1. DC8 photo of Mexico City by Cameron McNaughton, University of Hawaii, Feb 2006 Characterizing Megacity Pollution and Its Regional Impact with TES Measurements Changsub Shim, Qinbin Li, Ming Luo, Susan Kulawik, Helen Worden, and Annmarie Eldering The Jet Propulsion Laboratory California Institute of Technology Pasadena, California 3 rd GEOS-Chem User’s Meeting

2. Mapping pollution outflow using O 3 -CO correlation  The observed O 3 -CO relationship has been used to characterize continental pollution outflow [Fisherman and Seiler, 1983; Chameides et al., 1987; Parrish et al., 1993, etc.].  Positive O 3 -CO correlations and ∆O 3 /∆CO indicate photochemical O 3 productions.  Tropospheric Emission Spectrometer (TES) aboard the Aura satellite provides concurrent O 3 and CO retrievals and vertical profiles.  TES O 3 -CO correlation (at 618 hPa) has been used to map global continental pollution outflow [Zhang et al., 2006].  TES O 3 -CO correlation (at 618 hPa) has been used to map global continental pollution outflow [Zhang et al., 2006].

3. Objectives  Can we characterize megacity pollution and its regional impact with TES tropospehric ozone and CO retrievals?  We analyzed TES O 3 and CO data over the Mexico City Metropolitan Area (MCMA) and Southern U.S. (15-30°N and 90 - 105°W) during the MILAGRO/INTEX-B campaign (March 2006).  We first compared TES O 3 and CO retrievals with those from airborne measurements (C130 & DC8 flights) during this campaign.  The comparisons of O 3 -CO correlation between airborne measurements, TES retrievals, and GEOS-Chem model were then used to evaluate the TES capability to characterize urban outflow on a regional scale.

4. Mexico City Metropolitan Area (MCMA) (19°N, 99°W)  2 nd largest metropolitan area in the world (~20 million inhabitants) within area of ~1,500 km 2.  MCMA is surrounded by mountains and thermal inversions often trap pollution within the basin.  The elevation (~750 hPa) is about 2.2 km above mean sea level.  Lower pO 2 makes combustion ineffective, which enhances emissions of CO, VOCs, and O 3.  Lower pO 2 makes combustion ineffective, which enhances emissions of CO, VOCs, and O 3.  Motor vehicular exhaustion is a very important source of air pollution (3 million aged vehicles).

5. In-situ measurements during MILAGRO/INTEXB (C130 and DC8 )  NSF C-130 for MILAGRO covers (16 – 25°N and 93 – 101°W) in Mar 2006 (red).  NASA DC-8 for INTEX-B covers (15 – 35°N and 90 - 103°W) (blue).  ~6,000 coincident measurements of O 3 and CO from the two aircrafts (5- min merge).

6.  On-board the Aura satellite launched in July 2004 to provide simutaneous 3-D mapping of tropospheric O 3, CO, HDO and CH 4, among other species globally.  The Aura satellite moves in polar sun-synchronous orbit at 705 km height in the ascending node passing equator at 0145 and 1345 LT (16 days for global coverage).  TES has a spatial resolution of 5 x 8 km in nadir-viewing mode.  TES has the standard observations (“global surveys”: 108 km apart along the track) and the special observations (“step and stares”) with denser nadir coverage (45 km apart).  11 step and stares and 5 global surveys were used in this study for the MILAGRO/INTEX-B periods.  Version 2 data (V002, F03_03) with better quality flags. TES retrievals

7. TES orbital tracks over MCMA during MILAGRO/INTEX-B Typical TES O 3 and CO Averaging Kernel Step and stare Mar 12 th, 2006.

