Changes in nitrogen oxides emissions in California during 2005–2010 indicated from top‐down and bottom‐up emission estimates

Abstract

In California, emission control strategies have been implemented to reduce air pollutants. Here we estimate the changes in nitrogen oxides (NO x = NO + NO 2 ) emissions in 2005-2010 using a state-of-the-art four-dimensional variational approach. We separately and jointly assimilate surface NO 2 concentrations and tropospheric NO 2 columns observed by Ozone Monitoring Instrument (OMI) into the regional-scale Sulfur Transport and dEposition Model (STEM) chemical transport model on a 12 × 12 km 2 horizontal resolution grid in May 2010. The assimilation generates grid-scale top-down emission estimates, and the updated chemistry fields are evaluated with independent aircraft measurements during the NOAA California Nexus (CalNex) field experiment. The emission estimates constrained only by NO 2 columns, only by surface NO 2 , and by both indicate statewide reductions of 26%, 29%, and 30% from~0.3 Tg N/yr in the base year of 2005, respectively. The spatial distributions of the emission changes differ in these cases, which can be attributed to many factors including the differences in the observation sampling strategies and their uncertainties, as well as those in the sensitivities of column and surface NO 2 with respect to NO x emissions. The updates in California's NO x emissions reduced the mean error in modeled surface ozone in the Western U.S., even though the uncertainties in some urban areas increased due to their NO x -saturated chemical regime. The statewide reductions in NO x emissions indicated from our observationally constrained emission estimates are also reflected in several independently developed inventories:~30% in the California Air Resources Board bottom-up inventory,~4% in the 2008 National Emission Inventory, and~20% in the annual mean top-down estimates by Lamsal et al. using the global Goddard Earth Observing System (GEOS)-Chem model and OMI NO 2 columns. Despite the grid-scale differences among all top-down and bottom-up inventories, they all indicate stronger emission reductions in the urban regions. This study shows the potential of using space-/ground-based monitoring data and advanced data assimilation approach to timely and independently update NO x emission estimates on a monthly scale and at a fine grid resolution. The well-evaluated results here suggest that these approaches can be applied more broadly.

Improved western U.S. background ozone estimates via constraining nonlocal and local source contributions using Aura TES and OMI observations

“…These reductions are stronger than the Central Valley urban regions such as Fresno (FS 36.7°N, 119.75°W; À14.6%). These reductions can be partially due to the effective emission controlling strategies and the recent Russell et al, 2010Russell et al, , 2012Huang et al, 2014]. A possible additional reason is that the NEI 05 NO x emission estimates have spatially and temporally varying uncertainties for the base year of 2005; e.g., Lamsal et al [2014] showed that in 2005, the U.S. NO x emissions in NEI 05 was higher than their OMI-constrained emission estimate during summertime but is opposite for springtime.…”

“…The development and improvement in regional-scale assimilation capability should be strongly encouraged. Efforts could be made to increase the number of models that have the regional 4D-Var assimilation capability, to better understand the factors affecting the assimilation results in order to improve the similar assimilation methods, and to explore the alternative methods (e.g., see related discussions in Singh et al [2011b], Chai et al [2009], and Huang et al [2014]).…”

Revealing important nocturnal and day‐to‐day variations in fire smoke emissions through a multiplatform inversion

“…While some of these approaches have assimilated data exclusively from satellite retrievals of gases [Pfister et al, 2005;Arellano et al, 2006;Kopacz et al, 2010], aerosols [Zhang et al, 2005;Petrenko et al, 2012;Huneeus et al, 2012Huneeus et al, , 2013Zhang et al, 2014], or both [Konovalov et al, 2014], others have used ground-based measurements [Cohen and Wang, 2014;Mao et al, 2014aMao et al, , 2014bHakami et al, 2005]. Although examples of multiplatform inversions for other sources exist [e.g., Huang et al, 2014], there is a growing need for a detailed estimation of wildfire smoke emissions by using multiple observational data sets at high spatial and temporal resolutions [Hyer et al, 2011], as constraints based on single-species measurements are often inconsistent within each other. Key Points:…”

Impact of Aerosols From Urban and Shipping Emission Sources on Terrestrial Carbon Uptake and Evapotranspiration: A Case Study in East Asia

“…For example, satellite nitrogen dioxide (NO 2 ) columns have been used to constrain urban and shipping emissions of nitrogen oxides (NO x ; e.g., Huang et al, 2014;Vinken et al, 2014;Lu et al, 2015;Ding et al, 2018;Goldberg et al, 2019), namely, NO 2 and nitric oxide (NO), which are important contributors to secondary aerosol production in East Asian populated regions during warm seasons (e.g., Dong et al, 2014;Ge et al, 2013). However, satellite-observation-constrained emission estimates may be associated with variable levels of uncertainty depending on the emission inverse modeling approaches and the characteristics of the integrated satellite observations (e.g., Ding et al, 2017;Huang et al, 2014;Qu et al, 2019). It is therefore necessary to carefully evaluate the available satellite-observation-derived emissions, as well as their impacts on atmospheric conditions and atmosphere-biosphere interactions, for example, using stateof-the-art models and high-accuracy observations.…”