Water-soluble Ions Research Articles

Concentrations of aerosol water-soluble ions(WSI)with high-time-resolution observation over Antarctic Ocean

Concentrations of aerosol water-soluble ions(WSI)with high-time-resolution observation over Antarctic Ocean

Bio-Inspired Eco-Friendly Superhydrophilic/Underwater Superoleophobic Cotton for Oil-Water Separation and Removal of Heavy Metals.

Effective integrated methods for oil-water separation and water remediation have signifi-cance in both energy and environment fields. Materials with both superlyophobic and superlyophilic properties toward water and oil have aroused great attention due to their energy-saving and high-efficient advantages in oil-water separation. However, in order to fulfill the superlyophobicity, low surface tension fluorinated components are always being introduced. These constituents are environmentally harmful, which may lead to additional contamination during the separating process. Moreover, the heavy metal ions, which are water-soluble and highly toxic, are always contained in the oil-water mixtures created during industrial production. Therefore, material that is integrated by both capacities of oil-water separation and removal of heavy metal contamination would be of significance in both industrial applications and environmental sustainability. Herein, inspired by the composition and wettability of the shrimp shell, an eco-friendly chitosan-coated (CTS) cotton was developed. The treated cotton exhibits the superhydrophilic/underwater superoleophobic property and is capable of separating both immiscible oil-water mixtures and stabilized oil-in-water emulsions. More significantly, various harmful water-soluble heavy metal ions can also be effectively removed during the separation of emulsions. The developed CTS coated cotton demonstrates an attractive perspective toward oil-water separation and wastewater treatment in various applications.

Ambient particle composition and toxicity in 31 major cities in China

Current assessment of air quality or control effectiveness is solely based on particulate matter (PM) mass levels, without considering their toxicity differences in terms of health benefits. Here, we collected a total of 465 automobile air conditioning filters from 31 major Chinese cities to study the composition and toxicity of PM at a national scale. Dithiothreitol assay showed that normalized PM toxicity (NIOG) in different Chinese cities varied greatly from the highest 4.99 × 10−3 for Changsha to the lowest 7.72 × 10−4 for Yinchuan. NIOG values were observed to have significant correlations with annual PM10 concentration (r = -0.416, p = 0.020) and some PM components (total fungi, SO42− and calcium element). The concentrations of different elements and water-soluble ions in PM also varied by several orders of magnitude for 31 cities in China. Endotoxin concentrations in PM analyzed using limulus amebocyte lysate assay ranged from 2.88 EU/mg PM (Hangzhou) to 62.82 EU/mg PM (Shijiazhuang) among 31 Chinese cities. Besides, real-time qPCR revealed 10∼100-fold differences in total bacterial and fungal levels among 31 Chinese cities. The concentrations of chemical (water soluble ions and trace elements) and biological (fungi, bacteria and endotoxin) components in PM were found to be significantly correlated with some meteorological factors and gaseous pollutants such as SO2. Our results have demonstrated that PM toxicity from 31 major cities varied greatly up to 6.5 times difference; and components such as fungi and SO42− in PM could play important roles in the observed PM toxicity. The city-specific air pollution control strategy that integrates toxicity factors should be enacted in order to maximize health and economic co-benefits. This work also provides a comprehensive view on the overall PM pollution situation in China.

Pollution Characteristics of Water-Soluble Inorganic Ions in PM2.5 from a Mountainous City in Southwest China

