A top-down assessment using OMI NO 2 suggests an underestimate in the NO x emissions inventory in Seoul, South Korea, during KORUS-AQ

Goldberg, Daniel L.; Saide, Pablo E.; Lamsal, Lok N.; de Foy, Benjamin; Lu, Zifeng; Woo, Jung-Hun; Kim, Younha; Kim, Jinseok; Gao, Meng; Carmichael, Gregory; Streets, David G.

In this work, we investigate the inline-formulaNOx emissions inventory in Seoul, South Korea, using a regional ozone monitoring instrument (OMI) inline-formulaNO2 product derived from the standard NASA product. We first develop a regional OMI inline-formulaNO2 product by recalculating the air mass factors using a high-resolution (4 km inline-formula× 4 km) WRF-Chem model simulation, which better captures the inline-formulaNO2 profile shapes in urban regions. We then apply a model-derived spatial averaging kernel to further downscale the retrieval and account for the subpixel variability. These two modifications yield OMI inline-formulaNO2 values in the regional product that are 1.37 times larger in the Seoul metropolitan region and inline-formula>2 times larger near substantial point sources. These two modifications also yield an OMI inline-formulaNO2 product that is in better agreement with the Pandora inline-formulaNO2 spectrometer measurements acquired during the South Korea–United States Air Quality (KORUS-AQ) field campaign. inline-formulaNOx emissions are then derived for the Seoul metropolitan area during the KORUS-AQ field campaign using a top-down approach with the standard and regional NASA OMI inline-formulaNO2 products. We first apply the top-down approach to a model simulation to ensure that the method is appropriate: the WRF-Chem simulation utilizing the bottom-up emissions inventory yields a inline-formulaNOx emissions rate of inline-formula227±94 kt yrinline-formula−1, while the bottom-up inventory itself within a 40 km radius of Seoul yields a inline-formulaNOx emissions rate of 198 kt yrinline-formula−1. Using the top-down approach on the regional OMI inline-formulaNO2 product, we derive the inline-formulaNOx emissions rate from Seoul to be inline-formula484±201 kt yrinline-formula−1, and a inline-formula353±146 kt yrinline-formula−1inline-formulaNOx emissions rate using the standard NASA OMI inline-formulaNO2 product. This suggests an underestimate of 53 % and 36 % in the bottom-up inventory using the regional and standard NASA OMI inline-formulaNO2 products respectively. To supplement this finding, we compare the inline-formulaNO2 and inline-formulaNOy simulated by WRF-Chem to observations of the same quantity acquired by aircraft and find a model underestimate. When inline-formulaNOx emissions in the WRF-Chem model are increased by a factor of 2.13 in the Seoul metropolitan area, there is better agreement with KORUS-AQ aircraft observations and the recalculated OMI inline-formulaNO2 tropospheric columns. Finally, we show that by using a WRF-Chem simulation with an updated emissions inventory to recalculate the air mass factor (AMF), there are small differences (inline-formula∼8 %) in OMI inline-formulaNO2 compared to using the original WRF-Chem simulation to derive the AMF. This suggests that changes in model resolution have a larger effect on the AMFpage1802 calculation than modifications to the South Korean emissions inventory. Although the current work is focused on South Korea using OMI, the methodology developed in this work can be applied to other world regions using TROPOMI and future satellite datasets (e.g., GEMS and TEMPO) to produce high-quality region-specific top-down inline-formulaNOx emissions estimates.



Goldberg, Daniel L. / Saide, Pablo E. / Lamsal, Lok N. / et al: A top-down assessment using OMI NO2 suggests an underestimate in the NOx emissions inventory in Seoul, South Korea, during KORUS-AQ. 2019. Copernicus Publications.


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