General comments:

The present study analyzed and evaluated the spatial and temporal variations in dust activity in Australia for the period of 1980-2020 by using MODIS and MERRA-2 combined (M&M) DAOD, and the retrieved near-surface dust concentrations and PM10 were validated with ground-based visibility data sets and ground-based PM10 observation, respectively. With this, the authors  further explored the MERRA-2 dust flux with major dust pathways identified in previous studies and quantified the annual dust cycle for Australia over the period from 1980 to 2020, that providing useful information to evaluate the adverse impacts stemming from dust events in Australia, although some similar attempts had been conducted before. The manuscript was well written, Still, there are some things are unclear/invalid, and more discussion should be added to make the analysis more complete. Therefore I recommend the publication of this study after some issues were properly revised and improved.

Specific and technical comments:

1. Abstract, the authors claimed that the MERRA-2 dust flux shows the same major dust pathways as those in previous studies and similar dust emissions/deposition areas. What about the source of those previous studies? From the ground observation data or from the MODIS products?
2. Line 77, the limitations are refer to the study of Yang et al., (2021) or from the previous related studies? If it was the former, it is better to summarize the limitations from previous studies. In addition, I note that the author had published a similar study related to the MERRA-2 AOD and DAOD with MODISwhich also focus on the dust intensity in Australia(Che et al., 2022), what about the difference with the present study?
3. Line 90-93, it is unclear about the limitation of using site-based PM10 observations here with the example of Jesus et al. (2020).  
4. Line 163-165, 11). Are both thehourly BoM horizontal visibility data and the dust type SYNOP code were recorded by a weather observer or not? In addition, qs the manually estimated visibility have an upper limit of 10km, some low dust or PM10 condition would be unproperly analyzed with visibility data, did the authors compared the manually dataset with data from the automated instruments? like the Atmospheric Visibility Sensor which could be used in recent years.
5. Line 189-206, this part should be remove to the Introduction.
6. Line 224-225, the Eq 3 used in this study is not considered the contribution of nitrate aerosol, evidence about the minor role of nitrate aerosol for PM10 needed to be provided.
7. Line 366-368, it is unclear why using the example of Shao et al., (2017), it seems not support the conclusion below. Please added more explanation to clarify it.
8. Line 497-501, previous studies based on visibility data, weather codes and DSI seems not support the dust emission peaked in 1990 and 1996, please explain it.
9. Line 598-602, what the possible reasons caused the imbalance between source and sink of dust? In addition, the data source or the calculated of averaged dust dry/wet deposition, and the dust sedimentation should be provided here.
10. Line 604-621, Discussion in this part is weak and meaningless, as the main finding of the present study is not included.Is it consistent or deepen our understanding on the climatic control over dust activities compared with the previous studies?   

To reveal the temporal and spatial features of dust activity in Australia, the authors developed a new product of MODIS and MERRA-2 combined (M&M) DAOD. They further evaluated tis MODIS-MERRA DAOD by using multiple measurements. Then the authors presented many results on the spatial variations and seasonal features in dust activity.

Overall, this is a well-conducted study and the authors show some interesting results. The developed combined DAOD could be very helpful. However, I believe this manuscript can be improved by doing more in-depth analysis on the long-term trend of dust activity. Please find my comments below.

My major concern is about the analysis on temporal variations of Australia dust activity. The authors mainly talked about long-term trends of dust budget from 1980 to 2020, but in fact a further discussion on the key factors driving these trends is needed. In addition, Fig.12 only shows mean dust emission over 1982-2019; I think a spatial trend for dust emission should be given which might be linked to variations in rainfall and land cover.

Fig.3 looks like that the MODIS-MERRA DAOD is not in a good agreement with AERONET AOD. So I am not convinced by this validation.

L306: what’s the meaning of expected envelope and how is it determined?

L463: please replace “PM” by “PM10”

L513: what’s the reason of an increasing dust deposition after 2010? How about the trend in different seasons?