Compliance and port air quality features of ship fuel switching regulation : by a field observation SEISO-Bohai

Since January 1, 2017, ships berth at the core ports of three designated Domestic Emission Control Area (DECA) in China should use fuel with sulphur content less than or equal to 0.5 %. In order to evaluate the impacts of switching fuel, a measurement campaign (SEISO-Bohai) was conducted from 28 December 2016 to 15 January 2017 at JingTang Harbor, an area within the 7 busiest port in the world, including meteorological monitoring, pollutants monitoring, aerosol sampling and 15 fuel sampling. During the campaign, 16 ship plumes were captured by the on-shore measurement sites, and 4 plumes indicates the usage of high SF fuel. The average reduction of average ∆NOx ∆SO2 ⁄ ratio from high sulphur plumes (3.26) before January 1 to low sulphur plumes (12.97) after January 1 shows a direct SO2 emission reduction of 75 %, consistent with the sulphur content reduction (79 %). Average concentrations of PM2.5, NOx, SO2, O3 and CO during campaign were 147.85 μg·m, 146.93 ppb, 21.91 ppb, 29.68 ppb and 2.21 ppm, respectively, among which NOx reached a maximum hourly concentration of 692.6 20 ppb and SO2 165.5 ppb. Mean concentrations of carbonaceous and dominant ionic species in particles were 6.52 (EC), 23.10 (OC), 22.04 (SO4), 25.95 (NO3) and 13.55 (NH4) μg·m. Although the carbonaceous species in particles were not significantly affected by fuel switching, the gas and particle pollutants in ambient air exhibited clear and effective improvements from implementation of low sulphur fuel. Comparison with the prevailing atmospheric conditions and wind map of SO2 variation concluded the prompt SO2 reduction by 70 % in ambient air after fuel switching. Given the high humidity 25 in site, this SO2 reduction will abate the amount of secondary aerosols and improve the acidity of particulate matter. Based on enrichment factors of elements in PM2.5, vanadium was identified as marker for residual fuel ship emissions, decreasing significantly by 97.1% from 309.9 ng·m before fuel switching to 9.1 ng·m after, which indicated a crucial improvement due to the implementation of low sulphur fuel. Ship emissions were proven to be significantly influential both directly and indirectly on port environment and coastal areas around Bohai Bay, in where the population density reaches 650 per square 30 kilometre. The results from this study provide positive impact on air quality of fuel switching and indication of new method on identification of ship fuel type. Atmos. Chem. Phys. Discuss., https://doi.org/10.5194/acp-2018-1233 Manuscript under review for journal Atmos. Chem. Phys. Discussion started: 13 December 2018 c © Author(s) 2018. CC BY 4.0 License.

According to the United Nations Conference on Trade And Development (UNCTAD, 2018), the volume of world seaborne trade has continually grown by 66 % from 2000 to 2015.As global commerce expands, ocean-going vessels consume more fuels but generally the low-quality residual fuels containing high amount of sulphur and heavy metals (Lack et al., 2011), which differs greatly from inland fuel usage.In China, the average sulphur content of marine fuel (SF) was 2.43 % (by mass, i.e., 24300 ppm) before regulation (Liu et al., 2016), extremely higher than the sulphur content restriction 10 ppm applied for inland fuel (China National Standard GB 19147-2013 andGB 17930-2013), leaving ships one of the prominent contributor in major port cities (Lai et al., 2013;HKEPD, 2014;Zhao et al., 2013).In eastern China, ship emissions accounted for an annual increase of up to 5.2 μg•m -3 PM2.5, which influenced the air quality in not only coastal areas but also the inland areas hundreds of kilometres away from the sea (Lv et al., 2018).
These situations have constantly drawn attention on coastal air pollution and correlative emission control strategy.The International Maritime Organization (IMO), the European Union and the United States have implemented regulations in an effort to reduce ship emissions, among which the Fuel Quality Regulation has proven potent in many countries for addressing the issue of sulphur oxides (SOx) and particulate matter (PM) emissions.IMO has regulated SF on a global scale from current 3.5 % to 0.5 % by 2020, and implemented more stringent legislation in designated emission control areas (ECAs), in which considering SOx emissions include the Baltic Sea, the North Sea, the English Channel, and coastal waters around the Canada, US and the US Caribbean Sea.The allowed SF in ECAs was 1 % in 2010 and has shrunk into 0.1 % since 1 January 2015 (IMO, 2008).Estimation shows that IMO limitation of 0.1% SF in ECAs would reduce SO2 emissions by 82 % by 2020, and further 23,000 tons of SO2 and 46,000 tons of NOx totally by 2030 in European seas (Campling et al., 2013).This assumption was supported by other comparable results from sub-region assessment and in site measurements (Matthias et al., 2010;Viana et al., 2015;Zetterdahl et al., 2016).Likewise, EU Directive 2012/33/EU demands that ships at berth in Union ports use fuels with SF < 0.1 % since December 2012, which brings about 50 % reduction of PM2.5 emissions from ships between 2007 and 2012 in Venice, Italy (Contini et al., 2015).Beginning in July 2009, the US state of California introduced legislations limiting vessels operating within 24 nautical miles (44 km) of the California coastline to switch to marine gas oil (MGO) or marine diesel oil (MDO) with a maximum SF of 1.5 % or 0.5 %, respectively (by January 2012 SF shall be < 0.1 %) (CARB, 2009).
As a result, clear improvement of air quality was observed at the Port of Oakland and in the surrounding San Francisco Bay Atmos.Chem.Phys.Discuss., https://doi.org/10.5194/acp-2018-1233Manuscript under review for journal Atmos.Chem.Phys.Discussion started: 13 December 2018 c Author(s) 2018.CC BY 4.0 License.area in 2010 (Tao et al., 2013).Also, Lack et al. (2011) reported that fuel quality regulation along with speed restriction in California could generate an 88% reduction in gaseous and particle pollutant concentrations.
Based on widely acclaimed Fuel Quality Regulations above, China promulgated in 2015 the Implementation of the Ship Emission Control Area in Pearl River Delta, the Yangtze River Delta and the Bohai Rim (Beijing-Tianjin-Hebei area) (MOT, 2015), designing three DECAs with phased SF requirements.Since 1 January 2017, ships berth at the core port of three DECAs should use fuel with SF less than or equal to 0.5 %.This newly regulation provides an opportunity to measure the influence of limiting SF on the magnitudes of ship emissions in China.However, comparing to the fuel regulation after years of enforcement and optimization in Canada, Europe and USA, this one in China was incipient in clauses and vague in terms of supervision.
The possible effects of ship emission control are compelling indeed, but also difficult to evaluate due to the variability of complicated local emission sources and complexity of fleet management.Up to now, much of the previous research on the subject of ship emission control has been restricted to limited comparisons of emissions, failing to specify the compliance of vessels or a practical method to indicate it.
In order to explore the method to capture fuel-related emission change and the impact on air quality of switching fuel, we selected the Bohai Rim (Beijing-Tianjin-Hebei) as research area and conducted in situ measurement of meteorological conditions and pollutants along with chemical analysis of sampled fuels and aerosols, which is a series of typical method within the field of measuring air quality.The campaign ran from 27 December 2016 to 15 January 2017, covering the primary period of the newly regulation.By comparing ship emissions and air quality before and after switching fuel, this paper will shed light on the potential emission reduction effects of the enforced regulation.Meanwhile, certain features in ship plumes were found related to fuel type, hence providing another angle of supervising ship fuels in practice.This could be helpful in actual implementation and management of the new regulation.

