|Vernier et al. evaluated aerosol data collected on balloons launched into the Asian tropopause region during flight intensive flights (and one test flight). The authors generally have done a good job addressing many of the concerns raised by both reviewers, improving the paper. However, there are still some comments, as listed below, the authors should address before the paper should be accepted to ACP.|
1) Page 2, Line 15 - 16: Please rephrase to "since NAT has already been observed in the tropical upper tropopsphere and lower stratosphere in other studies."
2) Page 7, Line 17: remove the m in prepared
3) Page 8, Line 6 - 7: Please rephrase to "two flights samples collected during the summer 2017 campaign (ZF2, 15th Aug. and ZF3, 21st Aug.), in comparison"
4) Pag 9, Line 21 - 23: Please rephrase to "The derived particulate depolarization ratio from CALIOP level 2v4.1 within the layer was 0.47+/-0.06 (Fig. S3) and was associated with an optical depth of 0.03+/-0.02, indicating the presence of a subvisible cirrus cloud."
5) Section 4.1. I am slightly confused by the reasoning here that HNO3 is transported into the UTLS instead of being locally produced. E.g., Bela et al. (2016) found nearly 90% scavenging efficiency for HNO3 in convection. Reconciliation of this high scavenging efficiency needs to be addressed.
6) Page 10, lines 5 - 6: It is unclear what "buffering process results in nitrate naturalization" means.
7) Page 10, line 16 - 17: Please correct the capitalization of In after However
8) In all new text and throughout paper, please check the subscript of numbers and letters after chemical formulas (e.g., HNO2, NO2, NO3, NOx, etc.).
9) Addition of Sect. 5 is greatly appreciated; however, there are still some questions concerning it:
9a) As authors stated, K+ is signature for biomass burning. Why is no K+ observed?
9b) NOx is normally emitted at high concentrations with biomass burning. Why is there no nitrite and nitrate?
9c) Also, it's surprising that SO4 is so high in this plume, when it has generally been observed that SO4 is a minor component of biomass burning aerosol. Why do the authors think SO4 is the major anion?
10) Page 13, Line 1, please correct (1989 to (1989)
11) Page 13, Line 7: It is unclear what the authors mean that HNO2 undergoes rapid reduction. One of the challenges in measuring gas-phase HNO2, beyond wall loss as the authors note, is it's short lifetime due to photolysis, meaning it generally is at very low concentrations away from point sources. Please clarify.
12) Page 13, line 15 - 16: It is unclear why the authors mention nitrification. Are they suggesting that nitrification in the soils produces enough HNO2 to be observed in the UTLS or that nitrification is occurring in the UTLS?
13) Page 13, Line 24 - 29 and Page 14, Line 1 - 27: This should be in the methods section.
14) Page 15, Line 4 - 5: From the figure, it is unclear that BC is increasing. Instead, it appears BC has decreased in the region of the balloon launches. Please clarify.
15) Fig. 7, it would be beneficial to include a vertical bar for the flights
16) Page 15, Line 6: correct first
17) RC1.3 response. ISORROPIA has been evaluated extensively with in-situ nitrate observations, e.g., Guo et al., 2016, Guo et al., 2017, and Ibikunle et al., 2020, to name a few.
Bela et al., Wet scavenging of soluble gases in DC3 deep convective storms using WRF-Chem simulations and aircraft observations, JGR, 2016.
Guo et al., Fine particle pH and the partitioning of nitric acid during winter in the northeastern United States, JGR, 2016.
Guo et al., Fine particle pH and gas-particle phase partitioning of inorganic species in Pasadena, California, during the 2010 CalNex campaign, ACP, 2017.
Ibikunle et al., Fine particle pH and sensitivity to NH3 and HNO3 over summertime South Korea during KORUs-AQ, ACPD, 2020.