AQUA AURA The Berkeley High Spatial Resolution(BEHR) OMI NO2 Retrieval: Recent Trends in NO2 Ronald C. Cohen University of California, Berkeley $$ NASA

Air Quality Applications Of OMI NO2 Key elements: total columns trends over time differences and ratios in space the noontime chemical lifetime of NO2 of ~1-4hrs implies an e-folding distance of order 25km OH changes will be approximately equal to NO2 changes—a significant effect on lifetimes

L Valin et al., Atmos. Chem. Phys. 2011 Four Corners Power Plants: WRF-Chem L Valin et al., Atmos. Chem. Phys. 2011

Los Angeles: WRF-Chem

OMI NO2 Riyadh 8 hours 6 hours

Deriving NO2 column densities from space-based reflectance measurements

Summary of the NO2 retrieval process Step 1: DOAS fit to determine slant column Step 2: Subtract the Stratospheric contribution Step 3: Convert the tropospheric slant column into a vertical column Total Slant Column Density Stratospheric Vertical Column Density Tropospheric Vertical Column Density

Step 3: Convert the tropospheric slant column into a vertical column Atmosphere Absorption and Scattering by aerosols and molecules Absorption, Scattering, and Transmission through a cloud Absorption and Scattering by the surface Modified image from Richter, U Bremen Surface AMFs are sensitive to Viewing geometry Terrain pressure and reflectivity Shape (not magnitude) of the NO2 vertical profile Clouds AMF = Vertical Column Slant Column

Berkeley High Resolution Retrieval (BEHR) NASA standard BEHR Terrain pressure High-res terrain database, center of OMI footprint High-res terrain database, average over OMI footprint Terrain reflectivity Monthly 1° × 1° MODIS, 8 day 0.05° × 0.05° NO2 profile shape Annually 2° × 2.5° WRF-Chem, Monthly 4 × 4 km2 (CA&NV) 12 x 12 km2 U.S. Clouds OMI cloud product MODIS cloud product Russell et al., Atmos Chem & Phys 11, 8543-8554, 2011

NASA Standard Product June 2008 Terrain Reflectivity (Albedo) MODIS True Color OMI Monthly Albedo MODIS 8 day Albedo SP NO2 June 18, 2008 NASA Standard Product June 2008 BEHR June 2008 Russell et al., Atmos Chem & Phys, 2011

Terrain Reflectivity (Albedo) PDF of systematic errors Russell et al., Atmos Chem & Phys, 2011

Terrain Pressure PDF of systematic errors Russell et al., Atmos Chem & Phys, 2011

NO2 profile shape PDF of systematic errors Russell et al., Atmos Chem & Phys, 2011

The BEHR product is generally higher in urban regions and lower in rural regions than the operational products Standard Product BEHR % Difference Russell et al., Atmos Chem & Phys, 2011

molecules cm-2 Summer 2005 Russell et al., ACPD in press

molecules cm-2 Summer 2011 Russell et al., in press

Trends for select cities and power plants –– Weekdays - - Weekends –– All days Russell et al., in press

Trends in cities are similar while trends at power plants are more variable 47 cities, 23 power plants! Russell et al., in press

2005 – 2011 reductions in urban regions of the US are similar (–32 ± 7%). Russell et al., in press

The impact of the economic recession on emissions is observed by OMI 2005 – 2007 Russell et al., in press

The impact of the economic recession on emissions is observed by OMI 2005 – 2007 2007 – 2009 Russell et al., in preparation

The impact of the economic recession on emissions is observed by OMI 2005 – 2007 2007 – 2009 2009 – 2011 2005 – 2007 Russell et al., in press

Reductions on weekdays are larger than those on weekends due to reductions in diesel traffic 2005 – 2007 2007 – 2009 2009 – 2011 Weekday – 6 ± 4% – 9 ± 4% – 4 ± 4% Weekend – 7 ± 5% – 6 ± 7% – 1 ± 7% Russell et al., in press

Conclusions The BEHR product reduces biases in the NO2 column due to coarse resolution terrain and profile parameters. We can make it available upon request, rccohen@berkeley.edu. Analysis of 2005–2011 trends for cities and power plants in the US show how improved vehicle technology and the economic downturn have influenced emissions.

Ashley Russell Luke Valin (PhD May 2012) (PhD soon)

A.R. Russell, et al, Trends in OMI NO2 observations over the United States: Effects of emission control technology and the economic recession, ACPD. in press June 2012. L.C. Valin, et al, Effects of model resolution on the interpretation of satellite NO2 observations, ACP. 11, 11647-11655, 2011 A.R. Russell, et al., A high spatial resolution retrieval of NO2 column densities from OMI: Method and Evaluation, ACP, 11, 8543-8554, 2011. L.C. Valin, et al., Observation of slant column NO2 using the super-zoom mode of AURA OMI, AMT, 4, 1929-1935, 2011. A.K. Mebust,, Characterization of wildfire NOx emissions using MODIS fire radiative power and OMI tropospheric NO2 columns , ACP. 11, 5839-5851, 2011. R.C. Hudman, et al., Interannual variation in soil NOx emissions observed from Space, ACP. 10, 9943-9952, 2010. Thank you!

Update: Trends in urban regions of CA, 2005-2011 - 36% - 30% - 44% - 30% Russell et al., 2010 (updated)

I = Io e - σ ℓ N Beer-Lambert Law: Entangled ℓ CLOUDS SAMPLE POLISHED MIRROR LIGHT SOURCE (Io) ℓ MOLECULES PARTICLES Beer-Lambert Law: I = Io e - σ ℓ N DETECTOR (I) Entangled 28

WRF-CHEM 1km – 4-Corners Plume NO2 column OH Column

Large Area+Urban Sources in WRF-Chem

NOx Lifetime τ=Mobs / Erate e-kx; x = ut; τ=k-1 By Mass Integrated Observation By Decay Gradient e-kx; x = ut; τ=k-1 Resolved Observation