Measurement site
The measurement station (39.204576°N, 119.004028°E) for Shipping Emission and Impacts by Switching Oil in Bohai Bay (SEISO-Bohai)campaign is located at the corner of main navigational channel to the third pool in JingTang Harbor (JT for short), on the property and with the support of Hebei Tangshan Harbor Economic Development Zone Office (Fig. 1).Located in Bohai Bay, JT belongs to the Port of Tangshan, one of the core ports in the designated DECAs.China Port Yearbook (2017) reported a total throughput of 520 million tons in the Port of Tangshan, in which JT undertook over 270 million tons.Population density is high around JT and surround Port Economic Development Area, which is over 650 people per square kilometre.Details of JT is described elsewhere (Xiao et al., 2018).The station consists of a measurement container, meteorological observation on roof and aerosol sampling.

Meteorological monitoring
A small meteorological monitoring station was placed on the roof of the container and obtained temperature (℃), relative humidity (%), wind speed (m• s -1 ), wind direction and radiation intensity every 1 min, from 28 December 2016 to 15 January 2017.Abrupt high temperature values were subtracted from results because there was obvious mismeasurement when instrument indicated 40℃ for ambient temperature in winter.

Particle and gas monitoring
Continuous concentrations of 6 gases (NO, NO2, NOx, SO2, and O3 in ppb and CO in ppm) were measured every 1 min and PM2.5 and PM10 (in μg•m -3 ) every 1 hour with a Sailhero XHAQMS3000 air quality continuous monitoring system, from 28 December 2016 to 13 January 2017.Monitoring modules consist of NO, NO2 and NOx measurement by an analyser, SO2 detection by UV fluorometric, CO by IR absorption, O3 by UV spectrophotometry, and particles by β-ray absorption.The instrument had a short, erroneous measurement at the beginning of the campaign, due to maybe unskilled operation, which resulted in some negative values of gas pollutants and over-exaggerating values of SO2, CO and O3.We fixed the instrument immediately and to ensure the accuracy of data, those values above were removed.Mismeasurements of O3 occurred fitfully during the campaign, appearing as a sinusoid fluctuation below 10 ppb, which were subtracted from the results.It should be mentioned that air quality of Xinli Primary School (XL for short, an official air quality monitor site as shown in Fig. 1) as control group was provided by an official air quality monitor (see in http://www.aqistudy.cn).

Aerosol sampling
The campaign resulted in the collection of 14 valid samples in which two parallel samples per day were collected before 31 December 2016 and 1 sample per day after that.The aerosol samples were collected for 23 h (normally from 16:30 to 15:30 LST the next day, local standard time, and named after the ending date) on an 80 mm-diameter pre-fired quartz microfiber filters (CHM QF1 grade) by a Laoying Model 2030 TSP sampler.All samples were put in its original polyethylene plastic box immediately, wrapped in two layers of pre-stoved tinfoil, and then reserved in a refrigerator subsequently.In order to avoid any possible contamination of the samples, all the above procedures were strictly quality-controlled.

