Sulphur Emission Control Areas Research Articles

Optimizing Sulfur Emission Control Areas for Shipping

The design of emission control areas (ECAs), including ECA width and sulfur limits, plays a central role in reducing sulfur emissions from shipping. To promote sustainable shipping, we investigate an ECA design problem that considers the response of liner shipping companies to ECA designs. We propose a mathematical programming model from the regulator’s perspective to optimize the ECA width and sulfur limit, with the aim of minimizing the total sulfur emissions. Embedded within this regulator’s model, we develop an internal model from the shipping liner’s perspective to determine the detoured voyage, sailing speed, and cargo transport volume with the aim of maximizing the liner’s profit. Then, we develop a tailored hybrid algorithm to solve the proposed models based on the variable neighborhood search meta-heuristic and a proposition. We validate the effectiveness of the proposed methodology through extensive numerical experiments and conduct sensitivity analyses to investigate the effect of important ECA design parameters on the final performance. The proposed methodology is then extended to incorporate heterogeneous settings for sulfur limits, which can help regulators to improve ECA design in the future. Funding: This work was supported by the National Natural Science Foundation of China [Grants 72025103, 71831008, 72201163, 72071173, 72371221, 72394360, 72394362, 72361137001 and HKSAR RGC TRS T32-707/22-N]. Supplemental Material: The online appendix is available at https://doi.org/10.1287/trsc.2023.0278 .

Use of biofuels in marine diesel engines for sustainable and safe maritime transport

The article presents results of research on the use of fuel mixtures, containing with biodiesel fuel. The research was carried out on specialized sea vessels with a deadweight of 10,820 tons and 29,420 tons, which made passages in the waters of South America and the Caribbean, as well as in the Sulphur Emission Control Areas of Northern Europe. The operation of the ship's power plants (main and auxiliary engines) was provided both on marine fuel of petroleum origin and on a fuel mixture that consisted of petroleum fuel and biodiesel fuel. The experiments were carried out on marine medium-speed diesel engines 5DC-17A Daihatsu Diesel, 16V32 Wärtsilä-Sulzer and Volvo Penta TWD1645GE. Various kinds of marine fuels and as biodiesel fuel Fatty Acid Methyl Esters B99.9 FAME and B99.6 FAME were used. The concentration of biodiesel fuel in the fuel mixture was 5–20 %. The environmental friendliness of the work of sea vessels was assessed by the value of the emission of nitrogen oxides, sulphur, and carbon. As a result of the research, a variant of adjusting the sea crossing was proposed to ensure the continuous operation of the ship's power plant using biodiesel fuel.

Optimal Shipping Route under the Designation of the Mediterranean Sulfur Emission Control Area: Mathematical Models and Applications

In order to tackle sulfur oxides (SOx) emissions from maritime activities, both local governmental bodies and the International Maritime Organization (IMO) have implemented a range of regulations with the establishment of sulfur emission control areas (SECAs) being one crucial measure. Recently, the IMO made the significant decision to designate the Mediterranean as an SECA, aiming to promote environmental conservation as well as sustainable development in the maritime industry and mitigate the adverse health effects caused by air pollutants emitted from ships in Mediterranean regions. While this policy signifies significant progress in the reduction of sulfur emissions, it simultaneously presents intricate challenges for maritime enterprises. Notably, under the Mediterranean SECA designation, shipping companies may opt to bypass this region and choose routes through the Cape of Good Hope as a means of minimizing the overall costs, resulting in a potential increase in global carbon emissions. To support shipping companies in formulating optimal strategies within the framework of this new policy, the research introduces advanced techniques to make the optimal decisions concerning route selection, sailing speeds, and the appropriate number of ships for both SECAs and non-SECAs. Furthermore, we elucidate how these optimal decisions can be dynamically adapted in response to the dynamic fluctuations in fuel prices and the weekly operational expenditures incurred by maritime fleets. In the experimental results, taking into account factors like route distance and fuel costs, shipping companies select routes through the Mediterranean region in both eastward and westward directions. The total cost amounts to $6,558,766.78, utilizing eight vessels. Regarding ship speeds, vessels sail at reduced speeds in SECAs compared to non-SECAs. Furthermore, longer voyage distances require deploying a greater number of ships to maintain a weekly service frequency. This research exhibits robust timeliness and practicality, which is in line with practice. It not only timely supplements and enhances the extant body of knowledge concerning SECAs but also serves as a valuable point of reference and emulation for shipping companies seeking to optimize their operations within the framework of the new policy landscape. Furthermore, it offers pertinent insights for the IMO in formulating policies related to SECAs.

