Particulate Matter (PM) and Parent, Nitrated and Oxygenated Polycyclic Aromatic Hydrocarbon (PAH) Emissions of Emulsified Heavy Fuel Oil in Marine Low-Speed Main Engine.

To understand the influences of emulsified fuel on ship exhaust emissions more comprehensively, the emissions of particulate matter (PM), nitrated, oxygenated and parent polycyclic aromatic hydrocarbons (PAHs) were studied on a ship main engine burning emulsified heavy fuel oil (EHFO) and heavy fuel oil (HFO) as a reference. The results demonstrate that EHFO (emulsified heavy fuel oil) exhibits notable abilities to significantly reduce emissions of particulate matter (PM) and low molecular weight PAHs (polycyclic aromatic hydrocarbons) in the gas phase, particularly showcasing maximum reductions of 13.99% and 40.5%, respectively. Nevertheless, burning EHFO could increase the emission of high molecular weight PAHs in fine particles and pose a consequent higher carcinogenic risk for individual particles. The total average (gaseous plus particulate) ΣBEQ of EHFO exhausts (41.5 µg/m3) was generally higher than that of HFO exhausts (18.7 µg/m3). Additionally, the combustion of EHFO (extra-heavy fuel oil) can significantly alter the emission quantity, composition, and particle-size distribution of PAH derivatives. These changes may be linked to molecular structures, such as zigzag configurations in C=O bonds. Our findings may favor the comprehensive environmental assessments on the onboard application of EHFO.

Influence on the levels of PAHs and methylated PAHs in surface soil from pollution control in China: Evidence in 2019 data compared with 2005 and 2012 data.

To comprehensively clarify the pollution characteristics of persistent toxic substances, the Soil and Air Monitoring Program Phase III (SAMP-III) was conducted in 2019 in China. In total, 154 surface soil samples were collected across China, and 30 unsubstituted polycyclic aromatic hydrocarbons (U-PAHs) and 49 methylated PAHs (Me-PAHs) were analyzed in this study. The mean concentrations of total U-PAHs and Me-PAHs were 540 ± 778 and 82.0 ± 132 ng/g dw, respectively. Northeastern China and Eastern China are the two regions of concern with high PAH and BaP equivalency levels. Compared with SAMP-I (2005) and SAMP-II (2012), an obvious upward temporal trend followed by a downward trend of PAH levels was observed in the past 14 years for the first time. The mean concentrations of 16 U-PAHs were 377 ± 716, 780 ± 1010, and 419 ± 611 ng/g dw in surface soil across China for the three phases, respectively. Considering rapid economic growth and energy consumption, an increasing trend from 2005 to 2012 was expected. From 2012 to 2019, the PAH levels in soils across China decreased by 50 %, which was consistent with the decline in PAH emissions. The period of reduction of PAHs in surface soil coincided with the implementation of Air and Soil Pollution Control Actions in China after 2013 and 2016, respectively. Along with the pollution control actions in China, the pollution control of PAHs and the increase in soil quality can be expected in the near future.

Chemical signatures of polycyclic aromatic hydrocarbons in the emissions from in situ oil burns.

This study characterized the parent and alkylated polycyclic aromatic hydrocarbons (PAHs) in gaseous and particulate emissions from the in situ burning (ISB) of oils. The experimental results indicate that the burning of the heavy oil produced the most PAH emissions because of its longest burning time. In addition, the parent PAHs mainly exist in the particulate phase, while alkylated PAHs mostly accumulate in the gaseous phase. In particular, the diagnostic-ratios of PAHs with great stability in both gaseous and particulate emissions from ISB are identified by comparing the laboratory and field data. The presences of bell-, slope- and V-shaped distribution patterns of alkylated PAHs in the emissions precisely indicate their sources to be petrogenic and pyrogenic processes occurring during ISB. The formation of 2-methylanthracene during ISB is confirmed. The overall findings are expected to provide a prospective protocol to characterize PAH pollution from ISB emissions in case of oil spills.

Gas-particle partitioning of polycyclic aromatic hydrocarbons from oil combustion involving condensate, diesel and heavy oil.