Carbon analysis
0.55 cm 2 section of each aerosol sample and blank filters were measured for concentrations of organic carbon (OC) and elemental carbon (EC) by the Thermal Optical Transmission Method in a DRI 2001 organic carbon/elemental carbon (OC/EC) analyser.OC and EC values were determined through Interagency Monitoring of Protected Visual Environments Protocol (referred to as IMPROVEA method).Samples were heated in a completely oxygen-free helium atmosphere, by four increasing temperature steps to remove all OC on the filter, during which part of OC was pyrolized.Then the pure helium eluent was switched into a 10 % oxygen/helium mixture in the oven and stepped into 800℃ for EC determination.OC and EC are detected by a flame ionization detector after oxidation to carbon dioxide and then reduced to methane.The detection limit of this analysis is 0.82 μg• cm -2 for OC and 0.2 μg• cm -2 for EC.

Ion analysis
50 cm 2 section of each aerosol sample and blank filters were extracted with 10 ml ultra-pure water in an ultrasonic bath at 4 ℃ for 30 min.Inorganic ions of Na + , NH4 + , K + , Mg 2+ , Ca 2+ , Cl -, NO3 -, and SO4 2-were analysed using a DIONEX ICS-2100 ion chromatograph.The ion chromatograph system was firstly calibrated by a standard solution before running samples.Data obtained from a sample was compared to that from the known standard, achieving identification and quantification of sample ions.The detection limit was 0.1 μg• L -1 .

Element analysis
20 cm 2 section of each aerosol sample and blank filters were digested with 25 ml of an 8 %-HCl/ 3 %-HNO3 solution in an ultrasonic bath at 69 ℃ for 3 h.The solutions were cooled, vortex mixed, and then placed in a centrifuge at 2800 rpm for 15 min to settle any insoluble particle, of which a 5 ml aliquot is taken for analysis of 30 elements (Be, Na, Mg, Al, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Sr, Mo, Ag, Sn, Ba, La, Ce, Hg, TI, Pb, Th and U) by an X Series 2 ICP-MS mass spectrometer.Measured Be concentrations were mostly 0 μg• m -3 during the whole sampling, which was subtracted from results.
Cr was also removed since the blank value exceeded most of the sample results.Several concentrations of Cd and Mo were below detection, which was removed as well.

Ship plume event
Method of identifying ship plume event using direct and simultaneous measurements of trace gases with in situ instruments aims at the surveillance of emissions and fuel type on board of passing ships.Since the measurement site is in the vicinity of the channel and the berth, when wind directions are favourable for measurements, ship plumes passing the instrument leave a distinctive change of the measured components against background concentrations, which is defined as the ship plume event.
Several studies have confirmed that synchronic variation in pollutant concentrations can be used to identify the occurrence of ship plume events in observation near the harbour (Alföldy et al., 2013;Ault et al., 2010;Contini et al., 2015;Gao et al., 2016;Kattner et al., 2015;Lu et al., 2006): SO2, NOx, CO2, BC, PM2.5 concentrations and number concentrations of aerosol particle would increase simultaneously at the onset of the ship plume, but O3 concentration would decrease due to its reduction reaction with NO forming NO2.
Nitrogen compounds were abundant in JT due to the heavy traffic, while source of large amount of SO2 emissions was rather simple.Therefore SO2 peaks, or SO2 episodes, were used as an indicator for recent anthropogenic emissions.The background SO2 per day was set as the daily lowest concentration, and any enhancement that was more than 3 ppb was marked as the time stamp of a possible ship emission event.For these time stamps, peaks in NOx along with simultaneous valleys in O3 were then identified in valid data, which resulted in 16 ship plumes.The signals were only affirmed when there were significant peaks and clearly determinable backgrounds.Finally ship plume event were marked if the existence of ships was positive in the upwind direction of those signals.The combination of the trace gas peak time, the wind direction, and the ship traffic information (time of ships leaving and berthing) provided by marine administration in the port will enable the identification of the plume-related ship.For example, a ship plume event was identified in 5 January 2017 from 15:36 to 16:08 (Fig. 2).The timing and conditions associated with each positively identified ship plume event are listed in Table 1.
The ratio of ship-emitted NOx to SO2, i.e., the enhancement of NOx to SO2 in observation (∆NO x ∆SO 2 ⁄ ), correlates with the fuel type, and rises if ships switch to low sulphur fuel (McLaren et al., 2012;Sinha et al., 2003).In this study, data in ship plume event was averaged every 4 minutes, and the suitable baseline point was set as the background concentration either before or after ship plume event.Then the ∆NO x ∆SO 2 ⁄ ratios were calculated via a two-sided linear least squares regression of NO2 to SO2 using all points within each plume event including the baseline point (Fig. 2).This method is similar to that used for determination of emission ratios (McLaren et al., 2012) or emission factors (Williams et al., 2009) in ship plumes.

