Dramatic increase of reactive VOC emission from ships at berth after implementing the fuel switch policy in the Pearl River Delta Emission Control Area

Abstract. Limiting the fuel sulfur content (FSC) is a widely adopted approach to reduce ship emissions of sulfur dioxide (SO2) and particulate matters (PM) particularly in emission control areas (ECA), but its impact on the emission of volatile organic compounds (VOCs) is still not well understood. In this study, emissions from ships at berth in Guangzhou, south China, were characterized before and after implementing the fuel switch policy with a FSC limit of 0.5 % in the Pearl River Delta ECA in south China. After implementing the fuel switch policy, the emission factors (EFs) of SO2 and PM2.5 for coastal vessels dropped by 78 % and 56 % on average, respectively; the EFs of non-methane hydrocarbons (NMHCs), however, reached 1807 ± 1746 mg/kg, about 15 times that of 118 ± 56.1 mg/kg before implementing the new policy. This dramatic increase in the emission of NMHCs might be largely due to the replacement of high-sulfur residual fuel oil with low-sulfur diesel or heavy oils, which are typically more rich in short-chain hydrocarbons. Moreover, reactive alkenes overtook alkanes to become the dominant group among NMHCs and low carbon number NMHCs, such as ethylene, propene and isobutane, became the dominant species after the new policy. As a result of the largely elevated EFs of reactive alkenes and aromatics after the new policy, for per kilogram of fuel burned, emitted NMHCs had nearly 29 times larger ozone formation potentials (OFPs) and about 2 times higher secondary organic aerosol formation potentials (SOAFPs). Unlike coastal vessels, river vessels in the region used diesel fuels all along and were not affected by the fuel switch policy, but their EFs of NMHCs were even 90 % larger than that of coastal vessels after implementing the new policy, with about 120 % larger fuel-based OFPs and 70–140 % larger SOAFPs. The results from this study suggest that while the fuel switch policy could effectively reduce SO2 and PM emissions and thus help combat PM2.5 pollution, it would also lead to greater emissions of reactive VOCs, that may threatens ozone pollution control in the harbor cities. This change for coastal or ocean-going vessels, along with the large amounts of reactive VOCs from river vessels, raises regulatory concerns for ship emissions of reactive VOCs.


2 species we determined are C2-C12 hydrocarbons, sometimes we just used the term "NMHC" when 27 referring to the 68 VOCs in our manuscript. To avoid confusion, in the revised manuscript we have 28 replaced all "NMHCs" with "VOCs".

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2. More information about sampling and analysis is needed, such as sampling flow, sampling time, 30 sampling temperature, the auxiliary load, the devices used for conventional pollutants, and the standard 31 gas for VOC measurement.   Besides, we have also added sampling temperature and the auxiliary load in Table S1 in the supporting 51 information as showed below:

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Then, is there apparent difference of VOC compositions for tested ships using four different fuels?

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What is the trendy of the VOC emissions when correlating the diesel composition?

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Reply: We simply measured solvent-extractable fraction of the oils by GC-MSD as some fuels are very 70 sticky residue oils before the fuel switch policy. Nonetheless, as showed in Figure S1, we could see that

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Although the responses of the most hydrocarbons did not change very much, the responses of low 80 carbon number species, including naphthalene, tridecanes and methylnaphthalenes, became relatively 81 higher, and lower carbon number species such as indene (C8) were also detected. As a result, we found 82 the mass percentages of < C6 VOCs (VOCs with carbon numbers below 6) in the total VOCs in ship 83 exhaust increased from 8.5%-27.3% to 44.4%-86.6% after implementing the fuel switch policy. As 84 described in the manuscript, we noticed that the fuel used by the ships became more abundant in low 85 molecular weight fractions, but we did not conduct a comprehensive analysis of the fuel compositions 86 and we do not know if the fuels we samples are representative enough, so we feel it would be 87 inappropriate to go further saying more in this aspect. As a matter of fact, after we report our results to 88 local administrations, they determined to start a full-scale survey about fuels used by ships. 4. More concise. Academic writing is a big question for this manuscript. There are many simple 92 mistakes appeared in substantial sentences, which are mostly summarized in minor comments.

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Polishing the language is strongly suggested.

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Reply: Really sorry for making so many simple mistakes. Thanks a lot for your hard work in carefully 95 checking the manuscript. We have also requested an academic editing service "SPRINGER NATURE

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Author Services (SNAS)" to improve the English language, grammar, punctuation, spelling, and 97 overall style by one or more of the highly qualified native English speaking editors at SNAS. The

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Choose a suitable phrase for this expression.

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Reply: Thanks for the suggestion. In the revised manuscript, we use "the implementation of the fuel 104 switch policy" to unify the expression.

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Minor Comments 106 1. Line 24 The unit of EF is not unitized, mg/kg and mg kg-1.

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Reply: As suggested, we have unitized the unit of EF in mg kg -1 .

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2. Line 26 more rich… is it not richer?

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Reply: As suggested, we have replaced "more rich" with "richer".

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4. Line 34 "may threatens"? It doesn't need the plural form for the term "threaten".

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Reply: As suggested, we have replaced "ship emission" with "ship emissions".

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7. Line 57 Is it suitable using the word"combat"?

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Reply: As suggested, we have replaced "emissions from ship" with "emissions from ships". 133 11. Line 113 What is a PM2.5 cutting head? Please give an accurate description.

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Reply: As suggested, we have replaced "already used" with "have already used".

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14. Line 133 The EF of CO2 is calculated not determined. As follows not as following.

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Reply: As suggested, we have replaced "determined" with "calculated".  18. Line 161 The number of C6 should be subscripted.

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19. Line 156 What is NMHCs? Is the measured VOC species?

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Reply: Yes, it refers to the measured VOC species. We have replaced "NMHCs" with "VOCs".

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Reply: As suggested, we have replaced "limit" with "limited".

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Reply: As suggested, we have replaced "The EF of CO2" with "The EFs of CO2".

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23. Line 159-163 It should give a summary rather than displaying the tested results of every ship.

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Reply: Because ships C and D were tested both before and after the implementation of the fuel switch 161 policy, the changes in emissions for the two ships would be more convincing in reflecting the influence 162 of the fuel switch policy. This is why we particularly display the tested results of ships C and D.

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Reply: As suggested, we have replaced "that" with "those".

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25. Line 168 What is the carbonaceous aerosol? Does that mean OC and EC?

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Reply: Yes, carbonaceous aerosol included OC and EC. 167 26. Line 169 "As shown" is the correct form, please revise all of the forms in this manuscript.

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Reply: As suggested, we have replaced "As showed" with "As shown" in the whole manuscript.  188 Reply: Yes, we only measured acetylene in this study.

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Reply: As suggested, we have replaced "were" with "was".