the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Vertical aerosol particle exchange in the marine boundary layer estimated from helicopter-borne measurements in the Azores region
- 1Leibniz Institute for Tropospheric Research, Leipzig, Germany
- 2Environmental Chemistry and Air Research, Technische Universität Berlin, Germany
- apreviously at: Atmospheric Chemistry, University of Bayreuth, Germany
- 1Leibniz Institute for Tropospheric Research, Leipzig, Germany
- 2Environmental Chemistry and Air Research, Technische Universität Berlin, Germany
- apreviously at: Atmospheric Chemistry, University of Bayreuth, Germany
Abstract. Aerosol particles are important for radiation effects, cloud formation, and therefore, the climate system. A detailed understanding of the spatial distribution of aerosol particles within the atmospheric boundary layer, which depends on sources and sinks as well as long-range transport and vertical exchange, is important. Especially in marine regions, where the climate effect of clouds is comparable high, long-range transport with subsequent vertical mixing is dominating over local aerosol sources.
In this study, three different methods were applied to estimate the vertical aerosol particle flux in the marine boundary layer (MBL) and the vertical exchange between the MBL and the free troposphere (FT): Eddy covariance (EC), flux-gradient similarity (K-theory), and the mixed layer gradient method (MLG). For the first time, MBL aerosol fluxes derived from these three methods were compared in the framework of the "Azores stratoCumulus measurements Of Radiation, turbulEnce and aeroSols" (ACORES) field campaign in the Azores region in the North-East Atlantic Ocean in July 2017. Meteorological parameters as well as aerosol and cloud properties were measured in the marine troposphere using the helicopter-borne measurement platform ACTOS (Airborne Cloud Turbulence Observation System).
All three methods were applied to estimate the net particle exchange between MBL and FT. In many cases, the entrainment fluxes of the MLG method agreed within the range of uncertainty with the EC and K-theory flux estimates close to the top of the MBL, while the surface flux estimates of the different methods diverged. It was not possible to measure directly above the surface with the helicopter-borne payload, which might be a source of uncertainty in the surface fluxes. The observed particle fluxes at the top of the MBL ranged from 0 to 10 · 106 m−2 s−1 both in the upward and the downward direction, and the associated uncertainties were on the same order of magnitude. Even though the uncertainties of all three methods are considerable, the results of this study contribute to an improved understanding of the transport of particles between the MBL and FT, and their distribution in the MBL.
Janine Lückerath et al.
Status: closed (peer review stopped)
-
RC1: 'Comment on acp-2021-1071', Anonymous Referee #1, 11 Mar 2022
The paper reports a study of vertical aerosol fluxes and vertical concentration profiles in the marine boundary-layer. Three different approaches are used to estimate fluxes using helicopter-based measurements and results are compared. I believe that the topic is interesting and there are elements of innovation especially because the MBL is not frequently studied with these approaches and available information is limited in current scientific literature. I also believe that even if the different methods have relatively large uncertainties, results could give useful insights in the exchanges of particles in the marine boundary layer. The topic is suitable for the Journal.
A few aspects should be made more clear in a revision step as mentioned below.
Lines 50-57. Probably it could also be mentioned the work at Mace Head regarding fluxes focused on sea spray.
Line 99. Better to say less demanding or less difficult rather than less serious.
There is a confusion of time resolution (that should be in s) and frequency (in Hz), for example in line 112 or in Table 1.
Line 113. How have been done the correction for aerosol losses? For this is usually necessary to have a measurement of size distribution.
Lines 116-119. This pendulum motion was seen on meteorological measurements?
It could be useful to discuss how the magnitude of fluxes compare with measurements in different environments that could help the reader to make more sense of the large uncertainties and of the role of counting errors. They seems to be significantly lower than those observed in urban areas but likely larger or comparable with those observed in polar regions.
Median values are used instead of averages for gradient and MLG approach. Is there a reason? I mean did authors verified that it is better compared to the more widely used average values?
Line 223. Better airborne.
Caption of Table 2. It is needed a subscript in zP.
Considering that uncertainties are often quite large and in several instances also the sign of flux could be ambiguous, it would be useful an effort to summarise in the conclusions what can be concluded and what needs further studies regarding particle exchanges in the MBL. It would also be useful to conclude, if possible, what is the more suitable calculation approach for fluxes in the conditions studied.
-
RC2: 'Comment on acp-2021-1071', Anonymous Referee #3, 01 Apr 2022
The authors present a novel analysis of airborne (helicopter-based) vertical fluxes of aerosol particle number concentrations. Three separate techniques for deriving vertical fluxes are explored and a systematic discussion of their strengths and weaknesses are included. The authors present a fair assessment of the limitations of the techniques which will be valuable for future analyses. The paper focuses primarily on measurements of the entrainment flux of aerosol from the free troposphere, concluding that in the airmasses sampled here, entrainment could supply 30-40 particles/cm3 per hour to the MBL.
