Characteristics Of Water-soluble Inorganic Ions Research Articles

Characterization of fine particulate matter water-soluble inorganic ions and estimation of aerosol acidity at three COALESCE network sites - Mysuru, Bhopal, and Mesra - in India.

The study was carried out to understand the chemical, spatiotemporal characteristics of water-soluble inorganic ions (WSIIs), their association with PM2.5 mass, and aerosol acidity in three COALESCE (carbonaceous aerosol emissions, source apportionment, and climate impacts) network sites of India (Mesra - Eastern India, Bhopal - Central India and Mysuru - Southern India). Alternate-day 24-h integrated bulk PM2.5 samples were collected during 2019 along with on-site meteorological parameters. Annual average PM2.5 concentrations were 67 ± 46µgm-3, 54 ± 47µgm-3, and 30 ± 24µgm-3 at Mesra, Bhopal, and Mysuru, respectively. PM2.5 concentrations exceeded the annual mean (40µgm-3) recommended by the National Ambient Air Quality Standards (NAAQS) at Mesra and Bhopal. WSIIs existed in PM2.5 mass at Mesra (50.5%), Bhopal (39.6%), and Mysuru (29.2%). SO42-, NO3-, and NH4+ (SNA) were major secondary inorganic ions in total WSIIs, with an annual average of 88.4% in Mesra and 82.0% in Bhopal 78.4% in Mysuru. Low NO3-/SO42- ratios annually at Mesra (0.41), Bhopal (0.44), and Mysuru (0.24) indicated that stationary sources dominated vehicular emissions (1.0). Aerosol acidity varied from region to region and season to season depending on the presence of NH4+, the dominant counter-ion to neutralize anions. Aerosols were near-neutral or alkaline at all three sites, except during the pre-monsoon season in Mysuru. An assessment of neutralization pathways for major anions [SO42- + NO3-] suggests that they mainly existed as sulfate and nitrate salts such as ammonium sulfate ((NH4)2SO4) and ammonium bisulfate (NH4HSO4) in conjunction with ammonium nitrate (NH4NO3).

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.

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 Characteristics of Water-Soluble Inorganic Ions in Different Types of Asian Dust in Wajima, a Background Site in Japan

Two Asian dust (AD) events were observed in March 2021 (AD1: 16 March 2021 00:00 UTC~17 March 2021 12:00 UTC and AD2: 28 March 2021 00:00 UTC~31 March 2021 12:00 UTC). To determine the chemical characteristics of water-soluble inorganic ions (WSIIs) in different types of Asian dust, the total suspended particulates (TSP) were collected at Kanazawa University Wajima Air Monitoring Station (KUWAMS), a background site in Japan from 27 February to 4 March, 2021. Based on the lidar observations and the backwards trajectory analysis results, AD events were divided into two types: ADN (aerosols were mainly mineral dust) and ADP (aerosols were mixtures of spherical particles). During ADs, the concentrations of the TSP and WSII increased, with the highest TSP concentration in ADN (38.6 μg/m3) and the highest WSII concentration in ADP (5.82 μg/m3). The increase in (cations)/(anions) during AD indicates that the input of AD aerosol buffered the aerosol acidity. Additionally, a significant increase in Cl depletion, along with ADN events, was found (Cl depletion = 73.8%). To comprehensively analyse the different types of ADs on WSIIs, we refer to the previous data from 2010 to 2015 at KUWAMS. As a result, the increased Cl depletion was caused by the heterogeneous reaction of HNO3 with sea salt when the air mass passed over the Japanese Sea. Additionally, the chemical form of SO42− was highly dependent on the source and pathway, while SO42− mainly came from natural soil dust in ADN and from anthropogenic emissions in ADP. The enhancement of secondary NO3− was observed in AD via the heterogeneous hydrolysis of N2O5.