This study focuses on the gas-particle (G-P) partitioning of 16 polycyclic aromatic hydrocarbons (PAHs) from oil combustion, which is one of the important contributors of anthropogenic PAHs but has been rarely studied. The combustions of different types of oils involving ultra-light to heavy oils were investigated, and the PAH partitioning mechanism was determined by the widely used Junge-Pankow adsorption model, Koa absorption model, and dual sorption model, respectively. The results show that the source-specific diagnostic ratios of Ant/(Ant+Phe) are between 0.09 and 0.24, the estimated regression slopes of G-P partition coefficients (KP) of the total PAHs on their sub-cooled liquid vapor pressures (PLO) are in the range of - 0.34 to - 0.25, and the predicted fractions of PAHs in the particle phase (φ) by Koa absorption model are close to the measured values, while the log KPvalues of the LMW PAHs from the combustions of diesel and heavy oil are better represented by the dual sorption model. Our findings indicate that PAHs are derived from mixed sources that include the unburned original oil and combustion products, and the PAH partitioning mechanism is governed by the process of absorption into organic matter because of the unburned oil, but both adsorption and absorption exist simultaneously in the lighter PAHs from the combustions of heavier oils (i.e., diesel and heavy oil). Based on these findings, the understanding of the fate and transport of PAH emissions and the optimization of the emergency responses to accidents such as marine oil spills would be potentially improved.

The fingerprint stability of the biomarker hopanes and steranes in soot emissions from in-situ burning of oil.

The behavior of emissions is an important concern of in-situ burning (ISB) of spilled oils. In particular, the heavy soot originated from ISB can negatively impact the atmospheric environment. To track the behavior of ISB soot, the conservative biomarkers, such as hopanes and steranes, can be potentially used. In this study, the stability of chemical fingerprints of hopanes and steranes in the ISB soot were investigated based on the burning of two different types of oils, including one ultra-light condensate (i.e., surrogate Sanchi condensate) and one heavy oil. The results indicate that the chromatographic patterns and diagnostic ratios of hopanes and steranes in the ISB soot emissions almost remain identical to their corresponding source oils, proving the various oil source identification of ISB soot can be realized. This work attempts to provide novel insights into the application of biomarkers in the management of ISB emissions.

Chemical fingerprinting and characterization of spilled oils and burnt soot particles - A case study on the Sanchi oil tanker collision in the East China Sea.

The condensate spill accident from the Sanchi oil tanker collision in the East China Sea is unique in world history. To date, the spilled and burnt amounts of condensate remain unknown. The present study demonstrates the chemical fingerprints of a surrogate condensate (SC) from the same source, and of the carried heavy fuel oil (HFO) of the Sanchi accident. The evaporative features of the condensate are demonstrated by allowing the SC to naturally volatilize in a dark fume hood. In addition, the combustion emission of the SC is characterized by conducting a laboratory-scale combustion experiment. The evaporation experiment suggests that the volatilization process plays a significant role in the weathering of the condensate. The results show that the SC and HFO can be clearly distinguished based on their chemical fingerprints of C27-C35 hopanes and C9-C36 n-alkanes, along with priority polycyclic aromatic hydrocarbons (PAHs) and their alkylated derivatives. The compositional data reveal that the lighter component is predominant in the SC, thereby supporting its high volatility and flammability. The greater amounts of heavier components in the HFO indicate its long-term degradation and potential ecological risks to the environment. Further, the trisnorhopane thermal indicator (Ts/Tm) and C29/C30 ratio of hopanes are validated for identification of the SC and the HFO. More importantly, the changes in the hopane ratios of the soot particles are analyzed for the first time in this study, and the results demonstrate the validity of using hopane ratios to fingerprint the condensate soot particles. The diagnostic ratios of 2-MP/1-MP, 9/4-MP/1-MP, and InP/(InP+BghiP) also show decent performance on source identification after the condensate evaporation and combustion processes.

Electrochemical degradation performance and mechanism of dibutyl phthalate with hydrophobic PbO2 electrode.

