# Presentation: 501892

## Comparison of Eta/CMAQ and OMI – MLS Tropospheric Ozone

**Kenneth E. Pickering****1****, Jerry Ziemke****2****, Changwoo **
**Ahn****3****, P. K. Bhartia****1****, Lackson Marufu****4****, Russell Dickerson****4****, Rohit Mathur****5****, Paula Davidson****6**
**1**** NASA Goddard Space Flight Center, Greenbelt, MD USA**
**2**** GEST-UMBC, NASA Goddard, Greenbelt, MD USA**
**3**** SSAI, NASA Goddard, Greenbelt, MD USA**
**4**** University of Maryland, College Park, MD USA**
**5**** NOAA, Research Triangle Park, NC USA**
**6 ****NOAA, Silver Spring, MD USA**
** **

## Aura OMI-MLS Tropospheric Ozone

- Residual method [Fishman, et al., 1990] used to derive daily gridded tropospheric ozone maps
- MLS stratospheric column ozone (SCO) along orbital track derived by pressure integration of MLS ozone mixing ratio profiles down to NCEP tropopause
- MLS SCO gridded maps generated using 2D interpolation
- Gridded tropospheric column ozone (TCO) = OMI total ozone – MLS SCO
- TCO cloud filtered using OMI gridded reflectivity < 0.3
- 	TCO filtered for NCEP tropopause < 170 hPa
- Mean volume mixing ratio (**ppbv**) = 1.27×TCO (**DU**) / [P**TERRAIN** (**mb**) – P**TROPOPAUSE **(**mb**)]

## Eta/CMAQ Ozone Forecasting System

- Community Multiscale Air Quality (CMAQ) model developed by US EPA
- Driven by NCEP Eta weather forecast model
- Run at 12- km horizontal resolution with 22 layers in the vertical with model top at 100 hPa.
- Model domain – Eastern United States
- Model initialized at 1200 UT each day for a 48-hour forecast

## Comparison of OMI-MLS and Eta/CMAQ Tropospheric Column Ozone

- Use 1900 UT Eta/CMAQ data (7-hour forecast), which is closest to OMI overpass time in Eastern US
- Regrid Eta/CMAQ data to OMI 1 x 1.25 deg. grid and integrate model data from surface to NCEP tropopause.
- Filter OMI-MLS and Eta/CMAQ gridded data to remove regions with NCEP tropopause pressure > 170 hPa, such that strong stratospheric ozone gradients are eliminated.
- Obtain OMI “averaging kernel” (profile of efficiency factors) from Level 2 data.
- Apply “averaging kernel” to Eta/CMAQ tropospheric profile ozone data
- Compute OMI-MLS minus Eta/CMAQ (adjusted) for each grid cell and compute statistics for each day over model domain

## XCMAQadj =    [ Σ  E  (xCMAQ - x0a priori) ]       X0a priori

**Tropospheric column O3: **
**CMAQ adjusted for appropriate comparison with (OMI – MLS) **

**Layer O****3**** from CMAQ profile**

**Tropospheric column O****3**
** ****from a priori profile**

- Adjust CMAQ tropospheric column O3 using OMI “averaging kernel”

**Layer O****3**** from a priori profile**

**Layer efficiency from**
**OMI L2 data**

## July 22, 2005

**OMI - MLS**

**NCEP Tropopause Pressure**

**Filtered OMI - MLS**

## July 22, 2005

**CMAQ Model**

**CMAQ Filtered and Adjusted**

## Summary Statistics

- Ran CMAQ adjustment and comparison with (OMI – MLS) for 19 particularly low and high surface ozone days from 10 July to 15 Aug 2005 period over the Eastern US
- For (OMI – MLS) minus CMAQadj:
- Mean spatial correlation = 0.54
- Mean bias = -3.8 DU
- Mean absolute error = 7.1 DU

## OMI vs ETA/CMAQ Tropospheric Column O3 Comparisons With Efficiency Corrections & Tropopause Filtering

**r = 0.75**

**r = 0.66**

**r = 0.67**

**r = 0.41**

**r = 0.38**

**r = 0.43**

## August 12, 2005

**OMI - MLS Filtered**

**CMAQ Filtered and Adjusted**

**r = 0.56**
**Mean bias = -1.66 DU**
**Mean abs. error =**
**	****5.58 DU**

## August 13, 2005

**OMI – MLS Filtered**

**CMAQ filtered and adjusted**

**r = 0.57**
**Mean bias = -2.53 DU**
**Mean absolute error =**
**	****5.67 DU**

## University of Maryland Piper Aztec

**University of Maryland Piper Aztec**

**CO****	****Met.**
**O****3**
**SO****2**
**Aerosols**

**Spirals Sfc to ~ 3 km**
**over Mid Atlantic States**

## Aircraft vs. OMI Summary

**Eight early afternoon spirals over Maryland during Summer 2005:**
**(OMI-MLS) minus A/C:**
**Mean Absolute Difference:  A/C PBL   15.5 ppbv**
**	****	****	****	****	****       ****	**** ****A/C FT        5.9 ppbv**
**OMI-MLS much more closely related to pollution**
**above boundary layer – indicative of regional transport**

## Summary

**Preliminary results for comparisons between the OMI-MLS tropospheric ozone product show reasonable agreement on the pattern of this variable over the Eastern United States.**
**Spatial correlations exceeded 0.60 on 7 of 19 days studied.  **
**CMAQ tropospheric column ozone larger than OMI-MLS by 3.8 DU on average.  Model may be biased high due to NCEP/GFS boundary condition.**
**Both OMI-MLS and CMAQ show movement of high ozone region to East Coast during largest pollution event of Summer 2005.  Demonstrates usefulness for forecasting. **
**Based on comparison with UMD aircraft, OMI-MLS captures variability in O****3**** transport layer above PBL.**