Characteristics of Water-soluble Inorganic Ions in Aerosol and Precipitation and their Scavenging Ratios in an Urban Environment in Southwest China

Daily fine particulate matter (PM2.5) and precipitation samples were collected simultaneously at an urban site in southwest China in four segregated months in 2015 for measuring major water-soluble inorganic ions (WSIIs). Online hourly concentrations of PM10 and PM2.5 were also monitored, which showed annual mean concentrations of 67.8 and 41.6 µg m–3, respectively. PM2.5 showed the highest concentration in winter and lowest in summer. The annual mean concentration of the total WSIIs was 20.3 µg m–3, accounting for about 48.7% of PM2.5. Among the total WSIIs in ambient PM2.5, SO42– was the predominant component (49.7%), followed by NH4+ (24.1%) and NO3– (21.4%). NH4+ and SO42– were the two most abundant ions in precipitation, followed by Ca2+ and NO3–. Seasonal patterns of the major inorganic ions in precipitation were similar to those in PM2.5, with the highest concentration in winter and lowest in summer. The mean scavenging ratios were 454, 445, 364, 456, and 394 for SO42–, NO3–, NH4+, Cl–, and K+, and 116, 353, and 18 for gas SO2, HNO3, and NH3, respectively. The higher scavenging ratios of particulate ions than their gaseous precursors suggest the higher contributions of particles than gases to the total wet deposition.

Characteristics of Water-soluble Inorganic Ions in PM2.5 in Beijing During 2017-2018

To explore the characteristics of water-soluble inorganic ions (WSIIs) in PM2.5 during the process of continuous improvement of air quality in Beijing in recent years, a continuous collection of PM2.5 sample campaign was conducted in Beijing from 2017 to 2018. The PM2.5 mass concentration and WSIIs were then determined. The results showed that the average concentration of PM2.5 in Beijing was (77.1±52.1) μg ·m-3, with the highest and lowest values during spring [(102.9±69.1) μg ·m-3]and summer [(54.7±19.9) μg ·m-3], respectively. The average concentration of WSIIs was (31.7±30.1) μg ·m-3, accounting for 41.1% of the PM2.5 mass, and the seasonal contributions were: autumn (45.9%) > summer (41.9%) > spring (39.9%) ≥ winter (39.2%). SNA was an important component of the WSIIs that accounted for 86.0%, 89.5%, 74.6%, and 73.0% of the total WSIIs during spring, summer, autumn, and winter, respectively. With an increase in temperature, the concentration of NO3- increased initially and then decreased, while the concentration of SO42- increased. When the relative humidity was less than 90%, the concentrations of both NO3- and SO42- increased with an increase in relative humidity. With the aggravation of pollution, the overall contribution of WSIIs in PM2.5 increased significantly, and the evolution characteristics of different ions were different. Among them, the concentration and contribution of NO3- continued to increase, while the contributions of SO42- and the ions from dust (Mg2+, Ca2+, and Na+) decreased. During the observation period, the primary sources of WSIIs were secondary conversion, combustion source, and dust. The control of coal combustion and motor vehicles is critical to reduce the emission of WSIIs. The backward trajectory analysis showed that the air masses from the south and west of Beijing corresponded to the high PM2.5 concentration and proportion of WSIIs, and the contribution of secondary ions was significant. However, the concentrations and proportions of the air masses from the northwest and north were relatively low, but the contribution of Ca2+ was high.

Quantifying major NOx sources of aerosol nitrate in Hangzhou, China, by using stable isotopes and a Bayesian isotope mixing model