Properties of fuel samples
Intermediate fuel oil (IFO), or called heavy fuel oil, is typically used by marine vessels.As being the petroleum product left after distilling all other fractions from crude oil, IFOs have high density, carbon/hydrogen ratio and sulphur content (varying from 2 % to 5 %) compared with gas and oil products used by other means of transportation.In addition, high concentrations of organics, metals and the compounds between are obtained in IFOs from their presence in the original crude oil.IFOs are categorized into IFO380, IFO180 and IFO60 by their maximum viscosity measured at 50 ℃, and the fuel quality is relatively better as the viscosity reduces (Table 2).Recent on-board as well as in situ measurements revealed that high SF fuel generally gives higher sulphur, particle and soot emissions (Celo et al., 2015;Contini et al., 2015;Cooper, 2003;Fridell et al., 2008;Lack et al., 2011;Moldanová et al., 2009;Petzold et al., 2010;Sinha et al., 2003;Winnes and Fridell, 2010;Winnes et al., 2016).Significant metal contribution of residual fuel combustion was also noted (Lake et al., 2004), and the contribution to emission (Kweon et al., 2003;Lack et al., 2011;Lee et al., 1998) and formation (Ault et al., 2010) of particulate organic matter as well.
Research shows ships in SECAs would switch to marine diesel fuel (MDO), a cleaner kind typically used to meet the requirement of many fuel quality regulations and emission limits.Compared to IFOs, MDOs contain lower density, carbon/hydrogen ratio, and content of nitrogen (~10 % of IFOs), sulphur (~30 % of IFOs) and heavy metal (significant reduction) (Table 2).With low SF, these cleaner fuels prove to be better performance on emissions by promising reduction of emission (Cooper and Gustafsson, 2004) and further reaction of acidification and eutrophication (Bengtsson et al., 2011;Fridell et al., 2008;Sinha et al., 2003).Another record worth mentioning is that hybrid fuels that blend IFO and cleaner fuels to comply with SF limit are found widely used by ships operating in SECAs (Winnes et al., 2016;Zetterdahl et al., 2016), since the price of distillate fuels is an obstacle for contractors to completely abandon IFOs.As Table 2 shows, content of metals in hybrid fuels are in between that of IFOs and MDOs due to the blending, but density, carbon, hydrogen and nitrogen are consistent with that of IFOs, indicating a IFO-similar quality which was proven to be less improvement on particle emission and health risk than totally abandoning IFOs (Winnes et al., 2016).
In order to figure out the fuel type ships were to use after implementation in JT, three fuel samples were taken from the three vessels berthed at JT in 14 January 2017, one for each, and sent for analysis of fuel properties and chemical composition according to the petroleum industry standard (SH) and national standard (GB) of China.

Backward trajectory analysis
Back trajectories were used to identify the origin and potential influences of different source regions on V concentrations during each sampling day.The 24 h back trajectories of the air mass during each sampling day were computed at 500 m a.g.l (above ground level) using the HYSPLIT 4 model (NOAA, 2013).The GDAS meteorological data was used as input.

Other parameters
Enrichment factor (EF) was used for general evaluation of influences of anthropogenic sources on elements contents of particles (Zhao et al., 2013).EF is calculated following Eq.( 1): where (X/R) aerosol is the concentration ratio of the interest element X to the reference element R in aerosol, and (X/R) crust is the concentration ratio of X to R in crust.We used the composition of the continental crust from study of Wedepohl (1995) and used Al as the reference element R. Species with EFs less than 10 usually indicate a major crustal source, while species with high EFs probably indicate a significant anthropogenic source.
Sulfur oxidation ratio (SOR) and nitrogen oxidation ratio (NOR) are used to elucidate the SO4 2-and NO3 -contribution (Ohta and Okita, 1990;Ostro, 1995;Wang et al., 2005) according to: (2) (3) where square brackets are molar concentrations in units of mol• m -3 .SOR/NOR above 0.1 indicates photochemical redox reaction of SO2 or NOx in ambient air.Higher SOR and NOR values indicate larger amounts of secondary sulfates and nitrates formation (Khoder, 2002).The climate of JT is strongly influenced by the sea breeze.Mean value of relative humidity during campaign was 69.4 % (ranging from 21.8 % to 99.9 %), while that of temperature was -0.6 ℃.Temperature exhibited a clear diurnal cycle: went lowest before dawn (-2.3 ℃), then rose after sunrise (7:00 LST) and reached the highest (14 ℃) at 14:00 LST (Fig. 1).
Prevailing wind direction was W (23.4 %) and NNW (13.0 %).Wind speed mainly ranged between 1 and 4 m• s -1 (2.7 m• s -1 as average).Coastal meteorological patterns like above play an important role in the dispersion, transformation, accumulation or removal of air pollutants (Gariazzo et al., 2007).
During campaign, the day-to day variation was large due to variation in both complicated sources and removal in JT, but overall data exhibited a heavy polluted environment in JT.As the primary pollutant at site, PM2.5 concentrations were used to classify local pollution level.In over 50 % of days, PM2.5 concentration was above 115 μg• m -3 , which is the Grade Ⅳ criterion of China's daily Air Quality Standard (HJ 633-2012) (Fig. 3), and the mean concentration during campaign (147.85 μg• m -3 ) was much higher than that of city area in Tangshan (117.9 μg• m -3 ) in the same season (Zhang et al., 2017).The PM2.5 concentration was even 3 times the wintertime PM2.5 in Hong Kong (Gao et al., 2016), and twice the Yangshan Port, Shanghai (Zhao et al., 2013).This suggests severe air pollution in JT, which is understandable since winter (Dec-Feb) is the most polluted time in Tangshan due to higher emission and unfavourable atmospheric conditions (e.g.lower mixing heights and more frequent temperature inversions).Until the campaign, the PM2.5 concentration in the cold season always exceeds 100 μg•m -3 since December 2013, when an official air quality monitor station started to operate (http://www.aqistudy.cn).The situation indicates the necessity for implementing appropriate measures for particle emission reduction.Gas pollutants were abundant as well in JT due to the heavy traffic.Average concentrations of NOx, SO2, O3 and CO were 146.93 ppb, 21.91 ppb, 29.68 ppb and 2.21 ppm, respectively.NOx seemed more polluted in the port having a higher maximum hourly concentration of 692.6 ppb during the campaign, while SO2 reached the maximum of 165.5 ppb.Peak levels of NOx and SO2 were mainly linked with ship activities since measurement site was very close to channel and berth.A lower level of O3 was observed in JT compared to Yangshan Port in Shanghai (Zhao et al., 2013) and a clear diurnal cycle of O3 was spotted that the concentration rises in daytime (29.18 ppb) and goes downward at night (16.38 ppb).The combined influence of coastal meteorology was responsible in some degree.During daytime, photochemical reactions and transportation from ozone-rich air increase O3, while reaction with NO and dry deposition at night destroy O3.Cases show that O3 can be totally destroyed if NO source is large (Finlayson-Pitts and Pitts, 2000), and as being in a busy port, our data verifies that (e.g.O3 approximated to 0 ppb at 21:00 LST on 4 January 2017).Peaks of CO and NOx coexisted in some degree, but overall there was no evident pattern for CO due to much more complex local combustion emissions.the navigational channel of JT to our observational site (Fig. 5).As shown in Fig. 1(c), westerly wind blew through the 3 rd pool, and the northeasterly wind through the 2 nd pool, in both which direction the SO2 dropped significantly, while on the contrary, in the southwest direction where wind blew from city and road, SO2 barely changed, indicating steady non-marine anthropogenic emissions.From this perspective, switching fuel in JT indeed resulted in a reduction of around 70 % on ambient SO2 concentration.

