Rapid refreshing of anthropogenic NOx emissions through assimilating fused ground and satellite observations to support NOAA National Air Quality Forecast Capability

The time lag inherent in emission inventory updates is a bottleneck for NOAA National Air Quality Forecast Capability (NAQFC) to improve the accuracy of operational air quality forecasts. A recent assessment of the NAQFC emissions against satellite and ground observations revealed that the emission updates have not captured the gradual progression of the emission reduction in large cities. To reduce the time lag of emission updates, this study presents a new approach, called emission data assimilation, to rapidly update base emission inventories with fused ground and satellite observations. To test the effectiveness of this approach, it has been applied to predict the air quality effect of the 2008 Great Recession on air quality in the United States. The 2008 Great Recession, triggered by the bursting of housing bubble and aggregated by the subprime financial crisis, is one of the worst economic recessions since the Great Depression. Both satellite and ground observations have shown large variability in nitrogen oxides (NOx) emissions during the recession. Yet, the impact of the recession on air quality has not been well quantified. Using a regional chemical transport model CMAQ driven by assimilated NOx emissions, this study compares the changes in surface ozone concentration in response to NOx emission changes from 2005 to 2011 under two scenarios: no recession and recession. In the no recession case, the NOx emission reduction rate from the US EPA Cross-State Air Pollution Rule (CSAPR), which projects emission based on expected emission control regulations, is used to adjust the NOx emission inventories based on the observed NO2 changes prior to the recession (2005-2006). In the recession case, the actual NO2 trends observed from the EPA AQS monitors and NASA Aura OMI sensor are used to obtain realistic changes in the NOx emissions. Evaluation of the NAQFC simulation with ground and aircraft measurements shows that the model run with the assimilated emissions has captured the temporal spatial and variability in surface ozone concentration with reasonable accuracy.