Nitrogen oxides (NOx) from anthropogenic emissions oxidized to form nitrate (NO3−) and play a key role in air pollution. The aim of this study is to identify the NOx sources and their seasonal variations in Hangzhou, a typical city in East China. To achieve this, the chemical characteristics of water-soluble inorganic ions (WSIIs) and the stable isotopes of NO3− (δ15N–NO3- and δ18O–NO3-) were measured in fine particulate matter (PM2.5) and total suspended particle (TSP) aerosol samples that were collected between December 2018 and November 2019. It was found that the annual average concentration of PM2.5 (69.28 ± 34.69 μg/m3) in Hangzhou exceeded the Chinese air quality limit of 35.00 μg/m3. The results showed that NO3− accounted for the largest proportion of the WSIIs in both PM2.5 and TSP, and that major ions were mainly in the form of NH4NO3, (NH4)2SO4, Ca(NO3)2, CaSO4 in aerosol particles. High ratios of NO3−/SO42− in PM2.5 and TSP indicated that vehicle emissions became increasingly important source of aerosol pollution in Hangzhou during the study period. The δ15N–NO3- values ranged from +1.1‰ to +9.2‰ in PM2.5 and from −1.0‰ to +8.5‰ in TSP in Hangzhou. A Bayesian isotopic mixing model (stable isotope analysis in R (SIAR)) was applied to quantify the NOx sources in Hangzhou. This revealed that vehicle emissions, coal combustion and biomass burning were the main NOx sources of PM2.5 and TSP. The seasonal variation of the δ15N–NO3- values in PM2.5 and TSP in the study area were due to seasonal changes in the NOx contributions from different sources. The SIAR model results indicated that coal combustion increased in association with heating in north China during the winter (winter: 38.4% for PM2.5 and 36.4% for TSP, summer: 30.6% for PM2.5 and 29.8% for TSP) and the microbial N cycle increased with a higher application of fertilizer to crops during the summer (winter: 5.3% for PM2.5 and 5.6% for TSP, summer: 10.7% for PM2.5 and 11.6% for TSP). The improved SIAR model combined with the equilibrium fractionation reported the lower contributions from coal combustion (15.5–20.2%) and the higher contributions from Microbial N cycle (22.9–29.3%), as compared to the SIAR model. The seasonal variation of the δ18O–NO3- values was influenced by differences in the oxidation of NO2 via O3 (forming HNO3), whereby the N2O5 pathway dominated during the winter and the OH pathway dominated during the summer.

Characteristics and source apportionment of water-soluble inorganic ions in PM2.5 during a wintertime haze event in Huanggang, central China

Winter haze events are frequent occurrences in central China, however, their characteristics and formational mechanisms in the region are still poorly understood. In this study, we conducted continuous observations of PM2.5 during a haze event (from January 13 to 24, 2018) in Huanggang in central China to identify the characteristics of water-soluble inorganic ions (WSIIs) associated with PM2.5. The observation period was divided into the pre-haze episode (Pre-HE, January 13 to 14), haze episode (HE, January 15 to 21) and post-haze episode (Post-HE, January 22 to 24). The daily average PM2.5 mass concentration during the Pre-HE, HE and Post-HE was 51.7, 134.9 and 92.2 μg m−3, respectively. The WSIIs accounted for 57.3% of the total PM2.5 content throughout the entire observation period and were predominantly composed of nitrate, sulfate, and ammonium. During the HE, the major ions predominantly occurred in the form of (NH4)2SO4, NH4NO3, NH4Cl, and HCl. Moreover, the sulfur oxidation ratios and nitrogen oxidation ratios were relatively high, inferring the high contribution of secondary transformation. During the HE, homogeneous and heterogeneous reactions played an important role in the formation of nitrate and sulfate in PM2.5, respectively. The results of the principal component analysis-multiple linear regression suggest that the major sources of WSIIs were secondary inorganic aerosols, combustion and dust. The results of the backward trajectory analysis and the potential source contribution function model infer the strong influence of both local and regional air masses on haze formation and dissipation in Huanggang.

