Center for Satellite Applications and Research (STAR) Review 09 – 11 March 2010

Requirement: Provide information to air quality decision makers and improve NOAA’s national air quality forecast capability.Science: How can we use data from multiple sensors( GOME-2 and OMI) to understand the diurnal variation of NOX( nitrogen dioxide and nitric oxide) Emissions?Benefit: Will lead to improved surface ozone forecasts. Will improve identification of NOX sources and improved NOX budget.

Science Challenges: •Lack of in-situ observations.•Assimilation of data into air quality models.•Data continuity (NPP/NPOESS OMPS instrument cannot make NO2 retrievals).•No profile information.•Retrieval efficiency and communication of that information to users.Next Steps: Maintain science support to operational product processing including algorithm improvements.Transition Path: Instrument calibration and modeling studies will flow into improved operational air quality forecasts.

Near-real-time Tropospheric NO2 Retrievals for Air Quality Applications

T. Beck1 (Government Principal Investigator) and S. Kondragunta1

1NOAA NESDIS STAR

Algorithm: The retrieval uses a two step procedure to estimate tropospheric NO2. The 1st step uses the measured spectroscopy in the blue light region of the visible( 425nm to 455nm). Using a non-linear least square solver the amount of NO2 within the viewing field is estimated( slant column). To be useful for applications, the vertical column is needed; to estimate the vertical column, radiative transfer must be used to relate the two quantities. We use the LIDORT( LInearized DisORT) model.

The GOME-2 instrument is a nadir-scanning UV/visible spectrometer. It includes four main optical channels which focus the spectrum onto linear silicon photodiode arrays of 1024 pixels each, and two Polarization Measurements Devices (PMDs). The four main channels provide continuous spectral coverage of the wavelengths between 240 and 790 nm with a spectral resolution between 0.26nm and 0.51nm.

The Global Ozone Monitoring Experiment-2 (GOME-2) is one of the new-generation European instruments carried on MetOp and will continue the long-term monitoring of atmospheric NO2 started by GOME on ERS-2. MetOp was launched on October 19, 2006.

Once the total column NO2 is found the “Reference Sector Method” is used to remove stratospheric contribution. The assumption is that over much of the oceans there is none or very little NO2 pollution present( NO2 has a short lifetime). An average background NO2 amount is found using only the unpolluted measurements. The unpolluted field represents the stratospheric NO2. The initial assumption for the AMF calculation is there is no tropospheric NO2. When the total column NO2 exceeds twice the standard deviation of the zonal mean the measurement is assumed to be polluted, a new AMF calculation is done. Based on GEOS-CHEM model runs a polluted NO2 profile is interpolated. The polluted profile is used to generate the tropospheric AMF.

Solar Measurements

A wave 2 fit estimates the global background NO2.

The profile shape of the Strato-spheric NO2. It has a well defined Maximum.

In the troposphere Polluted NO2 profiles are supplied by GEOS-

CHEM modeling studies.

Operational Near Real Time NO2 Monitoring at NOAA http://www.osdpd.noaa.gov/ml/air/home.html

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The tropospheric NO2 will become operational in March 2010. The pre-operational images are available at the above website

Validation by comparison to OMI. 15 months of GOME-2 and OMI slant column NO2 data (2008-2009) were compared using SNO analysis. Number of matchups for this analysis were 77. SNO matchup criteria

± 2 minutes overpassSolar zenith angles less than 80o

View zenith angles less than 40o (nadir)OMI row anomaly flag used

ResultsMean bias is 0.23 (~ 2%)Correlation coefficient is 0.85

GOME-2 measured weekday averaged NO2. The overpass time is 10:00AM. The measurements generally agree however the rural background values are higher.

Weekend andWeekday averages for OMI and GOME-2. The drop in weekend NO2 is captured by both instruments.

The CMAQ model summertimeAverage at the GOME-2 overpass time. The model underestimates rural NO2. The major sources are comparable.

Modeled and Measured Diurnal Variation of NO2 in the U.S.

Ozone Non-Attainment Areas

OMI and GOME-2 measurements are plotted as filled circles. Continuous lines represent the CMAQ forecast at both overpass times. OMI is in an afternoon orbit and GOME-2 is in a morning orbit. Plans are underway to work with NOAA/ARL and NOAA/NWS to use the satellite retrievals in constraining the NOx emissions in the CMAQ model.

METOP/GOME-2

AURA/OMI

The GOME-2 NO2 retrievals are supporting the EPA AIRNow program. The Near-Real Time measurements are expected to improve surface ozone forecasts. http://www.airnow.gov