Comment on acp-2022-67

measurements characterized the physical and optical properties of BB aerosols for plume age from 10 h to 14+ days. The major findings include (1) This work supports the widespread influence of different wildfire emissions on aerosol properties in the western US; (2) The short and long-range transported plume aerosols present different physical and optical properties, which are related to sources and various chemical and physical processes during transport. well-written a valuable contribution

This manuscript by May et al. presents field measurements of BB aerosols transported to the MBO site, including long-range transported smoke from Alaskan and Siberian boreal forest wildfires and emissions from regional wildfires.
The measurements characterized the physical and optical properties of BB aerosols for plume age from 10 h to 14+ days. The major findings include (1) This work supports the widespread influence of different wildfire emissions on aerosol properties in the western US; (2) The short and long-range transported plume aerosols present different physical and optical properties, which are related to sources and various chemical and physical processes during transport. The paper is well-written and is a valuable contribution to the BB studies. I have some comments detailed below.
2) Line 285-287: Suggest adding more information, i.e. "The concurrent measurement of decreasing ΔOA/ΔCO with increased transport time in Farley et al. (2022) is still because that net OA loss through evaporation and deposition was great than the secondary processing. And OA is the majority component of PM 1 . Thus, the trend of ΔPM 1 /ΔCO follows the ΔOA/ΔCO, which can support the observation of PM 1 loss in this study".
2. Section 3.4, Page 13: the discussion of MAE and BC dominance Line 318: I prefer not to use "BC enhancement" in this para, it is "the normalized enhancement ratios of BC (ΔrBC/ΔCO) in Siberian events were identified higher than other cases" (Farley et al., 2022). In Farley et al. (2022), the highest ΔrBC/ΔCO ratios were measured during both Siberia and Oregon events, suggesting that these events had more influence from flaming fires. It is still not explained why the Siberian events exhibited a higher average MAE (0.60 m 2 g −1 ) than the SW OR events (0.30 m 2 g −1 ). Suggest checking BC fraction in PM 1 .
The mean MAE in the 8/12 Siberian event (0.48 m 2 g −1 ) is actually close to most other events, the mean MAE in the 8/17 Siberian event (0.72 m 2 g −1 ) is much higher, which leads to the higher average MAE of Siberia events. What caused this difference between the 8/12 and 8/17 Siberia events?
The discussions indicate that Siberia events in this study had more influence from flaming fires, thus having a high ΔBC/ΔCO and MAE. I agree with this, more flaming fires do generate plumes with enhanced BC emissions (ΔBC/ΔCO). However, in this study, the ΔBC/ΔCO ratios are not only related to the source fire conditions but also the transport processes, i.e., Siberia events are suggested to experience wet deposition. It's needed to mention that although the Siberia events experienced strong wet deposition, the ΔBC/ΔCO ratios are still higher than other events. A study ( https://doi.org/10.1029/2020GL088858) observed enhanced fraction of BC after vertical transport from the surface to the top of the boundary layer due to the lower removal efficiency of BC than the non-BC materials and the evaporation of other non-BC materials, which may be also related the transport processes.
3. Line 343: A recent laboratory study also found the imaginary part of BrC could be half decayed in a few hours, in line with the loss of its absorptivity after transport (https://doi.org/10.1021/acs.est.0c07569).
The laboratory work by Cappa et al., 2020Cappa et al., (hhttps://doi.org/10.5194/acp-20-8511-2020 and field observation from Wu et al., 2021Wu et al., (https://doi.org/10.5194/acp-21-9417-2021 suggest that the evolution of AAE and BrC absorptivity with photochemical aging is dependent on the fire burn conditions and initial emission particle properties. There is an initial enhancement stage of AAE and BrC absorptivity followed by the decrease with longer aging times for more flaming fires, while more smouldering fires are suggested to experience a net decrease upon aging. The short-range transported (10-15 h) SW OR events with the highest AAE may experience the initial enhancement stage or decrease during this short-range transport period depending on the fire condition. Suggest adding more clarification here. Line 393-395: "Notably, a portion of the 8/17 Siberian event exhibited a combination of elevated AAE and low SAE that is typically indicative of dust aerosols with enhanced absorption at short wavelengths." Siberia events did exhibit lower SAE than other events due to larger size mode particles. However, the AAE values in Siberia events were not elevated compared to other events. What does the "elevated AAE" mean? The AAE values in Siberia events were close to another long-range transport event (Alaska event). I don't think the AAE can be evidence of the dust aerosols mixing with plumes. 4. Page 22: For the aerosol size distribution in Siberia events, I agree that the observed <100 nm modes may be indicative of the influence of entrained background air and/or new particle formation. However, in Siberia events, the suggested wet deposition during transport would remove larger-size BB aerosols and would also result in a smaller size mode under 100 nm. Examples from Taylor et al., 2014Taylor et al., (https://doi.org/10.5194/acp-14-13755-2014 can support this. This is also related to the conclusion on Page 24.

Specific comments:
Line 143: need a full name for "PSAP".
Line 171: Please check the correction of OPC PM 1 measurements in the supplementary, not found.
Line 198: How do you get the BB event criteria of σ scat > 20 Mm −1 and CO > 110 ppbv?