Pollution Characteristics of Water-soluble Inorganic Ions in Chengdu in Summer and Winter

The water-soluble inorganic ions (WSIIs) in PM2.5 and gaseous precursors of Chengdu were continuously observed by a gas and aerosol collector combined with ion chromatography (GAC-IC) in the summer and winter of 2017, and both their pollution characteristics and a typical pollution process in winter were analyzed. It was found that the concentration of PM2.5 in winter (100.2 μg·m-3) was significantly higher than that in summer (34.0 μg·m-3). WSIIs were important components of PM2.5 and their total contributions to PM2.5 were 52.9% and 53.3% in summer and winter, respectively. Secondary ions (SNA) accounted for 73.2% and 87.6% of WSIIs in summer and winter, respectively. SO42- and NO3- dominated the SNA in summer and winter, and the contributions to SNA were 37.7% and 59.7%, respectively. The NO3-/SO42- ratio (2.7) in winter was significantly higher than that in summer (0.8), reflecting the important contribution of mobile sources (especially motor vehicles) to PM2.5 in this season. The diurnal variation of SNA in the two seasons was obviously different due to the differences in sources and meteorological conditions. In winter, with the aggravation of pollution, the concentrations of WSIIs and gaseous precursors increased significantly, and NO3- was the key component in causing heavy pollution. Backward trajectory analysis revealed that the air masses in the two seasons in Chengdu differed significantly from each other. The WSIIs in summer and winter were dominated by SO42- and NO3-, respectively. The short-distance and low-altitude transmission from the east and south of Chengdu contributed significantly to PM2.5 pollution in Chengdu.

Water-Soluble Inorganic Ions in Fine Particulate Emission During Forest Fires in Chinese Boreal and Subtropical Forests: An Indoor Experiment

Understanding of the characteristics of water-soluble inorganic ions (WSI) in fine particulate matter (PM2.5) emitted during forest fires has paramount importance due to their potential effect on ecosystem acidification. Thus, we investigated the emission factors (EFs) of ten most common WSI from combustion of leaves and branches of ten dominant tree species in Chinese boreal and sub-tropical forests under smoldering and flaming combustion stages using a self-designed combustion unit. The results showed that EF of PM2.5 was three times higher for the boreal (6.83 ± 0.67 g/kg) than the subtropical forest (1.97 ± 0.34 g/kg), and coniferous species emitted 1.5 times more PM2.5 (5.35 ± 0.64 g/kg) than broadleaved species (3.45 ± 0.37 g/kg). EF of total WSI was 1.27 ± 0.08 g/kg for the boreal and 1.08 ± 0.07 g/kg for the subtropical forest and 1.28 ± 0.09 and 1.07 ± 0.06 g/kg for broadleaved and coniferous species, respectively. Individual ionic species also varied significantly between forest types and species within forest types, and K+ and Cl− were the dominant ionic species in PM2.5, accounting for 25% and 30% for the boreal forest and 23% and 27% for the subtropical forest, respectively. Emissions of NO2− and SO42− were the lowest, accounting for 3% and 5% for the boreal forest and 4% for each of the subtropical forests, respectively. Combustion of leaves emitted significantly more ionic species (1.29 ± 0.05g/kg) than branches (1.05 ± 0.07 g/kg), and smoldering consistently emitted more ionic species (1.49 ± 0.09 g/kg) than flaming combustion (0.88 ± 0.03 g/kg). The cation to anion ratio was ≥1.0, suggesting that the particulate matter is neutral to alkalescent. As a whole, our findings demonstrate that forest fire in these regions may not contribute to ecosystem acidification despite the emission of a considerable amount of WSI during forest fires.

Characteristics and Sources of Water-Soluble Ions in PM2.5 in the Sichuan Basin, China

To track the particulate pollution in Sichuan Basin, sample filters were collected in three urban sites. Characteristics of water-soluble inorganic ions (WSIIs) were explored and their sources were analyzed by principal component analysis (PCA). During 2012–2013, the PM2.5 concentrations were 86.7 ± 49.7 μg m−3 in Chengdu (CD), 78.6 ± 36.8 μg m−3 in Neijiang (NJ), and 71.7 ± 36.9 μg m−3 in Chongqing (CQ), respectively. WSIIs contributed about 50% to PM2.5, and 90% of them were secondary inorganic ions. NH4+ and NO3− roughly followed the seasonal pattern of PM2.5 variations, whereas the highest levels of SO42− appeared in summer and autumn. PM2.5 samples were most acidic in autumn and winter, but were alkaline in spring. The aerosol acidity increased with the increasing level of anion equivalents. SO42− primarily existed in the form of (NH4)2SO4. Full neutralization of NH4+ to NO3− was only observed in low levels of SO42− + NO3−, and NO3− existed in various forms. SO42− and NO3− were formed mainly through homogeneous reactions, and there was the existence of heterogeneous reactions under high relative humidity. The main identified sources of WSIIs included coal combustion, biomass burning, and construction dust.