In order to explore the characteristics of water-soluble inorganic ions (WSIIs) in the atmosphere of Wanzhou, a small mountainous city in Chongqing, four representative seasonal PM2.5 samples and gaseous precursors (SO2 and NO2) were collected from April 2016 to January 2017. The WSIIs (including Cl−, NO3−, SO42−, Na+, NH4 +, K+, Mg2+, and Ca2+) were analyzed by ion chromatography. During the sampling period, daily PM2.5 concentration varied from 3.47 to 156.30 μg·m−3, with an average value of 33.38 μg·m−3, which was lower than the second-level annual limit of NAAQS-China. WSIIs accounted for 55.6% of PM2.5, and 83.1% of them were secondary inorganic ions (SNA, including SO42−, NO3−, and NH4+). The seasonal variations of PM2.5 and WSIIs were similar, with the minimum in summer and the maximum in winter. PM2.5 samples were the most alkaline in summer, weakly alkaline in spring and winter, and close to neutral in fall. The annual average ratio of NO3−/SO42− was 0.54, indicating predominant stationary sources for SNA in Wanzhou. NO3−, SO42−, and NH4+ mainly existed in the form of (NH4)2SO4 and NH4NO3. The results of the principal component analysis (PCA) showed that the major sources of WSIIs in Wanzhou were the mixture of secondary inorganic aerosols, coal combustion, automobile exhaust (49.53%), dust (23.16%), and agriculture activities (9.68%). The results of the backward trajectory analysis showed that aerosol pollution in Wanzhou was mainly caused by local emissions. The enhanced formation of SNA through homogeneous and heterogeneous reactions contributed to the winter PM2.5 pollution event in Wanzhou.

Chemical Component of Particulate Matters and VOCs Characteristics During Vehicle Brake Processes

Six sets of brake systems were tested using a brake dynamometer, and the brake wear particles (BWPs) and volatile organic compounds (VOCs) were collected during the braking process. In total, 39 elements, 12 water-soluble ions, 7 carbon components, and 18 polycyclic aromatic hydrocarbons (PAHs) in BWPs were extracted and detected, and 74 VOCs in gas samples were analyzed. The average mass fractions of 12 inorganic elements (i.e., Sb, Mg, Cu, Zn, Ti, Ca, Si, Zr, K, Ba, Al, and Fe) with higher contents in PM2.5 and PM10 were 43.4% and 40.3%, respectively, and the average mass fraction of Fe was the highest, accounting for 16.6% and 13.1% of PM2.5 and PM10, respectively. The average mass fractions of the 12 water-soluble ions in PM2.5 and PM10 were 16.5% and 12.6%, respectively, and NO3-, SO42-, and Ca2+ were the ions with high contents. The average mass fraction of total carbon (TC) in PM2.5 and PM10 were 21.9% and 18.1%, respectively, and the average mass fraction of organic carbon (OC) was approximately five times that of elemental carbon (EC). There were six types of PAHs with a detection rate greater than 50%, among which naphthalene (Nap) was the most abundant. The average mass concentration of 74 VOCs was 316.04 μg·m-3, of which the aromatic hydrocarbon had the highest mass concentration. The compositions of BWPs and VOCs emitted by the six sets of brake systems were quite different, which was mainly determined by the brand and raw materials of the brake pads.

Impact of fireworks burning on air quality during the Spring Festival in 2021-2022 in Linyi, a central city in the North China Plain.

The management of fireworks has been strengthened during the Spring Festival in 2022 compared with that in 2021 in Linyi, a central city in the North China Plain. Online measurements of the chemical components of PM2.5 were conducted during the Spring Festival in 2021-2022 to assess the influence of fireworks burning (FB) on air quality. Remarkable achievements have been made in improving air quality during FB period (FBP) in 2021-2022 attributing to the stringent regional emission reduction measures, fireworks control, and favorable meteorological conditions with the concentrations of PM2.5, water-soluble ions, and carbonaceous aerosols decreasing by 73.6%, 78.8%, and 73.5%, respectively. The PM2.5 concentrations increased by 96.3% during FBP compared with those during non-FB period (NFBP) in 2021, while the opposite phenomenon was observed in 2022 with PM2.5 concentrations decreasing by 56.2% because of the favorable meteorological condition during FBP in 2022. As indicators of FB, the Cl-, K+, and Mg2+ concentrations showed an increasing trend during FBP compared with that during NFBP, both in 2021 and 2022, but had little effect on other components. The contribution of FB to PM2.5 decreased from 68.4% in 2021 to 15.7% in 2022 based on the relative ratio method, indicating the various measures conducted by all districts and counties in Linyi helped achieve near zero fireworks emissions by 2022. Besides, the contribution of FB to PM2.5 showed a straight-line upward trend from 19:00 on New Year's Eve, reached its peak (76.1%) at 3:00 on Lunar New Year's Day, while the highest value was only 35.0% during FBP in 2022, indicating the implementation of fireworks ban measures in Linyi achieved a good effect on pollution peak cutting. This study has emphasized the necessity of FB restricting during special holidays.