My only comment is that it would be helpful to expand on this last point a bit more to include a short discussion on the sources and sinks of particles in the MBL and the extent to which numbers of this magnitude (30 p/cm3 h) compare with what one might estimate for dry deposition to the ocean surface or that needed to sustain some of the larger NPF events that have been sampled at ENA. This might help the reader (and future scientists) get a better handle to the limitations of this approach in the context of the magnitude of the fluxes required to change particle concentrations in the MBL.
-
RC3: 'Comment on acp-2021-1071', Anonymous Referee #2, 04 Apr 2022
The paper by Luckerath et al. addresses an important topic of aerosol dynamics in the boundary layer where large uncertainties exist in estimating particle fluxes either directly by flying platforms or by indirect/ground measurements. Although scientifically the study does not deliver substantial results, method comparison using specific experimental platform is very important in understanding advantages and limitations of different methods and their uncertainties. The paper is written and developed very well and should be suitable for publication after providing a better context and clarifying few details.
The study was performed over the Northeast Atlantic and the authors should be aware of the number papers over the same region which are relevant both methodologically as well as for their comparative value(Flanagan, Geever et al. 2005, Geever, O'Dowd et al. 2005, Ceburnis, O'Dowd et al. 2008, Ceburnis, Rinaldi et al. 2016)
Comments
Line 36 Very much disputed aspect that sea spray contributes little to aerosol number <300nm. Please refer to (Ovadnevaite, Manders et al. 2014, Xu, Ovadnevaite et al. 2021)
Line 59. Azores are indeed a good location for flight-borne measurements, but is it perfect given dominant high-pressure systems, contributing to mixing? Methods confirm this by 2/3 of the campaign characterized by dry weather with low cloud fraction. Mid-latitude oceans on the other hand are dominated by low pressure systems.
Line 101. I wonder how much of the disturbance helicopter created during the ascent? Wouldn't the descent profile make more sense considering that external cargo was hanging below a helicopter?
Equation 3. Doesn't this formula produce unrealistic K values? E.g. K=0.3*0.3*20*48=86.4m2/s
Line 164. Should vTAS be vair?
Line 185. derivative instead of specification
Table 2. Comparison to environmental variables is lacking, like horizontal wind speed, etc.
Ceburnis, D., C. D. O'Dowd, G. S. Jennings, M. C. Facchini, L. Emblico, S. Decesari, S. Fuzzi and J. Sakalys (2008). "Marine aerosol chemistry gradients: Elucidating primary and secondary processes and fluxes." Geophysical Research Letters 35(7): L07804.
Ceburnis, D., M. Rinaldi, J. Ovadnevaite, G. Martucci, L. Giulianelli and C. D. O'Dowd (2016). "Marine submicron aerosol gradients, sources and sinks." Atmospheric Chemistry and Physics 16(19): 12425-12439.
Flanagan, R. J., M. Geever and C. D. O'Dowd (2005). "Direct measurements of new-particle fluxes in the coastal environment." Environmental Chemistry 2(4): 256-259.
Geever, M., C. D. O'Dowd, S. van Ekeren, R. Flanagan, E. D. Nilsson, G. de Leeuw and U. Rannik (2005). "Submicron sea spray fluxes." Geophysical Research Letters 32(15): Artn L15810.
Ovadnevaite, J., A. Manders, G. de Leeuw, D. Ceburnis, C. Monahan, A. I. Partanen, H. Korhonen and C. D. O'Dowd (2014). "A sea spray aerosol flux parameterization encapsulating wave state." Atmospheric Chemistry and Physics 14(4): 1837-1852.
Xu, W., J. Ovadnevaite, K. N. Fossum, C. S. Lin, R. J. Huang, C. O'Dowd and D. Ceburnis (2021). "Seasonal Trends of Aerosol Hygroscopicity and Mixing State in Clean Marine and Polluted Continental Air Masses Over the Northeast Atlantic." Journal of Geophysical Research-Atmospheres 126(11).
Status: closed (peer review stopped)
-
RC1: 'Comment on acp-2021-1071', Anonymous Referee #1, 11 Mar 2022
The paper reports a study of vertical aerosol fluxes and vertical concentration profiles in the marine boundary-layer. Three different approaches are used to estimate fluxes using helicopter-based measurements and results are compared. I believe that the topic is interesting and there are elements of innovation especially because the MBL is not frequently studied with these approaches and available information is limited in current scientific literature. I also believe that even if the different methods have relatively large uncertainties, results could give useful insights in the exchanges of particles in the marine boundary layer. The topic is suitable for the Journal.
A few aspects should be made more clear in a revision step as mentioned below.
Lines 50-57. Probably it could also be mentioned the work at Mace Head regarding fluxes focused on sea spray.
Line 99. Better to say less demanding or less difficult rather than less serious.
There is a confusion of time resolution (that should be in s) and frequency (in Hz), for example in line 112 or in Table 1.
Line 113. How have been done the correction for aerosol losses? For this is usually necessary to have a measurement of size distribution.
Lines 116-119. This pendulum motion was seen on meteorological measurements?
It could be useful to discuss how the magnitude of fluxes compare with measurements in different environments that could help the reader to make more sense of the large uncertainties and of the role of counting errors. They seems to be significantly lower than those observed in urban areas but likely larger or comparable with those observed in polar regions.
