the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 28 Jun 2024
Measurement report: Aerosol vertical profiling over the Southern Great Barrier Reef using lidar and MAX-DOAS measurements
Abstract. Aerosol vertical profile measurements were made using multi-axis differential optical absorption spectroscopy (MAX-DOAS) and mini-Micropulse LiDAR (MPL) at One Tree Island in the Southern Great Barrier Reef from February to April 2023. This is an understudied location in terms of atmospheric aerosols and chemistry but is growing in importance as multiple research streams examine the influence of aerosols on radiation over the Great Barrier Reef. Solar radiation management proposals require regional-scale aerosol modelling, which is evaluated against aerosol extinction and optical depth measurements, necessitating a thorough understanding of measurements of these quantities. MPL aerosol retrieval showed extinction-to-backscatter ratios (0.031 on average) and depolarization ratios (0.015 on average) consistent with clean, unpolluted Southern hemispheric marine aerosol. The maximum depolarization ratio tended to be above the layer of maximum MPL backscatter, which is attributed to dried sea-salt layers above the boundary layer. MAX-DOAS and MPL extinction profiles show aerosol layers extending beyond 2 km altitude in the middle of the day, but predominantly below 1 km at other times. We also compared aerosol optical depth measurements from integrating the MAX-DOAS and MPL extinction profiles, with observations from a hand-held Microtops sun photometer. Mean aerosol optical depth (AOD) values across the campaign compare well, being 0.083 ± 0.002 for the Microtops, 0.090 ± 0.032 for the MAX-DOAS and 0.104 ± 0.028 for the MPL. However, AOD observations at a given time, and the AOD diurnal cycle, often varied between instruments. This likely indicates strong horizontal inhomogeneity in aerosol in this environment, a factor which makes it challenging to accurately compare AOD estimates from different viewing geometries, but which is important for future aerosol modelling studies in this region to consider.
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RC1: 'Comment on egusphere-2024-1111', Anonymous Referee #1, 27 Aug 2024
The manuscript is logically coherent and well-structured. However, the research content appears somewhat simplistic. While related studies have already been published, this research does have the novelty of being the first conducted on One Tree Island in the Southern Great Barrier Reef. Nonetheless, the overall content of the paper may be considered relatively simple for a journal of ACP's standards, and the innovation presented is not particularly strong. I recommend adding new research content to enrich the manuscript and enhance its contribution to the field.
Citation: https://doi.org/10.5194/egusphere-2024-1111-RC1 -
RC2: 'Comment on egusphere-2024-1111', Anonymous Referee #2, 05 Oct 2024
This paper offers valuable aerosol vertical profiles through Max-DOAS and MPL, which should have provided significant scientific insights for the community. However, the current manuscript did not match the journal's quality. Besides, some additional work needs to be addressed. Here are my comments and suggestions:
Major comments:
- line 240-243: “Examining the cloud filtered aerosol extinction profiles in Figure 4(c), we find the high depolarization ratio values directly above the boundary layer are present during both cloud-flagged and cloud-free periods. This indicates a change in the scattering characteristics (shape and/or composition) of aerosols at or just above the boundary layer, whether clouds are present or not.“ The boundary layer is mentioned several times in the paper, what is the exact altitude of the boundary layer? Is the determination of the boundary layer consistent in MAX-DOAS and MPL?
- Equations (10) and (11), as well as a description and explanation of the calculation method, should be placed in section 2.
- Line 333-336: “In almost all hourly bins, the smoothing of MPL extinction by MAX-DOAS averaging kernels brought the MPL AOD closer to the MAX-DOAS AOD. However, the smoothed MPL AOD remains higher than the MAX-DOAS in almost all hourly bins even with vertical sensitivity and resolution accounted for.” Can you try to explain why this phenomenon occurs?
- Line 349-350: ”It is important context for proposed marine cloud brightening experiments at the GBR that aerosol layers can exist up to 2 km altitude.” Could you elaborate on the effect of the height of the aerosol layer on marine cloud brightening in the manuscript based on this observation？
- The aerosol vertical profile and the aerosol optical depth are analyzed in detail from MAX-DOAS and MPL at One Tree Island in the Southern Great Barrier Reef in the paper. In this observation, can you provide a comparison of the similarities and differences between the results of the two measurement and their respective applications?
Minor comments:
- Line 233: “0.112 and 0.294 counts.km2 [(𝛍J) (𝛍s)]-1”, “𝛍” should be “μ”. Same as Figure 2
- Line 238: “pattern of being <0.01” needs space between “<” and “0.01”. Same as line 238: ” >0.02”, and line 325: ” a factor >2.5”.
- In Figure 3 Pictures (a) and (b) are resized consistently, and (c) (d), and (e) will look better if they are resized consistently. In addition, the background color of (a), (b), (c), （d）, and (e) can be removed.
Citation: https://doi.org/10.5194/egusphere-2024-1111-RC2
Data sets
Data for One Tree Island Aerosol Measurement Paper Robert Ryan and Robyn Schofield https://doi.org/10.26188/25868881
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