Water-soluble Inorganic Ions Research Articles

Seasonal Variations, Size Distributions, and Sources of Chemical Components of Submicron Particulate Matter in Nanjing

Size-segregated particulate matter (PM) samples were collected in different seasons from 2016 to 2017 at the Xianlin Campus of Nanjing University. Mass concentrations of water-soluble inorganic ions, carbonaceous components, and elements were analyzed for PM with an aerodynamic diameter ≤ 1.1 μm (PM1.1; <0.4 μm, 0.4-0.7 μm, and 0.7-1.1 μm). The results showed that PM1.1, OC, NO3-, SO42-, and NH4+ exhibited higher ambient levels in fall-winter than those in spring-summer, which was attributed to the changes in local diffusion conditions, evaporation, and decomposition of non-refractory components. Elemental carbon (EC) reached its maximum concentration[(1.87±0.98) μg·m-3]in spring due to the increase in industrial and road dust resuspension. According to the characteristic ratio between bulk components, the anions in PM1.1 were dominated by NO3-, SO42-, and Cl- in Nanjing, and the carbonaceous components were mainly from fossil fuel combustions and associated aging processes. As the ambient temperature increased, the size distributions of thermo-unstable components including NH4+, NO3-, and OC shifted towards finer particles, whereas EC became more enriched in coarse particles, possibly due to the increase in emission intensity of motor vehicles and fugitive dust contributions. Since high relative humidity (>70%) is often accompanied by high temperature (>20℃) and improved diffusion conditions, a relative humidity of 60%-70% was more conducive to the formation of secondary inorganic ions in PM1.1. Source apportionment results based on the speciation data of PM1.1 showed that secondary formation processes[(66.6±18.3)%]and dust resuspension[(16.8±14.8)%]were the main contributors to PM1.1 in Nanjing, and further control of the emissions of gaseous precursors and dust is necessary.

PPWD-SDEP-IC monitoring system for atmospheric precursor inorganic gases and PM2.5 water-soluble ions

To resolve the potential evaporation loss of about 14% NH4+ in the particle into liquid sampler (PILS), a novel two-stage semi-dry electrostatic precipitator (SDEP) was developed successfully for monitoring atmospheric PM2.5 water-soluble inorganic ions (WSIIs) with the high collection efficiency and good accuracy. The number-based collection efficiency was >95% for particle sizes ranging from 14 nm to 11 μm, and the mass-based collection efficiency for PM2.5 was also as high as 94.4–98.1%. With an efficient pulse water jet system, the SDEP had a high ion recovery rate of 93 ± 10% for Na+, 103 ± 15% for NH4+, 92 ± 5.6% for SO42−, and 96 ± 8% for NO3−, respectively. The SDEP was coupled with the parallel plate wet denuder (PPWD) and ion chromatography (IC) as the PPWD-SDEP-IC semi-automatic monitoring system for the hourly precursor gases and PM2.5 WSII concentrations. The field comparison test for three-month measurements showed that the daily average results of the PPWD-SDEP-IC had a good agreement with those of the porous-metal denuder sampler (PDS), showing the linear regression slopes of 0.99–1.05 and 0.98–1.05, respectively, for precursor gases (NH3, HONO, SO2 and HNO3) and PM2.5 WSIIs (Na+, NH4+, K+, F−, Cl−, NO3− and SO42−) with high R2 values of 0.92–0.99 and 0.96–0.99, respectively. Moreover, the results of the hourly concentration comparison between the PPWD-SDEP-IC and the PPWD-PILS-IC showed linear regression slopes of 0.90–0.99 and 0.84–0.97 for precursor gases and WSIIs with high R2 values of 0.93–0.96 and 0.90–0.96, respectively. The PILS showed an underestimation of NH4+ concentration by about 15.6 ± 6.3% when compared to NH4+ from the SDEP owing to the volatilization loss of NH4+ caused by the mixing of aerosols with high-temperature steam in the PILS. Thus, the current PPWD-SDEP-IC system can be a viable tool for accurate semi-continuous monitoring of precursor gases and PM2.5 WSII concentrations.

