Water-soluble Inorganic Ions In PM2 Research Articles

In situ continuous hourly observations of wintertime nitrate, sulfate and ammonium in a megacity in the North China plain from 2014 to 2019: Temporal variation, chemical formation and regional transport

Nitrate (NO3−), sulfate (SO42−) and ammonium (NH4+) in airborne fine particles (PM2.5) play a vital role in the formation of heavy air pollution in northern China. In particular, the increasing contribution of NO3− to PM2.5 has attracted worldwide attention. In this study, a highly time-resolved analyzer was used to measure water-soluble inorganic ions in PM2.5 in one of the fastest-developing megacities, Tianjin, China, from November 15 to March 15 (wintertime heating period) in 2014–2019. Severe PM2.5 pollution episodes markedly decreased during the heating period from 2014 to 2019. The highest concentrations of NO3− and SO42− were recorded in the heating period of 2015/2016. Afterwards, NO3− decreased from 2015/2016 (20.2 ± 23.8 μg/m3) to 2017/2018 (11.6 ± 14.8 μg/m3) but increased with increasing NOx concentrations during the heating period of 2018/2019. A continuous decrease in the SO2 concentration led to a decrease in SO42− from 2015/2016 (16.8 ± 21.8 μg/m3) to 2018/2019 (6.5 ± 8.9 μg/m3). The NO3− and SO42− concentrations increased as the air quality deteriorated. However, the proportion of NO3− and SO42− in PM2.5 slightly increased when the air quality deteriorated from moderate pollution (MP) to severe pollution (SP) levels. The average molar ratios of NH4+ to [NO3−+2 × (SO42−)] were 1.7, 0.9, 1.2, 1.2 and 1.5 for the heating periods of 2014/2015, 2015/2016, 2016/2017, 2017/2018 and 2018/2019, respectively, most of which were higher than 1.0, thus revealing an overall excess of NH4+ during the heating periods. However, the molar equivalent ratios of [NH4+] to [NO3−+2 × (SO42−)] were less than 1 under increasing PM2.5 pollution. The molar equivalent ratios of [NO3−]/[SO42−] were positively correlated with those of [NH4+]/[SO42−]. When the molar equivalent ratios of [NH4+]/[SO42−] were more than 1.5, those of [NO3−]/[SO42−] increased from close to 1 to higher values, indicating that the dominance of NO3− formation played an important role. The results of nonparametric wind regression exhibited distinct hot spots of NO3−, SO42− and NH4+ (higher concentrations) in the wind sectors between NE and SE at wind speeds of approximately 6–21 km/h. The southern areas in the North China Plain and parts of the western areas of China contributed more NO3−, SO42− and NH4+ than other areas to the study site. The abovementioned areas were also characterized by a higher contribution of NO3− than of SO42− to the study site and by NH4+-rich conditions. In summary, more efforts should be made to reduce NOx in the Beijing-Tianjin-Hebei region. This study provides observational evidence of the increasingly important role of nitrate as well as scientific support for formulating effective control strategies for regional haze in China.

Spatial Distribution and Formation Mechanism of Water-soluble Inorganic Ions in PM2.5 During a Typical Winter Haze Episode in Guilin, China.

A 5-day PM2.5 sampling campaign was conducted during a typical haze episode from December 16 to 20, 2016, at five urban sites and one background site in Guilin, a famous tourist city in Southern China. A total of 30 PM2.5 samples were collected, and water-soluble inorganic ions (WSII) (SO42-, NO3-, NH4+, Ca2+, K+, Cl-, Na+, and Mg2+) were determined using ion chromatography. Correlation analysis, principal component analysis, and coefficient of divergence were applied to identify the formation mechanisms of secondary inorganic ions, potential sources, and spatial distribution of WSII. The average mass concentrations of PM2.5 at each sampling site were 71.6-127.85μgm-3, which were more than the National Ambient Air Quality Standard (GB3095-2012, GradeII (35μgm-3)) in China. SO42- NO3-, and NH4+ were the major WSII, accounting for 34.43-40.59% of PM2.5 mass. NO3-/SO42- ratio revealed that stationary sources-induced PM2.5 was still remarkable. Cl-/Na+ ratio and their strong correlation (r = 0.824) indicated that atmospheric transport from outside urban region played an effective role during the haze episode. Spatial variations of WSII are not pronounced at five urban sites except the background site. High relative humidity and O3 contributed to evidently influence the transformation of SO2 to SO42- but not obvious to NOx oxidation. Finally, the major sources of WSII are identified as the mixture of sea salt, coal combustion, biomass burning, vehicle exhaust and agricultural emissions (66.892%), and fugitive sources (19.7%).

