the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 07 Mar 2024
Real-world emission characteristics of VOCs from typical cargo ships and their potential contributions to SOA and O3 under low-sulfur fuel policies
Abstract. Mandatory use of low-sulfur fuel according to global sulfur limit regulation has reduced the emissions of SO2 and PM significantly on ships, while it also leads to very large uncertainty on VOCs emission. Therefore, on-board test of VOCs from 9 typical cargo ships with low-sulfur fuels in China were carried out in this study. Results showed that emission factor of VOCs (EFVOCs) varied largely from 0.09 to 3.01 g kg-1 fuel, with domestic coastal cargo ships (CCSs) had the highest levels and ocean-going vessels (OGVs) the lowest. The switch of fuels from heavy fuel oil (HFO) to diesel increased EFVOCs by 48 % on average, which enhanced both O3 and secondary organic aerosol (SOA) formation potentials, especially for OGVs. Besides, the use of low-sulfur fuels for OGVs also lead to significant increase of naphthalene emission. These indicated the implementation of globally ultra-low-sulfur oil policy in the near future needs to be optimized. Moreover, aromatics were the most important common contributors to O3 and SOA in ship exhausts, which need to be controlled with priority. It was also found that benzene, toluene, and ethylbenzene ratio of 0.5:0.3:0.2 on average could be considered as a diagnostic characteristic to distinguish ship emission from other emission sources.
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RC1: 'Comment on egusphere-2024-652', Tom Eckel, 10 May 2024
quality of the preprint
This is a well-researched paper that approaches a high priority area with very little previous work. The emission regulatory agencies and commercial maritime industries are beginning to incorporate VOC and HAPS into the regulatory discussions, and there is shockingly little available data. I understand that due to the scope of the work, some finer details can be lost, but the work itself is tremendous. The dataset that has been produced gives a broad look into the emissions profiles of vessels in that region. This also highlights key differences in the emissions profiles of different types of vessels that serve different purposes, and demographics. This paper does an excellent job of contextualizing the at-risk communities for each vessel type in the background section. The conclusions were also quite compelling. Using T/B/E as a marker to track ship VOC emissions will have a huge impact in the modeling and sampling communities, and this information needs to be relayed so that work on VOC emissions of vessels of different types can begin in earnest, and so that researchers have more tools at their disposal to understand the magnitude of the issue at hand. Excellent paper, well conceptualized, good delivery.
specific comments
I worry that since this paper is so dense, there are a lot of important details about the sources your tested that haven’t been mentioned in the SI. I would like to see a small discussion in your paper about how representative these engines would be relative to the engines that are typically deployed on inland, coastal, and ocean-going vessels in this region. It would also be nice to see more discussion on vessel information and what type of activity each vessel was involved in. Possibly a travel route with a speed or engine load overlay for the in-use testing. One of the bigger components about mobile source testing that is becoming more and more prevalent is activity, which is defined as the type of activity the source is involved in, what the typical engine loads encountered for this activity are, and how that may affect the emissions signal. On that same note, it was never discussed in the SI how the average emissions factors were arrived at. Were the D-2 and E-3 certification test cycles used or was the average performed unweighted?
Try to revisit your “low medium and high load” graph in figure 2, do the same low medium and high, except separate OGV, CCS, and ICS. You might see a much tighter resolution on data by load if you incorporate the data points from outside studies that would lead to a better reader understanding of what the engines are doing.
There needs to be a more explicit discussion on how you arrived at your modal emissions factors. Incorporate a subsection into your methods for this.
Technical corrections
88 references missing
114 healthy
115 researches
126 valuated or evaluated
208 controls
317-318 confusing wording
392 needs a semicolon
397-399 A recent study reported that the addition of additives including naphthalene to low-sulfur fuel during the blended fuel manufacturing process to improve stability could lead to an increase in PAHs, especially naphthalene (Yeh et al., 2023).
You are stating that by adding naphthalene, you increased naphthalene. This is a bit confusing. Are you saying this addition yields increased naphthalene in exhaust? If so, just clarify.
Citation: https://doi.org/10.5194/egusphere-2024-652-RC1 - AC1: 'Reply on RC1', Fan Zhang, 06 Jun 2024
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RC2: 'Review of egusphere-2024-652', Anonymous Referee #2, 11 May 2024
The study egusphere-2024-652 by Fan Zhang et al. titled "Real-world emission characteristics of VOCs from typical cargo ships and their potential contributions to SOA and O3 under low-sulfur fuel policies" presents a significant amount of field data for operational cargo ships in China.
This study presents valuable data and makes an outstanding effort to place it in the context of previous work. I commend the authors on their work and recommend publication of this manuscript after the following relatively minor comments are addressed.
Major comments
The discussion does not make a connection between the 106 VOCs measured in this study and the ozone and SOA FP. The manuscript needs to answer the questions:
a) Why measure these specific 106 VOCs? Does this subset of VOCs cover the major species observed in previous mass balances?
b) Why assume that these VOCs can explain the ozone and SOA FP? If the SOA FP of 5 unmeasured VOCs was 100x larger than these 106, then the results of the study would not be representative.
c) How do different environmental conditions influence the accuracy of the SOA and ozone formation?
These are questions which have been considered by previous studies, and the authors should be able to address them relatively easily by adding citations and comments in the introduction, methods, and discussion sections.
Minor comments
The abstract summarizes results for CCS and OGVs but not ICS. Please add ICS to the abstract, which will help readers better anticipate the contents of the work.
I find Figure S1 quite valuable and recommend moving the information to the manuscript. However, please find a way to add error bars (or some other measure of variability, like a second Y axis of "standard deviation") to the plot. Please modify the figure caption to explain how the data from different ships were summarized -- it looks like the authors are plotting the mean values? Please comment on the variability between ships? (In contrast, Figure S2 appears to be a summary of Figure S1 and I would leave it in the SI.)
In contrast, Figure 3 is very detailed and not really digestible to the reader. I would move this figure to the SI, and report all data as downloadable data files so that readers requiring this level of detail can use it. I cannot read the x axis of Figure 3. Consider plotting this instead as "mass fraction of Alkanes" with subcategories of the measured alkanes (i.e. subdivide Figure S2) instead.As noted above, the introduction should mention and cite studies which explain the connection between VOC chemistry and SOA formation potential.
The introduction should introduce the concepts of IVOCs and OVOCs, which appeared in line 169 without definition. Especially since these definitions are different from the common IVOC, SVOC, LVOC categories.
Line 142, for the reader's benefit, please add the range of years meant by "older", based on Table 1, after making this subjective comment.
Table 1, which engines were sampled? Note this in the caption, please.
Line 23, "emission of EF" change to "the EF" (EF is "emission" already)
Figure 4 caption should point to the section where the source ratios are cited, please.
Figure 4: I do not disagree with the authors that the B:T:E ratios could be used as tracers for ship emissions. But please add a box to highlight the region you are suggesting. Specify the recommended region explicitly in the text for clarity.
Citation: https://doi.org/10.5194/egusphere-2024-652-RC2 - AC2: 'Reply on RC2', Fan Zhang, 06 Jun 2024
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