Pollution Characteristics and Sources of Water-soluble Ions in PM2.5 in Zhengzhou City

In order to explore the pollution characteristics, seasonal variations, and sources of water-soluble inorganic ions (WSIIs) in PM2.5 in Zhengzhou, PM2.5 samples were seasonally collected from December 2020 to October 2021; then, combining gaseous pollutants (SO2, NO2, and O3) and meteorological parameters (temperature and relative humidity), nine WSIIs (NO3-, NH4+, SO42-, Ca2+, K+, Na+, Mg2+, F-, and Cl-) were analyzed. The results showed that the annual average concentration of the total water-soluble ions (TWSIIs) was (39.34±21.56) μg·m-3for the four seasons, showing obvious seasonal variations with the maximum value in winter and the minimum value in summer. Annual PM2.5 was slightly alkaline in Zhengzhou, and NH4+ most likely existed in the form of NH4NO3 and (NH4)2SO4. The average sulfur oxidation ratio (SOR) and nitrogen oxidation ratio (NOR) were 0.35 and 0.19, respectively, indicating that SO42- and NO3- mainly derived from secondary formation. The main potential source regions of WSIIs obtained by the concentration weight trajectory (CWT) model showed temporal and spatial variations. The significant sources of WSIIs based on principal component analysis (PCA) were dust, secondary generation, combustion, and industrial activities, which were obviously influenced by wind direction and speed in Zhengzhou.

Variations in PM2.5 Composition and Sources During 2020-2021 COVID-19 Epidemic Periods in Nanjing

To understand the changes in chemical composition and sources of PM2.5 under the extreme reduction background during the COVID-19 epidemic periods in Nanjing, hourly observation results of PM2.5 components (water-soluble inorganic ions, carbonaceous components, and inorganic elements) of two epidemic events from January to March 2020 and June to August 2021 were analyzed. In comparison to that during pre-epidemic periods, the concentration of NO3- during the two epidemic control periods decreased by 52.9% and 43.0%, respectively, which was larger than the decreases in NH4+(46.4% and 31.6%) and SO42-(33.8% and 16.5%). Since the observation site was located close to a main road, the decrease in elemental carbon (EC, 35.4% and 20.6%) was higher than that in organic carbon (OC, 11.1% and 16.2%). In reference to the variations in the characteristic ratios of the bulk components mentioned above, the epidemic control showed a more substantial influence on traffic emissions than industrial activities. The concentration time series of PM2.5 major components over the epidemic periods indicated that NOx from local traffic emissions had substantial contributions to the formation of NO3-, which led to local short-term PM2.5 pollution. In addition, the positive matrix factorization (PMF) model was used to analyze the hourly observation data of PM2.5 components. The seven identified factors were linked with metallurgy, firework and firecracker combustions, road traffic emissions, coal combustion, dust resuspension, secondary sulfate, and secondary nitrate. Because the nitrate was unstable under high temperature, the contribution of secondary nitrate to PM2.5 during the epidemic control period of 2021 (summer, 21.2%) was much lower than that during the epidemic control period of 2020 (winter, 60.6%); however, the formation of secondary components always dominated the contribution of PM2.5 sources. Therefore, emissions of NOx and SO2 should be further controlled to continuously reduce ambient PM2.5 concentrations in Chinese cities.

Interannual variation and chemical characterization of major water-soluble inorganic ions in snow across Northwest China

From November 2018 to April 2020, 438 snow samples were collected near two field observation sites in Heihe and Altay, Northwest China, and the pH and major water-soluble inorganic ions (Ca2+, SO42−, Na+, NO3−, Cl−, K+, Mg2+, and NH4+) were analyzed. To identify the source of ions, the enrichment factor method, Pearson correlation analysis, and HYSPLIT (Hybrid Single Practical Lagrangian Integrated Trajectory) backward trajectory analysis were employed. The snow was nearly pH neutral, and Ca2+ was the dominant cation present. The anion concentration demonstrated high variability. Affected by geographical location and atmospheric circulation, the concentration of soluble inorganic ions in snow from the Altay region was higher than that in the Heihe region and remote areas at high altitude or high latitude. Compared with 2018/2019, ion concentrations in snow increased in 2019/2020, especially in the Altay region. Moreover, the temporal trend of ion concentrations was stable, indicating that the source and migration path of ions had strong consistency. Our study suggested that terrestrial sources are the main driving factors for the ions observed in snow samples from Northwest China, and some ions are also the result of anthropogenic sources (NH4+, SO42−, and NO3−), marine sources (Cl− and Na+), and salt mine dust (Cl−, Na+, SO42−, and K+).