Seasonal Control of Water-Soluble Inorganic Ions in PM2.5 from Nanning, a Subtropical Monsoon Climate City in Southwestern China

In this study, we measured the daily water-soluble inorganic ions (WSIIs) concentration (including SO42−, NO3−, NH4+, Ca2+, K+, Cl−, Na+, Mg2+, and F−) of PM2.5 (particulate matter with a diameter smaller than 2.5 μm) throughout the year in Nanning (a typical subtropical monsoon climate city in southwestern China) to explore the influence of seasonal climate change on the properties of PM2.5 pollution. This suggested that SO42−, NO3−, and NH4+ were the main component of WSIIs in Nanning. Secondary inorganic ions from fossil fuel combustion, agricultural activities, and automobile emissions were the main contributors to PM2.5, contributing more than 60% to PM2.5. Compared with the wet season, the contributions of different sources increased in the dry season (including pollution days); of these sources, automobile emissions and coal combustion emissions increased the most (about nine times and seven times, respectively). Seasonal weather and climate change affected the concentration level of WSIIs. During the wet season, higher temperatures and abundant rainfalls contributed to the volatilization and removal of WSIIs in PM2.5, while in the dry season and on pollution days, lower temperatures and less precipitation, higher emissions, and poor diffusion conditions contributed to the accumulation of WSIIs in PM2.5. NH4HSO4, (NH4)2SO4 and NH4NO3 were the main chemical forms of secondary inorganic ions. Sufficient NH3, intense solar radiation, and moist particulate matter surface promoted the formation of secondary inorganic ions. The higher temperature contributed to the volatilization of secondary inorganic ions.

Chemical characterization and source analysis of water-soluble inorganic ions in PM2.5 from a plateau city of Kunming at different seasons

Abstract Water-soluble inorganic ions (WSIIs) in PM2.5 from different cities have been studied in previous studies. However, the studies of WSIIs in plateau cities are relative deficient. Due to differences in topography, climate and emission sources, the WSIIs characteristics of plateau cities are expected to be different. Here, we determined the concentrations of WSIIs (SO42−, NO3−, NH4+, Ca2+, Mg2+, Na+, K+, F−, Cl−, NO2−) in PM2.5 from different seasons of Kunming, a typical plateau city in southwest China. The data will improve our understanding of the chemical characterization and source of PM2.5 in plateau environment. Our results showed that the secondary aerosols were the main pollutants (contributing >50% to PM2.5) in PM2.5 of Kunming, which mainly from coal combustion, agricultural activities and vehicle exhaust. Seasonally, high volatility of the NO3− and NH4+ and washout effects of rainfall in hot months (wet seasons) were favorable for the decreased of pollutants, while high emission, poor dispersion conditions and low removal rate could lead to the increased of pollutants in cold months (dry seasons). It suggested that adequate NH3 and intense solar radiation promotes the photochemical reactions of SO2, NOx and NH3 to form NH4HSO4, (NH4)2SO4 and NH4NO3. High temperature in hot months would promote the volatilization of NH4NO3 in Kunming.