Seasonal Characteristics of Sulfate and Nitrate in Size-segregated Particles in Ammonia-poor and -rich Atmospheres in Chengdu, Southwest China

ABSTRACT In order to determine the seasonal characteristics of water-soluble inorganic ions (WSIIs) in aerosols in urban atmospheres, size-segregated particulate matter (PM) samples were collected over a one-year period from February 2012 to January 2013 in a typical urban location, Chengdu in Southwest China, using an Andersen cascade impactor sampler. The PM mass concentrations, particularly the fine fraction, peaked during winter, and the WSIIs were more enriched in the fine fraction (21.7%) than the coarse fraction (9.2%). The sums of the equivalent ratios of cations (Na+, NH4+, K+, Mg2+, and Ca2+) to anions (SO42–, NO3–, Cl–, and F–) indicated that the fine particles (0.86) were more acidic than the coarse ones (1.60). The average NH4+/SO42– molar ratio (A/S) in the fine fraction (1.79) was much higher during winter than the other three seasons (< 1.5), implying a generally NH3-poor atmosphere in Chengdu; hence, the NO3– in the fine particles was principally formed through homogeneous reactions involving ammonia and nitric acid during winter, whereas it was heterogeneously formed during the other three seasons. Significant positive correlations were observed between the A/S and NO3– molar concentrations during spring and winter; therefore, the formation of particle-phase NO3– may be accelerated by increased A/S in both NH3-poor and -rich atmospheres. Moreover, the A/S and NO3–/SO42– molar ratios displayed negative and positive correlations during spring and winter, respectively, suggesting that the variation in atmospheric NH4+ (or NH3) during winter affected the formation of NO3– more strongly than that of SO42–, whereas more SO42– than NO3– was formed in the NH3-poor atmosphere during spring, when most of the NO3– in the aerosols would be expected to form via heterogeneous reactions.

Size Distribution Characteristics of Water-Soluble Inorganic Ions During Summer and Autumn in Zhengzhou

To study the compositional characteristics of atmospheric particulates with different particle sizes in the central city of Zhengzhou, China, a Tisch graded impact sampler was used to sample atmospheric particulates in summer and autumn. The mass concentrations of water-soluble inorganic ions, including anions (Cl-, F-, NO3-, and SO42-) and cations (Na+, Ca2+, NH4+, K+, and Mg2+) were measured by ion chromatography, and the online ion chromatography-based analyzer MARGA monitored the real-time concentration of particulate nitrate. The results showed that the average concentration of water-soluble ions in Zhengzhou City was (70.9±52.1) μg·m-3 during the sampling period, and the order of water-soluble ion mass concentrations was NO3- > SO42- > NH4+ > Ca2+ > Na+ > Cl- > Mg2+ > K+ > F-; NO3-, SO42-, and NH4+ accounted for 79.9% of total water-soluble ions. The NO3- concentration was mainly concentrated in the 0.65-3.3 μm particle size segment, despite the SO42- concentration being concentrated in the ≤ 1.1 μm particle size segment in autumn or summer. Both NO3- and SO42- had a bimodal distribution in summer and autumn and were mainly distributed as fine particles. NH4+ showed seasonal variation with a bimodal distribution in summer and a unimodal distribution in autumn. Zhengzhou City had serious ozone pollution in summer, and O3 and NO3- showed the "staggered peak" phenomenon, indicating photochemical reactions in the atmosphere. In autumn, water-soluble inorganic ion concentration in particulate matter was high, and the ratio of[NO3-]/[SO42-] was higher than 0.5. The mobile source is an important source of particles. NOR and SOR peaks were on the 1.1-2.1 μm particle size segment in summer, whereas those in the 0.65-1.1 μm particle size segment occurred in autumn. The sulfur gas-to-grain conversion in summer was larger than that of nitrogen, contrary to the result in autumn.