8. GEOS-Chem simulations  GEOS-4 met fields (2x2.5° with 30 layers) from NASA GMAO.  Standard full chemistry simulations (O 3 -NOx-VOC) [version 7- 04 -10].  Monthly biomass burning emission inventory [Duncan et al., 2003].  Fossil fuel emission inventory: EDGAR inventory scaled for time and the model grid [Benkovitz et al., 1996; Bey et al., 2001]. EPA/NEI 99 and BRAVO inventories [U.S. EPA, 2004; Kuhns et al., 2005] are used for U.S. and Mexican fossil fuel emissions respectively.  Lightning NOx emissions with parameterization based upon cloud top height and regionally scaled to OTD/LIS observations.  Biogenic emissions: MEGAN inventory [Guenther et al., 2006].  3-hour O 3 and CO model results were sampled along TES orbits.  For comparison with TES retrievals, local TES averaging kernels were applied to GEOS-Chem vertical profiles [Zhang et al, 2006].

9. Observed (in-situ) vertical distributions of O 3, CO, and NOx (Mar. 2006) Altitude of MCMA ! O3O3 NOxCO MCMA pollution outflow concentrated at 600-800 hPa. TES has large sensitivity to 600 – 800 hPa pressure levels.  TES data are ideal for analyzing the MCMA outflows!

10. Comparisons of O 3 over the MCMA (Mar. 2006) There is considerable O 3 enhancement in the in situ data at 600 – 800 hPa over MCMA. The enhancement is not apparent in TES data nor GEOS-Chem results.

11. Comparisons of CO over the MCMA (Mar. 2006) The CO enhancement in aircraft data over MCMA at 600 – 800 hPa is not apparent in TES retrieval nor GEOS-Chem results.  Why?

12. Time series (daily) comparisons over the MCMA (C130 & DC8 coverage gridded in 2 x 2.5°) between 600 – 800 hPa C130+DC8 GC raw TES (co-located) TES (all)  TES orbit did not cover the MCMA for the days of three high pollution events (Mar. 9 th, 22 th, and 29 th.).  But the TES data generally show good agreements with aircraft measurements.  The GEOS-Chem model underestimates both O 3 and CO by ~29% and ~45% respectively (at 600 – 800 hPa).

13. O 3 -CO correlations and ∆O 3 /∆CO between Aircraft, TES, and GEOS- Chem over MCMA and surrounding regions.  All results are gridded in 2 x 2.5° and sampled along with aircraft measurements.  The O 3 -CO correlation derived from TES data is in good agreement with those from in situ and GEOS-Chem/AK resuts, reflecting significant O 3 production and transport over the MCMA and surrounding regions. Height (hPa) R ∆O 3 /∆CO MCMA in-situ 600 – 800 0.780.28 MCMA TES 600 - 800 0.50.43 MCMA CTM 600 - 800 0.580.25 INTEX-NA Surf - 600 0.5 – 0.7 0.31 - 0.44 US (Parrish et al) Surf0.820.33 US (Chin et al) Surf 0.7 – 0.9 ~ 0.3 TRACE-P Surf - 600 0.60.15 ICARTT (Zhang et al) 6180.340.72

14. Conclusions  The pollution outflow from the MCMA and the surrounding regions during MILAGRO/INTEX-B were characterized with aircraft observations, TES tropospheric O 3 and CO retrievals, and GEOS-Chem results.  The aircraft observations show significant enhancement of O 3, CO, and other chemical species at 600 – 800 hPa, reflecting pollution outflow from the MCMA. The observed vertical distributions over the MCMA are not apparent in TES O 3 and CO retrievals due in part to the limited coverage missing three high pollution events. However, the TES data shows fairly good agreements with the aircraft measurements on a daily basis.  The O 3 -CO correlations derived from TES data are in good agreement with those derived from aircraft observations and GEOS-Chem results (r: 0.5 – 0.9; ∆O 3 /∆CO: 0.3 – 0.5), reflecting significant O 3 production and transport over the MCMA and surrounding regions.  TES data provides valuable information to capture regional scale pollution outflows and we may extend this analysis to global-scale study.