Characteristics and source apportionment of water-soluble inorganic ions in atmospheric particles in Lvliang, China.

Seasonal atmospheric particulate matter samples with different particle sizes (< 2.5μm [PM2.5], 2.5-5μm [PM2.5-5], 5-10μm [PM5-10], and 10-100μm [PM10-100]) were collected to analyze the mass concentration and distribution characteristics of nine water-soluble ions (WSIs; F-, Cl-, NO3-, SO42-, Na+, NH4+, K+, Mg2+, and Ca2+) in Lvliang in China. The results of chemical composition analysis indicated that the average concentration of total WSIs was 29.08µg·m-3 and accounted for 40.45% of PM2.5, 80.99% of which was attributable to SO42-, NH4+, and NO3-; the concentration demonstrated obvious distribution characteristics. NO3- and NH4+ primarily exist as NH4NO3 and (NH4)2SO4, respectively, in fine particles but as NaNO3 and NH4Cl, respectively, in coarse particles. The PM2.5 was alkaline overall, and K+ and NH4+ caused the highest RC/A values in autumn. Stationary sources contribute more to WSIs in particulates than mobile sources. The secondary transformation degree of SO2 was higher than that of NOx, especially in fine particles. The positive matrix factorization (PMF) and potential source contribution function (PSCF) models were combined to determine the sources of WSIs in PM2.5. Through use of the PMF model, five source factors were categorized: secondary aerosols (43.0%), biomass combustion (21.7%), coal combustion (17.6%), dust (10.9%), and vehicular traffic (6.8%). The results of the PSCF model suggested that the transport of pollutants from Shanxi, northwestern Shaanxi, Gansu, Inner Mongolia and Henan, had the greatest effect on air quality in Lvliang.

Characteristics and Sources of Water-Soluble Inorganic Ions in PM2.5 in Urban Nanjing, China

In this study, the water-soluble inorganic ions (WSIIs) composition of fine particulate matter (PM2.5) was measured in the northern Nanjing city from 2015 to 2021. NH4+, NO3− and SO42− concentrations dominated in total WSIIs (Na+, NH4+, K+, Mg2+, Ca2+, Cl−, NO3− and SO42−), accounting for 87.8%. The nitrate with highest average concentration among all ions was 11.0 μg·m−3. Total WSIIs concentrations were higher in winter and lower in summer, with the highest levels in December (45.6 μg·m−3) and the lowest levels in August (15.1 μg·m−3). NO3−/SO42− was higher than 1, indicating the important contribution of mobile sources. The aerosols exhibited a weak acidic by the molar ratio of water-soluble anions and cations. Positive matrix factorization (PMF) analysis results showed that secondary nitrate and sulfate were the major pollution sources in December 2016 and 2020. The contribution of secondary nitrate in 2020 increased by 47.6% compared to 2016, while that of secondary sulfate decreased by 42.4%. The potential source contribution results demonstrated that for secondary aerosol concentrations, the contribution of regional transport from north of Anhui increased, while the contribution of local emissions decreased. The results from this study could contribute to the better prevention and control of regional air pollution in the future.

