the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Alicenet – An Italian network of Automated Lidar-Ceilometers for 4D aerosol monitoring: infrastructure, data processing, and applications
Abstract. The vertically-resolved information on aerosol particles represents a key aspect in many atmospheric studies, ranging from aerosol-climate interactions to those investigating aerosol impacts on air quality and human health. This kind of information can be primarily derived by lidar active remote sensing and extended networks of these systems are currently run at the global scale. A network of Automated Lidar-Ceilometers (ALCs), Alicenet, was set up in Italy in 2015 by the Institute of Atmospheric Sciences and Climate (ISAC) of the National Research Council (CNR). Alicenet grew up in these years as a cooperative effort of Italian institutions dealing with atmospheric science and monitoring, and includes regional Environmental Protection Agencies, Universities and Research Centres. In the current configuration, the network runs both single-channel ALCs and dual channel, polarisation-sensitive systems (PLCs) operating in very different environments (urban, coastal, mountainous and volcanic areas) from Northern to Southern Italy, thus allowing the continuous monitoring of the aerosol vertical distribution across the country. Alicenet also contributes to the EUMETSAT program E-PROFILE, filling an Italian observational gap compared to other EU Member States. In this work, we present the Alicenet infrastructure and a detailed description of the specifically-developed data processing chain converting raw instrumental (Level 0) data into quantitative information on aerosol properties, with output products ranging from attenuated backscatter to aerosol mass and vertical stratification from the surface up to the upper troposphere (output data Levels 1–3). Overall, this setup provides from near real-time to long-term overviews of the 4D aerosol field over Italy. Examples of both are reported in this work. Specific comparisons of the Alicenet products to relevant independent measurements of different parameters (e.g. surface PM10, sunphotometer AOD) are also included, revealing the good performances of the Alicenet algorithms. Overall, Alicenet represents a valuable resource to extend the current aerosol observational capabilities in Italy and in the Central European Mediterranean area, and contributes to bridge a gap between atmospheric science and its application to specific sectors, among which: a) air quality, b) solar energy, c) aviation safety. More in general, the maturity of the ALC/PLC instrumentation and of the data processing tools available within the wider international scientific/technical atmospheric community suggest lidar-ceilometer networks could usefully integrate current EU Atmospheric Research Infrastructures for aerosol studies.
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RC1: 'Comment on egusphere-2024-730', Anonymous Referee #2, 22 May 2024
Review of “Alicenet – An Italian network of Automated Lidar-Ceilometers for 4D aerosol monitoring: infrastructure, data processing, and applications” by A. Bellini et al.
This manuscript describes Alicenet, the network of Automated Lidar-Ceilometers (ALC) in Italy. The used instruments, sites, data quality control and processing are described, including the cloud screening, the denoising, the overlap correction and the absolute calibration. The retrievals of aerosol optical and physical properties are then presented with comparison with collocated or near-by Aeronet AOD and PM mass measurements. Alicenet also proposes an automatic identification of aerosol layers (ALADIN) with a distinction between the mixed, the continuous and the elevated aerosol layers. Case study and a 7 year climatology of the three layers are also described. The potential of Alicenet is finally emphasize by the description of the detection of a local dust front in the Po Valley, of a Saharan and biomass burning advection over Italy and of a volcanic eruption in Sicily. A lot of detailed information on the data processing, the retrieval and the automatic aerosol layers detection are given in the supplement.
The content of the manuscript suits AMT and the various tools developed by Alicenet are valuable. The manuscript is then worth publication in AMT.
Major comments:
- The general description of the network, the data processing, the aerosol retrievals and layers identification as well as a part of the technical descriptions are part of the manuscript whereas the detailed technical descriptions of the cloud screening, the overlap correction, the absolute calibration, the retrieval of aerosol properties and the identification of aerosol layers constitutes the supplement with additional figures. The supplement is then as important as the main paper for readers directly implicated in similar networks and related products. To some extent I really missed information of the supplement to practically understand e.g. some products during the reading of the manuscript. I would suggest to the authors to reconsider the subdivision of information between the main manuscript and the supplement. The criteria should be that the main manuscript allows to clearly understand the applied algorithms whereas only readers interested in reproducing the algorithms would refer to the supplement.