Performance assessment of state-of-the-art and novel methods for remote compliance monitoring of sulfur emissions from shipping

Abstract. The fuel sulfur content (FSC) of ocean-going and inland vessels was measured simultaneously by eight different state-of-the-art and novel monitoring systems during a 6-week campaign at the Elbe River, at a distance of about 10 km to the port of Hamburg, Germany. Both stationary and airborne systems on unoccupied aerial vehicles (UAVs) were operated by four participating partners in a side-by-side measurement setup to measure the emission factors of the same emission sources. A novel laser spectrometer, with significantly better-precision specifications as compared with the other instruments, was used for the first time for emission monitoring regarding the International Convention for the Prevention of Pollution from Ships (MARPOL) Annex VI regulations. The comparison took place in the North Sea sulfur emission control area (SECA), where the allowed FSC is limited to 0.10 %Sm/m. The unit %Sm/m relates to the percentage of mass sulfur per mass combusted fuel. In total, 966 plumes that originated from 436 different vessels were analysed in this study. At the same time, fuel samples obtained from 34 different vessels and bunker delivery notes (BDNs) from five frequently monitored vessels were used as a reference to assess the uncertainties of the different systems. Seven of the eight measurement systems tended to underestimate the FSC found from fuel samples and BDNs. A possible relation between underestimation and high relative humidities (above 80 %) was observed. The lowest systematic deviations were observed for the airborne systems and the novel laser spectrometer. The two UAV-borne systems showed total uncertainties of 0.07 %Sm/m and 0.09 %Sm/m (confidence level: 95 %). The novel laser spectrometer showed the lowest total uncertainty of 0.05 %Sm/m compared with other stationary sniffer systems, whose total uncertainties range from 0.08 %Sm/m to 0.09 %Sm/m. It was concluded that non-compliant vessels, with an actual FSC of the combusted fuel above 0.15 %Sm/m to 0.19 %Sm/m, can be detected by the compared systems with 95 % confidence.

Optimization of Fleet Scrubber Installation and Utilization Considering Sulfur Emission Control Areas and Marine Fuel Switching

With the rising environmental consciousness, emission pollution has become one of the major concerns of the maritime industry, which is the artery of international trade. To handle the significant cost increase resulting from stringent emission regulations, ship operators have adopted multiple methods, including operational and technical methods. Scrubbers are a mature and effective technology that can reduce sulfur dioxide and particulate matter emissions by cleaning the exhaust gases before emitting them. However, the existing literature regarding the operation of scrubbers does not consider the prohibition of open scrubber usage in the vicinity of certain ports or the variable costs of using scrubbers. Therefore, this study explores the fleet scrubber installation and utilization problem, considering sulfur emission control areas, marine fuel switching, and open-scrubber-prohibited areas. A mixed-integer nonlinear model was developed to formulate and address the problem. Numerical experiments and sensitive analyses based on practical data were conducted to validate the originally proposed model and show the effectiveness of this technology under various scenarios. The results indicated that the operational cost was effectively reduced by using scrubbers, compared to not using them. Additionally, the disparity between total costs with and without scrubbers was significant, regardless of the sailing speed and proportion of the regulation areas. It was also proven that spreading the scrubber installation work over several years will relieve financial pressures due to scrubber investment and thus obtain a better installation plan.

A two-phase optimization model for low-sulphur operation of container liners in the context of carbon neutrality

The shipping industry is under significant pressure to reduce carbon emissions, and it is crucial to ensure that current efforts to reduce sulphur dioxide (SO2) emissions do not result in increased carbon dioxide (CO2) emissions. Against the background of carbon neutrality and sulphur emission control area (SECA) policies, this paper proposes a two-phase mathematical model to study the impact of liner low-sulphur compliance operation on carbon emissions. The model addresses four key problems: fleet deployment (phase Ⅰ); compliance option decisions, speed optimization and cargo allocation (phase Ⅱ). To solve these problems, a novel dual population evolutionary algorithm has been designed. The results show that implementing low-sulphur compliance operations for liner companies does not simultaneously reduce both total costs and CO2 emissions, and the rise in the price of low-sulphur oil, the preference for cost decision-making and the expansion of SECAs will increase CO2 emissions; the current sulphur limit policy needs to be adjusted urgently to implement the carbon neutrality goal of the shipping industry; government subsidies can reduce CO2 emissions to some extent, but low-carbon or zero-carbon alternative energy is an inevitable choice for achieving carbon neutrality in the shipping industry.

