In this study, the author attempted to sequentially incorporate several potential HONO sources and processes into the CMAQ modeling framework. And the simulation performances of the modified CMAQ models were then evaluated by comparing the modeled HONO mixing ratios with the HONO mixing ratios observed at the Olympic Park station in Seoul, South Korea. The simulation results have been improved than the original CMAQ model. However, there are several issues in the article.

1. In Lines 179-180, the average values of simulation results in Table S2 are not sufficient to confirm the good prediction of the model, and the comparisons of time series of observation and modeled outputs are needed.
2. In table 1, the emission factor of gasoline and diesel vehicles are 0.8% and 2.3% in all studies areas. However, there are significant differences in traffic volumes and vehicle types in different areas.
3. In lines 205-207, is the equation for the relationship between J_NPHEand J_NO2 also in this reference (Stockwell et al., 1990)? And how J_HONO is calculated?
4. In table 3, how HONO emission rates of traffic calculated?
5. In lines 276-277, why are the uptake coefficients of NO₂at nighttime and daytime are 8.0×10^-6 and 1.3×10^-4, respectively? Also how is the 900 for this factor taken into account? The same issue in Lines 292-293.
6. In Line 412, is there much improvement in model results if NO₂daytime sources are enhanced?
7. In Line 447, “Its contribution increases to 4.2% during the daytime”,which source is this contribution?

See attached. Thank you.