|In general the authors have satisfactorily addressed reviewer comments. I recommend that the authors consider the below comments and also recommend that the authors review the manuscript in careful detail to ensure that the manuscript uses accurate and precise language on specific details (E.g., along the lines as described in the paragraph below for the Introductory paragraph) |
The first paragraph of the introduction should be edited for clarity and accuracy. 1) NO reaction with HO2 or RO2 does not “accelerate” O3 production, it is the only major known reacting leading to net production of NO2 and subsequently O3 in the troposphere. 2) lightning NOx is not biogenic, but geogenic. 3) NOx does not ‘transform’ in to HNO3, but rather NO2 reacts with OH or N2O5 reacts in aqueous solution to form HNO3.
The authors indicated in their response that there was no NOy simulation results archived (comment for P10L32), for the purpose of analyzing NOx lifetime in the simulation, but they added a comparison of model output to NOy observations in the revised manuscript. Please, consider a comparison of NOx:NOy in model as well as has been shown for NOx:NOy in observations.
P13 L19 – L30 of annotated revised manuscript: The discussion of NO2 lifetime should edited for clarity before publication. To be an accurate means of inverting NOx emissions in the EMG method, the effective lifetime derived from NO2 column measurements must be directly, physically related to the PBL NOx lifetime (The EMG method accounts for background NO2 and NO2:NOx ratio). I.e., PBL NOx MASS = NOX EMISSIONS * NOX PHOTOCHEMICAL LIFETIME. I understand that any error in wind direction results in the inference of a biased NOx lifetime value, but that doesn’t mean that the gradient has no bearing on the rate at which NOx is being removed from the boundary layer. The question instead should be “what factors affect the spatial pattern of NO2 column downwind of a city that should be accounted for when estimating the NOx photochemical lifetime. The authors should also note here that there are oscillating thermally-driven wind flows in the basin that are challenging to resolve and may also lead to biased lifetime calculation. In the current version of the manuscript, these effects are only discussed in the conclusions section (P15 L16-25 of annotated revised manuscript). I would also disagree with the authors: there would be systematic impacts of local circulations on the spatial pattern of NO2 columns that would not necessarily be captured in the larger scale synoptic flow patterns. During night, air would flow downslope and out over the Yellow Sea. During daytime, the flow would reverse to the E. In general, the large scale flows during this time of year would be northwesterly. I don’t expect the authors to fully account for these but to acknowledge that they may exist.
P13 L19 – L30: “It should be noted that the NO2 photochemical lifetime derived here is a fundamentally different quantity than the NO2 lifetime observed by in situ measurements (de Foy et al., 2014; Lu et al., 2015) or derived by model simulations 20 (Lamsal et al., 2010). This is because the lifetime calculation is extremely sensitive to the accuracy of the wind direction (de Foy et al., 2014). Inaccuracies in the wind fields introduce noise that shorten the tail of the fit. As a result, NO2 photochemical lifetimes derived here are considered “effective” photochemical lifetimes and are universally shorter than the tropospheric column NO2 lifetimes derived by model simulations (Lamsal et al., 2010). NOx sources at the outer portions of urban areas will lead to an artificially longer NO2 lifetime. This partially 25 compensates for the bias introduced by the wind direction. The effective photochemical lifetime is also different from the NO2 lifetime derived by in situ measurements of NO2 at the surface or within the boundary layer. In the boundary layer, NO2 is consumed faster yielding lifetimes that are shorter than the lifetimes based on tropospheric columns (Nunnermacker et al., 2007).”