Investigation of NOx emissions and NOx-related chemistry in East Asia using CMAQ-predicted and GOME-derived NO2 columns
Authors: Han K. M. , Song C. H. , Ahn H. J. , Lee C. K. , Richter A. , Burrows J. P. , Kim J. Y. , Woo J. H. , Hong J. H. 
Published: April 2010

Abstract. This study examined the estimation accuracy of NOx emissions over East Asia with particular focus on North China and South Korea due to their strong source (North China)-receptor (South Korea) relationship. In order to determine contributions of North China emissions to South Korean air quality accurately, it is important to examine the accuracy of the emission inventories of both regions. In this study, NO2 columns from the US EPA Models-3/CMAQ model simulations carried out using the 2001 ACE-ASIA (Asia Pacific Regional Aerosol Characterization Experiment) emission inventory over East Asia were compared with the GOME-derived NO2 columns. There were large discrepancies between the CMAQ-predicted and GOME-derived NO2 columns in the fall and winter seasons. In particular, while the CMAQ-predicted NO2 columns produced larger values than the GOME-derived NO2 columns over South Korea (receptor region) for all four seasons, the CMAQ-predicted NO2 columns produced smaller values than the GOME-derived NO2 columns over North China (source region) for all seasons with the exception of summer. It is believed that there might be some estimation error in the NOx emissions as well as large uncertainty in NOx loss rates over North China and South Korea. Regarding the latter, this study further focused on the biogenic VOC emissions that were strongly coupled with NOx chemistry in East Asia. It was found that the rates of NOx loss determined by CMAQ modeling studies might be significantly low due to the possible overestimation of biogenic isoprene emissions during summer, particularly in China. In addition, due to the possible overestimation of isoprene emissions, the CMAQ-modeled NO2/NOx ratios might show an incorrectly high level, compared with the actual NO2/NOx ratios. In addition to the retarded NOx chemical loss rates and overestimated NO2/NOx ratios, the omission of soil NOx emissions over North China during summer can lead to an underestimation of NOx emissions over North China during summer. Overall, it is estimated that the NOx emissions in North China are underestimated possibly by ~50% over an entire year. In order to confirm the uncertainty in NOx emissions, the NOx emission over South Korea was further investigated using the ACE-ASIA inventory, REAS (Regional Emission inventory in ASia) and CAPSS (Clean Air Policy Support System) by NIER (National Institute of Environmental Research) in Korea. The NOx emissions from ACE-ASIA and the REAS inventories appear to be approximately 2 times larger for mega-cities in Korea than that from the CAPSS inventory. In contrast, the NOx emissions of ACE-ASIA and REAS inventories are only 10% smaller for North China than the recently-estimated "date-back" ANL (Argonne National Laboratory) inventory. A comparison between the CMAQ-predicted and GOME-derived NO2 columns indicated that both the ACE-ASIA and REAS inventories have some uncertainty in NOx emissions over North China (A) and South Korea (C), which can lead to some error in modeling the formation of ozone and secondary aerosols in South Korea and North China.