Coupling Effects of Sandstorm and Dust from Coal Bases on the Atmospheric Environment of Northwest China

The coupling effects of sandstorm and dust from coal bases themselves can have a major impact on the atmospheric environment as well as on human health. The typical coal resource city of Wuhai in Inner Mongolia was selected in order to study these impacts during a severe sandstorm event in March 2021. Particulate matter (PM1, PM2.5 and PM10) and total suspended particulate matter (TSP) samples were collected during the sandstorm event of 15–19 March 2021 and non-sandstorm weather (11–13 March 2021) and analyzed for their chemical composition. The concentrations of PM1, PM2.5, PM10 and TSP in Wuhai city during the sandstorm were 2.2, 2.6, 4.8 and 6.0 times higher than during non-sandstorm days, respectively. Trace metals concentrations in particles of different sizes generally increased during the sandstorm, while water-soluble ions decreased. Positive matrix fraction (PMF) results showed that the main sources of particles during both sandstorm and non-sandstorm days were industrial emissions, traffic emissions, combustion sources and dust. The proportion of industrial emissions and combustion sources increased compared with non-sandstorm days, while traffic emissions and dust decreased. The backward trajectory analysis results showed that airflows were mainly transported over short distances during non-sandstorm days, and high concentration contribution source areas were from southern Ningxia, southeast Gansu and western Shaanxi. The airflow was mainly transported over long distances during the sandstorm event, and high concentration contribution source areas were from northwestern Inner Mongolia, southern Russia, northern and southwestern Mongolia, and northern Xinjiang. A health risk analysis showed that the risk to human health during sandstorm days related to the chemical composition of particles was generally 1.2–13.1 times higher than during non-sandstorm days. Children were more susceptible to health risks, about 2–6.3 times more vulnerable than adults to the risks from heavy metals in the particles under both weather conditions.

Quantification of Water-Soluble Inorganic Ions of PM10 Particles in Selected Areas of Kolkata Metropolitan City, India

Quantification of Water-Soluble Inorganic Ions of PM10 Particles in Selected Areas of Kolkata Metropolitan City, India

Effect of crack width and wet-dry cycles on the chloride penetration resistance of engineered cementitious composite (ECC)

• Influence of crack width and wet-dry cycles on the chloride ingress in cracked ECC was investigated. • Chloride penetration profile as well as the change of total and water-soluble chloride ion content was measured. • The “maximum phenomenon” is observed for both water-soluble and bound chloride ions profiles under wet-dry cycles. • The change of the mineral phases and porosity is related with the chloride binding behaviour. The resistance of cracked ECC against chloride ingress is mainly governed by the accumulated crack width of all the cracks rather than the maximum width of multiple cracks. However, most studies focus on the influence of a single fine crack (<100 μm), which is far smaller than the accumulated crack width. To this end, this study focuses on a relatively large crack width scale. Cracks with widths of 0.1, 0.2 and 0.3 mm were notched on an ECC specimen. Both NaCl solution immersion and wet-dry cycles conditions were applied. Chloride penetration profile as well as the change of total and water-soluble chloride ion content was measured. Relationship between the bound chloride and water-soluble chloride was studied. X-ray diffraction (XRD) and mercury intrusion porosimetry (MIP) tests were carried out to show the influence of crack width and wet-dry cycles on the changes of the mineral phases, porosity and pore size distribution in the vicinity of the crack.

