Interactive comment on “ Detection in the summer polar stratosphere of air plume pollution from East Asia and North America by balloon-borne in situ CO measurements ” by G . Krysztofiak

Introduction Conclusions References


General/major comments:
(1) My first concern about the presented study is that while it explores different sources of the observed pollution event in the lowermost stratosphere using comprehensive tools, it fails at pinpointing down the quantitative information on the source regions in a conclusive way.It is for example interesting to use masked regions to infer the contributions of a certain region, however, this method seems insofar flawed to me that the total of the individual contributions from the different regions exceed the value derived in the whole-world simulation.I know that you point out a problem in the use of REPROBUS, but you need to guide the reader in the conclusion section as well and in a better way on how much we can learn from your results, what are the relative contributions of the different pollution sources, and what uncertainty these numbers are associated with.At present, the conclusions are not very contenting since it seems to highlight the role of the jet-stream as major pathway of pollutant transport between the continents, a result well known from many earlier studies.
(2) Another concern I have is about the particular use of the CO-O3 correlation tool to argue that August 7 represents a special event.I suspect that the comparison to August 24 looks so extraordinary mostly due to the fact that the latter profile is cut off well above the tropopause or in other words that the profile had been sampled in a very strong stratospheric intrusion event, in which the relations between the tropopause and potential temperature are highly different.Tracer-tracer correlations cannot be used to argue for mixing events without discussing the position of the tropopause.You further extrapolate some to me rather arbitrary mixing lines between a theoretical L-shaped correlation expected in an atmosphere without any mixing, a mid-latitudinal and a polar reference point taken from mid-latitudinal observations and your measurements, respectively.This to me is not a scientifically sound method, since there is no argument for using the data point of stratospheric background value you have chosen.You basically could use any point on the stratospheric branch to draw your mixing lines in any way to fit your data points.We know that the chemical transition region between the troposphere and the stratosphere is dependent on latitude and if you instead compare your results to Figure 7 of Hegglin et al. (2009), you'll see that your balloon measurements do not show any unexpected values, but nicely fall in between the envelope for the NH summer polar CO-O3 correlation provided by the satellite measurements (e.g., CO values around 70 ppbv at about 300 ppbv O3).This is not to say that we are not interested in the origin of the air masses that lead to this observed mixing layer, rather the contrary, but that the motivation of and approach taken in this discussion section in particular needs to be cleaned up.

Minor and technical comments:
(1) Introduction, P15506 L5: The SPURT campaign (Engel et al., 2006) has been sampling the polar lowermost stratosphere in all seasons.Please add a reference to these results.
(2) Introduction, P15506 L20 onward: You write about chemistry and lifetimes in the troposphere, however, you study pollutant transport into the lowermost stratosphere where CO lifetimes are somewhat longer and ozone chemistry is expected to be different from that in the troposphere.Here ozone chemistry is dependent on season (Hegglin et al., 2006).Increased CO (and NOx) levels lead to ozone production mainly during spring and summer and depend on background ozone values.
(3) The interpretation of the elevated CO values in L2 is rather minimal.Could it be that due to the drift in longitude-latitude along the balloon is experiencing during its travel, it is getting into a region of lower PV again?I suggest to plot both PV (interpolated onto the balloon pathway) and/or the distance to the dynamical (2 PVU) tropopause into Figure 2.
(4) I don't understand how you derive the tropopause in your study shown in Figure C5691 2. The 'cold point' tropopause (as you call it and I would understand the term) is used in the tropics, in the extratropics either the thermal tropopause (WMO, 1957) or the dynamical tropopause (WMO, 1987) are used.In tropopause folds, the dynamical PV is often more meaningful.Please add the PV tropopause and explain in more detail how you derive the tropopause you use.
(5) Figure 1: please consider putting a black thin contour around the SWIR data points.It is very hard to distinguish the circles from the squares.(6) Figure 2: It would be helpful for the interpretation of the profiles to add PV vertical profiles to this plot and extend the tracer profiles to the ground if available.
(7) Figure 3: It would be helpful to overplot the position of the latitude-longitude box shown in Figure 1 onto the PV maps, in order to obtain a better picture of whether the strong gradient seen in the IASI CO observations on the 24 August coincides with the strong PV gradient at the edge of the streamer.
(8) Figure 5, caption.As mentioned in the major comments, I think it is not correct to draw the mixing line the way it is done here.Point (1) on the stratospheric branch is chosen in a rather arbitrary way.
(9) Does REPROBUS not allow for tagging the origin of air parcels?This would yield a less ambiguous quantification of the sources.