Application of Satellite Observations for Timely Updates to Bottom-up Global Anthropogenic NO x Emission Inventories L.N. Lamsal 1, R.V. Martin 1,2, A. Padmanabhan 1, A. van Donkelaar 1, Q. Zhang 3, C. Sioris 4, K. Chance 2, and T. Kurosu 2 1 Dalhousie University, 2 Harvard Smithsonian, 3 Tsinghua University, 4 Environment Canada Nitrogen oxides (NO x = NO + NO 2 ) are key actors in air quality and climate change. Global anthropogenic NO x emissions are expected to change rapidly over the coming decades due to economic development and emissions controls. The bottom-up approach of estimating NO x emissions aggregating activity data and emission factors is a major undertaking that often suffers from a time lag of years between the occurrence of emissions and completion of inventories. Timely and improved NO x emissions estimates are needed for better understanding of air pollution, acid deposition, and climate change. Satellite observations of tropospheric NO 2 columns provide near-real-time and independent information on NO x emissions and their trends. Here we present an approach to rapidly update bottom-up NO x emissions inventories using top-down trend analysis of satellite observations of tropospheric NO 2 columns. We retrieved tropospheric NO 2 columns from the SCIAMACHY instrument for , and to interpret these observations, we developed a global simulation capability for GEOS-Chem at a global resolution of 1 °x1.25°. Using GEOS- Chem, we first examine how a changes in NO x emissions changes the NO 2 columns. We take advantage of the most recent emission statistics for 2006 and the most historical year (2003), overlapping with SCIAMACHY observations, implemented in the GEOS-Chem model. Regional inventories for these years are available for North America, Europe, and East Asia that dominate total NO x emissions. We evaluate our approach by comparing the bottom-up and hindcast emissions for Below we summarize our method, demonstrate how the 2006 inventory hindcasted to 2003 using SCIAMACHY observations compares with the bottom-up NO x inventory for 2003, and then proceed to forecast emissions for igac_inventory_prediction_potrait.ppt presented at 2010 IGAC-ICACGP Joint Conference, Halifax, Canada. This work was supported by NASA’s Atmospheric Composition Program and by Environment Canada. Bottom-up NO x Emission Inventory Spatial distribution of bottom-up anthropogenic NO x emissions at 1 ° x1.25 ° for 2003 (top) and 2006 (middle). The bottom-panel shows the difference between anthropogenic emissions for 2006 minus those for Global anthropogenic NO x emissions increase by 5.2% from 22.9 Tg N Y -1 in 2003 to 24.1 Tg N Y -1 in 2006, with global growth partially counteracted by the reduction in North America and Europe. East Asian emissions increase by 25% over the three years. The changes in anthropogenic emissions in Africa, South America, and Oceania are minor contributor (<10 10 atoms N cm -2 s -1, <0.1Tg N). Inventory Hindcast and Forecast Using SCIAMACHY Data Annual anthropogenic NO x emissions. The top panel shows the bottom-up inventory for the year Presented in the middle and bottom panel are the inventories predicted from SCIAMACHY observations for the years 2003 and 2009, respectively. The spatial distribution of bottom-up and predicted inventories for 2003 are highly consistent (r=0.87, N=2464). The predicted inventory (17.7 Tg N Y -1 ) is 3% lower than the bottom-up (18.3 Tg N Y -1 ). The two inventories exhibit larger regional differences of 11% over North America and 14% over OECD Europe, within the uncertainty in the bottom-up emissions of 25% over these regions. Response of NO 2 Columns to NO x Emissions We use the GEOS-Chem model to examine the relationship between tropospheric NO 2 columns and surface NO x emissions. Two simulations, one with NO x emissions (E) for the year 2006 and another with anthropogenic NO x emissions perturbed by 15% (E’), are performed to calculate the sensitivity of changes in NO 2 columns to changes in NO x emissions: Ω and Ω’ are the simulated tropospheric NO 2 columns with emissions E and E’, respectively. β is a unitless trend factor that describes how a change in NO x emissions changes the NO 2 columns. β reflects the feedback of NO x emissions on NO x chemistry and is affected by transport of NO x between grid cells. Annual average value of β calculated with GEOS- Chem. White areas indicate where anthropogenic sources contribute <50% of total NO x emissions and tropospheric NO 2 columns are <1x10 15 molec cm -2. The global mean value of β is close to unity (0.99), indicating a near direct relation between NO x emissions and NO 2 columns. β tends to be greater than one in remote regions where an increase in NO x emissions decreases the NO x lifetime. In polluted regions, β tends to be less than one since an increase in NO x consumes OH and increases the NO x lifetime. Changes in anthropogenic emissions for 2006 minus 2003 (top) and 2009 minus 2006 (bottom) inferred from SCIAMACHY observations. The top- down emission changes are broadly consistent with the changes in the bottom-up inventory. The hindcast inventory exhibits stronger emissions growth and larger heterogeneity in spatial distribution. The predicted NO x emissions are in close agreement with the bottom-up inventory in East Asia, where predicted and bottom-up inventories increase by 21% and 22%, respectively. The inventory forecast for 2009 is larger than the 2006 inventory by 9.1% globally and by 21% in East Asia, in contrast with an 11% decrease in North America. Overview We use β to translate the changes in tropospheric NO 2 columns from satellite to the changes in NO x emissions each year, which is then combined with available bottom-up NO x emissions E i for the year i to predict emissions E j for the year j: We partition the top-down NO x emissions according to the distribution of the bottom-up to derive the anthropogenic component of the predicted emissions.