General comments

This study describes European Natural Airborne Disaster Information and Coordination System for Aviation (EUNADICS-AV) Early Warning System (EWS). The EUNADICS EWS greatly extends the existing Support to Aviation Control System (SACS) automatic alert system for airborne volcanic sulfur dioxide SO2 and ash to include other airborne hazards (dust, smoke and radionuclide clouds) with creation of multiple new alert products (email and web pages with NRT maps, data files) and convenient formats (NetCDF). These new data are provided by EUNADICS partners and external data sources. The EUNADICS system further combines satellite data with the European ground-based networks (lidar and passive) and regional measurements from volcanic observatories in Iceland and Sicily.

EUNADICS serves European users, primarily Volcanic Ash Advisory Centers (VAACs) in London and Toulouse that have operational responsibility for volcanic ash advisories and forecasts. New message formats (NetCDF alert data products) will facilitate using the alerts to initialize plume dispersion models.

There is room for English and punctuation improvements, which would make paper easier to read.  Many sentences need re-wording and/or clarification.  Specific suggestions are mentioned below.

I found the paper informative and suitable for publication after language and syntax  improvements.

Specific comments

The aviation hazards satellite data sources are comprehensive, except for direct readout data for Iceland and Europe from Satellite Measurements from Polar Orbit (SAMPO) service (https://sampo.fmi.fi/products). Using SAMPO data would help reducing alert latency time and geographical coverage of the EUNADICS system.

Abbreviations should be explained when first used.

Consider removing abbreviation from the title.

Technical corrections

Abstract is not clear to a general reader, not familiar with the EUNAUDICS project. I suggest explanation of the abbreviation “EUNADICS” in the abstract.

45 ATM – explain abbreviation

47 have shown significant

48 satellite[s]

51 e.g.[,]

55 service[s]

57 to proceed – consider changing this verb

58 … highlighting the capability of operating early warnings … - consider re-wording

75 implication in meteorological processing…  – clarify

80 particles

81 satellite [data]

84 It makes it possible as it can to provide information

94 https://meteoalarm.org

149 The results - objectives?

153 Copernicus Atmosphere [Monitoring] Service (CAMS)

165-166 … specialization [in] atmospheric transport modelling

Figure 1: SAMPO service

186 boards

195 i.e.,

207 were

217 possibility -> discussion with ?

218 Tables 1 and 2  -> 2 and 3?

227 overpass

243 particulate matter (PM)

243 volcanic ash total column [number or mass density]

245 averaging kernel

250 We reviewed …

252 products

253 section 2.2?

276, 277 .. Observatory which operates …

281 e.g.,

296 e.g.,

308 at NOAA

312 MWOs – explain abbreviation

316 aim at -> with the goal of supporting …

317 satellites

345 use ground observations

404 when

405 up to the lower stratosphere – why not in the middle and upper stratosphere?

405 Eight? satellites sensors …

407 Yang et al., [2007] -  OMI product has been replaced with conceptually new OMI SO2 product: Li et al., New-generation NASA Aura Ozone Monitoring Instrument (OMI) volcanic SO2 dataset: Algorithm description, initial results, and continuation with the Suomi-NPP Ozone Mapping and Profiler Suite (OMPS), Atmos. Meas. Tech., 10, 445-458, doi:10.5194/amt-10-445-2017, 2017.

415 between 3 and 21 km,  - why is the upper limit 21km?

421 e.g.,

423 expressed in Kelvin degree (K)

432 missing reference: Virtanen et al., (2014)

438 to define

443 illustrates

447 a fast? ash detection

448 i.e.,

469 presented

470 is based

487 is obtained ?

503 triggered

Figure 13, left map: should the white box show station Finokalia (Crete), shown on the right?

549 ash advections have not been observed

555 networks

560, 561,566: e.g.,

608 ZAMG and STUK – explain abbreviations

609 ZAMG

610 remove “have been designed”

613 delete “proceeding”. … is implemented?

643 new alert products

644 creates

667-670  repeat of 645-650

683 quantity product – just use product

715 nuclear central - plant?

749 remove “thanks to”

751 explain TRL

753 i.e.,

757 allows consultation -> visualization?