A polytetrafluoroethylene (PTFE) doped PbO2 anode with a highly hydrophobicity was fabricated by electrodeposition method. In this process, vertically aligned TiO2 nanotubes (TiO2NTs) are formed by the anodic oxidation of Ti plates as an intermediate layer for PbO2 electrodeposition. The characterization of the electrodes indicated that PTFE was successfully introduced to the electrode surface, the TiO2NTs were completely covered with ß-PbO2 particles and gave it a large surface area, which also limited the growth of its crystal particles. Compared with the conventional Ti/PbO2 and Ti/TiO2NTs/PbO2 electrode, the Ti/TiO2NTs/PbO2-PTFE electrode has enhanced surface hydrophobicity, higher oxygen evolution potential, lower electrochemical impedance, with more active sites, and generate more hydroxyl radicals (·OH), which were enhanced by the addition of PTFE nanoparticles. The electrocatalytic performance of the three electrodes were investigated using dibutyl phthalate (DBP) as the model pollutant. The efficiency of the DBP removal of the three electrodes was in the order: Ti/TiO2NTs/PbO2-PTFE > Ti/TiO2NTs/PbO2 > Ti/PbO2. The degradation process followed the pseudo-first-order kinetic model well, with rate constants of 0.1326, 0.1266, and 0.1041 h-1 for the three electrodes, respectively. The lowest energy consumption (6.1 kWh g-1) was obtained after 8 h of DBP treatment using Ti/TiO2NTs/PbO2-PTFE compared to Ti/TiO2NTs/PbO2 (6.7 kWh g-1) and Ti/PbO2 (7.4 kWh g-1) electrodes. Moreover, the effects of current density, initial pH and electrolyte concentration were investigated. Finally, the products of the DBP degradation process were verified based on gas chromatography-mass spectrometry analysis, and possible degradation pathways were described.

Variations and characteristics of carbonaceous substances emitted from a heavy fuel oil ship engine under different operating loads.

Heavy fuel oil (HFO) accounts for approximately 80% of the fuel consumption of ocean-going ships in the world. Multiple toxic species are found in HFO exhaust, however, carbonaceous substances emitted from low-speed marine engine exhaust at different operating loads have not been thoroughly addressed. Therefore, a bench test for a low-speed marine engine with HFO fuel under different operating modes was carried out in this study. Emission factors and characteristics of CO2, CO, organic carbon (OC), elemental carbon (EC), as well as OC and EC fragments, organic matters of n-alkanes and polycyclic aromatic hydrocarbons (PAHs) are given and discussed. Combined with the correlation analysis results among the measured species and engine technical parameters, the formation processes and influence factors of carbonaceous components are also inferred in this study. Besides, together with OC to EC ratio, n-alkanes to PAHs ratio, etc., EC1 to soot-EC ratio in PM can be considered as tracer characteristic of high-sulfur-content HFO ship distinguished from diesel fuel ships. Profiles of n-alkanes and PAHs in PM can be used to distinguish shipping emission source from other combustion sources. Moreover, characteristics of carbonaceous components in size-segregated particles are also discussed, including OC, EC, OC and EC fragments, as well as organic matters. Results show that most of the particle mass, OC, EC, and organic matters are concentrated in fine particles with size of less than 1.1 µm, indicating the significance of ultrafine particles. Formation processes of OC and EC fragments, EC1 and soot-EC are also deduced and proved combined with the characteristics of OC and EC fragments, organic matters, and especially PAHs. Besides, the large variations of OC to EC ratios and speciated profiles of n-alkanes and PAHs in different particle size bins indicate that particle size should be considered when they are used as characteristic tracer in source apportionment studies.

Application of a fugacity model to estimate emissions and environmental fate of ship stack PAHs in Shanghai, China.

The understandings of environmental activities and regional inventory of ship stack PAHs are very limited in Shanghai due, in part, to the lack of source-segregated analysis. To address this, measured PAHs in organic film on ship surfaces were employed to reconstruct concentrations in various compartments through a fugacity model to investigate the level, transport, fate and annual emission of ship stack PAHs in Shanghai. The results revealed that ship stack PAHs results in 11.2-181 ng L-1 and 71.0-1710 ng g-1 in water and sediment of Shanghai, respectively. After being released into air, ship stack PAHs mainly concentrated in organic films and sediments while sunk in water and sediment. Crucial mass transfer pathways include deposition of airborne and sediment PAHs. The mass loss of ship stack PAHs was primarily through air advection, followed by degradation in sediment. The ship emissions (53.7 tons annually) accounted for approximate one tenth of the regional total in Shanghai (in 2017). Additionally, shipping was estimated to release 127 tons of PAHs annually into the Shanghai section of Yangtze River. Our results suggest our fugacity-based approach can be used to estimate the regional emissions and inventory of ship stack PAHs in the surrounding environment.

Polycyclic aromatic hydrocarbon contamination along roads based on levels on vehicle window films.

