|The manuscript was majorly revised and improved. Detailed analysis in the manuscript and supporting information would be valuable for the science community in this field. However, I would like to recommend authors to rewords abstract and main text to reflect what is in the manuscript considering uncertainties in the data and analysis. Main concerns are addressed below.|
I would like to ask the authors to inform uncertainties in mixing heights retrieved from lidar during nighttime (or stable condition). The mixing height determined by aerosol backscatter may not be a direct indicator for stable boundary layer height, but the residual layer of aerosols. Compton et al. (2013) evaluated the lidar mixing height observed only during daytime. Because ELF data are not a reliable stable boundary layer height, the updates in this manuscript should be regarded as a sensitivity test, not a correction. In this regard, abstract and main text need to be reworded carefully. More information on the location and characteristics (number of data and uncertainty) of ELF observations would be helpful. Note that nocturnal boundary layer height from original YSU scheme is within the range of boundary layer height measured and modeled (Steeneveld et al., 2007; Koracin and Berkowics, 1988; Nieuwstadt and Tennekes, 1981). In the abstract, “However, nighttime mixing in the model needs to be enhanced to reproduce the observed NO2 diurnal cycle in the model”. Based on the comments above, I think this should be rephrased. Furthermore, uncertainties in the NOx emissions in nighttime were not well estimated or understood. This part needs to be mentioned.
Nighttime biases in NO2 and NOy at the surface were much reduced when the updated YSU Kzz was used. However, column NO2 concentration in Figure 10 during nighttime are much larger than those from PANDORA. It is possible that the PANDORA observations are underestimated in the morning and late afternoon, but it is also possible that the model columns are overestimated due to the emission uncertainty and this problem could not be fixed with the updated Kzz. Figure S2 exhibits dynamic changes in PANDORA NO2 columns during daytime and the model well reproduced these changes except late afternoon to nighttime (Figure S23). In the abstract, “Another discrepancy is that Pandora measured NO2 TVCDs show much less variation in the late afternoon than simulated in the model”. Can it be the case that the model columns vary too much?
In Figure 14, the authors indicated that the purple circle denote a small region surrounded by high-NOx emission pixels and with high NO2 VCDs in the 4-km REAM but low NO2 VCDs in ACAM. But Figure S25 shows enhanced columns in the purple circle region in ACAM (purple circle not shown in the figure). The purple area is on the edge of land and is filtered out in Figure S24 and S26 (potentially due to clouds). Is it possible that undersampling issues in this area highlight the differences in spatial distributions in Figure 14? R square values in Figure S24-S26 are quite reasonable, considering that it is comparisons at fine-resolution. It is not convincing that the results in the manuscript suggest spatial allocation problems in NEI as written in the abstract.
Compton, J. C., Delgado, R., Berkoff, T. A., and Hoff, R. M.: Determination of planetary boundary layer height on short spatial and temporal scales: A demonstration of the covariance wavelet transform in ground-based wind profiler and lidar measurements, Journal of Atmospheric and Oceanic Technology, 30, 1566-1575, https://doi.org/10.1175/JTECH-D-12-00116.1, 2013.
Steeneveld et al. (2007), Diagnostic equations for the stable boundary layer height: evaluation and dimensional analysis, Journal of Applied Meteorology and Climatology, 46, 212-225.
Koracin and Berkowics (1988), Nocturnal boundary-layer height: observations by acoustic sounders and predictions in terms of surface-layer parameters, Boundary-Layer Meteorology, 43, 65-83.
Nieuwstadt and Tennekes (1981), A rate equation for the nocturnal boundary-layer height, Journal of the Atmospheric Sciences, 38, 1418-1428.