Use of space-based tropospheric NO2 observations in regional air

quality modelingRobert W. Pinder1, Sergey L. Napelenok1,

Alice B. Gilliland1, Randall V. Martin2

1. Atmospheric Sciences and Modeling Division, NOAA, in partnership with USEPA2. Dalhouise University and Harvard-Smithsonian Center for Astrophysics

TROPOMI WorkshopKNMI, Utrecht, The Netherlands

March 5-6, 2008

Case Study: NOx State Implementation Plan Call

• From 2002 – 2005, NOx emission reductions from power plants in Midwestern United States (22% ↓)

• Simultaneous gradual reduction in vehicle NOx emissions (18% ↓)

• Goal: Use satellite data to infer emission changes

Surface change in total nitrate, 2002-05

Tools:• CMAQ:

Community Multi-scale Air Quality Model

• Surface networks: HNO3, O3, deposition

• Can satellite data augment these tools?

2003 2004 2005SCIAMACHY

2003 2004 2005SCIAMACHY

2003 2004 2005SCIAMACHY

How does the change in the satellite observations correspond to

changes in emissions?

(1) Develop method using air quality model to relate emissions to column density

(2) Apply method to relate trend in satellite data to trend in emissions (in development)

Use Air Quality Model and Satellite Data to Infer Emission Change

• Begin with a priori emission estimate• Use emissions as input to CMAQ to estimate

NO2 column density

• Based on difference between CMAQ estimate and observed value, use an inverse technique to derive a new emission estimate

• Repeat until emission estimate converges (a posteriori)

Focus on Southeast United States in 2004

• Isolated urban areas

• Good spatial coverage in satellite data

• High quality surface NO2 observations

Continental US Southeast USC

MA

QS

CIA

MA

CH

Y

Missing NO2 Aloft

• When paired with aloft measurements from NASA INTEX, CMAQ underpredicts NO2 above the mixed layer

• On average 1.07 (1015 molecules cm-2)

Singh, et al. (2007) Reactive Nitrogen Distribution and Partitioning in the North American Troposphere andLowermost Stratosphere

Similar error found in other models

SC

IAM

AC

HY

CM

AQ

Continental US Southeast US+

IN

TE

X

Emissions

(tons NOx day-1)

Comparison of CMAQ and SCIAMACHY

r2

Atla

nta

Birm

ingh

am

Ge

org

ia

Alab

am

a

a priori 0.68 513 202 574 852

a posteriori

CMAQ0.89 482 182 1171 1718

a posteriori

CMAQ + INTEX0.93 435 138 364 782

RESULTS

Urban areas decrease;consistent with updatedemissions data

Rural areas aresensitive to NO2 aloft

Inverse improves surface concentrations

• Inverse-adjusted emissions improves agreement with independent surface NO2 observations

• Sensitivity test demonstrates proper accounting of NO2 aloft is importantNO2

Work in Progress: Next Steps

• More information is available on ACPD (Napelenok et al., A method for evaluating spatially-resolved NOx emissions using Kalman filter inversion, direct sensitivities, and space-based NO2 observations)

• Improve simulation of NOx above the planetary boundary layer

• Improve inverse methods to better quantify uncertainty

• Apply method to trends in 2003, 2004, and 2005

• Beyond SCIAMACHY NO2 data

Considerations for Future Missions

• Consistency across multiple years• Horizontal and vertical resolution• Reduce uncertainty and global daily coverage• Multiple observations per day, but need to

consider chemical state

• Harmonizing regional models and retrieval• More transparency in retrieval methods and

uncertainty calculations to ease interpretation and comparison

ACKNOWLEDGEMENTS: Aloft NOx measurements collected by Ron Cohen and the NASA INTEX team.

Helpful comments and advice from Rynda Hudman, Dev Roy, Robin Dennis, David Mobley, and Ann Marie Carlton.

DISCLAIMER: The research presented here was performed under the Memorandum of Understanding between the U.S. Environmental Protection Agency (EPA) and the U.S. Department of Commerce's National Oceanic and Atmospheric Administration (NOAA) and under agreement number DW13921548. This work constitutes a contribution to the NOAA Air Quality Program. Although it has been reviewed by EPA and NOAA and approved for publication, it does not necessarily reflect their policies or views.