- The English phrasing should be revised. Minor comments point to some (but not all) problematic sentences. Parenthesis are too extensively used. Acronyms are not always explained.
Minor comments:
Abstract:
- L15: “in these years”, english?
- L24-26: The sentence “Examples of both …” could be merged with the previous one.
- L30: please remove a), b) and c).
- L32: suggest that???
- Introduction:
- L38-39: two times “Particularly” in the same sentence.
- 41: Consider deleting “ represented by
- L 43-44: what is meant by “large-to-small scale atmospheric processes influencing local air quality” and by “it affects () high-elevation environments”?
- L 54 the acronym ACTRIS should be explained.
- L55 ACTRIS or EARLINET ?
- L57 variabilities?
- L64-65: I have the impression that the sentence missed the point that ALC’s (originally conceived …) provide now complete aerosol backscatter profiles.
- L67: Consider replacing “radiation elastically scattered back” by “elastically scattered back radiation”, “elastically back-scattered radiation” or “radiation that is elastically backscattered”.
- L68-70 please revise the sentence (at least the beginning)
- L74 national meteorological services
- L75 remove such
- L78-81. Please rephrase
- L86 what is meant by “particles reaching down to be boundary layer”?
- L96-99: please rephrase
- L112-115: please use a similar structure for sect2 to sect 5 or rephrase the whole §.
Alicenet sites and instruments:
- Table 1: the beginning of measurements could be added since long-term time series are also discussed. If information from the supplement is moved to the manuscript, Table 1 could perhaps appears in the supplement in order to shorten the main paper.
Alicenet data processing and relevant products:
- L163: are (aerosol + molecules) and (aerosol + molecular) both necessary ?
- L166: please rephrase: “Fig. 2 describes …” and remove “in this section”.
- L187: Batt: att in indices (please check the whole manuscript for exponent/indice).
- 2: all used acronym should be described in the figure or in the caption. E.g. PM, Sp, Vp, Mp, MAL, CAL, EAL,… are not described.
- L177-179: please rephrase
- L179-180: this sentence could be deleted since it is explained in the figure caption.
- L189: “and centralised at CNR-ISAC”: already said.
- L211 (if needed) has to be deleted
- L214: give the definition of the SNR acronym the first time it is used
- L228-230: please rephrase
- L244-246: change the sentence in order to remove the ()
- L258-260: Foehn events are then frequent and the aerosol load is then lower than in non-foehn event. Could you please add a reference for this statement.
- L276-278: The word “reproduce” seems not corectly used. Alicenet correction produce a nearly-molecular correction with profile similar to the molecular profile but shifter to higher backscattering values due to the presence of weak aerosol load.
- L302-305: please summarize the QC2 control in the manuscript. It seems me important that the reader has a clear overview of the absolute calibration without referring to the supplement.
- L312: the bar below Batt is strange and not described at L313
- L316: supplement
- 5: is it right that the CL value reported on Fig. 5a and 5b are the same ? this does not correspond to the text. Fig5c: Is there an explanation to the lower CL value at Roma and to the stronger seasonal cycle at Aosta and Messina?
- L329: A reference to PROBE documentation is needed.
- L362, the “-1” should be in exponent.
- 3.3.1:1) The impact of the iterative procedure to derive the aerosol backscatter and extinction has to be described. AOD with only constant LR could be also plotted on Fig. 6b and the results discussed. Is this impact similar for urban and remote stations (e.g. Roma and Aosta)? Are the constant LR method always worst than the iterative procedure (e.g. in presence of dust)?
2) Fig 6b shows cases where AOD from Aeronet is not comprised within the expected uncertainties of ALC AOD (L377-378). There is an underestimation in case of dust that is described in the manuscript. What about the overestimation systematically found at around midday (Fig. 6b), particularly on the 2017-07-13?