Forecast Analysis of Pollutant Emissions of Cruise Ship Routes in Western Mediterranean

The cruise shipping industry has a steadfast commitment to the environmentally sustainable operation of ships through many initiatives to reduce greenhouse gas emissions. This paper presents a forecast analysis of the emission inventory of NOx, SO2, and CO2 during the sailing phase associated with cruise routes in the Western Mediterranean. Five scenarios were raised to obtain projections about future emissions considering the evolution of cruise traffic; the implementation of the Sulfur Emission Control Area (SECA) in the Mediterranean by 1 May 2025, and variations in the specific fuel consumption of the engines of the cruise ships. To this extent, a time series of cruise calls during 2019 in Mediterranean ports is used to identify the main routes and their associated emission inventory. Network analysis is applied to identify the routes associated with the cruise calls, and the emission inventory is estimated using a bottom-up approach. A total of 292 cruise routes were identified. The estimations reveal that the emissions of the cruise activities assessed are approximately equivalent to 0.58% of NOx, 0.28% of SO2, and 1% of CO2 of the entirety of the emissions associated with maritime transport at the European level in 2019. The projection of the scenario with the highest cruise activity and the SECA being enforced leads to a reduction of 77% of the emissions of SO2 considering the activity of 2019. The research conducted enables us to assess the environmental impact of the intense cruise ship activity registered in the Mediterranean and the positive footprint of the implementation of new regulations on emissions.

Configuration design of the emission control areas for coastal ships: A Stackelberg game model

Several countries and regions have announced sulphur emission control areas (SECAs) to regulate sulphur emissions from ships. Incorporating environmental benefits and economic impacts, a bi-level programming model following the Stackelberg game regime is proposed to capture the SECA design problem for a given coastal area, in which the irregular polygon of the SECA is assumed to be a convex hull and described by a system of linear constraints. The government, as the leader, minimizes total sulphur emissions of ships over the entire coastal area with the voyage cost constraint. The ships, as followers, minimize individual voyage costs by jointly choosing the sailing trajectories and speed profile inside and outside the SECA between the associated port pairs with the given geometric configuration of the SECA. We first derive the optimal trajectory and speed profile for each ship, which can be simplified to a shortest path problem. Subsequently, a heuristic algorithm based on the steepest descent method is proposed to obtain the Pareto optimal solution in the sense of simultaneous minimization of total emissions and voyage costs. Finally, two announced SECAs are adopted to illustrate the validity of the proposed model and algorithm.

Effects of IMO sulphur limits on the international shipping company's operations: From a game theory perspective

The International Maritime Organization (IMO) implements sulphur limits to control sulphur dioxides (SO2) emissions. Their measures include global sulphur cap (GSC) and emission control areas (ECA) regulations. The purpose of this study is to investigate the effects of IMO sulphur limits on vessel speeds, and examine the effectiveness of IMO sulphur limits in cross-linkage of SO2 and CO2 emissions, from a game theory perspective. We propose an integrated game model for multiple shipping companies in which the vessels sail at different speeds inside and outside ECAs. Besides the fuel costs, the cargo’s in-transit inventory cost and fixed cost are considered in the model. The analytical results suggest that the optimal speeds are strongly affected by fuel prices. IMO sulphur limits are not always effective in reducing SO2 and CO2 emissions, which depends on conditions such as the additional operational cost per nautical mile arises from ECA regulations and fuel prices. When fuel prices are sufficiently low or high, CO2 emissions will increase because of the new GSC. In numerical study, three scenarios and sensitivity analysis are examined. It is found that the new GSC and ECA regulations always reduce SO2 emissions. However, CO2 emissions may be increased due to the new GSC.