Determination of water-soluble nitrate ions in PM2.5 particles using UiO-67 modified glassy carbon electrode

Determination of water-soluble nitrate ions in PM2.5 particles using UiO-67 modified glassy carbon electrode

Chemical characteristics and sources of PM2.5 in the urban environment of Seoul, Korea

In Seoul, Korea, episodes of high concentrations of PM2.5 (particulate matter ≤2.5 μm) continue to occur despite the enforcement of air quality standards. Seoul has several sources of pollution owing to its high population density. Therefore, this study evaluated the chemical characteristics of PM2.5, including inorganic ions and various gases, focusing on those with concentrations exceeding the standard limit. The study was conducted from June 1 to August 22, 2018, in Seongbuk, and from March 29 to May 31, 2019, in Jungnang. Water-soluble inorganic ions of PM2.5 were measured every 30 min using a particle-into-liquid sampler (PILS) combined with two ion chromatographs. In Seongbuk, ammonium sulfate was mainly caused by ammonium-poor conditions. In Jungnang, ammonium nitrate production occurred mainly due to ammonium-rich conditions. In both regions, during the occurrence of concentrations of PM2.5 exceeding the standard limit, the proportion of nitrate among inorganic ions was the highest. In Jungnang, two emission sources located in the west and southwest were identified using a conditional probability function. Contaminants from the southwest had high concentrations of nitrates, presumably due to atmospheric stagnation and nitrate mixing in lower planetary boundary layer height due to an decrease in surface temperatures at dawn. Pollutants from the west had high concentrations of sulfates. These are generated through photochemical reactions from industrial complexes. Cluster analysis confirmed that 27.2% of the air was stagnant and flowed from the south. In most cases, air pollutants originated from western Korea and coastal China.

Characteristics of Water-Soluble Inorganic Ions in PM2.5 in Typical Urban Areas of Beijing, China.

Following the implementation of “coal-to-gas conversion” policy in the Haidian District of Beijing during summer, the present comparative study was performed employing 41 PM2.5 samples as precursors to analyze the characteristics of water-soluble inorganic ions. The concentrations of water-soluble inorganic ions in PM2.5 were analyzed by ion chromatography, and the occurrence form of ions was characterized via time-of-flight secondary ion mass spectrometry (TOF-SIMS). Results revealed that the daily average mass concentration of PM2.5 in Beijing during the sampling period was 94.28 ± 52.49 μg/m3. As compared to the winter of 2016, the average daily PM2.5 concentration in Beijing decreased by 29 μg/m3 in 2017 (28.2% decrease), with a remarkable decline in the number of days with pollution. During the pollution period, the concentrations of NO3–, SO42–, and NH4+ were significantly higher in PM2.5 as compared to the cleaning period. The ratio of the concentrations of [NO3–]/[SO42–] was greater than 1, and the contribution from mobile sources was relatively large, indicating that the implementation of the “coal-to-gas conversion” policy in Beijing has led to the reduction of SO42– emissions from fixed sources, such as coal. Furthermore, TOF-SIMS analysis results showed that NH4+ tended to exist in the form of molecular ammonium sulfate or ammonium hydrogen sulfate during the period of pollution.

Chemical Characterization, Source Identification, and Health Risk Assessment of Atmospheric Fine Particulate Matter in Winter in Hangzhou Bay

PM2.5 is an important pollutant which affects air quality and human health. In this study, chemical components (water-soluble inorganic ions, organic carbons (OC), elemental carbons (EC), and elemental metals) and health effects were analyzed in wintertime in a suburban area in Hangzhou Bay. OC and SNA (sulfate, nitrate, and ammonium) contributed 76.2% to local PM2.5. NH4+ existed mainly in the form of (NH4)2SO4 and NH4NO3. Seven sources were resolved from PMF analysis, namely secondary inorganic aerosol (31.8%), vehicle exhaust (19.5%), industry mixed with coal combustion (16.3%), crustal dust (9.5%), biomass burning (9.4%), sea salt (8.7%), and the leather industry (4.8%). Potential source contribution function (PSCF) and concentration weighted trajectory (CWT) analysis were applied to study regional transport in this region. Secondary inorganic formation was enhanced from the air plume from the northwest, especially from north Jiangsu Province. The results of the health risk assessment of associated metals indicated the higher potential of Cr and Mn to cause noncarcinogenic effects in children. A significant carcinogenic risk was observed for all people of Cr emitted from the leather industry. Our results showed the chemical characterization and sources of PM2.5 in a suburban region, the health effects of which should be addressed in future policies to safeguard public health, especially in the leather industry.

