Abstract. To evaluate the accuracy of bottom-up NOx emissions in East Asia, CMAQ-calculated NO2 columns were compared with OMI-retrieved NO2 columns. For a direct comparison between the two NO2 columns, the averaging kernels (AKs) retrieved from the Royal Netherlands Meteorological Institute (KNMI) algorithm were applied to the CMAQ model simulations. When the two NO2 columns before and after the applications of AKs were compared over East Asia, it was found that, for example, the normalized mean errors (NMEs) between the CMAQ-estimated and OMI-retrieved NO2 columns were reduced significantly, from ∼103% to ∼46%, from ∼112% to ∼ 45%, and from ∼135% to ∼40% during spring, fall, and winter, respectively. Also, the two tropospheric NO2 columns were better correlated spatially in East Asia (R = 0.71–0.94) after the application of the AKs. From this study, it was found that the NOx emissions used were, on annual average, ∼28% underestimated in East Asia, although some overestimates were also found, partly over southern Central East China, the Sichuan Basin, and South Korea regions during the winter. However, these results can also be influenced by several uncertainty factors in the CMAQ model simulations, such as monthly variation and the strength of the NOx emissions. Thus, we also applied different monthly variation and different strengths of the NOx emissions to the CMAQ model simulations over East Asia. The results showed strong impacts on the tropospheric NO2 columns in East Asia, indicating that these two factors are also important. Further sensitivity analysis was conducted with reaction probabilities of N2O5 onto atmospheric aerosols. Those results are also discussed in detail in this manuscript. Although several uncertainty factors are discussed, it was concluded that the consideration of the AKs is the single most important factor in investigating the accuracy of bottom-up NOx emissions generally being used in CTM simulations.
A sub-decadal trend of diacids in atmospheric aerosols in East Asia