Characteristics and formation mechanisms of secondary inorganic ions in PM2.5 during winter in a central city of China: Based on a high time resolution data

Abstract This study aimed to investigate the characteristics of the water-soluble ions concentrations in atmospheric particulates. Highly time-resolved measurements of inorganic ions associated with PM2.5 were conducted from December 1, 2017 to February 28, 2018 in Zhengzhou. The hourly mean and standard deviation of PM2.5 concentration during the observation episodes were 108.2 ± 80.7 μg/m3. The hourly mass concentration of PM2.5 increased from 8 μg/m3 to 438 μg/m3 throughout the entire observation. The proportion of water-soluble inorganic ions in PM2.5 was 52.5% throughout the entire observation period. The ions existed mainly in the form of (NH4)2SO4 and NH4NO3. The average mass concentration ratio of NO3− to SO42− was 1.9 ± 0.8 throughout the entire observation period, which initially increased and then decreased with the increased pollution level. The average ratio of the molar equivalent concentration of [NH4+] to that of [NO3− + SO42−] was 1.14 ± 0.27, which decreased with the increased pollution level. Homogeneous reactions played an important role in the formation of nitrate, while, the heterogeneous reactions were important in the formation of sulfate. Both of the values of sulfur oxidation ratios (SOR) and nitrogen oxidation ratios increased with relative high humidity (RH) condition; especially, the SOR values sharply increased when the RH was above 50%. The results of potential source contribution function model demonstrated that the western and northeastern regions of Zhengzhou had a greater influence on PM2.5 pollution in Zhengzhou. All these results suggested that reducing the emission of precursors of secondary inorganic ions was highly important in controlling PM2.5 pollution in Zhengzhou.

Comparative study on water-soluble inorganic ions in PM2.5 from two distinct climate regions and air quality

Recently, air quality has significantly improved in developed country, but that issue is of concern in emerging megacity in developing country. In this study, aerosols and their precursor gas were collected by NILU filter pack at two distinct urban sites during the winter and summer in Osaka, Japan and dry and rainy seasons in Ho Chi Minh City (HCMC), Vietnam. The aims are to investigate the contribution of water-soluble inorganic ions (WSIIs) to PM2.5, thermodynamic characterization and possible formation pathway of secondary inorganic aerosol (SIA). The PM2.5 concentration in Osaka (15.8 μg/m3) is lower than that in HCMC (23.0 μg/m3), but the concentration of WSIIs in Osaka (9.0 μg/m3) is two times higher than that in HCMC (4.1 μg/m3). Moreover, SIA including NH4+, NO3− and SO42− are major components in WSIIs accounting for 90% and 76% (in molar) in Osaka and HCMC, respectively. Thermodynamic models were used to understand the thermodynamic characterization of urban aerosols. Overall, statistical analysis results indicate that very good agreement (R2 > 0.8) was found for all species, except for nitrate aerosol in HCMC. We found that when the crustal species present at high amount, those compositions should be included in model calculation (i.e. in the HCMC situation). Finally, we analyzed the characteristics of NH4+– NO3−– SO42− system. A possible pathway to produce fine nitrate aerosol in Osaka is via the homogeneous reaction between NH3 and HNO3, while non-volatile nitrate aerosols can be formed by the heterogeneous reactions in HCMC.

Characteristics and Source Analysis of Water-Soluble Ions in PM2.5 in Zhengzhou

In order to explore the pollution characteristics of water-soluble ions in PM2.5 in Zhengzhou, high time resolution and continuous observation of water-soluble inorganic ions in PM2.5 was conducted from December 1, 2017, to November 30, 2018, in Zhengzhou. The results showed that during the observation period, the average concentration of total water-soluble ions in Zhengzhou was 42.7 μg·m-3. The order of mass concentration of each ion, from large to small, was as follows:NO3-(17.7 μg·m-3), SO42-(10.2 μg·m-3), NH4+(9.0 μg·m-3), Cl-(2.3 μg·m-3), K+(1.3 μg·m-3), Na+(1.3 μg·m-3), Ca2+(0.8 μg·m-3), and Mg2+(0.1 μg·m-3). The mass concentration of total water-soluble ions was the highest in winter, slightly higher in autumn than in spring, and lowest in summer. The diurnal variation in single peak distribution was observed across the whole year in spring, summer, and autumn, while there was no significant diurnal variation in winter. The mass concentration of secondary inorganic ions (SO42-, NO3-, and NH4+) accounted for 43.8% of PM2.5, mainly in the form of (NH4)2SO4 and NH4NO3. There was a large degree of secondary transformation throughout the observation period; relative humidity had a significant influence on the sulfur oxidation rate, and temperature had a significant influence on the nitrogen oxidation rate. During the observation period, there was a good correlation between secondary ions, and K+ showed a good correlation with Mg2+ and Cl-. The main source of the secondary ions was the secondary conversion of gaseous pollutants. Mg2+ and Ca2+ were derived from soil dust and construction dust. K+ was one of the main biomarkers of biomass combustion. Na+ was mainly derived from sea salt and soil dust, and Cl- was derived not only from sea salt but also biomass and fossil fuel combustion. The results of principal component analysis showed that the water-soluble ions in PM2.5 in Zhengzhou were mainly affected by secondary transformation, combustion sources, and dust emission from soil or building construction.