Evaluating the influence of constant source profile presumption on PMF analysis of PM2.5 by comparing long- and short-term hourly observation-based modeling

Hourly PM2.5 speciation data have been widely used as an input of positive matrix factorization (PMF) model to apportion PM2.5 components to specific source-related factors. However, the influence of constant source profile presumption during the observation period is less investigated. In the current work, hourly concentrations of PM2.5 water-soluble inorganic ions, bulk organic and elemental carbon, and elements were obtained at an urban site in Nanjing, China from 2017 to 2020. PMF analysis based on observation data during specific pollution (firework combustion, sandstorm, and winter haze) and emission-reduction (COVID-19 pandemic) periods was compared with that using the whole 4-year data set (PMFwhole). Due to the lack of data variability, event-based PMF solutions did not separate secondary sulfate and nitrate. But they showed better performance in simulating average concentrations and temporal variations of input species, particularly for primary source markers, than the PMFwhole solution. After removing event data, PMF modeling was conducted for individual months (PMFmonth) and the 4-year period (PMF4-year), respectively. PMFmonth solutions reflected varied source profiles and contributions and reproduced monthly variations of input species better than the PMF4-year solution, but failed to capture seasonal patterns of secondary salts. Additionally, four winter pollution days were selected for hour-by-hour PMF simulations, and three sample sizes (500, 1000, and 2000) were tested using a moving window method. The results showed that using short-term observation data performed better in reflecting immediate changes in primary sources, which will benefit future air quality control when primary PM emissions begin to increase.

Organic Acids in Sequential Volume-Based Rainwater Samples in Shanghai: Seasonal Variations and Origins

Organic acids were investigated in the rain sequence. Samples were collected in Shanghai (East China) over a one-year period using an automatic volume-based sequential rain sampler designed by ourselves. Organic acids significantly contributed (17.8 ± 10.2%) to the acidity of rainfall events in Shanghai. We observed that the concentration of each water-soluble ion in the sequential volume-based rainwater samples did not change significantly after the cumulative rainfall reached ~1.2 mm, on average. The volume-weighted mean (VWM) concentrations of formic acid, acetic acid, and oxalic acid were 13.54 μeq L−1, 8.32 μeq L−1, and 5.85 μeq L−1, respectively. Organic acids might mostly come from fine particles, which was the reason for the differences in acid concentrations in rainfall events, cloud water, and early sequences of rainfall events. The VWM concentrations of organic acids in rainfall events, cloud water, and early sequences of rainfall events were highest in spring and lowest in winter. Further analysis, including positive matrix factorization (PMF), suggested that vehicle exhaust and secondary emission sources were dominant contributors of organic acids in rainfall events (40.5%), followed by biological emission sources (37.3%), and biomass combustion sources (18.6%). The overall results not only reveal the critical role of organic acids in cloud water and rainfall events but also indicate organic acids might pose an ecological threat to the local surface ecosystem.

Comparison of the Chemical Characteristics and Toxicity of PM2.5 Collected Using Different Sizes of Cyclones

Cyclone sampling devices have been helpful in assessing the toxic effects of fine particulate matter (PM2.5). The particle collection efficiency of sampling devices is critical. This study investigated the effect of cyclone size on particle size, chemical composition, and particle toxicity. Three cyclones with different inner diameters (12–68 mm) were tested for penetration using an aerodynamic particle sizer, fluorescent polystyrene latex, and a differential mobility analyzer. The elemental and water-soluble ion compositions of the particles collected by different cyclones were compared. An evaluation of the particles’ toxicity was conducted by comparing the results of dithiothreitol (DTT), limulus amebocyte lysate (LAL), and cell exposure assays. The experimental evaluation showed a 50% cut-size of the cyclones between 0.17–0.28, 0.34–0.36, and 0.70 μm for the small, medium, and large cyclones, respectively. To collect PM2.5 and evaluate separation performance in the real environment, the small and large cyclones were selected according to the particle penetration and flow rate. A comparison of chemical composition and enrichment factor values found that the particles in the small cyclone samples contained smaller and more anthropogenic sources than those in the large cyclone samples. The oxidative potential (OP) measured by the DTT assay of the samples collected using the small and large cyclones differed across sampling periods and associated with the transition metals. The viability of human epithelial A549 cells after exposure to the collected particles using the cyclones was different across sampling periods and associated with OP. The endotoxin concentrations measured in the LAL assay were found only in the large cyclone samples; they affected the estimated level of cytokine based on IL(interleukin)-6 release from human leukemia monocytic (THP-1) cells derived macro-phage-like cells. Regardless of the size, the cyclone techniques used in this study to collect aerosol particles would be a powerful tool for a detailed evaluation of particle toxicity.