Evasion strategy for a coastal cargo ship with unpunctual arrival penalty under sulfur emission regulation

To comply with the sulfur emission control area (ECA) regulation, a ship can burn expensive MGO (marine gas oil) inside ECA but relatively cheap VLSFO (very low sulfur fuel oil) outside ECA. This paper investigates a coastal cargo ship’s evasion strategy, which refers to a detour decision that decreases its sailing distance within ECA and increases its sailing distance outside ECA to save fuel costs. To this end, a voyage cost minimization model is proposed to determine the optimal sailing trajectory and speed profile inside and outside ECA. A distinguishing feature is that the ship’s sailing time is endogenously determined, depending on the penalties imposed on early and late arrivals. The necessary and sufficient conditions are obtained so that the ship operators can quickly determine whether ECA evasion can save voyage costs. It is demonstrated that the evasion triggering condition depends on the fuel price ratio of VLSFO to MGO and the relative position between the ports and the ECA boundary. Compared with non-evasion, the ship operators have less incentive to arrive punctually under evasion. The proposed models are applied to compare the evasion behavior of ships operating in the coastal ECAs of China and the US. The resultant economic and environmental impacts of ship’s evasion behavior are further discussed from the government’s perspective. The numerical results suggest significant differences arise due to the different widths of the two ECAs.

Characterizations and comparison of low sulfur fuel oils compliant with 2020 global sulfur cap regulation for international shipping

The International Marine Organization 2020 Global Sulfur Cap requires ships to burn fuels with <0.50% S and some countries require <0.10% S in certain Sulfur Emission Control Areas but little is known about these new types of fuels. Using both traditional GC–MS and more advanced chromatographic and mass spectrometry techniques, plus stable isotopic, δ13C and δ2H, analyses of pristane, phytane and n-alkanes, the organic components of a suite of three 0.50% S and three 0.10% S compliant fuels were characterized. Two oils were found to be near identical but all of the remaining oils could be forensically distinguished by comparison of their molecular biomarkers and by the profiles of the heterocyclic parent and alkylated homologues. Oils could also be differentiated by their δ13C and δ2H of n-alkanes and isoprenoids. This study provides important forensic data that may prove invaluable in the event of future oil spills.

Airborne monitoring of compliance to sulfur emission regulations by ocean-going vessels in the Belgian North Sea area

Air pollution from fossil fuel powered ocean-going vessels (OGVs) is responsible for various environmental and human health issues worldwide. Specifically for sulfur oxides (SOx), from 2010 onwards, stricter standards came into force regarding the maximum allowable fuel sulfur content (FSC) in marine fuels in the European Sulfur Emission Control Area (SECA). A method was developed for the airborne monitoring of OGVs to evaluate their compliance by equipping the Belgian coastguard aircraft with a sniffer sensor. The sensor allows a highly accurate FSC determination based on real-time CO2 and SO2 measurements in the smoke plume of OGVs. For 5 years the aircraft collected the largest set of airborne emission measurement data from OGVs as of today. This article demonstrates the effectiveness and reliability of the airborne monitoring methodology in an operational setup for targeting ship inspections in ports and a more efficient impact monitoring of shipping on air quality.

Open-Loop Exhaust-Gas Cleaning System: Analysis of Effects Produced on Barcelona Port Water pH

The implementation of a 0.5% mass/mass sulphur cap in fuels used by ships has become a reality. Furthermore, regulation 14 of the MARPOL Convention–Annex VI (amended) establishes that the limit on fuel used by ships operating in a Sulphur Emission Control Area (SECA) cannot exceed 0.1% of mass/mass. To deal with these requirements while considering nature of the shipping business, which is the continuous carriage of cargo around the world, shipowners or shipping companies have few options for following this regulation. Apart from the use of a low-sulphur-content fuel is the use of an exhaust-gas cleaning system, also known as “scrubbers”, as an alternative. The use of these systems, specifically the open-loop system, entails the discharge to the sea of residual water used during the cleaning process of exhaust gases from ship engines. The objective of this paper is to study the effect produced by discharging this residual water on the acidity level (pH) of Barcelona port water. This objective was achieved through the periodical sampling and analysis of Barcelona port water in collaboration with the IDAEA (CSIC) laboratory. We analysed the evolution of the pH results obtained so far and obtained an initial picture of the pH Barcelona port water situation in real time regarding the effect of wash-water discharges from open-loop scrubbers. Furthermore, this paper describes the implementation of a system which is going to improve the operation of open-loop exhaust-gas cleaning systems.