Nitrate dominates the chemical composition of PM2.5 during haze event in Beijing, China

Water-soluble inorganic ions (WSI), a major component of PM2.5, often increased rapidly during the haze event in Beijing. Sulfate (SO42−), Nitrate (NO3−), and Ammonium (NH4+) are three main components of WSI. Since year 2015, sulfate concentrations in PM2.5 has gradually decreased owing to the effective control of SO2 emissions. However, the contribution of nitrate to PM2.5 has significantly increased during haze events in Beijing at the same time. In this study, a highly time-resolved online analyzer (Monitor for Aerosols and Gases, MARGA) was employed to measure the WSI in PM2.5 in Beijing from 5 February to 15 November 2017. Three typical haze events during this sampling period were investigated. During heavy pollution episodes in winter, nitrate concentrations increased from 7.5 μg/m3 to 45.6 μg/m3 (45.0% of WSI), while sulfate increased from 4.2 μg/m3 to 20.1 μg/m3 (19.8% of WSI). This indicated that nitrate is more important than sulfate as a driver for the growth of PM2.5 during the period of heavy air pollution in winter. Nitrate also dominates the increase of WSI in the pollution episodes in autumn, with an average concentration of 52.5 μg/m3, and contributed up to 67% of WSI. The average concentration ratio of NH4+ to SO42− was higher in autumn (1.02) than that in summer (0.74) and close to that in winter (1.00). This is mainly because the emission control of coal combustion in Beijing and surrounding areas results in an NH3-rich and SO2-lean atmosphere, which promoted the formation of ammonium nitrate. Our study indicates that nitrate has become the most important component of WSI in PM2.5 and is driving the rapid growth of PM2.5 concentrations during heavy pollution episodes in Beijing. Therefore, more efforts shall be made to reduce the nitrogen oxide and ammonia emissions in Beijing and surrounding areas.

Seasonal variations and source apportionment of water-soluble inorganic ions in PM2.5 in Nanjing, a megacity in southeastern China

Daily PM2.5 samples were collected in Nanjing, a megacity in southeastern China, for a period of one-half of a month during every season from 2014~2015. Mass concentrations of nine water soluble inorganic ions (F−, Cl−, SO42−, NO3−, Na+, NH4+, K+, Mg2+ and Ca2+) were determined using ion chromatography to identify the chemical characteristics and potential sources of PM2.5. The mass concentrations of daily PM2.5 ranged from 31.0 to 242.9 μg m−3, with an annual average and standard deviation of 94.4 ± 31.1 μg m−3. The highest seasonal average of PM2.5 concentrations was observed during winter (108.5 ± 31.8 μg m−3), and the lowest average was observed during summer (85.0 ± 22.6 μg m−3). The annual average concentration of total water soluble inorganic ions was 39.82 μg m−3, accounting for 44.4% of the PM2.5. The seasonal variation in water soluble inorganic ions in PM2.5 reached its maximum during autumn and reached its minimum during spring. Sulfate, nitrate and ammonium were the dominant water soluble inorganic species, with their combined proportion of 82.0% of the total water soluble inorganic ions and 36.8% of the fine particles. Seasonal variations in aerosol acidity and chemical forms of secondary inorganic ions were discussed. The average ratio of NO3−/SO42− was 0.95. According to the results of principal component analysis, secondary sources, burning processes, and airborne dust were the dominant potential sources of PM2.5 in Nanjing.

Characteristics and formation mechanisms of autumn haze pollution in Chengdu based on high time-resolved water-soluble ion analysis.