Tracing the predominant sources of carbon in PM2.5 using δ13C values together with OC/EC and select inorganic ions over two COALESCE locations

As part of the COALESCE (Carbonaceous Aerosol Emissions, Source apportionment and Climate Impacts) campaign, ambient PM2.5 was collected at two regional sites (Bhopal and Mysuru) in India during 2019. We utilized organic carbon (OC), elemental carbon (EC) and water-soluble inorganic ions together with δ13C values, to better understand total carbon (TC) sources at these locations.The annual average δ13C values (−26.2 ± 0.6‰) at Mysuru and Bhopal (−26.6 ± 0.6‰) were comparable. However, at Mysuru, except during winter, day-to-day variability was much lower (narrow range of −26.8 to −26.0‰) than that at Bhopal (range: −28.1 to −24.7‰), suggesting that TC was contributed by few sources, likely dominated by vehicular emissions. Seasonal average δ13C values at Bhopal increased slightly (−25.8 ± 0.5‰) during the winter (Jan–Feb) and decreased (−27.0 ± 0.3‰) during the monsoon (Jun–Sep) season compared to the annual average. The decrease in δ13C values during the monsoon season was likely driven by enhanced secondary organic aerosol formation. Further, based on MODIS derived fire spots and back trajectories, we infered that the δ13C values (−27.5 to −26.0‰) in Bhopal during the post-monsoon season (Oct–Dec) were indicative of dominant biomass burning contributions. The inorganic ions/TC ratio during this season suggested that biomass burning aerosol was aged and may have been transported from crop residue burning in the Indo-Gangetic plains. At Mysuru, like the trend at Bhopal, the δ13C values during the monsoon season were lower than those during the winter season.Finally, δ13C values were input to a Bayesian model–MixSIAR to demonstrate the usefulness of such models in apportioning TC. In its simplest implementation, the model separated TC sources into fossil fuel emissions and non-fossil fuel sources . Fossil fuel combustion emissions accounted for 47 ± 19% and 62 ± 22% of the TC at Bhopal and Mysuru, respectively.

Composition and size of retained aerosol particles on urban plants: Insights into related factors and potential impacts

The role of plants in alleviating aerosol pollution has drawn extensive attention. Most studies focus on compositions of aerosol particles on urban plants, while the leaf traits related to particle retention have not yet been intensively studied. This study selected five typical urban plants (Loropetalum chinense, Rhododendron simsii, Euonymus japonicus, Photinia × fraseri, Osmanthus fragrans), and employed scanning electron microscope (SEM) and ion chromatography, aiming to investigate the accumulation features of aerosol particles and the relationships between leaf traits and particle retention. Results show that aerosol particles were mainly retained on the adaxial leaf surface, the fine particles (Φ ≤ 2.5 μm) were the predominant components (77.8 % by number) on the leaves, and the dominant water-soluble ions of particles were Ca2+, SO42−, and NO3−. By comparison, E. japonicus and P. fraseri were efficient in the retention of fine and coarse particles (2.5 <Φ ≤ 10 μm), but L. chinense was capable to retain more large particles (Φ > 10 μm). The correlation analysis indicates that leaf traits are closely related to the accumulation of aerosol particles. The result shows that plant leaves with larger stomatal area, lower stomatal density, smaller specific leaf area and higher in epicuticular wax content can retain more aerosol particles. This result indicates that the leaves are capable of retaining aerosol particles via the synergy of multiple leaf traits, such as higher wax content and the fewer but larger stomata on their leaf surfaces. This study is helpful to understand the interactions between leaf traits and particle retention, and it further contributes to the selection of potential dust-retaining plants, which is of great significance for the alleviation of urban air pollution.