Impact of Sulphur Emission Control Areas on port state control’s inspection outcome

ABSTRACT With the rapiddevelopment of internationalshipping, ship source pollution is increasingly non-negligible. To control emissions of sulphur oxides from ships, many Sulphur Emission Control Areas (SECAs) have been established, in which stricter emission restriction policies were implemented. Because there are some genuine connections between SECA and PSC (Port State Control), it is natural to ask whether will the SECA policy make a difference on PSC’s inspection outcome? Therefore, this study investigates the effect of the SECA establishment, reflected by changes in the deficiency rate in PSC inspections, on the PSC’s inspection result. The deficiency rate in PSC inspections represents the percentage of deficiencies in the ship inspected, which can embody the overall outcome of the PSC inspections. It employs the difference-in-differences (DID) model to evaluate the effect as which is a common and mature tool for evaluating policy effectiveness. Robustness tests of parallel trend and Placebo tests both confirm the appropriateness of the DID model. The empirical results find that after the implementation of the SECA emission control policies, PSC inspections become stricter, thus changing the rate of deficiencies recorded during those inspections. A more stringent SECA policy is beneficial to identify more deficiencies and further ensure ships’ compliance.

Economic Cost Model of Options to Global Sulphur Cap considering Speed Differentiation

The 2020 global sulphur cap has been implemented to reduce the sulphur emission of the maritime transportation industry. It is a huge challenge for the ship owners to select a proper strategy to comply with the regulation. This study analyzes the economic costs of measures to comply with the sulphur cap including switching to low sulphur fuel oil (LSFO) and scrubbers. Meanwhile, considering the influence of the speed optimization on the voyage cost, an economic cost model of the LSFO method is combined with speed differentiation inside and outside the Sulphur Emission Control Area (SECA). The route from Shanghai to Los Angeles is set as a case study. The optimal speeds inside and outside the SECA are calibrated. Then, the economic costs of both methods are calculated and compared. The results show that the speed differentiation strategy can reduce the economic cost of the LSFO method and thus reduce its cost disadvantage over scrubbers. In addition, a low discount rate would benefit the scrubber option based on sensitivity analysis.

Ammonia as Clean Shipping Fuel for the Baltic Sea Region

Abstract The international shipping industry transports about 90 per cent of the global trade volume and is responsible for only two per cent of the anthropogenic carbon dioxide emissions. Consequently, the shipping sector is considered as an environmentally friendly transport mode. Nevertheless, global shipping can also improve its environmental footprint. So that in recent years clean shipping initiatives have been placed on the political agenda with the implementation of the Sulphur Emission Control Area (SECA) and Nitrogen Emission Control Area (ECA) regulations and the Global Cap. The next target of the International Maritime Organisation (IMO) in the sequel of the Paris Agreement of climate protection is dedicated to reduction of the Greenhouse Gas (GHG) emissions by up to 50 % until the year 2050. The paper investigates and discusses the research questions to what extent ammonia can be used in Baltic Sea Region (BSR) to propel merchant vessels and how ammonia can fulfil future demands under technical, economic and infrastructural aspects to become the green fuel for the Baltic Sea Region (BSR) shipping industry. The study benchmarks the properties of ammonia as marine fuel against Marine Gas Oil (MGO) and Liquified Natural Gas (LNG). The research is based on secondary data analysis that is complemented by expert interviews and case studies, and the results are empirically validated by data that were collected during the EU projects “EnviSuM”, “GoLNG”, “CSHIPP” and “Connect2SmallPorts” that took place within the last four years in the BSR.

A method for assessing of ship fuel system failures resulting from fuel changeover imposed by environmental requirements

Environmental regulations instigated the technological and procedural revolution in shipping. One of the challenges has been sulfur emission control areas (SECA) and requirement of fuel changeover. Initially, many reports anticipated that new grades of low sulfur fuels might increase various technical problems in ship operation. This research develops a simple and easy to use method of the failure severity and intensity assessment in relation to fuel changeover. The scale of failure rate in the ship’s fuel system was evaluated qualitatively and quantitively, using developed failure frequency indicator and the time between failure. Based on 77 records of fuel system failures collected on seven ships, it has been found that frequency of failures related to SECA fuel changeover is on average nearly three times higher compared to the rest of sailing time. Their severity did not significantly change, but the structure of failures changed considerably. The method and presented results may help in improvement of ship’s systems design and on-board operational procedures.