763 burst -> cloud

801 remove “same”

814 consider

839 is operated -> is implemented ?

855 NCAP fiel ->  file?

857 details

P36 868 possible

870 link not found

873 MWOs – explain

890-891  was designed with the goal of …

891 passed

895 obtained -> has been demonstrated?

899 satellites

906 has developed

907 notifications

908 include

913 better spatial resolution – better than what?

916 Only one aspect

919 interest -> usefulness?

920 of using EUNADICS system in

921 activity about -> utility for …

925,930 in the framework of …

928 proceeding -> implementing

958 the alert

971 details

972 provided

991 e.g.,

The paper describes the results of the EUNADICS AV project, which developed different natural hazards observation and notification products, with the goal to support aviation in the cases of airborne natural hazards. My expertise is in aviation, so I cannot judge the background scientific quality, even though it seems impressive to me - the number of different tools, observations and notifications.

I do have several comments, that would require minor text revisions:

1. In the abstract the authors say "All the ATM stakeholders (e.g. pilots, airlines and passengers) can access and benefit of these alert products through this free channel." I find this a bit strong as a statement. Any memeber of public can access these products, that is true, but it is unclear how they can benefit, as there is no explanation of the meaning of any of the products - one would need to be a scientist to understand what they are looking at. This is true even for graphical products where different colors are set for different concentrations (or similar), but there is no explanation what it means for layman - even for aviation stakeholder - what is red zone? Can I fly through it or not? If not, how far should I keep? All this to say that these products have greaat value for aviation, but they are still missing an important part which is the "translation" of its meaning for aviation stakeholders that are not meterologists or atmoshperic scientist (if this is a good term at all). 
2.  In section 5 the authors say "EUNADICS is a SESAR (Single European Sky ATM Research; https://www.sesarju.eu) enabling project with regard to the definitions provided in the SESAR 2020 Programme Execution Framework, delivering SESAR Technological Solutions." I would strongy suggest to rephrase this sentence, as the project itslef is not even connected to SESAR, and the products developed are not "enabling" in the sense that is used in SESAR (enabling in SESAR means a technology that is a necessary building block of an ATM infrastructure - in a sense that without it, there is no new ATM infrastructure. I would suggest to rephrase into "supporting" or similar wording.
3. Next, the authors say:"EUNADICS pass maturity phase V2 with regard to the 7-phase concept as introduced by the European Operational Concept Validation Methodology (E-OCVM, 2010)..." E-OCVM presents guidance for V1-V3 of the 8 phases  of ATM products life-cycle. However, I don't think that EUNADICS can claim V2 maturity level according to EOCVM, as human factors, safety, business, environmental and standards cases were not performed for any of the products. The point of the cases is to assess the impact of the soluton on a wide set of matters in the ATM. These cases are requirements that need to be passed, in order for a solution/product to mature from V1 to V2 or from V2 to V3. The EUNADICS project could easily claim TRLs 2,3 or even 4, of the H2020 technology levels, but not V2 of EOCVM. mainly because the EOCVM requires the assessment of how the products can be implemented in ATM and what would the impact be, and that was not done (the various cases) in the project, nor was that the point of the project). 
4. In line 925, what do you mean by "environment). EUNADICS EWS passes with success the performance verification."?
5. Finally, a suggestion to authors regarding the TRL levels of their products, in aviation setting. A product can be deemed operational in aviation if intended end-users can access the information, understand it and make decisions based on the understood information. If the presented information is not understandable by the end-user (e.g. pilot, air traffic controller), the product will not be used, even if it is completely accurate, and reliable. That is the reason for having various cases in the EOCVM methodology - to make new technology not only work, but to be understood. Some of the next steps, in my opinion should be identification of the end-users, and tailoring of the product for their use. If the end-users are only national meteorological providers, VAACs and similar, then the TRL of EUNADICS products is very high, and probably close to operational. But, if the products should be shared with other, non-scientific types of end-users, there is still a lot of work to reach high TRL levels, and that work is mainly on making the information understandable to these users. 
6. Please review the paper for English proofing. It is overall of good quality, but there are typos and some non-English phrases that make reading slightly harder.