Carbonaceous and ion species affected by marine vessels
Variation of carbonaceous and ion species was depicted in Fig. 6.Mean (range) concentrations of carbonaceous species determined in PM2.5 were 6.52 (5.46-7.69)μg•m -3 for EC, and 23.10 (9.88-41.60)μg•m -3 for OC (OC levels are uncorrected for artifacts from absorption/volatilization of gaseous organic species).Levels of EC and OC were fairly consistent with that of PM2.5 collected in the same period in Beijing (Li et al., 2018b).EC is considered as tracer for primary emissions (incomplete combustion), from sources such as ship, vehicle and power plant in our study, which is affected by fuel quality and combustion.
However, little variation after fuel switching was observed here due to the complicated contributors in JT.On the contrary, OC concentrations were much higher with large variation, showing a clear prevalence of organic carbonaceous species over EC.Still, no discernible effects of switching fuel was found on OC concentrations.
Being the major long-range transported aerosol components, SO4 2-, NO3 -and NH4 + dominated the ionic species, with strong correlations between each other and an average concentration of 22.04, 25.95 and 13.55 μg• m -3 , respectively.Ca 2+ , Mg 2+ , Na + , K + and Cl -are major constituents of sea salt and mineral dust, with an average concentration of 1.10, 0.21, 0.84, 2.10 and 3.90 μg• m -3 , respectively (Fig. 6).Port-related emissions were proven to be one of the major sources of local emission in JT.Cl - was relative abundant since the Cl -/Na + ratio in the aerosol was 4.79, much larger than in the sea salt (1.8), indicating other strong anthropogenic sources like coal combustion (Yao et al., 2002) and biomass burning (Li et al., 2007;Li et al., 2009).
Ca 2+ , as an indicator of mineral dust, was higher than that in city area of Tangshan (0.7 μg• m -3 ), which was considered correlative of port activities (load and unload bulk materials).Moreover, the mass ratio of Mg 2+ /Na + (0.27) were higher than the value of 0.12 reported for sea water, suggesting additional magnesium sources such as dolomite containing soil dust, which may be relative to port activities as well.To evaluate the contribution of stationary emissions and mobile emissions towards air pollution (Gao et al., 2011), mean mass ratio of NO3 -/SO4 2-in JT was calculated, and the result (1.19) was higher than that of that in city area of Tangshan (0.7), indicating that JT was more affected by mobile sources than city area.
High humidity in JT will promote secondary aerosol formation of local emissions (Yu et al., 2018).Samples were categorized into polluted day and clean day based on corresponding PM2.5 mass concentration for comparison, since the chemical composition of atmospheric particulate matter are largely affected by prevailing weather conditions (Röösli et al., 2001).The proportion of sulfates and nitrates in polluted days rose from 55 % of clean days to 70 %, showing a large amount of secondary aerosols either by transportation or by formation.Generally, SOR and NOR in JT were higher than that of city area in Tangshan and Beijing (Fig. 7), and increased significantly from clean day (0.14 and 0.10 respectively) to polluted day (0.48 and 0.37 respectively), suggesting a strong localized photochemical redox reaction.The OC/EC ratio could be used as an indicator for the extent to formation of secondary organic aerosols (Cabada et al., 2004).In this study, the mean OC/EC ratio was 3.58, much higher than that of Thessaloniki port in Greece (Tolis et al., 2015) and Hong Kong (Gao et al., 2016).Ships were likely responsible for this situation since their OC/EC emission ratio (typically over 10) (Celo et al., 2015;Moldanová et al., 2009;Sippula et al., 2014) was much higher than that of on-road diesel engine (typically ranging from 0.25 to 1) (Oanh et al., 2010).
Therefore, the localized photochemical reaction and aerosol formation driven by ship emissions were contributing remarkably to air pollution in JT.This shed light in the pollution control of this Harbor that the secondary pollution should be treated by reduction of local SO2 emission, which can be achieved by reducing ship emission from switching fuel.