3) Fig. S3 shows that Roma and Messina have much more coarse mode aerosol and both stations have a better correlation between AOD from Alicenet and Skynet. This should be the inverse since continental aerosol properties were chosen for the retrieval. Could you please comment on that point?
- L390: S4
- L409: Consider replacing “when the two are to be compared” by something similar to “before comparing them” or “when comparing them”.
- L428: to which type of aerosol corresponds the chosen density? Please also indicated the aerosol-type of the chosen gamma exponent (L431) and what is MERIDA.
- L433-435: please rephrase and consider using a relative sentence.
- Fig. 8 and related description: it would be nice to have an estimation of the maximal difference between ALC and OPC mass estimates and of these differences as a function of humidity in order to estimate the adequation of the humidity correction.
- -L459-461: please rephrase
- -L459-475: please consider using the name of the source of uncertainties instead of the first, second, …factor.
- -L476-478: what about the uncertainty of the humidity correction?
- -L485-487: please rephrase
- L 490-508 The expression mixed layer or mixing layer is more often used than mixed boundary layer. Generally, the use of standard names and acronyms would be helpful (see e.g. Kotthaus et al., 2023 that you cite), e.g. MAL is rarely used. It should also be worth relating your atmospheric layers to standard ones: is MAL similar to your previously mentioned MBL and to ML or convective boundary layer? If not (L517-518), what is the link/interaction between them? Which conventional layers are comprised into the CAL?
- L533: Does “centre” mean “center”? If yes, please use the English word. Otherwise, please explain the significance or acronym.
- L534-546: this § is quite difficult to follow. I understand that specific details and detailed algorithms are only described in the supplement. The data treatment in Alicenet and particularly in ALADIN should however remained comprehensive in the main manuscript. A schematic description of ALADIN can perhaps be helpful. I suppose that some restrictions like MAL<CAL<EAL are also applied? L553-555 and Fig. 10 allows to see than EAL<CAL. In usual ABLH description, the residual layer is not considered as an elevated aerosol layer. Only layers above the CBL and RL are described as EAL (see remark on L490-508).
- Equ. 6 is the median done only on the numerator? If the median of the whole expression is taken, please use median (…) instead of the misleading overline.
- L571: CAL diurnal cycle is clearly visible only in June, July and August. The thicker CAL during night in winter is not obvious.
- L580-582: Even if there is an increase of aerosol emission at ground in the early morning, what is the mixing mechanism allowing aerosol to reach a higher altitude than TKE during the first part of the day? Concerning the land-sea breeze, the afternoon should lead to a breeze from sea to land during the afternoon (=sea-land breeze?). Could the land to sea breeze in the morning explain the measured effect?
- Fig. 12b: the mention of the station (Milan) and of the time on the webcam pictures will be helpful.
- L749 “, ,”
- Summary and future perspective: The future perspectives are well described. A more extended mention of the data chain, of the aerosol optical and physical retrievals and of ALADIN is however necessary for reader restricting themselves to the summary in order to deserve Alicenet’s potential.
Supplement:
- (1): to be coherent with the text, the c of Fc(r) should be written as indices.
- L 26: over an ALC dataset longer than one year.
- L29-36: The description of the applied overlap correction is quite difficult to follow. Please reformulate so that the same procedure can really be applied without potential error. Your condition of filtering out the overlap corrections associated with Mov < 0.05 means that you select RD(r) sufficiently different than RDnear(r) or that the T difference with the internal T is sufficiently large?
- L45-59: too long sentence
- L49: “is performed”
- L50: please add the name and the formula of the adjusted R2 parameter so that a similar procedure could be applied without using the bgtest R package.
- L55: To this purpose ??
- L54: A mention of QC1 could be helpful
- (4): please put “slope” as exponent.
- L62: if CL is a median, please provide equ.(4) including the median.
- S3: please add AOD in the x and y labels
- L90: why is CAL mentioned but not described? If described in the manuscript, please add a sentence with a reference to the CAL description.
- L108: SD in indices?
- L110-111 should probably be aligned similarly to L108-109
- L112: are you sure that an additional continuity criterion will be benefitable?