To investigate the characteristics and formation mechanisms of haze pollution in the autumn season in the Sichuan Basin, hourly concentrations of water-soluble inorganic ions in PM2.5 (Na+, K +, NH4+, Mg2+, Ca2+, Cl-, NO3-, and SO42-) and major gaseous precursors (HCl, NH3, SO2, HONO, and HNO3) were measured by a gas and aerosol collector combined with ion chromatography (GAC-IC) from September to November 2017 at an urban site in Chengdu. The average mass concentration of total water-soluble ions was 36.9 ± 29.4μgm-3, accounting for 62.8% of PM2.5 mass. Nitrate was the most abundant ion, comprising 41.2% of the total ions, followed by sulfate (27.1%) and ammonium (18.1%), indicating the important contribution of motor vehicle emissions to PM2.5 in Chengdu. Secondary formation of inorganic ions and biomass burning emissions played a vital role in the haze pollution processes. The formation of nitrate aerosol was particularly dominant and exhibited the most substantial increase during haze processes. It was likely to be produced primarily through homogeneous reactions, whereas heterogeneous reactions dominated sulfate formation. Additionally, distinct differences in diurnal patterns of secondary inorganic ions between clean days and polluted days were observed, reflecting different formation characteristics under polluted conditions. Due to a large increase of acidic aerosols, most particles collected on polluted days were acidic, and ammonium in most samples existed mainly as NH4HSO4 and NH4NO3. Furthermore, backward-trajectory cluster analysis revealed that air masses originating from the northeast of Chengdu prevailed in the autumn season, and haze pollution was dominated mainly by short-distance transport within the Sichuan Basin.

Deposition of water-soluble inorganic ions in PM2.5 in a typical forestry system in Beijing, China

BackgroundRapid economic development in China has resulted in an increase in severe air pollution in city groups such as the Beijing–Tianjin–Hebei Metropolitan Region. PM2.5 (fine particles with an aerodynamic equivalent diameter of 2.5 μm or less) is one of the most important pollutants. The deposition process is an important way of removing particles from the air. To evaluate the effect of an urban forest on atmospheric particle removal, a concentration gradient method was used to measure the deposition velocities of water-soluble inorganics in PM2.5 in two national forest parks in Beijing, China. The following eight water-soluble inorganic ions in PM2.5 were investigated: sodium, ammonium, potassium, magnesium, calcium, chloride, nitrate, and sulfate.MethodsSamples were taken from two sites in Beijing from the 7th to the 15th May, 2013. The concentrations of water-soluble inorganic ions were analyzed with ion chromatography. We used the concentration gradient technique to estimate the deposition flux and velocity. To determine the relationships between leaf traits and particle accumulation, typical leaf samples from each selected species were studied using scanning electron microscopy.ResultsThe total deposition flux and total deposition velocity during the daytime were higher than those at night. Sulfate showed the biggest deposition flux and velocity at both study sites, whereas the other ions showed different trends at each site. Result from higher proportion of coniferous to broadleaved trees, the total deposition flux of the eight ions measured in Jiufeng National Forest Park was greater than that in Olympic Forest Park.ConclusionsThe deposition velocity was affected by meteorological conditions such as wind speed, temperature, and humidity. The deposition velocity was also influenced by tree species. The surface of plants is an important factor influencing particle deposition. The results of this study may help in assessing the effects of forestry systems on particle removal and provide evidence for urban air pollution control and afforestation of urban areas.

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.

Observational evidence of cloud processes contributing to daytime elevated nitrate in an urban atmosphere

Nitrate has become the most important hydrophilic chemical component in PM2.5 during serious air pollution periods in urban areas of the Pearl River Delta (PRD) region of south China, but there is a lack of fully understanding of its formation mechanisms and controlling factors, especially during daytime nitrate episodes. To fill the knowledge gap, water-soluble inorganic ions in PM2.5 and trace gases including SO2, HNO3, NH3, NOx and O3, particle size distribution, vertical profile of aerosol backscatter density, and ground-level and vertical profiles of key meteorological variables were simultaneously measured at high time resolution in urban Guangzhou of the PRD. The remarkably enhanced nitrate mass concentrations observed at the surface-level during daytime were identified to be caused by strong boundary-layer turbulent mixing of residual aerosols produced from evaporation of low-level shallow stratocumulus clouds. This finding may have important implications on the sources of secondary inorganic aerosols in this and other similar cloudy regions.