Characteristics of PM2.5 and secondary inorganic pollution formation during the heating season of 2021 in Beijing

Water-soluble inorganic ions (WSIIs) were measured online in Beijing during the heating season of 2021, during which Beijing 2022 Olympic and Paralympic Winter Games were hosted. The characteristics of PM2.5 and water-soluble inorganic ions were investigated in general, as well as during the clean period, polluted period, and Olympic and Paralympic Winter Games periods. It was found that most of the polluted episodes occurred under conditions of low wind speed, temperature inversion, and high relative humidity. The total mass concentration of water-soluble inorganic ions during the polluted period and the clean period accounted for 38.2% and 61.4% of the PM2.5 mass concentration, respectively. Both the sulfur oxidation ratio (SOR) and nitrogen oxidation ratio (NOR) showed a strong relationship with relative humidity. During the polluted period, the concentrations of secondary aerosols such as sulfate, nitrate, and ammonium (SNA) increased significantly. Secondary transformation was enhanced compared with that in the clean period. A polluted process after a snowfall event was selected to explore the mechanism of sulfate and nitrate formation under high relative humidity. The results would be beneficial to understanding the causes of pollution and helping the government to formulate effective measures to control air pollution in winter.

The chemical characterization and source apportionment of PM2.5 and PM10 in a typical city of Northeast China

This paper analyzed the chemical characterization of PM2.5 and PM10 in a typical city of Northeast China during the heating period, including trace elements, water-soluble inorganic ions (WSII), organic carbon (OC), and element carbon (EC). The results showed that PM2.5 and PM10 concentrations were 66.55 ± 28.89 μg/m3 and 92.99 ± 31.00 μg/m3. The concentrations of As and Cr in the atmosphere were beyond the current air quality standard in China (6 ng/m3 for As, 0.025 ng/m3 for Cr). Secondary inorganic ions (NH4+, NO3−, and SO42−) dominated the WSII, accounting for 40.54% of PM2.5 and 33.80% of PM10. High OC/EC ratios implied a high proportion of secondary organic carbon (SOC). Positive matrix factorization (PMF) was used to identify the sources of PM2.5 and PM10. Six factors were analyzed and identified as secondary aerosol, industry, coal combustion, vehicle emissions, biomass burning, and dust, of which secondary aerosol was the largest contribution to PM2.5 and PM10.

Chemical composition, sources and evolution of PM2.5 during wintertime in the city cluster of southern Sichuan, China

The city cluster of southern Sichuan is not only the key haze area in the Sichuan Basin, China, but also seriously affects the air quality of surrounding areas. In order to obtain comprehensive information on the characteristics of air pollution in this area, this study conducted synchronous sampling and analysis of fine particulate matter (PM2.5) in four cities (Zigong, Luzhou, Neijiang and Yibin) in this area during the wintertime of 2018–2019. The results showed that the average concentration of PM2.5 in these four cities was 111–124 μg m−3, with more than 90% of days being polluted days. The contributions from carbonaceous components, water-soluble inorganic ions (WSIIs) and trace elements to PM2.5 were 17.3–18.9%, 34.3–38.2% and 2.2–3.0%, respectively. The contributions of secondary inorganic ions (SO42−, NO3− and NH4+) to WSIIs were 91.1–93.0%. The changes in the chemical components during the process of pollution aggravation were significantly different from those in most cities in China, with the contribution from organic carbon increasing, while the contribution from WSIIs decreased. PM2.5 mainly came from dust, combustion, vehicular emissions, industrial processes and secondary inorganic sources. Compared with most megacities or provincial capitals in China, the contributions from dust (18.1–23.6%), combustion (17.9–21.1%) and industrial processes (9.2–12.0%) were at a higher level, and these sources can be regarded as the primary targets for pollution reduction in the future. The formulation of air pollution reduction policies needs to consider local conditions, such as sources, energy structure, management level.