Mass Concentrations and Size Distributions of Water-soluble Inorganic Ions in Atmospheric Aerosols in Beibei District, Chongqing

In order to study the concentration and distribution characteristics of water-soluble inorganic ions in aerosol particles of the Beibei district of Chongqing, aerosol samples were collected with an Andersen cascade impactor between March 2014 and February 2015. Water-soluble inorganic ions, including Na+, NH4+, K+, Mg2+, Ca2+, F-, Cl-, NO3-, and SO42- were determined for different particle sizes (9.00, 5.80, 4.70, 3.30, 2.10, 1.10, 0.65, and 0.43 μm) using the ion chromatography method. Results showed that SO42-, NH4+, NO3-, Cl-, Na+, and K+ were mainly distributed in fine particles, while Mg2+, Ca2+, and F- were mainly present in coarse particles. SNA (SO42-, NH4+, and NO3-) exhibited clear unimodal distribution, with peaks in the droplet mode of 0.65-1.10 μm, mainly present in the form of (NH4)2SO4 and NH4NO3 in fine particles. The formation of SO42- is mainly attributed to in-cloud processes and partly to oxidation of SO2. Na+, Cl-, and Mg2+ exhibited bimodal distribution in coarse and fine particles; K+ was a single peak distribution in the range of 0.43-1.10 μm, while peaks of F- and Ca2+ concentrations were in coarse particles. Average annual concentrations of total water-soluble ions in PM2.1 and PM9.0 were (32.68±15.28) μg·m-3and (48.01±19.66) μg·m-3 over the observation period. Seasonal variations of PM2.1 and PM9.0concentrations decreased in the order of winter > spring > summer > autumn. This was the same for most ions, but a small number of ions (F-, Mg2+ and Ca2+) had a different pattern in the spring, summer, and winter. The SNA were the major components of water-soluble ions in PM2.1, and Ca2+ was the major component of water-soluble ions in PM9.0 besides SNA. The concentration of cations was significantly higher than that of anions' in PM2.1 and PM9.0, with a certain correlation between different ions. Emissions from motor vehicle exhaust, combustion processes, soil sources, and fugitive dust were the major sources of water-soluble ions in this area. The effect of air temperature on secondary ions is significant (P<0.05), but relative humidity and wind speed have no significant effect (P>0.05).

The characterization of water-soluble inorganic ions in PM2.5 during a winter period in Xi'an, China

ABSTRACTThe characteristics of water-soluble inorganic ions (WSIIs) during a winter period in a suburb of Xi'an, China, were investigated. Our results show that the total mass concentration of the dominant WSIIs (8) was 91.27 µg m–3, accounting for 50.1% of the total mass concentration of PM2.5 (particulates with a size of 2.5 µm or less). Secondary inorganic aerosols (SO42−, NO3− and NH4+) were the most abundant ions, accounting for up to 95.12% of the total ions. By using the anion and cation equivalence ratio method, PM2.5 was shown to have weak alkalinity, and the chemical forms of WSIIs were mainly (NH4)2SO4 and NH4NO3. The sulfur oxidation ratio (SOR) and nitrogen oxidation ratio (NOR) suggested that larger proportions of SO42− and NO3− were formed by gas-phase SO2 and NO2 in the sampling site. Ratio analysis also indicated that anthropogenic sources significantly contributed to WSII pollution. Among the anthropogenic sources, fixed pollution sources were found to be dominant over mobile sources.