Insights into factors affecting size-segregated nitrate formation in a coastal city through measurements of dual isotopes

Due to the effective control of SO2 emissions in China, nitrate becomes a key component in atmospheric aerosols, especially in haze episodes. Therefore, it is important to elucidate the formation pathways and sources of ambient NO3−. In this study, size-segregated particles were collected in Xiamen urban area from August 2019 to February 2021. Water-soluble inorganic ions and the dual isotope compositions (δ15N and δ18O) of NO3− were measured. A Bayesian isotope mixing model was used to investigate the formation pathways and contributions of different NOx sources to NO3−. The results showed that NO3− exhibited pronounced seasonal variations in concentrations and size distributions. The δ15N–NO3- and δ18O–NO3- values in different modes were lower in the warm season (May to November) than in the cold season (December to Feburary), attributing largely to the source and formation pathway changes. Bayesian model indicated that the contribution of the NO2 + ⋅OH pathway in the warm season was higher than in the cold season, and the contribution decreased with the increase of particle size. However, opposite seasonal trends were observed for N2O5 + H2O, N2O5 + Cl− and NO3 + HC pathways. The size distribution of δ15N–NO3- values was more influenced by the formation pathway than the isotopic fractionation. Results also indicated that the average contribution of soil emission (13.5%) to ambient NO3− was significantly lower than that of coal combustion (30.4%), ship emission (26.6%) and vehicle exhaust (29.6%). The contribution of soil emisison was almost double in warm season (17.7%) compared to cold season (9.3%) whereas coal combustion and vehicle exhaust decreased and ship emission remained relatively stable. Our results highlight the influence of formation pathways on the size distribution of δ15N–NO3- and the importance of after emission treatment of ship exhaust in reducing particle pollution in port cities.

Seasonal source analysis of nitrogen and carbon aerosols of PM2.5 in typical cities of Zhejiang, China.

Fine particulate matter (PM2.5) significantly impacts global air quality and human health due to its smaller particle size and larger specific surface area. Nitrogen and carbon aerosols, as the main components of PM2.5, play key roles in air pollution. This study identified the sources and seasonal variation of nitrogen and carbon aerosols in PM2.5 in typical cities of Zhejiang. The annual average PM2.5 concentrations of Hangzhou (HZ), Ningbo (NB), and Huzhou (HUZ) were 39.8±19.1μg m-‍3, 40.0±21.5μgm-3, and 50.1±22.6μgm-3, respectively, which exceeded the Chinese air quality limit of 35.0μgm-3. The results showed that the concentrations of nitrogen aerosols (NO3- and NH4+) in water-soluble inorganic ions were higher at 9.6±4.6μgm-3, 9.0±4.5μgm-3 and 11.5±5.4μgm-3 in HZ, NB and HUZ, respectively, especially in winter, accounting for over 60% of the total. The annual average δ15N values of PM2.5 were 6.2±1.9‰, 6.4±2.2‰ and 6.7±1.9‰ in HZ, NB and HZ, respectively; the δ15N values in winter were relatively low. A Bayesian isotopic mixing model was employed to analyse the sources of nitrogen aerosols in winter; the results showed that nitrogen concentration was mainly affected by NH3 and NOX emitted by motor vehicle exhaust, coal combustion, biomass combustion, biogenic soil emissions, animal wastes and ocean evaporation (NB). In addition, the carbon component analysis of PM2.5 showed that the annual average mass concentration of TC accounted for 18.7%, 16.4% and 20.1% of PM2.5 in HZ, HUZ and NB, respectively. The same isotope model was used to analyse the sources of carbon aerosols; the results showed that carbon aerosols were mainly affected by the sources of motor vehicle exhaust, coal combustion, biomass combustion and dust. In the PM2.5 in Zhejiang, the most contributory sources of nitrogenous aerosols and carbon aerosols were motor vehicle exhaust sources.