The manuscript deals with barium containing aerosols originating from fireworks, addressing chemical alteration and the related health effects. Combination of single-particle analysis with monitoring of metal content and concentration of ionis species in PM2.5 fraction provides comprehensive information on barium containing particles.

General comments

1. Ageing and mixing state of Ba-containing aerosol particles is well addressed and discussed based on combined data set of single-particles and bulk analyses. However, health effects are estimated using simple calculations based on average Ba concentrations of PM2.5 and seems to be a marginal part of the manuscript.

2. The abstract should reflect the manuscript content, however the estimation of health effects are not even mentioned in it.

Specific comments

3. Abstract, l.17-19: The authors state: "The highest concentrations occurred in restricted zones rather than the more densely populated urban core, demonstrating the effectiveness of localrestriction policies." As such, the sentence seems to be contradictory. It should be mentioned that fireworks are prohibited in the urban core.

4. Figure 1 panel (c) l. 290. Size distributions are usually lognormal. Number size distribution of Ba containing particles should be plotted as dN/dlogD. The same comment is valid for Figure S5 panel (b) and Figure S6 in Supplement.

Technical comments

5. Health risk assessment, l. 116: Equations should be independent on the units of measure, "(mgkg-1day-1)" should be moved to the definition of Dinh in l.115.

6. Figure 1, l.290: "Number of Ba" should be clarified. 

7. Supplement, Figure S1: Secondary Y axis title "Mass" is erroneous, should read "Number of Ba-containing particles"  

8. Figure S4: Barium as the element of interest is missing from the plot.

9. Figure S6, caption: "The relative number fractions and size distribution of the main types of Ba-containing particles." Size distribution is not plotted just relative number fractions of of the main types of Ba-containing particles in each size bin. 

The manuscript presents field observations of firework-related Ba-containing aerosols in Guangzhou during the Chinese Spring Festival and Lantern Festival. By combining online metal measurements, water-soluble ions, gaseous pollutants, and single-particle aerosol mass spectrometry, the authors examine the temporal variation, spatial heterogeneity, mixing state, and possible aging pathways of Ba-containing particles. The topic is important and relatively underexplored, and the multi-site single-particle dataset is valuable for understanding the atmospheric processing of firework-derived metal aerosols. I recommend minor revision. However, several conclusions should be interpreted more cautiously, as detailed below:

1. The interpretation of nitrate enrichment as evidence of atmospheric aging needs clarification. Fireworks commonly contain nitrate-based oxidizers, such as KNO3 or Ba(NO3)2, which may directly emit primary nitrate-containing particles during combustion. Thus, the increase in nitrate-rich particles cannot be attributed solely to secondary nitrate formation or chloride-to-nitrate conversion. The authors should better distinguish primary nitrate emissions from secondary nitrate produced during post-emission aging. Analyses of the temporal relationships among K+, Ba, Cl-, and NO3-, or changes in NO3-/K+ and NO3-/Ba ratios during and after firework events, would help support the proposed mechanism. The conclusion that nitrate formation is a key aging pathway should be stated more cautiously unless primary nitrate contributions can be excluded or quantified.

2. The manuscript identifies OClN particles as relatively fresh emissions and N particles as aged products. However, OClN particles already contain nitrate, and fresh primary firework emissions were not directly sampled. Therefore, OClN should be described as an “early-aged” or “less aged” state rather than a fresh emission type unless source samples or near-source measurements are available. Additional evidence, such as the temporal evolution of OClN/N ratios after known firework periods, site-to-site aging gradients, wind-direction analysis, or trajectory support, would strengthen this interpretation.

3. The policy effectiveness conclusion is somewhat overstated. The higher Ba concentrations in restricted zones than in the urban prohibited zone are consistent with a policy effect, but they do not quantitatively demonstrate policy effectiveness. Site differences may also reflect local firework activity, enforcement intensity, meteorology, population behavior, transport, and distance to emission hotspots. The authors should revise this conclusion more cautiously. A stronger policy claim would require additional evidence such as enforcement records, observed firework activity, wind fields, or comparisons with pre-policy periods.

4. The health risk assessment is too simplified for the conclusions drawn. The use of an oral reference dose as a substitute for inhalation exposure and the reliance on average concentrations provide only a preliminary screening-level estimate. Firework exposure is highly episodic, and short-term peaks may be more relevant than long-term average HQ values, especially for children and individuals with respiratory or cardiovascular conditions. The authors should clearly present this analysis as preliminary, justify the use of oral RfD for inhalation more carefully, and discuss uncertainties related to Ba chemical speciation, solubility, and bioavailability.

5. The manuscript should define all abbreviations when first used, including OClN, N, NS, S, HMOC, and RPA.

6. The health risk section should avoid the heading “Health effects of Ba from fireworks” because the study does not directly measure health effects. A better heading would be something like “Preliminary exposure and risk assessment.”

7. The manuscript should be carefully edited for grammar, formatting, and consistency, including spacing around units, use of subscripts/superscripts, and consistency in the terms “firework” and “fireworks.”