference in tropospheric AMFs

_**April**_** ****difference in tropospheric AMFs**
**Difference = (Monthly – Annual) / Annual**

***Figure  4***

**       ****(a)**
**Monthly means based on GMI profiles, annual means from GEOS-Chem profiles. **
**(Monthly mean SZA, albedo and terrain pressure used at each grid location)**
**       ****(b) **
**Same as (a), except annual and monthly mean profiles are both from GMI.**

## October difference in tropospheric AMFs

_**October**_** ****difference in tropospheric AMFs**
**Difference = (Monthly – Annual) / Annual**

***Figure  6***

**       ****(a)**
**Monthly means based on GMI profiles, annual means from GEOS-Chem profiles. **
**(****Monthly mean SZA, albedo and terrain pressure used at each grid location)**
**       ****(b) **
**Same as (a), except annual and monthly mean profiles are both from GMI.**

## AMFs for April (based on GMI monthly meanNO2 profiles )

**AMFs for April ****(based on GMI monthly meanNO****2**** profiles )**

**(a) Tropospheric NO****2**** AMFs.  Large gradients near coast and in complex terrain are due to variation in profile as well as SZA, albedo and terrain pressure, all of which have been averaged over the GMI grid cells (2 ****x**** 2.5 deg****2****).  In the OMI algorithm, albedos and terrain pressures are from a higher-resolution database sampled at OMI pixel locations.**

***Figure  7***

**(b) Same as (a), except SZA, albedo and terrain pressure are spatially uniform across the field.  The gradients in AMF reflect only the differences in NO****2**** profile shape in each of the model’s 2 ****x**** 2.5 deg****2**** grid cells.**

##              Difference in annual mean tropospheric AMFs

***Figure  8***

-              **Difference in annual mean tropospheric AMFs**
**	**** ****Difference = (New – Old) / Old**
**                  ****Old: Based on GEOS-Chem annual mean NO****2**** profiles**
**                       ****New: Based on GMI annual mean NO****2**** profiles**
**                       ****Annual mean SZA, albedo and terrain pressure used in AMF calculation at each grid location**