Elemental enrichment factors and marker for ship emissions
The ranges and mean concentrations of all measured elements are shown in Fig. 8. Overall, the mass concentrations of Al, Ti, Mg, Fe, Na, K, Mn, V, Ni, Zn and Pb were abundant and they varied largely with sampling time.Samples were categorized into three batches based on the PM2.5 limit of AQI level (HJ 633-2012) during sampling, considering the influences of ambient pollution on particulate chemical composition, while one specific sample 2017/01/04 was set as a background/control group due to none ship activity during its sampling time according to provided ship traffic information.Intra-batch comparison was then performed to estimate variation of elements after fuel switching.
Enrichment factor (EF) was used to normalize the observed concentrations of elements and to evaluate influences of crustal and anthropogenic sources.Generally, elements from Ca to K in Fig. 8 mainly come from geological source, thus classified as crustal elements.Ca mostly came from stable crustal sources having the lowest EF values.With EF values around 10 without evident temporal variation, elements from Ti to U could have a major local crustal origin such as dust.Regression analysis comparing EF-Na and EF-K revealed a strong correlation with coefficients (R 2 ) of 0.994, implying a main contribution of marine source.On the other hand, elements Co, Mn and V were moderately (EF<100) and elements from Ni to Se were highly (EF>100) enriched due to the contribution of anthropogenic sources, which all were classified as pollution elements.Co could come from various bulk materials carried with harbour areas, as well as Mn, Cu and Zn (Almeida et al., 2012;Moreno et al., 2007).With EF values strongly correlated with each other, Mn, TI, Cu, As, Sn, Zn, Pb, Hg and Ag would have a same major anthropogenic source, which is likely the traffic pollution.According to tunnel studies (Lawrence et al., 2013;Li et al., 2018a) and in situ measurements (Terzi et al., 2010;Thorpe and Harrison, 2008), Mn, Cu, Sn, Zn and Pb in PM2.5 are related to vehicle emissions as well as tire and brake wear.Weckwerth (2001) reported As-enrichment in PM2.5 from shaking rusting rails due to passing trains, explaining our observation since our measurement site was in the vicinity of the train rails around the 1 st pool.
There were not enough values for Mo and Cd to present patterns, however, literature shows that Mo could be a contribution of diesel exhaust and brake wear (Weckwerth, 2001), and Cd the motor vehicle emissions (Li et al., 2018a).Again, it was proved that JT was more affected by mobile sources, which heavy metals came mainly from.
Marker for ship emissions was crucial, once confirmed, to deduce the variation of ship emissions.There has been a particular focus on Ni and V in PM2.5, since several recent studies have clearly revealed that V and Ni are representative for ship exhaust particles using Aerosol Time-of-Flight Mass Spectrometer (Ault et al., 2010;Healy et al., 2009) and furthermore, higher V levels in ship emissions were found to be associated with the residual fuel combustion instead of the distillate fuel (Agrawal et al., 2008;Celo et al., 2015).In JT, V and Ni were considered mainly from anthropogenic sources, while they were considered crustal elements in city area of Tangshan.This indicated a unique contributor in JT, which is clearly the ships consuming residual fuel.However in this study, Ni was proven less credible for being a residual fuel marker, since the concentration of Ni was even inconsistent between parallel samples collected in the same day.On the contrary, concentration of V, with significant intra-batch decreases in all three pollution level, proved to be highly related to fuel switching, and whereby V was identified as the perfect marker for residual fuel emission in JT.
Chemical composition of MDO/MGOs indicates that V is below detection limit, but PM2.5 samples presented existence of V after switching fuel.It suggests that regional transmitted V should not be overlooked.According to back trajectories, during sampling 2017/01/04 when no ship activity existed, air mass in control group went into the Bohai Bay, and then turned back to JT.This air mass was able to bring in particles with a large amount of V from ships cruising in the sea that still used IFO legally, verifying the influence of air transportation on particle content (Fig. 9).Since the pathway would effectively influence the content of air mass, other trajectories were clustered into three typical types based on transport pathways of air masses, each representing continental dominant, marine dominant and mixing airflows, plotted in Fig. 9. V concentration after fuel switching, was 17.4 ng• m -3 under coastal airflows (marine and mixing airflow together), much higher than 9.0 ng• m -3 under continental airflows, indicating the significant effect of ship emission on coastal areas.As shown in Fig. 9, samples that shared similar transport patterns from Mongolia-Inner Mongolia region were compared to rule out the portion of transmitted V.
Results showed ships have switched fuel in advance and most importantly, the implementation of low SF fuel reduced shipsource V by 97.1% from 309.9 ng• m -3 before fuel switching to 9.1 ng• m -3 after.