- L122: if ‘centres’ means centers, please change the world into the English’s one.
- L126 : the potential bottom and top semi-amplitudes of 150-1500 m means that the EAL thickness is estimated between 300-3000 m? or that its elevation has to be comprised between 150-1500 m? Please clarify.
- 7. Why not using the usual integral symbol?
- L131-136: Will it be easier for the reader to give the equation instead of a description?
Citation: https://doi.org/10.5194/egusphere-2024-730-RC1 -
RC2: 'Comment on egusphere-2024-730', Anonymous Referee #1, 23 May 2024
The manuscript describes the Italian network of automated lidar and ceilometer measurements, Alicenet. The network consists of state-of-the-art ceilometers distributed from the north to the south of the country. The manuscript describes the quality control of the data and the algorithms to derive optical and physical aerosol properties, as well as a new procedure for aerosol layer identification. The derived properties are compared to AERONET AOD and in-situ measurements for validation. Long-term monitoring over seven years and several case studies show the capabilities of the network.
The algorithms used in the manuscript are based on established methods used in other lidar and ceilometer networks, but were further developed to improve the results derived from the relatively simple ceilometer instruments having only one wavelength. These algorithms have the potential to be included to the wider e-profile network and to provide further products on a European scale.
The manuscript is suitable for publication in AMT, but may be considered to be divided into a more technical and an experimental part.
Major comments:
Did all instruments measure at all times? Or were some added later? The specific measurement periods or the start of the measurements could be added to Table 1.
The description of the technical details of the data quality control and the algorithm development may be moved to the supplement to improve the readability of the manuscript, as already suggested by another review.
Throughout the whole manuscript: the language should be improved, sometimes this makes the understanding of the meaning difficult. Too many parentheses, as already stated in the quick review.
Minor comments and some suggestion:
Line 13: these -> such systems
Line 17-20: long sentence
Line 21-24: long sentence
Line 245: Overall, this setup provides from near real-time to long-term overviews of the 4D aerosol field over Italy. ...
is difficult to follow.Maybe rather:Overall, this setup provides near real-time as well as to long-term overviews of the 4D aerosol field over Italy.
Line 27-30: long sentence
Line 31: of the data processing tools available -> of the available data processing tools
Line 32: “could usefully integrate“ , what do you mean? ALC networks can integrate other EU infrastructures, or vice versa?
Some specific remarks:
Line 132: “having a sufficiently high SNR” what is sufficient? At what altitudes? Any reference in the literature?
Table 1 and, among others, L 135: Change CHM15K to CHM15k
Eq. (3) and line 313, where is the overbar? Below beta?
Fig. 5: Are the CL values really the same? Minimum and maximum for spring and autumn, as stated in the text? I would recommend to add date and time information on top of each subplot a) and b) for easier visual identification.
Line 358: More specifically, an iterative procedure is used to derive 𝛽p(r) and αp(r) vertical profiles.
Line 391: correct notation would be: Ångstrøm
Section 3.4. the use of “new” names and abbreviations for the different boundary layer parts is misleading. I would suggest to use the established ones as: planetary boundary layer - PBL, mixing layer - ML, residual layer, to avoid confusion. CAL, EAL, MAL are not very common.
Line 549 and Eq. 6: again: overbar for median and division lines are not clear.
Line 749, two , ,
Line 705: Italian observational gap at EU level. This has been emphasized 3 times. Was there a gap before, and it is now filled since 2017?
Citation: https://doi.org/10.5194/egusphere-2024-730-RC2 -
CC1: 'Errata Corrige on egusphere-2024-730', Francesca Barnaba, 31 May 2024
We would like to correct a unintentional mistake in the abstract of the submitted manuscript (EUMETSAT was used instead of EUMETNET).
Therefore, the corrected sentence at lines 19-20 should be 'Alicenet also contributes to the EUMETNET program E-PROFILE, filling an Italian observational gap compared to other EU Member States'.
We apologize for the inconvenience.
Francesca Barnaba on behalf of all co-authors
Citation: https://doi.org/10.5194/egusphere-2024-730-CC1
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