A one-year, on-line, multi-site observational study on water-soluble inorganic ions in PM2.5 over the Pearl River Delta region, China

As the significant components of PM2.5, almost all of previous studies on water-soluble inorganic ions (WSIIs) have been limited by the use of single sampling station, short sampling times or low temporal resolution. This paper focuses on analysing one-year (2012) observations of WSIIs at a regional central (RCEN) site, a coastal urban (CURB) site and a coastal rural (CRUR) site in the Pearl River Delta region. On average, secondary inorganic aerosols (SIA) were the most abundant component and accounted for over 80% of the total WSIIs. The ratio among sulfate, nitrate and ammonium mass concentrations was close to 2:1:1 (5:2:1) at the RCEN and CURB sites (CRUR site). Most components (except Na+) showed higher concentrations in the dry season. The diurnal variations of different ions showed obvious differences, which were partially controlled by photochemical reactions and diffusion conditions in the boundary layer. Ionic formation patterns were different among the three sites. Secondary inorganic pollution was much more serious in the northwestern PRD, and it had a significant effect on pollution in the coastal areas. High SO42− concentrations at the CRUR site may be associated with local emissions, such as dimethysulfide (DMS). Long-range transport along the southeastern coastline also played an important role in SO42− pollution over the PRD region. Sea salt aerosols were an important source in coastal regions; they contributed large amounts of Cl−, Na+, Mg2+ at the CRUR site and large amounts of Na+, Mg2+ at the CURB site. The case studies found that sea salt aerosols concentrations increased obviously during the heavy precipitation period of typhoon. The presence of warm-wet air masses before continuous moist weather (CMW) was favourable for the formation of SIA. On the other hand, during CMW periods, SIA concentrations decreased rapidly.

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 Variations and Correlation Analysis of Water-Soluble Inorganic Ions in PM2.5 in Wuhan, 2013

Daily PM2.5 and water-soluble inorganic ions (NH4+, SO42−, NO3−, Cl−, Ca2+, Na+, K+, Mg2+) were collected at the Hongshan Air Monitoring Station at the China University of Geosciences (Wuhan) (30°31′N, 114°23′E), Wuhan, from 1 January to 30 December 2013. A total of 52 effective PM2.5 samples were collected using medium flow membrane filter samplers, and the anionic and cationic ions were determined by ion chromatography and ICP, respectively. The results showed that the average mass concentration of the eight ions was 40.96 µg/m3, which accounted for 62% of the entire mass concentration. In addition, the order of the ion concentrations was SO42− > NO3− > NH4+ > Cl− >K+ > Ca2+ > Na+ > Mg2+. The secondary inorganic species SO42−, NO3− and NH4+ were the major components of water-soluble ions in PM2.5, with a concentration of 92% of the total ions of PM2.5, and the total concentrations of the three ions in the four seasons in descending order as follows: winter, spring, autumn, and summer. NH4+ had a significant correlation with SO42− and NO3−, and the highest correlation coefficients were 0.943 and 0.923 (in winter), while the minimum coefficients were 0.683 and 0.610 (in summer). The main particles were (NH4)2SO4 and NH4NO3 in PM2.5. The charge of the water-soluble ions was nearly balanced in PM2.5, and the pertinence coefficients of water-soluble anions and cations were more than 0.9. The highest pertinence coefficients were in the spring (0.9887), and the minimum was in summer (0.9459). That is, there were more complicated ions in PM2.5 in the summer. The mean value of NO3−/SO42− was 0.64, indicating that stationary sources of PM2.5 had a greater contribution in Wuhan.