Characteristics of Water-Soluble Inorganic Components and Acidity of PM2.5 in a Coastal City of China

To investigate the characteristics of water-soluble inorganic ions (WSIIs) of PM2.5 and aerosol acidity in a coastal city, 352 samples were collected at four sites representing four functional zones (FJ: living town; XY: industrial area; TZ: scenery areas; HR: harbor) in Xiamen, China in 2015–2016. Mass concentrations of PM2.5, nine WSIIs, total acidity and in-situ acidity of aerosol/non-sea-salt aerosol were measured. Overall, the mean mass concentrations of PM2.5 in the study area in spring, summer, autumn and winter were 57.5 ± 22.3, 28.1 ± 12.6, 46.8 ± 18.3 and 62.4 ± 22.1 µg m–3, respectively. WSIIs accounted for 36%–56% of PM2.5 at four sites. Secondary ions (non-sea-salt SO42–, NO3– and NH4+) contributed more than 74% to total WSIIs. Neutralization degree distributions indicated that 79.5% of PM2.5 was acidic. Total acidity and in-situ acidity both showed obvious seasonal variations, exhibited the peak values of 193.20 and 130.17 nmol m–3 at HR site in summer. Sea-salt contributed 2.58%–17.74% to acidity in four seasons. The normalized ammonium concentration ([NH4+]/[SO42–]) and normalized nitrate concentration ([NO3–]/[SO42–]) showed greater correlation coefficients after eliminating the ammonium-poor data points (greater than 0.66), especially at HR site. NH4HSO4 was the major form of WSIIs in PM2.5 and the formation of aqueous HNO3 could enhance aerosol acidity.

Highly time-resolved characterization of water-soluble inorganic ions in PM2.5 in a humid and acidic mega city in Sichuan Basin, China.

To investigate the characteristics of water-soluble inorganic ions (WSIIs) in Chongqing, a well-known foggy and acid region in southwestern China, hourly real-time concentrations of five cations (Na+, K+, NH4+, Ca2+, and Mg2+) and six anions (F-, Cl-, NO2-, NO3-, PO43-, and SO42-) in PM2.5 during winter (from Dec. 18, 2015 to Mar. 20, 2016) in Chongqing were collected by applying In-situ Gas and Aerosol Compositions Monitor. The hourly total concentration of WSIIs was 38.5μg/m3 on average, accounting for 57% of PM2.5 mass concentration. Secondary inorganic aerosols (NH4+, NO3-, and SO42-) were dominant WSIIs, accounting for 91% of WSIIs mass. Compared to ten years ago, SO42- concentrations were decreased by 31% but NO3- levels were doubled, likely indicative of sharply enhanced contribution to fine particle pollution from mobile sources over stationary sources. NO3- originated from the current fluxes of NH3 and HNO3 onto sulfate particles and/or from in-cloud processes were critical pathways under humid conditions in the study area. Water content and/or RH might be important factors controlling nitrate formation. Trajectory analysis manifested that aerosol pollutions in Chongqing were mostly caused by local emissions.

Seasonal characteristics of water-soluble inorganic ions and carbonaceous aerosols in total suspended particulate matter at a rural semi-arid site, Kadapa (India).

To better understand the sources as well as characterization of regional aerosols at a rural semi-arid region Kadapa (India), size-resolved composition of atmospheric particulate matter (PM) mass concentrations was sampled and analysed. This was carried out by using the Anderson low-pressure impactor for a period of 2years during March 2013-February 2015. Also, the variations of organic carbon (OC), elemental carbon (EC) and water-soluble inorganic ion components (WSICs) present in total suspended particulate matter (TSPM) were studied over the measurement site. From the statistical analysis, the PM mass concentration showed a higher abundance of coarse mode particles than the fine mode during pre-monsoon season. In contrast, fine mode particles in the PM concentration showed dominance over coarse mode particle contribution during the winter. During the post-monsoon season, the percentage contributions of coarse and fine fractions were equal, whereas during the monsoon, coarse mode fraction was approximately 26% higher than the fine mode. This distinct feature in the case of fine mode particles during the studied period is mainly attributed to large-scale anthropogenic activities and regional prevailing meteorological conditions. Further, the potential sources of PM have been identified qualitatively by using the ratios of certain ions. A high sulphate (SO4) concentration at the measurement site was observed during the studied period which is caused by the nearby/surrounding mining activity. Carbon fractions (OC and EC) were also analysed from the TSPM, and the results indicated (OC/EC ratio of ~4.2) the formation of a secondary organic aerosol. At last, the cluster backward trajectory analyses were also performed at Kadapa for different seasons to reveal the origin of sources from long-range transport during the study period.

