An accurate description of emissions is crucial for model simulations to reproduce and interpret observed phenomena over extended time periods. In this study, we used an approach based on activity data to develop a consistent series of spatially resolved emissions in the United States from 1990 to 2010. The state-level anthropogenic emissions of SO₂, NO_x, CO, NMVOC (non-methane volatile organic compounds), NH₃, PM₁₀ and PM_2.5 for a total of 49 sectors were estimated based on several long-term databases containing information about activities and emission controls. Activity data for energy-related stationary sources were derived from the State Energy Data System. Corresponding emission factors reflecting implemented emission controls were calculated back from the National Emissions Inventory (NEI) for seven years (i.e., 1990, 1995, 1996, 1999, 2001, 2002 and 2005), and constrained by the AP-42 (US EPA's Compilation of Air Pollutant Emissions Factors) dataset. Activity data for mobile sources including different types of highway vehicles and non-highway equipment were obtained from highway statistics reported by the Federal Highway Administration. The trends in emission factors for highway mobile source were informed by the 2011 National Transportation Statistics. Emissions for all non-energy-related sources were either scaled by the growth ratio of activity indicators or adjusted based on the NEI trends report.

Because of the strengthened control efforts, particularly for the power sector and mobile sources, emissions of all pollutants except NH₃ were reduced by half over the last two decades. The emission trends developed in this study are comparable with the NEI trend report and EDGAR (Emissions Database for Global Atmospheric Research) data, but better constrained by trends in activity data. Reductions in SO₂, NO_x, CO and EC (speciation of PM_2.5 by SMOKE, Sparse Matrix Operator Kernel Emissions) emissions agree well with the observed changes in ambient SO₂, NO₂, CO and EC concentrations, suggesting that the various controls on emissions implemented over the last two decades are well represented in the emission inventories developed in this study. These inventories were processed by SMOKE and are now ready to be used for regional chemistry transport model simulations over the 1990–2010 period

Abstract.Trends in air quality across the Northern Hemisphere over a 21-year period were simulated using the Community Multiscale Air Quality (CMAQ) multiscale chemical transport model driven by meteorology from Weather Research and Forecasting (WRF) simulations and internally consistent historical emission inventories obtained from EDGAR. Thorough comparison with several ground observation networks mostly over Europe and North America was conducted to evaluate the model performance as well as the ability of CMAQ to reproduce the observed trends in air quality over the past 2 decades in three regions: eastern China, the continental United States and Europe.The model successfully reproduced the observed decreasing trends in SO 2 , NO 2 , 8 h O 3 maxima, SO 2− 4 and elemental carbon (EC) in the US and Europe. However, the model fails to reproduce the decreasing trends in NO − 3 in the US, potentially pointing to uncertainties of NH 3 emissions. The model failed to capture the 6-year trends of SO 2 and NO 2 in CN-API (China -Air Pollution Index) from 2005 to 2010, but reproduced the observed pattern of O 3 trends shown in three World Data Centre for Greenhouse Gases (WDCGG) sites over eastern Asia. Due to the coarse spatial resolution employed in these calculations, predicted SO 2 and NO 2 concentrations are underestimated relative to all urban networks, i.e., US-AQS (US -Air Quality System; normalized mean bias (NMB) = −38 % and −48 %), EU-AIRBASE (European Air quality data Base; NMB = −18 and −54 %) and CN-API (NMB = −36 and −68 %). Conversely, at the rural network EU-EMEP (European Monitoring and Evaluation Programme), SO 2 is overestimated (NMB from 4 to 150 %) while NO 2 is simulated well (NMB within ±15 %) in all seasons. Correlations between simulated and observed O 3 wintertime daily 8 h maxima (DM8) are poor compared to other seasons for all networks. Better correlation between simulated and observed SO 2− 4 was found compared to that for SO 2 . Underestimation of summer SO 2− 4 in the US may be associated with the uncertainty in precipitation and associated wet scavenging representation in the model. The model exhibits worse performance for NO − 3 predictions, particularly in summer, due to high uncertainties in the gas/particle partitioning of NO − 3 as well as seasonal variations of NH 3 emissions. There are high correlations (R > 0.5) between observed and simulated EC, although the model underestimates the EC concentration by 65 % due to the coarse grid resolution as well as uncertainties in the PM speciation profile associated with EC emissions.The almost linear response seen in the trajectory of modeled O 3 changes in eastern China over the past 2 decades suggests that control strategies that focus on combined control of NO x and volatile organic compound (VOC) emissions with a ratio of 0.46 may provide the most effective means for O 3 reductions for the region devoid of nonlinear response potentially associated with NO x or VOC limitation resulting from alternate strategies. The response of O 3 is ...

Abstract. Trends in air quality across the Northern Hemisphere over a 21 year period (1990–2010) were simulated using the CMAQ multiscale chemical transport model driven by meteorology from WRF simulations and internally consistent historical emission inventories obtained from EDGAR. Thorough comparison with several ground observation networks mostly over Europe and North America was conducted to evaluate the model performance as well as the ability of CMAQ to reproduce the observed trends in air quality over the past two decades in three regions: eastern China, the continental United States and Europe. The model successfully reproduced the observed decreasing trends in SO2, NO2, maxima 8 h O3, SO42− and EC in the US and Europe. However, the model fails to reproduce the decreasing trends in NO3− in the US, potentially pointing to uncertainties of NH3 emissions. The model failed to capture the 6 year trends of SO2 and NO2 in CN-API from 2005–2010, but reproduced the observed pattern of O3 trends shown in three WDCGG sites over eastern Asia. Due to the coarse spatial resolution employed in these calculations, predicted SO2 and NO2 concentrations are underestimated relative to all urban networks, i.e., US-AQS (NMB = −46 and −54%), EU-AIRBASE (NMB = −12 and −57%) and CN-API (NMB = −36 and −68%). Conversely, at the rural network EU-EMEP SO2 is overestimated (NMB from 4 to 150%) while NO2 is simulated well (NMB within ±15%) in all seasons. Correlations between simulated and observed winter time daily maxima 8 h (DM8) O3 are poor compared to other seasons for all networks. Better correlation between simulated and observed SO42− was found compared to that for SO2. Underestimation of summer SO42− in the US may be associated with the uncertainty in precipitation and associated wet scavenging representation in the model. The model exhibits worse performance for NO3− predictions, particularly in summer, due to high uncertainties in the gas/particle partitioning of NO3− as well as seasonal variations of NH3 emissions. There are high correlations (R > 0.5) between observed and simulated EC, although the model underestimates the EC concentration by 65% due to the coarse grid resolution as well as uncertainties in the PM speciation profile associated with EC emissions. The almost linear response seen in the trajectory of modeled O3 changes in the eastern China over the past two decades, suggests that control strategies that focus on combined control of NOx and VOC emissions with a ratio of 0.46 may provide the most effective means for O3 reductions for the region devoid of non-linear response potentially associated with NOx or VOC limitation resulting from alternate strategies. The response of O3 is more sensitive to changes in NOx emissions in the eastern US because the relative abundance of biogenic VOC emissions tends to reduce the effectiveness of VOC controls. Increasing NH3 levels offset the relative effectiveness of NOx controls in reducing the relative fraction of aerosol NO3− formed from declining NOx emissions in the eastern US, while the control effectiveness was assured by the simultaneous control of NH3 emission in Europe.