Median values are used instead of averages for gradient and MLG approach. Is there a reason? I mean did authors verified that it is better compared to the more widely used average values?
Line 223. Better airborne.
Caption of Table 2. It is needed a subscript in zP.
Considering that uncertainties are often quite large and in several instances also the sign of flux could be ambiguous, it would be useful an effort to summarise in the conclusions what can be concluded and what needs further studies regarding particle exchanges in the MBL. It would also be useful to conclude, if possible, what is the more suitable calculation approach for fluxes in the conditions studied.
-
RC2: 'Comment on acp-2021-1071', Anonymous Referee #3, 01 Apr 2022
The authors present a novel analysis of airborne (helicopter-based) vertical fluxes of aerosol particle number concentrations. Three separate techniques for deriving vertical fluxes are explored and a systematic discussion of their strengths and weaknesses are included. The authors present a fair assessment of the limitations of the techniques which will be valuable for future analyses. The paper focuses primarily on measurements of the entrainment flux of aerosol from the free troposphere, concluding that in the airmasses sampled here, entrainment could supply 30-40 particles/cm3 per hour to the MBL.
My only comment is that it would be helpful to expand on this last point a bit more to include a short discussion on the sources and sinks of particles in the MBL and the extent to which numbers of this magnitude (30 p/cm3 h) compare with what one might estimate for dry deposition to the ocean surface or that needed to sustain some of the larger NPF events that have been sampled at ENA. This might help the reader (and future scientists) get a better handle to the limitations of this approach in the context of the magnitude of the fluxes required to change particle concentrations in the MBL.
-
RC3: 'Comment on acp-2021-1071', Anonymous Referee #2, 04 Apr 2022
The paper by Luckerath et al. addresses an important topic of aerosol dynamics in the boundary layer where large uncertainties exist in estimating particle fluxes either directly by flying platforms or by indirect/ground measurements. Although scientifically the study does not deliver substantial results, method comparison using specific experimental platform is very important in understanding advantages and limitations of different methods and their uncertainties. The paper is written and developed very well and should be suitable for publication after providing a better context and clarifying few details.
The study was performed over the Northeast Atlantic and the authors should be aware of the number papers over the same region which are relevant both methodologically as well as for their comparative value(Flanagan, Geever et al. 2005, Geever, O'Dowd et al. 2005, Ceburnis, O'Dowd et al. 2008, Ceburnis, Rinaldi et al. 2016)
Comments
Line 36 Very much disputed aspect that sea spray contributes little to aerosol number <300nm. Please refer to (Ovadnevaite, Manders et al. 2014, Xu, Ovadnevaite et al. 2021)
Line 59. Azores are indeed a good location for flight-borne measurements, but is it perfect given dominant high-pressure systems, contributing to mixing? Methods confirm this by 2/3 of the campaign characterized by dry weather with low cloud fraction. Mid-latitude oceans on the other hand are dominated by low pressure systems.
Line 101. I wonder how much of the disturbance helicopter created during the ascent? Wouldn't the descent profile make more sense considering that external cargo was hanging below a helicopter?
Equation 3. Doesn't this formula produce unrealistic K values? E.g. K=0.3*0.3*20*48=86.4m2/s
Line 164. Should vTAS be vair?
Line 185. derivative instead of specification
Table 2. Comparison to environmental variables is lacking, like horizontal wind speed, etc.
Ceburnis, D., C. D. O'Dowd, G. S. Jennings, M. C. Facchini, L. Emblico, S. Decesari, S. Fuzzi and J. Sakalys (2008). "Marine aerosol chemistry gradients: Elucidating primary and secondary processes and fluxes." Geophysical Research Letters 35(7): L07804.
Ceburnis, D., M. Rinaldi, J. Ovadnevaite, G. Martucci, L. Giulianelli and C. D. O'Dowd (2016). "Marine submicron aerosol gradients, sources and sinks." Atmospheric Chemistry and Physics 16(19): 12425-12439.
Flanagan, R. J., M. Geever and C. D. O'Dowd (2005). "Direct measurements of new-particle fluxes in the coastal environment." Environmental Chemistry 2(4): 256-259.
Geever, M., C. D. O'Dowd, S. van Ekeren, R. Flanagan, E. D. Nilsson, G. de Leeuw and U. Rannik (2005). "Submicron sea spray fluxes." Geophysical Research Letters 32(15): Artn L15810.
Ovadnevaite, J., A. Manders, G. de Leeuw, D. Ceburnis, C. Monahan, A. I. Partanen, H. Korhonen and C. D. O'Dowd (2014). "A sea spray aerosol flux parameterization encapsulating wave state." Atmospheric Chemistry and Physics 14(4): 1837-1852.
Xu, W., J. Ovadnevaite, K. N. Fossum, C. S. Lin, R. J. Huang, C. O'Dowd and D. Ceburnis (2021). "Seasonal Trends of Aerosol Hygroscopicity and Mixing State in Clean Marine and Polluted Continental Air Masses Over the Northeast Atlantic." Journal of Geophysical Research-Atmospheres 126(11).
Janine Lückerath et al.
Janine Lückerath et al.
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