Vehicular emissions are known to be major contributors of airborne polycyclic aromatic hydrocarbons (PAHs) in cities. In order to assess the long-term contamination of PAHs along roads, we collected organic films from vehicle windows (26 private cars and 4 buses, in Shanghai, China) and used mathematical models to convert the film-bound PAH concentrations to the airborne PAH concentrations. The field measurements of airborne PAHs revealed that the partitioning and Level III fugacity model was suitable to estimate the airborne concentrations of high and low volatile PAHs (expect for naphthalene), respectively. The total airborne PAH concentrations along roads in Shanghai ranged from 0.83 to 3.37 µg m-3 and the incremental lifetime cancer risks (ILCRtotal) by exposure to PAHs along roads were greater than the USEPA lower guideline of 10-6, indicating non-negligible carcinogenic risks to drivers and passengers, especially via ingestion processes. This study provided a practicable method to investigate long-term air contamination of PAHs in vehicles and along roads based on film-bound PAH on vehicle windows. In addition, it was also possible to investigate the health risk in vehicles as a result of exposure to PAHs. Comparisons of PAHs between roads and shipping lanes also facilitated the delineation of vehicular and shipping PAH inventories. A capsule that summarizes the main finding of the work: Investigating film-bound PAH on vehicle windows is a practicable pathway to investigate the long-term contamination of PAHs in vehicles and along roads. This method can not only simplify the sampling processes, but the model calculations. The results also enabled investigations into ILCR in vehicles and specified source apportionment of traffic PAHs.

Characterization of polycyclic aromatic hydrocarbons in the surface sediments around the sunken Sanchi oil tanker.

The Sanchi oil tanker collision has attracted worldwide attention for its uniqueness in history. This study investigates the contamination level, spatial distribution, sources, and ecological risk level of polycyclic aromatic hydrocarbons (PAHs) present in the surface sediments collected from around the sunken tanker. The results indicated that the total PAH contents in the study area were in the range of 26.42-226.94 ngˑg-1, with an average of 106.86 ngˑg-1. The highest PAH concentration was observed at the station closest to the Sanchi wreckage, indicating potential PAH contamination due to the accident. The PAH ratios and statistical analysis revealed that the PAHs were mainly generated by coal and fuel oil combustion, with certain petrogenic inputs. The ecological risk assessment results suggested that adverse ecological effects to the benthic ecosystem due to PAH contamination was rare. However, long-term monitoring of the local sedimentary environment is highly recommended because of the prominent presence of high molecular weight PAHs.

New equation to predict size-resolved gas-particle partitioning quotients for polybrominated diphenyl ethers.

Gas/particle (G/P) partition quotients of semi-volatile organic compounds (SVOCs) for bulk air have been widely discussed in experimental and theoretical contexts, but research on size-resolved G/P partition quotients (KPi) are scarce and limited in scope. To investigate G/P partition behavior of polybrominated diphenyl ethers (PBDEs) for size-segregated particles in the atmosphere, 396 individual size-segregated particulate samples (36 batches × 11 size-ranges), and 108 pairs of concurrent gaseous and bulk particulate samples were collected in Harbin, China. A steady-state equation based on bulk particles is derived to determine G/P partition quotients of PBDEs for size-segregated particles, which depends on the organic matter contents of size-segregated particles (fOMi). This equation can well predict KPi with knowledge of bulk partition quotient (KPS), ambient temperature, and fOMi, the results of which match well with monitoring data in Harbin and other published data collected in Shanghai and Guangzhou of China and Thessaloniki of Greece, and remedies a defect of over-estimate KPi for high-brominated PBDEs by the previous equation. In particular, the new equation contributes to obtaining the PBDEs concentrations in all atmospheric phase from partial phase, then provides a credible path to evaluate healthy exposure dose from the airborne PBDEs, by co-utilization with exposure models.

Sedimentary polycyclic aromatic hydrocarbons (PAHs) along the mouth bar of the Yangtze River Estuary: Source, distribution, and potential toxicity.

The source, distribution, and potential toxicity of sedimentary polycyclic aromatic hydrocarbons (PAHs) along the mouth bar of the Yangtze River Estuary were investigated. Total concentrations of 17 PAHs in the study area ranged from 34.94 to 580.26 ng/g (mean value 146.31 ng/g). Results of PMF model revealed that mixed vehicle emissions (38.43%), natural gas combustion (24.98%), biomass combustion (20.76%) and coal combustion (15.83%) were sources of these sedimentary PAHs. The ERL/ERM, TEL/PEL and TEC/PEC values showed that the potential toxicity of PAHs was at low to medium level, but the presence of benzo[a]pyrene (BaP) and benzo[e]pyrene (BeP) requires more attention and research. Sedimentary PAHs pollution level in the three shoals (East Nanhui Shoal, Jiuduansha Shoal and Hengsha Shoal) was higher than that of the two passages (South Passage and North Passage), which demonstrates the possibility of restoration of the adjacent shoals by dredged soils in terms of PAHs pollution.

