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Comments on manuscript egusphere-2024-2064: "Downward and upward revisions of Chinese emissions of black carbon and CO in bottom-up inventories are still required: an integrated analysis of WRF/CMAQ model and EMeRGe observations in East Asia in spring 2018” by Phuc Thi Minh Ha et al.

General remarks and questions

This preprint reports aircraft measurements of black carbon (BC), CO, and CO2 measured in the lower troposphere eastward along the Asian continent over the sea and around Japan and the Philippines. Pollution plumes with elevated levels of CO and BC are investigated and the observed concentrations are compared with predictions from the WRF-CMAQ model. Observed to modeled concentration ratios derived from this are proposed as correction factors for emission inventories used in the model. Such an investigation of emission inventories is useful to achieve improved air quality predictions in the regions studied, and the aircraft measurements presented here provide a rare and good opportunity to extend analyses from ground based measurements.

Unfortunately, the presentation of the scientific approach and results in this paper is somewhat confusing and difficult to understand in places. The following aspects are not addressed clearly enough for general understanding and require a more detailed discussion. Major revisions are required before the paper is suitable for publication in ACP.

(1) To what extent can CO, CO2, and BC be considered as inert tracers that are essentially only subject to transport and deposition after emission on a 5d time scale, as considered in the backward trajectory calculations. To what extent could other chemical or physical processes influence their concentrations observed on the aircraft?

(2) Which source regions were exactly investigated using the approach with model calculations and flight measurements? Line 108 states: “Pollution plumes from major population centers in Asia were detected during parts of flights.” Which major population centers are specifically meant? Asia is a very large continent. Generalized statements such as “The results suggested that downward and upward revisions of Chinese emissions ... are required” (see abstract) is VERY general and should be formulated more cautiously and refer specifically to the regions or areas investigated. The authors should also consider making the title of the paper more specific. Also, to what extent could the findings be limited in time, e.g., only for the season or year investigated? How representative were the environmental conditions (fire activity, traffic, meteorology) prevailing during the flight campaign for the years before and after?

(3) The title of the paper states “Downward and upward revisions … are still required…”. Is this statement still valid approximately seven years after the aircraft campaign? Have there been any developments in East Asia since then with regard to biomass burning, industrial emissions, or traffic that would warrant a new investigation?

(4) There is only very limited information given on the EMERGE campaign and the aircraft measurements. A brief overview should therefore be provided in Section 2.1. The following information would be of interest. Why was springtime chosen for the campaign? What altitude range was covered during the measurement flights and what altitude range was specifically evaluated? Which measuring instruments were used (manufacturer, model) and what are their total measurement errors (precision, accuracy)? Which particle sizes were detected by the BC measuring device and how was the photometer signal converted into mass concentration? For which reference conditions (T, p) do the specified mass concentrations apply? Were other compounds (e.g., NOx, VOCs) measured and used in this work, e.g., for the identification of plumes, apart from BC, CO, and CO2? A PTR-MS instrument is mentioned in line 112. What was measured by this instrument and were the corresponding data used in any way?

(5) Section 2.2: which processes (apart from emission, transport, and deposition) play a role for the simulation of BC, CO, and CO2 on the 5d time scale of the backward trajectories investigated? Table 1 lists various types of emissions. Apart from direct emissions of BC, CO, and CO2, do other emitted substances, for example biogenic VOCs mentioned in the table, play a role? If so, which chemical processes were involved? Which processes represented in the AERO 6 aerosol module are relevant for the modeled results of BC in this study? What role do the volcanic emissions listed in Table 1 potentially play?

(6) For each model component listed in Table 1, references should be provided where a description or corresponding data can be found.

(7) In Section 2.4, the general description of the concept of "residual ratios" and "baseline values" is hard to understand and should be rephrased for clarity.

Minor Comments

Abbreviations (EMERGE, WRF-CMAQ, GFED, HTAPv2.2z, etc.) should be defined at the beginning of the paper when they are first used.

Line 42: Typo “nanometre-sized”

Lines 96-97: The sentence is unclear. Which other pollutants (apart from CO, CO2, BC) were investigated?

Line 105: Typo “Deutches”

What is the meaning of the given quantities (e.g., max = 1.3 mm) for APT3 in lines 340 and 575?

Table S3 appears to have no use in the paper and should be deleted.