Characteristics of Water-soluble Inorganic Ions in Atmospheric Aerosols in Shenyang

To investigate the levels and seasonal variation of water soluble inorganic components in ambient aerosol in Shenyang, 25 samples were collected with Andersen cascade sampler from Jun. 2012 to May. 2013 and nine water-soluble ions in samples were analyzed by IC. The different characteristics of aerosols between clean and pollution days in winter were discussed based on these samples. The results showed that the annual concentrations of total water soluble inorganic ions were 22.30 μg·m^-3 and 14.29 μg·m^-3 in fine and coarse particles, and SO4^2- and Ca²⁺ were the most abundant ions, respectively. The ratio of mass concentration between SO4^2- and NO3^- was 2.28 and the NH4⁺ existed in the form of (NH4)2SO4 and NH4NO3 in fine particles. The concentrations of total water soluble ions in fine particles were higher in winter and spring compared with those in summer and autumn, and they varied significantly between different seasons. The fossil fuel consumption led to the maximum values of secondary inorganic ions in fine particles during winter. The concentrations of total water soluble ions in coarse particles varied slightly though they were higher in autumn and lower in winter, and the wind-drifting sand was responsible for the higher concentration of Ca²⁺ in autumn in coarse particles. The concentration of SO4^2-, NO3^-, NH4⁺ accounted for 80% of total water soluble inorganic ions during clean days and rose to 94% during pollution days. The ions were mostly concentrated in the size ranges of 0.43-0.65 μm and 0.43-2.1 μm respectively during clean and pollution days in fine mode. The peaks of SO4^2-, NO3^-, NH4⁺ in fine mode shifted from 0.43-0.65 μm to 1.1-2.1 μm, which meant these ions were transformed from condensing mode to droplets mode during pollution days. The air mass produced at Lake Baikal and transported through high altitude to the sampling point caused clean days, however the air mass transported through industrial areas might bring pollutions to the sampling point then caused pollution days.

Characteristics of water-soluble inorganic ions in PM2.5 and PM2.5–10 in the coastal urban agglomeration along the Western Taiwan Strait Region, China

PM2.5 and PM2.5-10 aerosol samples were collected in four seasons during November 2010, January, April, and August 2011 at 13 urban/suburban sites and one background site in Western Taiwan Straits Region (WTSR), which is the coastal area with rapid urbanization, high population density, and deteriorating air quality. The 10 days average PM2.5 concentrations were 92.92, 51.96, 74.48, and 89.69 μg/m(3) in spring, summer, autumn, and winter, respectively, exceeding the Chinese ambient air quality standard for annual average value of PM2.5 (grade II, 35 μg/m(3)). Temporal distribution of water-soluble inorganic ions (WSIIs) in PM2.5 was coincident with PM2.5 mass concentrations, showing highest in spring, lowest in summer, and middle in autumn and winter. WSIIs took considerable proportion (42.2 ∼ 50.1 %) in PM2.5 and PM2.5-10. Generally, urban/suburban sites had obviously suffered severer pollution of fine particles compared with the background site. The WSIIs concentrations and characteristics were closely related to the local anthropogenic activities and natural environment, urban sites in cities with higher urbanization level, or sites with weaker diffuse condition suffered severer WSIIs pollution. Fossil fuel combustion, traffic emissions, crustal/soil dust, municipal constructions, and sea salt and biomass burnings were the major potential sources of WSIIs in PM2.5 in WTSR according to the result of principal component analysis.