Container fleet renewal considering multiple sulfur reduction technologies and uncertain markets amidst COVID-19

The onset of 2020 is marked by stricter restrictions on maritime sulfur emissions and the spread of Coronavirus Disease 2019 (COVID-19). In this background, liner companies now face the challenge to find suitable sulfur reduction technologies, make reasonable decisions on fleet renewal, and prepare stable operation plans under the highly uncertain shipping market. Considering three sulfur reduction technologies, namely, fuel-switching, scrubber, and liquefied natural gas (LNG) dual-fuel engine, this paper develops a robust optimization model based on two-stage stochastic linear programming (SLP) to formulate a decision plan for container fleet, which can deal with various uncertainties in future: freight demand, ship charter rate, fuel price, retrofit time and Sulfur Emission Control Area (SECA) ratio. The main decision contents include ship acquisition, ship retrofit, ship sale, ship charter, route assignment, and speed optimization. The effectiveness of our plan was verified through a case study on two liner routes from the Far East to Northwest America, operated by COSCO Shipping Lines. The results from SLP model show that large-capacity fuel-switching ships and their LNG dual-fuel engine retrofits should be included in the long-term investment and operation plan; slow-steaming is an important operational decision for ocean liner shipping; if the current SECA boundary is not further expanded or the sulfur emission restrictions not further tightened, the scrubber ship will have no advantage in investment cost and operation. However, considering the probabilities of more flexible scenarios, the results from the robust model suggest that it is beneficial to install scrubber on medium-capacity fuel-switching ships, and carry out more LNG dual-fuel engine retrofits for large-capacity fuel-switching ships. Compared with SLP, this robust strategy greatly reduces sulfur emissions while slightly pushing up carbon emissions.

Detection of ship plumes from residual fuel operation in emission control areas using single-particle mass spectrometry

Abstract. Ships are among the main contributors to global air pollution, with substantial impacts on climate and public health. To improve air quality in densely populated coastal areas and to protect sensitive ecosystems, sulfur emission control areas (SECAs) were established in many regions of the world. Ships in SECAs operate with low-sulfur fuels, typically distillate fractions such as marine gas oil (MGO). Alternatively, exhaust gas-cleaning devices (“scrubbers”) can be implemented to remove SO2 from the exhaust, thus allowing the use of cheap high-sulfur residual fuels. Compliance monitoring is established in harbors but is difficult in open water because of high costs and technical limitations. Here we present the first experiments to detect individual ship plumes from distances of several kilometers by single-particle mass spectrometry (SPMS). In contrast to most monitoring approaches that evaluate the gaseous emissions, such as manned or unmanned surveillance flights, sniffer technologies and remote sensing, we analyze the metal content of individual particles which is conserved during atmospheric transport. We optimized SPMS technology for the evaluation of residual fuel emissions and demonstrate their detection in a SECA. Our experiments show that ships with installed scrubbers can emit PM emissions with health-relevant metals in quantities high enough to be detected from more than 10 km distance, emphasizing the importance of novel exhaust-cleaning technologies and cleaner fuels. Because of the unique and stable signatures, the method is not affected by urban background. With this study, we establish a route towards a novel monitoring protocol for ship emissions. Therefore, we present and discuss mass spectral signatures that indicate the particle age and thus the distance to the source. By matching ship transponder data, measured wind data and air mass back trajectories, we show how real-time SPMS data can be evaluated to assign distant ship passages.

Influence of sulfur emission control areas on particulate matter emission: A difference-in-differences analysis

As the shipping industry calls for a more sustainable development approach to minimize ecological footprints, emission control areas (ECAs) requiring low-sulfur fuel content have been established worldwide. Particulate matter (PM) is directly related to marine fuel quality; hence, based on classical emission calculation models, ECAs could theoretically reduce PM. However, empirical evidence and testing using econometric analyses are scarce. This retrospective study uses empirical meteorological data to examine whether China’s ECAs contribute to PM reduction using a difference-in-difference approach. Notably, China’s ECA policy has resulted in different outcomes in the country’s Yangtze River Delta, Pearl River Delta, and Bohai Rim regions. Only the Yangtze River Delta region has shown a significant PM reduction effect as a result of the ECA policy, while the Pearl River Delta and Bohai Rim regions have not recorded similar results. Possible explanations are proposed as well.