the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 24 May 2024
Two distinct ship emission profiles for organic-sulfate source apportionment of PM in sulfur emission control areas
Abstract. Source apportionment quantitatively links pollution to its source, but can be difficult to perform in areas like ports where emissions from ship and other port-related activities are intrinsically linked. Here we present the analysis of aerosol chemical speciation monitor (ACSM) data and combined organic and sulfate ion positive matrix factorization (PMF) during an intensive measurement campaign in Dublin Port. Two main types of ship emissions were identified by this technique: sulfate-rich (S-Ship) and organic-rich (O-Ship). The S-Ship emissions were attributed to heavy fuel oil use and are characterised by particles with standard V/Ni ratios from 2.7–3.9 and a large fraction of acidic sulfate aerosol. The O-Ship emissions were attributed to low-sulfur fuel types and were comprised mostly of organic aerosol (OA) with the V/Ni ratios ranging only from 0–2.3. O-Ship plumes occurred over three-times more frequently than S-Ship plumes during the measurement period. Ship plumes had PM1 concentrations in the range 4–252 µg m-3, with extreme concentrations usually lasting for 5–35 minutes. A third minor ship emission factor (X-Ship) was resolved by PMF, but not clearly attributable to any specific fuel type. Despite their short duration, shipping emission plumes were frequent and contributed to at least 28 % of PM1 (i.e. 14 % O-Ship, 12 % S-Ship, and 2 % X-Ship). Moreover, hydrocarbon-like organic aerosol (HOA) and black carbon could also originate, at least in part, from ship emissions and shipping related activities, suggesting that the shipping contribution to ambient PM is likely higher, with a maximum of 47 %.
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RC1: 'Comment on egusphere-2024-1262', Anonymous Referee #1, 12 Jun 2024
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This study presents in-situ measurements taken at a port area within SECA. The authors identified the reference mass spectrum for two distinct types of ship plumes. Based on this, they performed a source apportionment analysis to characterise contributions from both shipping and regional residential emissions. The PMF factors developed in this study will inform future aerosol mass spectrometry research, aligning well with the scope of the ACP journal. However, the discussions and the definitions of terms require improvements to enhance clarity.
Major comments
- The terms given to the shipping emission types throughout the manuscript are inconsistent. In the PMF section (Section 3.2), the authors identify the reference mass spectra profiles as "O-ship" and "S-ship" (Figure 3). However, these terms change to "VLSFO" and "HFO" in Figure 5 (Section 3.3), with additional discussions on the usage of "MGO" fuel. In the conclusions section, the authors state in Lines 486-487 that the organic-sulfate PMF can identify "HFO" and "VLSFO" emissions. I suggest the authors revise their terminology and provide clear definitions for each term.
- Following comment #1, for Section 3.3, Although the statistical increase in NOx and SO2 concentrations indicated the presence of a ship plume during the "bat-ear" period, the particle mass concentration remained low, possibly because the smaller particle sizes were below the detection limit of the ACSM. Is this low mass concentration period also classified as an “O-ship” plume period? If so, could the low mass concentrations during these periods affect the composition breakdown pie chart results in Figure 4, and potentially underestimating the contribution of O-ship to the aerosol mass concentration?
- Page 16, Line 396 – 402, In addition to the fuel types, other factors such as variations in engine loadings and the use of lubricating oil may also influence the absolute number concentrations. Furthermore, since the measurements were not taken directly at the stack, the absolute concentrations may be diluted during plume transport.
- Page 14, Figure 3, Although all PMF factors have distinctive mass spectrum profiles and generally weak correlations over the entire campaign period, S-ship related OA shows a peak during nighttime (from 8 pm to 3 am), which is similar to the trend of peat-related OA. In contrast, the diurnal pattern of O-ship related OA is more irregular which makes sense. Given that residential solid fuel combustion may also contribute to sulfate emissions (Lin et al., 2021), is the S-ship factor slightly influenced by regional emissions, particularly during the night period?
Minor comments
- Page 1, Line 40. Should be contributed to “PM1” instead of total “PM”.
- Page 3, Line 64 – 86, though wet scrubbers or poor quality low-sulfur fuel may have some disadvantages, previous studies (e.g. Yu et al., 2020) have shown that the IMO 2020 regulation will lead to significant reduction of aerosol emissions. Please add some information about the positive part of the new IMO regulations.