∆NO x ∆SO 2 ⁄ ratios and indicated fuel type in ship plumes
In this study, ship plume event was used for the surveillance of emissions and fuel type on board of passing ships (see Sect. 2.3).Altogether 16 ship plume events were measured during the campaign, for which the molar ∆NO x ∆SO 2 ⁄ ratios fell in the range of 0.92-17.89(Table 1).The accuracy of the molar ratios were justified by proving that losses of NOx and SO2 in the plumes during the transit time to the instrument was small.Potential losses of NOx include photolysis at daytime (Makkonen et al., 2012), conversion to NO3, N2O5 and subsequently HNO3 at night (McLaren et al., 2010), and heterogeneous conversion of NO2 to HONO on the aqueous surface of the ocean (Wojtal et al., 2011).The furthest berth in the prevailing direction was 1.5 km away from the site indicating a maximum plume transport time of 9 min at the wind speed of 2.7 m• s -1 .Using the transport time and a NOx lifetime of 3.7 h measured in ship plumes (Beirle et al., 2004), we concluded a maximum potential loss of 4 % NOx.Also, loss of SO2 was attributed to heterogeneous reaction to form particle sulfate with equivalent lifetimes, which counteracts the potential for NOx reactions to bias the ∆NO x ∆SO 2 ⁄ ratios.Therefore, the maximum error in our measured ∆NO x ∆SO 2 ⁄ ratios due to such loss processes is estimated as < 4 %.
Previous inventories, measurements and ship plume studies have proved a direct correlation between SF and NO x SO 2 ⁄ molar emission ratio, which also help on the determination of critical point in this work.For high SF fuels (2.43 %), several emission inventories for Bohai Bay indicated that the NO x SO 2 ⁄ emission ratio was between 1.8 and 2.0 (Liu et al., 2016;Song, 2015;Xing et al., 2016), comparable with the ratio of 2.6 observed from residual fuel plumes (Ault et al., 2010).And for 0.5 % SF fuels, the inventory indicated 10.51 (Liu et al., 2016), which is also comparable with the ratio of 11.6 observed from distillate fuel plumes (Ault et al., 2010).The NO x SO 2 ⁄ emission ratio rises correspondingly with the drop of SF, but also is affected by ship engine model, load, operation conditions and combustion conditions in practical conditions (McLaren et al., 2012).Thus the variability in the observed ∆NO x ∆SO 2 ⁄ ratios were expected even when ships consumed the same type of fuel.
Considering all the aspects above, we concluded a ratio over 7.5 as a suggestion of fuel with SF below 0.5 %, otherwise as a suggestion of high and incompliant SF, each shown as areas divided by the x axis in Fig. 10.The y-axis in Fig. 10 stands for the starting of ship fuel regulation within three DECAs in the Implementation Plan.The axes make up four quadrants, each representing different scenarios.The ratios in 1 st quadrant indicate compliance of ship towards the regulation, and most of them were higher than 10.51, implying the SF much lower than 0.5 %.Being above the x-axis as well, ratios in the 2 nd quadrant also indicate compliance and the action of advance fuel switching before due.Ratios in the 3 rd quadrant (plume #1-5) had an average ∆NO x ∆SO 2 ⁄ ratio of 1.92, conform to the emission ratio in inventory (1.82 and 2.0) before the DECA implementation.
Ratios in the 4 th quadrant indicate usage of high SF fuel.As shown in Fig. 10, most of plumes indicate compliance with the 0.5 % SF limit, while there were still some high sulphur plumes occurred.In this case, precise identification of high sulphur plume contributor and reinforcement of supervision are indeed necessary.Generally, SO2 reduction of average ∆NO x ∆SO 2 ⁄ ratio was 75 % from high sulphur plumes (3.26) to low sulphur plumes (12.97), consistent with the SF reduction (79 %) and also the reduction of gas SO2 in ambient air (70 %, in Sect.3.1.1),which proves the practicability of this method.One uncertain factor for this method is the difficulty on identifying hybrid fuels whose SF is around 0.5 %.For SF around 0.5 %, the NO x SO 2 ⁄ emission ratio was observed either way below or consistent with inventory estimate (around 6 in Winnes et al., 2016;around 11 in Zetterdahl et al., 2016), which may be attributed to the diversity of blending IFOs and MDOs.In this way, ships using hybrid fuels were unable to identify and some could be mistaken as incompliance.Further research is required in this subject.

Compliance based on the plumes
Test showed that three ships we sampled from in 14 Jan 2017 burned MDOs (Table 2), which was in conformity with the implementation of fuel regulation in JT.There would be obvious benefits such as significant improvements of emissions and air quality once all vessels complied and switched to MDOs or other alternative distillate fuels.Nevertheless, in this act, it is crucial to ensure the compliance of ships, which requires a more convenient and timely method to indicate fuel quality instead of analysing fuel samples.