Characteristics of concentrations and water-soluble inorganic ions in PM2.5 in Handan City, Hebei province, China

In order to explore the spatial, temporal, and chemical characteristics of fine particulate matter (PM2.5) pollution in Handan city, China, a comprehensive dataset including continuous online observations at four air quality monitoring stations in 2013 and 2014, and the concentrations of water-soluble inorganic ions (WSII) (NO3−, SO42−, NH4+, Cl−, Na+, Mg2+, K+, Ca2+) in PM2.5 samples collected in four representative seasons in 2013 and 2014 are analyzed in this study. And the principal component analysis (PCA) method is applied to identify the source of WSII in Handan. Our results indicate that PM2.5 concentration decreased from 139.4μg/m3 in 2013 to 116.0μg/m3 in 2014 on annual average. Spatial variations of PM2.5 mass are not pronounced, indicating that PM2.5 is nearly evenly spread over the study area. The seasonal variations of PM2.5 concentration are significant, normally with 1.7 to 2.4 times higher in winter than in summer. The concentrations of TWSII (total water-soluble inorganic ions) remain relatively stable in two years, with annual averages of 63.1μg/m3 in 2013 and 57.2μg/m3 in 2014. SNA (SO42−, NO3−, NH4+) dominates in the TWSII, accounting for ~87% of the TWSII. Similar to PM2.5, WSII exhibits obvious seasonal variations with higher concentrations in autumn and winter, lower in spring and summer. PM2.5 samples are acidic in spring, summer and autumn of 2013, while in winter of 2013 and all seasons of 2014, they are alkaline. SO42−, NO3− are formed mainly through homogeneous reactions, heterogeneous reactions also exist in winter. Finally, the major sources of WSII in Handan are identified as the mixture of secondary origin, coal combustion, biomass burning (46.1%), dust sources (25.8%), and motor vehicle (12.3%).

Characterization of Gaseous Pollutants and Water-Soluble Inorganic Ions in PM2.5 during Summer Time at an Urban Site of North India

AbstractGaseous toxic air pollutants are normally associated with acute short-term and chronic long-term health effects, and hence measurement of these pollutants is essential on a daily basis to understand the science of their occurrences. In this study, gaseous O3, SO2, NO2, NH3, HNO2, HNO3, and HCl and water-soluble inorganic ions (Na+, K+, Ca2+, Mg2+, NH4+, NO3−, SO42−, and Cl−) in PM2.5 were measured during a summer in Kanpur, India, using an annular denuder technique on a time resolution of 12 h. The denuder technique revealed that evaporation losses of NH4+, Cl−, and NO3− from a Teflon filter and trapped in nylon filters were temperature sensitive. The evaporation losses were 17.8±8.7%, 29.5±19.3%, and 37.1±25.9% during daytime, and 10.2±6.4%, 17.7±10.1%, and 19.3±12.2% during nighttime for NH4+, Cl−, and NO3−, respectively. Overall, 24 h average concentrations of O3, SO2, NO2, NH3, HNO2, HNO3, and HCl were 49.6, 8.6, 34.2, 21.5, 3.6, 9.8, and 1.4 μgm−3, respectively; and 2.1, 1.5, 2.9, 1.1, 13.1,...

Variability, formation and acidity of water-soluble ions in PM2.5 in Beijing based on the semi-continuous observations

Daily PM2.5 and hourly water-soluble inorganic ions in PM2.5 and gaseous precursors were measured during June–November 2009 at an urban site in Beijing. The average mass concentration of the total water-soluble ions was 44μgm−3, accounting for 38% of PM2.5. Sulfate (SO42−), nitrate (NO3−) and ammonium (NH4+) were dominant ions. The summer–fall difference in seasonal average mass concentrations was smaller than 30% for SO42−, but was up to a factor of 2.0 for NO3− and NH4+. A pronounced diurnal cycle was found for most ions and gaseous precursors and could be explained by their respective sources, formation mechanisms and meteorological conditions. The average oxidation/conversion ratio for SO42− (SOR), NO3− (NOR) and NH4+ (NHR) were estimated to be 63%, 15% and 15%, respectively. The low NHR value suggests that NH3 was mainly from local sources and that excessive NH3 existed and thus was not a limiting factor in the formation of NH4+. As a result, the diurnal pattern of NH4+ was similar to that of SO42− to some extent, but differed significantly from that of NH3. Based on the estimated H+ concentration and acidity purity (f), 75% of data samples were strongly acidic and a few percent might be alkaline. Seasonal variations in aerosol acidity and chemical forms of major ions were also briefly discussed.