Polycyclic aromatic hydrocarbon contaminations along shipping lanes and implications of seafarer exposure: Based on PAHs in ship surface films and a film-air-water fugacity model.

Polycyclic aromatic hydrocarbons (PAHs) are one of the most toxic compounds in ship tailpipe exhausts. The long-term contamination of PAHs along shipping lanes and ports is difficult to assess using conventional methods such as AIS-EFs-data based (AIS, Automatic identification system; EFs, emission factors) or field sampling methods. To address this, we collected the organic films on ship surfaces and used a modified film-air-water fugacity model to convert the film-bound concentrations to the airborne (gaseous plus particulate) concentrations. Not surprisingly, concentrations of PAHs on organic films on ship surfaces were greater than those measured on films on residential buildings. The airborne total PAH concentrations along shipping lanes in Yangtze River Delta area ranged from 63.3-325 ng m-3, which were in the same order of magnitude to those in Beijing during haze days. The incremental lifetime cancer risks by exposure to PAHs in ship indoor air were higher than the US EPA lower guideline, indicating considerable carcinogenic risks to seafarers. Our study proposes an alternative method to estimate the long-term contaminations of PAHs along shipping lanes and highlights a notable health risk to seafarers.

Emissions of intermediate volatility organic compound from waste cooking oil biodiesel and marine gas oil on a ship auxiliary engine.

Ship auxiliary engines contribute large amounts of air pollutants when at berth. Biodiesel, including that from waste cooking oil (WCO), can favor a reduction in the emission of primary pollutant when used with internal combustion engines. This study investigated the emissions of gaseous intermediate-volatile organic compounds (IVOCs) between WCO biodiesel and marine gas oil (MGO) to further understand the differences in secondary organic aerosol (SOA) production of exhausts. Results revealed that WCO exhaust exhibited similar IVOC composition and volatility distribution to MGO exhaust, despite the differences between fuel contents. While WCO biodiesel could reduce IVOC emissions by 50% as compared to MGO, and thus reduced the SOA production from IVOCs. The compositions and volatility distributions of exhaust IVOCs varied to those of their fuels, implying that fuel-component-based SOA predicting model should be used with more cautions when assessing SOA production of WCO and MGO exhausts. WCO biodiesel is a cleaner fuel comparing to conventional MGO on ship auxiliary engines with regard to the reductions in gaseous IVOC emissions and corresponding SOA productions. Although the tests were conducted on test bench, the results could be considered as representative due to the widely applications of the test engine and MGO fuel on real-world ships.

Emission of intermediate volatility organic compounds from a ship main engine burning heavy fuel oil.

Intermediate volatility organic compounds (IVOCs) are crucial precursors of secondary organic aerosol (SOA). In this study, gaseous IVOCs emitted from a ship main engine burning heavy fuel oil (HFO) were investigated on a test bench, which could simulate the real-world operations and emissions of ocean-going ships. The chemical compositions, emission factors (EFs) and volatility distributions of IVOC emissions were investigated. The results showed that the main engine burning HFO emitted a large amount of IVOCs, with average IVOC EFs of 20.2-201 mg/kg-fuel. The IVOCs were mainly comprised of unspeciated compounds. The chemical compositions of exhaust IVOCs were different from that of HFO fuel, especially for polycyclic aromatic compounds and alkylcyclohexanes. The volatility distributions of IVOCs were also different between HFO exhausts and HFO fuel. The distinctions in IVOC emission characteristics between HFO exhausts and HFO fuel should be considered when assessing the IVOC emission and related SOA formation potentials from ocean-going ships burning HFO, especially when using fuel-surrogate models.

Gas/particle partitioning, particle-size distribution of atmospheric polybrominated diphenyl ethers in southeast Shanghai rural area and size-resolved predicting model.

A size-segregated gas/particle partitioning coefficient KPi was proposed and evaluated in the predicting models on the basis of atmospheric polybrominated diphenyl ether (PBDE) field data comparing with the bulk coefficient KP. Results revealed that the characteristics of atmospheric PBDEs in southeast Shanghai rural area were generally consistent with previous investigations, suggesting that this investigation was representative to the present pollution status of atmospheric PBDEs. KPi was generally greater than bulk KP, indicating an overestimate of TSP (the mass concentration of total suspended particles) in the expression of bulk KP. In predicting models, KPi led to a significant shift in regression lines as compared to KP, thus it should be more cautious to investigate sorption mechanisms using the regression lines. The differences between the performances of KPi and KP were helpful to explain some phenomenon in predicting investigations, such as PL0 and KOA models overestimate the particle fractions of PBDEs and the models work better at high temperature than at low temperature. Our findings are important because they enabled an insight into the influence of particle size on predicting models.

