Dear Dr. Nie,

I sent the revised version of your manuscript to two experts (Referee #1 and Referee #3) for further review. Now I have received a report from Referee #3. Unfortunately, Referee #1 declined my invitation. In the first round of review, the major concerns from Referee #3 are about the calculation of OH concentration and the use of chemical reactions for OH production. I agree with the referee. Moreover, I think using simple parametrization of OH by J(O1D) does not fit and should be discouraged in this and other similar studies. Please see the attachment for my comments in detail. It would be very appreciated if these issues could be clarified before the acceptance of your manuscript.

Sincerely,

Jianzhong Ma

Dear Dr. Nie,

Many thanks for your revised manuscript and responses, which have removed most of my concerns.

As I understand now, Eq. (2) actually reflects the changes of [OH] with J(O1D) as well as other J_values, e.g., J(HONO), J(H2O2), J(HCHO), and J(NO2). Although J(O1D) is used as an index in the empirical model, this does not necessarily mean a dominant role of effective photolysis of O3 in the OH budget. As the experiments covered long periods, it is reasonable that the effects of UV variation with solar zenith angle and clouds on [OH] become more prominent compared to those of NOx and VOCs variations. Figure S1(d) provides the uncertainties in calculated P_unknown from this empirical approach, which is what I expected to see.

With regards to the term - kNO+OH[NO][OH] in Eq. (3), your argument seems not to be so convincing to me. This term stands for the HONO formation rate or the OH loss rate by NO, either of which should be accounted for P_OH(HONO) from a chemical dynamical point of view. Moreover, the reaction O3+OH is not considered in Eq. (4). To match the P_OH(O3) well, I would suggest that only the photolysis of HONO is considered in Eq. (3) while the second and third terms being removed. Correspondingly, the primary OH productions by photolysis of O3 and HONO be compared Figure 3, as done in previous studies (e.g., An et al., 2009).

Sincerely,

Jianzhong Ma


References

An, J. L., Zhang, W., and Qu, Y.: Impacts of a strong cold front on concentrations of HONO, HCHO, O3, and NO2 in the heavy traffic urban area of Beijing, Atmos. Environ., 43, 3454-3459, 10.1016/j.atmosenv.2009.04.052, 2009.