Conclusions and discussion
Field measurement was conducted at the measurement station in JingTang Harbor, including continue monitoring of meteorological conditions and gas and particle concentrations, from 28 December 2016 to 15 January 2017.Samples of PM2.5 were collected every day from 28 December 2016 to 11 January 2017.Moreover, three fuel samples were taken from three vessels berthed at JingTang Harbor in 14 January 2017.Profiles of meteorological conditions and pollutants were obtained, and the chemical characterisation of aerosol and fuel samples as well.
Profiles of pollutants exhibited a heavy polluted environment in wintertime of JT.In over 50 % of days, PM2.Enrichment factors of elements in PM2.5 were used for determination of marker for residual fuel emissions, which was V in this study.Analysis of carbonaceous and ion species revealed that local port-related emissions were one of the major sources of pollution in JT, especially the mobile sources.High humidity in port just added another straw on the polluted air by promoting localized photochemical reaction and secondary aerosol formation of ship emissions.Moreover, the effect of ship emissions were proven wide because the concentration of V, the identified marker for residual fuel emissions, was much higher in coastal areas than continental areas.5 Atmos.Chem.Phys.Discuss., https://doi.org/10.5194/acp-2018-1233Manuscript under review for journal Atmos.Chem.Phys.Discussion started: 13 December 2018 c Author(s) 2018.CC BY 4.0 License.
Atmos.Chem.Phys.Discuss., https://doi.org/10.5194/acp-2018-1233Manuscript under review for journal Atmos.Chem.Phys.Discussion started: 13 December 2018 c Author(s) 2018.CC BY 4.0 License.on port air quality with switching fuel 3.1.1SO2 reduction in the polluted port area SO2 level reduced apparently by maximum hourly concentration dropping from 165.5 ppb before 1 January 2017 to 67.4 ppb after with similar vessel activity.Variation in Fig.4confirms this distinct reduction in JT.SO2 exhibited a prompt drop from Atmos.Chem.Phys.Discuss., https://doi.org/10.5194/acp-2018-1233Manuscript under review for journal Atmos.Chem.Phys.Discussion started: 13 December 2018 c Author(s) 2018.CC BY 4.0 License.77ppb to 20 ppb on 30 December 2016 compared to the high and steady concentration in XL, the control group from upwind of JT.This SO2 reduction was mainly attributed to local sources, since JT was under influence of prevailing atmospheric conditions in XL through diffusion and transmission (NOx and PM2.5 covaried in both sites) where SO2 did little change.More precisely, the reduction was most likely a direct response to the action of switching fuel, compared with all other variables at port.Wind map shows that the reduction of SO2 was even more comprehensive in almost every wind direction that blew from Atmos.Chem.Phys.Discuss., https://doi.org/10.5194/acp-2018-1233Manuscript under review for journal Atmos.Chem.Phys.Discussion started: 13 December 2018 c Author(s) 2018.CC BY 4.0 License.
Atmos.Chem.Phys.Discuss., https://doi.org/10.5194/acp-2018-1233Manuscript under review for journal Atmos.Chem.Phys.Discussion started: 13 December 2018 c Author(s) 2018.CC BY 4.0 License.After identifying low SF (compliant) and high SF (potential incompliant) ship plumes, we matched each plumes with certain vessels by the ship traffic information which contains a series of arrival and departure logs to help estimate the time when different ships passed the sampling site.Using the plume conditions, wind direction and ship traffic information to trace the specific source of measured plumes, we noted that most plumes were likely linked to several ships because the wind often blew through the busy pools and navigational channel where many ships were manoeuvring and at berth.For high SF plume #9, five ships were in berth in the upwind direction and two ships were passing by during the plume time, indicating a mixture of different individual plumes.Similar situation was found for other high SF plumes, that five at berth and two passing by were matched with plume #10, five at berth and five passing by with plume #12, and four at berth and four passing by with plume #14.In this case, to achieve a comprehensive and accurate surveillance of compliance of individual vessel, a more detailed and precise database of vessel activity such as AIS data is in need.

Figure 1 :
Figure 1: (a) Location of JingTang Harbor (JT) at a large scale and location of an official air quality monitoring station, Xinli Elementary School (XL) at a smaller scale (map inset).(b) Location of measurement station (yellow marker) and distribution of pools, berths and load areas of the port area.Wind rose (c), daily variation of temperature (d) and relative humidity (e) of measurement station from December 28, 2016 to January 13, 2017.5

Figure 7 :
Figure 7: Sulfur Oxidation Rate (SOR) and the Nitrogen Oxidation Rate (NOR) of particles collected in this study, city area of Tangshan (Zhang et al., 2017) and Beijing (Li et al., 2018b).

Figure 8 :Figure 9 :
Figure 8: Enrichment factor of elements in PM2.5 in JingTang Harbor.The mean, minimum and maximum concentrations of each element are also illustrated.5

Figure 10 :
Figure 10: Molar △NOx/△SO2 ratios of all 16 ship plumes.X axis stands for date with positive area meaning time after 1 January 2017.Y axis stands for △NOx/△SO2 ratio with positive area meaning SF < 0.5% in fuel.Plumes within four quadrants are distinguished by different marks.
a concentrations provided by air monitor station in Xinli Primary School (XL).