Occurrences, composition profiles and source identifications of polycyclic aromatic hydrocarbons (PAHs), polybrominated diphenyl ethers (PBDEs) and polychlorinated biphenyls (PCBs) in ship ballast sediments.

The aim of this study was to investigate the levels of persistent organic pollutants (POPs) including polycyclic aromatic hydrocarbons (PAHs), polybrominated diphenyl ethers (PBDEs) and polychlorinated biphenyls (PCBs) in ship ballast sediments. The ballast sediment samples were collected from six merchant ships docked in 2015 in Jiangyin City, China. Ballast sediments represent a potential vector for the transport of POPs and invasive species between marine environments. An attempt was also made to determine the sources of these compounds in the ballast sediment. The results indicated ballast sediments generally contain greater amounts of BDE-209 and comparable amounts of PAHs, PBDEs (exclusive of BDE-209) and PCBs compared to those in marine surface sediments. Based on the sediment quality guidelines, PAHs and PCBs in ballast sediments were estimated to have median or high potential of posing ecological risks, respectively, to marine life if ballast sediments were disposed without specific treatment. POPs in ballast sediments were derived from multiple sources with atmospheric deposition being an important origin. Ship activities including diesel exhaust and illegal oil sewage discharge were considerable contributors of certain individual POPs to ballast sediments. Our study is important because it represents the first report on levels, health risk assessment and source apportionments of POPs in ballast sediments and is a first step in the implementation of specific ballast sediment management measures.

Laboratory study of the particle-size distribution of Decabromodiphenyl ether (BDE-209) in ambient air.

Laboratory measurements for particle-size distribution of Decabromodiphenyl ether (BDE-209) were performed in a 0.5 m(3) sealed room at 25 °C. BDE-209 was manually bounded to ambient particles. An electrostatic field-sampler was employed to collect particles. The number of collected particles (n(i,j), i and j was the class of particle diameter and applied voltage on electrostatic field-sampler sampler, respectively) and the corresponding mass of BDE-209 in collected particles (m(∑i,j)) were determined in a series of 6 experiments. The particle-size distribution coefficient (ki) was calculated through equations related to n(i,j) and m(∑i,j), and the particle-size distribution of BDE-209 was determined by ki·n(i,j). Results revealed that BDE-209 distributed in particles of all size and were not affiliated with fine particles as in field measurements. The particle size-fraction should be taken into account when discussing the particle-size distribution of BDE-209 in ambient air due to the normalized coefficients (normalized to k1) and were approximately in the same order of magnitude for each diameter class. The method described in the present study was deemed feasible in determining the particle-size distribution of BDE-209 from vaporization sources and helpful to understanding the instinct rule of particle-size distribution of BDE-209, and potentially feasible for other SVOCs.

[Morphology determination of multi-needle bipolar corona discharge by OES].

Using the method of OES (optical emission spectrum) for measuring N2 emission spectrum, the spacial distribution of energetic electrons in multi-needle bipolar corona discharge at atmospheric pressure was investigated. According to the distribution of N2 second positive band's intensity ISPB, the outline of ionisation region was drawn accurately. The relationship between ISPB and discharge current I was obtained through the sum of ISPB. There are two ionisation regions in the multi-needle bipolar corona discharge. One is near the HV electrode and the other is near the grounded electrode. The ionisation region exists around the needlepoint within 2-3 mm. The volume of ionisation region becomes big with the applied voltage U increasing. The ionisation region of negative corona is bigger than that of positive corona. Near the HV discharge electrode, the outline of electron avalanche is similar to the configuration of electric field lines in the ionisation region, so the electron avalanche along the axis direction of needle develops farther than that along the radial direction. The electric field in the migration area is weak, and the distribution of space charges is large along the radial direction. The sum of ISPB in each ionisation region is second order linear with I, but the quadratic coefficient is very small. So the sum of ISPB is nearly linear with I, the distribution of ISPB is corresponding to the density distribution of energetic electrons. So the charged particles forming the discharge current in ionisation region are electrons. No emission spectrum of N2 can be measured in migration area, so there is no energetic electron. The energetic electrons only exist in ionisation region and the charged particles in migration area are ions.