Please see uploaded file.

The authors simulated a fog event with high aerosol loading over the Indo Gangetic Plains of India, and estimated the role of atmospheric aerosols in severe winter fog through aerosol-radiation interaction and aqueous phase chemistry. Overall, this is well-executed study and the topic is very interesting. The authors made great efforts in model evaluation and sensitivity simulation. However, several conclusions in the main text should be further explained and the presentation quality can be improved. I suggest a major revision before it can be accepted.

Major comments:

I am very curious about if the fog event is due to radiation or advection. If this is a radiation fog, then the role of AR feedback could be a major reason. However, if this is an advection fog, the authors may need to pay attention on wind changes.

Simulated PM2.5. In L363, the authors mentioned that the observed high PM2.5 can be predicted by model but not for PM2.5 composition (Fig.7). I am very confused about this. The model strongly underestimated observed inorganic PM2.5 composition on 24^th Dec; then why was total PM2.5 mass concentration well simulated?   

Decreased PM2.5 in CIGP due to AR feedback. The authors mentioned this issue in L427-436 but didn’t explain the reason clearly. How about the changes in winds due to AR, which may be a reason.

High particulate Cl. The model can’t reproduce the observed high Cl that could come from trash-burning and industrial emissions. I am wondering if trash-burning emissions from Chaudhary et al. (2021) can represent Cl emissions at a city scale.

Fog duration. In Fig.15, I find the results from three simulations are quite similar and I suggest the authors to clearly identify their difference.

Minor comments:

L18-20: the model tends to strongly underestimate observed PM2.5.

L33: “These processes” refers to aerosol-radiation interaction and aqueous phase chemistry? The latter can’t change PBL meteorology.

L42: “NOx” refers to emission or concentration?

L47&L55: duplication for NAAQS

L123-125: I suggest to move this description to Section 2.2 Observations

L183: please rephrase “aromatic compounds HONO”

L270-272: again, this information should be given in the Observations part if not.

L300: in Fig.2, I find most of the correlation coefficient (r) for RH is below 0.87. so I am not convinced by the “r2>0.75”.

L308: please change “are” to “is”.

L351-352: I suggest the authors to show the correlation coefficient using daily data to justify this argument.

Section4: It looks the authors failed to discuss about the uncertainties in chemistry scheme used in the model, which is also an importance source of model biases.

L532: In fact, the model can’t reproduce the observed aerosol composition. The following discussions on previous studies couldn’t be helpful.