Seasonal Variation of Aerosol Composition and Sources of Water-Soluble Organic Carbon in an Eastern City of China

The mitigation of aerosol pollution is a great challenge in many cities in China, due to the complex sources and formation mechanism of particulate matter (PM) in different seasons. To understand the particular features of pollution in China and formulate different targeted policies, aerosol samples of PM2.5 were collected from January to October of 2018 in Longyou. The temporal profile of the meteorological parameters and the concentrations of water-soluble inorganic ions (WSIs) and organic matter (OM) were characterized. An Aerodyne High-Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-TOF-AMS) was also applied to further analyze the composition of water-soluble organic carbon (WSOC). The sources of WSOC were resolved by positive matrix factorization (PMF) analysis. The origin of air parcels and potential sources of WSOC were analyzed using a backward trajectory and potential source contribution function (PSCF). Winds from the northeast dominated each sampling period, and the relative humidity did not show a significant difference. The results showed that the proportion of OM in PM2.5 was the highest in summer and decreased in spring, autumn, and winter in turn. Four organic aerosol (OA) factors, including a hydrocarbon-like factor, a coal combustion factor, and two oxygenated OA factors, were identified in the WSOC by means of PMF analysis. The hydrocarbon-like OA (HOA) contributed the majority of the WSOC in summer, while the contribution of the coal-combustion OA (CCOA) increased significantly in winter, suggesting the presence of different sources of WSOC in different seasons. The air parcels from the north of China and Zhejiang province contributed to the CCOA in winter, while those from the marine regions in the south and southeast of China mainly contributed to the HOA during spring and summer. The weighted PSCF (WPSCF) analysis showed that the regions of east Zhejiang province were the main contributors, which means that local and regional emissions were the most probable source areas of WSOC. It implied that not only were the emissions control of both local and regional emissions important but also that the transport of pollutants needed to be sufficiently well accounted for to ensure the successful implementation of air pollution mitigation in Longyou.

Insights into the roles of aerosol soluble iron in secondary aerosol formation

Aerosol soluble iron (Fe) is crucial in the biogeochemical cycle and atmospheric processing. In this study, soluble Fe and their solubility in fine particles (PM2.5) were investigated over Xi'an, China to insight the iron sources and the roles in aerosol formation. Our results showed that most Fe in PM2.5 was insoluble (Fe solubility: 25.5 ± 11.3%). Seasonal variations exhibited that the highest soluble Fe(II) showed in winter (308.9 ng m−3) and the highest Fe(III) levels were in summer (116.3 ng m−3). Source identification of soluble Fe illustrated that industrial coal combustion contributed most in summer, whereas mineral dust, biomass burning, and coal combustion dominated in spring, autumn, and winter, respectively. Moreover, strong correlations between soluble Fe and water-soluble inorganic ions suggested soluble Fe is related to not only primary sources but also secondary formations. Furthermore, a negative correlation (R = −0.56) was observed in winter between Fe(III) and SO42−, indicating that the oxidation pathway of Fe(III) catalysis should play a vital role in sulfate formation in winter. In addition, secondary brown carbon presented positive correlations with soluble Fe(II), while negatively correlated with soluble Fe(III), potentially suggested an important pathway for the formation of secondary BrC. Our study provides a broader understanding of Fe solubility and their roles in atmospheric chemical processing.

Fine particulate pollution driven by nitrate in the moisture urban atmospheric environment in the Pearl River Delta region of south China

To identify potential sources of fine particles (PM2.5, with aerodynamic diameter (Da) ≤ 2.5 μm) in urban Dongguan of south China, a comprehensive campaign was carried out in the whole 2019. Hourly PM2.5 and its dominant chemical components including organic carbon (OC), elemental carbon (EC), water-soluble inorganic ions (WSIIs) and thirteen elements were measured using online instruments. Gaseous pollutants including NH3, HNO3, NO2, NO and O3 and meteorological parameters were also synchronously measured. PM2.5 was dominated by carbonaceous aerosols in summer and by WSIIs in the other seasons. PM2.5 and its dominant chemical components mostly peaked around noon (10:00–14:00 LST). Furthermore, high PM2.5 levels during the daytime were closely related with the increased NO3− levels. The high mass concentrations of NO3− in urban Dongguan during the daytime were likely related with regional transport of NO3− from suburban Dongguan, which was originated from the reaction between NO2 and O3 under the moisture condition during the nighttime. Seven major source factors for PM2.5 including secondary sulfate, ship emission, traffic emission, secondary nitrate, industrial processes, soil dust and coal combustion were identified by positive matrix factorization (PMF) analysis, which contributed 26 ± 14%, 16 ± 16%, 16 ± 10%, 14 ± 11%, 12 ± 11%, 8 ± 6% and 8 ± 6%, respectively, to annual PM2.5 mass concentration. Although secondary sulfate contributed much more than secondary nitrate to PM2.5 on annual basis, the latter exceeded the former source factor when daily PM2.5 mass concentration was higher than 60 μg m−3, indicating the critical role nitrate played in PM2.5 episode events.

