The manuscript focuses on identifying the composition of organic aerosol at two sites in the Po Valley during 2021. The authors collected PM2.5 samples and analyzed them using ultra-high performance liquid chromatography paired with ultra-high resolution mass spectrometry and hierarchical clustering analysis. The study provides important insight into the differences in organic aerosol composition between a rural and an urban site over a year.

Overall the dataset and comparison between rural and urban sites in a hot spot for air pollution is important. However, the discussion has some inconsistencies with how results are discussed and could use more support in some places. The methods are also missing some information including the full method for ion chromatography.

L37-L39: This needs more description about the study referenced. What method did they use?

L64: “away” should replace “far”

L45-L70: The summary of previous studies in the region is good, but it feels like it is missing some context as to why this region is a hot spot for air pollution. Is it geographical? Or solely from large emissions?

L93: A map would be beneficial to show the relationship of the two sites to one another.

L99-105: Were the filters treated or baked before use? How were blanks collected and how often? These details are important and should be included.

L107: Please provide details or a reference for the IC method used.

L228-233: The discussion focuses heavily on CHN species, please expand on why that is and why other species are not discussed as in depth or at all.

L263-264: This sentence sounds as if the authors did not identify a second and third highest signal at SKI and instead are reporting what other studies found. The authors should clarify what their data shows.

L296-298: Please expand here. The author is discussing wintertime increases but offering summertime photochemical degradation as a possible reason.

L450-457: This section is confusing as written. The authors should clarify why they believe those fractions indicate tractor emissions.

L506: “unpolar” should be “nonpolar”

L528: Why were samples from June and December excluded? Did no samples meet the criteria? If so that seems worth a small discussion.