- Page 4, Line 100- 105. Dublin port is within SECA (regulated fuel sulfur content < 0.1%), and the authors declare that the VLSFO (fuel sulfur content < 0.5%) is used here for the engine. As 0.5% is the regulated level for the open sea shipping lane, is the fuel with fuel sulfur content larger than 0.1% but smaller than 0.1% allowed to be used within SECA?
- Page 8, Section 2.2.3, Please give more details how the AE33 is corrected for the multiple-scattering factor.
- Page 16, Line 396 – 402, please bring the SMPS results in Figure S10 to the main context to support your discussions about the size modes of ship plumes.
- Page 18, Line 457 – 460, The authors could benefit from incorporating discussions of previous studies that characterise emissions from various ship operation modes (Wu et al., 2021).
References:
Lin, C., Ceburnis, D., Trubetskaya, A., Xu, W., Smith, W., Hellebust, S., Wenger, J., O'Dowd, C. and Ovadnevaite, J., 2021. On the use of reference mass spectra for reducing uncertainty in source apportionment of solid-fuel burning in ambient organic aerosol. Atmospheric Measurement Techniques, 14(10), pp.6905-6916.
Wu, Y., Liu, D., Wang, X., Li, S., Zhang, J., Qiu, H., Ding, S., Hu, K., Li, W., Tian, P. and Liu, Q., 2021. Ambient marine shipping emissions determined by vessel operation mode along the East China Sea. Science of The Total Environment, 769, p.144713.
Yu, C., Pasternak, D., Lee, J., Yang, M., Bell, T., Bower, K., Wu, H., Liu, D., Reed, C., Bauguitte, S. and Cliff, S., 2020. Characterizing the particle composition and cloud condensation nuclei from shipping emission in Western Europe. Environmental Science & Technology, 54(24), pp.15604-15612.
Citation: https://doi.org/10.5194/egusphere-2024-1262-RC1 -
RC2: 'Comment on egusphere-2024-1262', Anonymous Referee #2, 14 Jun 2024
reply
The study analyzed ship emissions at Dublin Port using Aerosol Chemical Speciation Monitoring (ACSM) data and Positive Matrix Factorization (PMF) methods. It identified two main types of ship emissions: sulfate-rich S-Ship and organic-rich O-Ship. S-Ship emissions are associated with the use of heavy fuel oil, while O-Ship emissions are attributed to low-sulfur fuel types. The study is innovative and, after making some minor revisions, it is recommended for publication.
- The author mentions in Section 3.2.1 that Appendix Figure S2 shows the results for 2 to 10 factors, but where is this information in Appendix Figure S2?
- The core of this article is based on the ratio of vanadium to nickel and sulfate fragments; however, to my knowledge, ship emissions cannot be solely reliant on the ratio of V to Ni. The V/Ni ratio is also not a standard tracer for ship emissions. Especially since 2020, there have been strict regulations on the fuel used by ships in emission control areas, which necessarily affects the usability of the V/Ni ratio. The author needs to provide more direct evidence. Furthermore, the measurement of vanadium and nickel is conducted in PM2.5, whereas ACSM measures PM1. How does the author account for this discrepancy?
- The author spends a considerable amount of content introducing the ship scrubber device, which in my view, is unnecessary to elaborate on to such an extent.
- In the manuscript, the author notes that Dublin experiences poor air quality daily due to the burning of domestic solid fuel for home heating, particularly during the colder months (mainly winter), especially at night. This could have a significant impact on the results of this study. Since another assumption of this study is that sulfate fragments are primarily derived from ship emissions, the author should provide more convincing discussions.
- I didn't see any diagrams or introductions regarding wind direction and air mass trajectories, which makes the reader suspect whether the monitoring site is influenced by emissions from nearby factories.
- In line 234, the author indicates that a considerable number of pollution peaks have a V/Ni ratio below 2.5, suggesting the use of different types of fuels in the port area. Where does this conclusion come from?
- Line 255. “The comparison (Fig. S6) shows that while some regional pollution events occur simultaneously at both sites, the pollution spikes at Dublin Port are unique and localised.”, “Using this approach, around 50 plumes were manually identified with the V/Ni ratio in the expected range for HFO emissions, and occurred when the wind direction was primarily from the South (Southwest to Southeast included)” These two sentences need to be clearly explained. Because from Figure S1, I can see that under higher wind speeds, the factory is likely to contribute some pollutants.
- What does the "4ion fraction" on the right coordinate of the O-ship mass spectrum in Figure 3 mean?
Citation: https://doi.org/10.5194/egusphere-2024-1262-RC2
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