Characterization and Formation Mechanism of Water-soluble Inorganic Ions in PM2.5 and PM10 in Summer in the Urban Agglomeration of the Ili River Valley

The simultaneous observation and analysis of atmospheric particles on a regional scale is an important approach to developing control strategies for air pollution. To study the spatial distribution characteristics of particulate matter and water-soluble inorganic ions in the Ili Valley Urban agglomeration, PM2.5 and PM10 samples were synchronously collected from July 19 to July 29, 2021 in Yining City and the surrounding three counties, and then nine types of water-soluble inorganic ions (WSIIs) were analyzed. The spatial distribution characteristics, existence form of WSIIs, and influencing factors were discussed in depth. The results showed that the average ρ(PM2.5) and ρ(PM10) in the Ili River Valley urban agglomeration in summer were 23 μg·m-3 and 59 μg·m-3, respectively. The emission of local industrial and mobile sources in Yining City was higher than that of the surrounding three counties, resulting in the highest ρ(PM2.5) in the region (25 μg·m-3). Due to the influence of dust sources and topography, the ρ(PM10) in Yining county was the highest in the region (63 μg·m-3). Huocheng county is located upwind of the region, and these favorable diffusion conditions resulted in the lowest ρ(PM2.5) and ρ(PM10) (20 μg·m-3 and 49 μg·m-3, respectively). The concentrations of WSIIs in PM2.5 and PM10 ranged from 28.2%-29.9% and 16.0%-20.2%, respectively. The four main ions (SO42-, NO3-, NH4+, and Ca2+) accounted for approximately 90% of WSIIs mass concentrations. The concentration order of the four main ions in PM2.5 was SO42->Ca2+>NH4+>NO3- and SO42->Ca2+>NO3->NH4+ in PM10. The results of correlation analysis showed that the similar SO42- concentrations in the four cities were mainly caused by regional transport. Ca2+ was the highest-concentration ion in PM10 of Yining City and Qapqal Xibe Autonomous county, and the proportion of Ca2+ was significantly higher than that in most cities in China, which reflected that the cities in the core area of the Ili Valley were greatly affected by the dust sources. The ratios of n(NO3-)/n(SO42-) in PM2.5 and PM10 were 0.78 and 0.76, respectively, indicating that the influence of stationary sources was greater than that of mobile sources. The ratio of n(NO3-)/n(SO42-) in Yining City>Huocheng county>Yining county>Qapqal Xibe Autonomous county, which was consistent with the motor vehicle populations of the four cities, reflecting that Yining City was affected by motor vehicle sources more than the surrounding three counties. The secondary components mainly existed in the form of (NH4)2SO4, NH4HSO4, and NH4NO3. There was excess ammonia after the reaction between NH4+ and SO42- in each city. NH4NO3 mainly existed in Yining City, which was mainly related to high NO2 in Yining City. The NOR of the four cities were 0.03-0.10 and 0.03-0.16 in PM2.5 and PM10, respectively, and the secondary transformation of NO3- was weak due to the influence of high temperatures in summer. The SOR were 0.21-0.41 and 0.23-0.44, respectively. The SOR of Qapqal Xibe Autonomous county was the highest due to the relatively high humidity, whereas the SOR of Huocheng county was higher than that of the three sites in Yining City due to the influence of regional transportation. The formation mechanisms showed that SO42- in Qapqal Xibe Autonomous county and Yining City were mainly produced by the heterogeneous reaction, and in Yining county it was mainly formed via the homogeneous reaction. However, the formation mechanism in Huocheng county was complex and was affected by both homogeneous and heterogeneous reactions.

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.

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

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.

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.

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.

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.