Vertical distribution of aerosol optical properties in the Po Valley during the 2012 summer campaigns

Bucci, Silvia; Cristofanelli, Paolo; Decesari, Stefano; Marinoni, Angela; Sandrini, Silvia; Größ, Johannes; Wiedensohler, Alfred; Di Marco, Chiara F.; Nemitz, Eiko; Cairo, Francesco; Di Liberto, Luca; Fierli, Federico

doi:https://doi.org/10.5194/acp-18-5371-2018

Articles | Volume 18, issue 8

https://doi.org/10.5194/acp-18-5371-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 3.0 License.

https://doi.org/10.5194/acp-18-5371-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 18, issue 8

Research article

|

20 Apr 2018

Research article |

| 20 Apr 2018

Vertical distribution of aerosol optical properties in the Po Valley during the 2012 summer campaigns

Silvia Bucci, Paolo Cristofanelli, Stefano Decesari, Angela Marinoni, Silvia Sandrini, Johannes Größ, Alfred Wiedensohler, Chiara F. Di Marco, Eiko Nemitz, Francesco Cairo, Luca Di Liberto, and Federico Fierli

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Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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RC1: 'See suplement', Anonymous Referee #2, 29 Jun 2017
RC2: 'Comment on 'Vertical distribution of aerosol optical properties in the Po Valley during the 2012 summer campaigns'', Anonymous Referee #3, 03 Oct 2017
- AC2: 'Author's response to reviewer 2 (RC2)', Silvia Bucci, 22 Dec 2017
AC1: 'Author's response to reviewer 1', Silvia Bucci, 22 Dec 2017

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

AR by Silvia Bucci on behalf of the Authors (19 Jan 2018) Author's response Manuscript

ED: Referee Nomination & Report Request started (23 Jan 2018) by Aijun Ding

RR by Anonymous Referee #2 (09 Feb 2018)

Suggestions for revision or reasons for rejection

The authors have done a great job and most of the questions and doubts have been successfully answered. Therefore, I have no objection for the publication of this article provided that the following remarks are addressed.

P7-L10: “the well-known value of the air molecule linear depolarization ratio (Behrendt and Nakamura , 2002)”.

Behrendt and Nakamura [2002] describe the method to estimate the linear depolarization ratio of air molecules (delta_mol). Nevertheless, the value of this parameter depends on air temperature, laser wavelength and, mainly, on the shape and bandwidth of the optical filters used by the polarized channels of the lidar. Therefore, the value is not “well-known” but it has to be estimated taking into account the properties of the lidar system.

I agree with the authors that the absolute values of aerosol linear depolarization ratio do not affect the main purpose of this parameter, which is to classify aerosols. Nevertheless it would be desirable that the authors specified the value of delta_mol used for the calibration.

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Section 7: Figure 11 shows the mean delta_a, RH and TH profiles obtained during dust-free and dust days. In the right panel it can be observed that high RH values lead to low delta_a values close to the surface. However, there are some problems using this figure to infer the hygroscopic growth of dust (as pointed out in the revision). The first one is that dust layers arrive several kilometers above ground level. Therefore, it is no surprise to observe the highest mean delta_a values at higher altitudes (where dust is present during most of the time) rather than at lower altitudes, regardless of the values of RH. And second, if we assume that there is hygroscopic growth of the dust, and that this growth leads to a decrease in delta_a, then this parameter cannot be used to confirm the presence of dust in the lower altitudes.

The presence of dust in the lower altitudes can be confirmed with measurements of the APSS, provided that this system measures the aerosols in dry conditions (and thus large particles due to hygroscopic growth are not confused with dust particles). If this is the case, authors should add a figure comparing the coarse mode fraction, the relative humidity at surface level and delta_a at the lower altitudes during the dust events (similar to Figure 2 in the author response but adding the measurements from the APSS). This figure will add valuable information that will allow the authors to confirm or review their conclusions.

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Language:

P3-L38: “…compared to the urban one…” -> “…compared to the urban ones…”
P9-L31: “…as seem to be suggested by the observed corresponding…” -> as suggested by the observed corresponding

In some cases the word diurnal is used as daily, although they do not mean the same. Diurnal makes reference only to those things happening during daylight hours. Check it.

In the expressions “above/below X m height” the word “height” should be removed.

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Figures:

Fig. 2, 3 and 4. For better reading, indicate in the figures the periods classified as dust.

Fig. 3. Panel a). For a better visualization of the wind direction, use a color bar in which both extremes have the same color.

Fig. 6. Label the panels.

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ED: Publish subject to minor revisions (review by editor) (09 Feb 2018) by Aijun Ding

AR by Silvia Bucci on behalf of the Authors (19 Feb 2018) Author's response Manuscript

ED: Publish as is (26 Feb 2018) by Aijun Ding

AR by Silvia Bucci on behalf of the Authors (07 Mar 2018)

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Short summary

This paper analyses some of the processes affecting PM levels over the Po Valley, one of the most polluted regions of Europe, during the 2012 summer campaigns. Under conditions of air transport from the Sahara, data show that desert dust can rapidly penetrate into the lower atmosphere, directly affecting the PM concentration at the ground. Processes of particles growth in high relative humidity and uplift of local soil particles, potentially affecting PM level, are also analysed.