Sources Of Water-soluble Ions Research Articles

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.

Spatial distribution and potential sources of arsenic and water-soluble ions in the snow at Ili River Valley, China

Trace elements and water-soluble ions in snow can be used as indicators to reveal natural and anthropogenic emissions. To understand the chemical composition, characteristics of snow and their potential sources in the Ili River Valley (IRV), snow samples were collected from 17 sites in the IRV from December 2018 to March 2019. Inverse distance weighting, enrichment factor (EF) analysis, and backward trajectory modelling were applied to evaluate the spatial distributions and sources of water-soluble ions and dissolved arsenic (As) in snow. The results indicate that Ca2+ and SO42− were the dominant ions, and the concentrations of As ranged from 0.09 to 0.503 μg L−1. High concentrations of As were distributed in the northwest and middle of the IRV, and the concentrations of the major ions were high in the west of the IRV. The strong correlation of As with F−, SO42−, and NO2− demonstrates that As mainly originated from coal-burning and agricultural activities. Principal component analysis showed that the ions originated from a combination of anthropogenic and crustal sources. The EFs showed that K+, SO42−, and Mg2+ were mainly influenced by human activities. Backward trajectory cluster analysis suggested that the chemical composition of snow was affected by soil dust transport from the western air mass, the unique terrain, and local anthropogenic activities. These results provide important scientific insights for atmospheric environmental management and agricultural production within the IRV.

Characteristics and Source Analysis of Water-soluble Inorganic Pollution in PM2.5 During Summer in Central China

In order to investigate the pollution characteristics and sources of water-soluble ions in atmospheric PM2.5 in different regions of central China during summer, Wuhan, Suizhou, and Pingdingshan were selected as urban, suburban, and rural monitoring stations, respectively, to collect PM2.5 samples, and the mass concentration of PM2.5 in the atmosphere and the contents of eight water-soluble ions were analyzed. The results showed that ρ(water-soluble ions) at the three sites showed obvious spatial distribution characteristics, with Pingdingshan[(36.29±9.82) μg·m-3] > Wuhan[(32.55±10.05) μg·m-3] > Suizhou[(26.10±6.23) μg·m-3], accounting for 52.47%, 51.32%, and 48.61% of the PM2.5 mass concentration, respectively. In the Pingdingshan station, the proportion of water-soluble ions was the largest due to biomass combustion in the rural area. Additionally, SNA (SO42-, NO3-, and NH4+) were the main ionic components, accounting for 95.65%, 96.12%, and 97.33% of the total water-soluble ions, respectively. The mean values of SOR of the Wuhan (0.64) and Suizhou (0.63) stations were higher than that of the Pingdingshan station (0.50), whereas the NOR values of the Wuhan (0.18) and Pingdingshan (0.19) stations were higher than that of the Suizhou station (0.15). The difference in SOR and NOR among stations was affected by the secondary conversion mechanism, the ammonia-rich environment, and the surrounding traffic sources, respectively. The PM2.5 at the Wuhan and Pingdingshan stations was in general alkaline, whereas at the Suizhou station it was neutral or weakly acidic, which was mainly caused by differences in NH4+. NH4+ mainly existed in the form of (NH4)2SO4 and NH4NO3 at the Wuhan and Pingdingshan stations, whereas at the Suizhou station it mainly existed in the form of (NH4)2SO4 or (NH4)HSO4. PCA-MLR analysis revealed that the Wuhan (89.27%) and Suizhou (67.38%) stations were the most affected by secondary conversion sources, whereas the Wuhan station was also affected by industrial sources (8.54%) and coal sources (2.27%). The pollution sources of the Suizhou station also included biomass combustion (24.42%) and dust sources (8.25%). The Pingdingshan station was most affected by biomass combustion (58.37%), followed by dust and combustion sources (38.05%) and traffic sources (3.58%). The analysis of potential sources of SNA (PSCF) showed that the main potential source areas of Wuhan were the boundary of Hubei, Henan, and Anhui and the southwest area of Anhui. Suizhou and Pingdingshan were affected by long-distance transport, and the main potential source regions were distributed in Shanghai, Jiangsu, and Anhui provinces from the east coast to the west.

The characteristics and sources apportionment of water-soluble ions of PM2.5 in suburb Tangshan, China

To study characteristics and sources of water-soluble ions, the samples of PM2.5 were collected at suburb area of Tangshan. The main water-soluble ions in PM2.5 were analyzed and the source of water-soluble ions was discussed. The results showed that PM2.5 concentration was 128.45 ± 80.54 μg/m3 (winter indoor) > 112.44 ± 82.90 μg/m3 (summer indoor) > 112.44 ± 82.90 μg/m3 (winter outdoor) > 34.73 ± 31.92 μg/m3 (summer outdoor). The ion of Cl−, SO42−, NO3− and NH4+ were the main water-soluble ions in PM2.5 indoor and outdoor winter. The ion of NH4+, SO42−, NO3− and Ca2+ were the main water-soluble ions in PM2.5 indoor summer. The ion of SO42−, NO3−, NH4+ and K+ were the main water-soluble ions in PM2.5 outdoor summer. The main water-soluble ions existed in form of CaCl2, NH4NO3 and (NH4)2SO4 in winter-indoor, and in form of KCl, NH4NO3 and (NH4)2SO4 in winter-outdoor, and in form of NH4HSO4, NH4NO3 and KCl in summer-indoor, and in form of NH4HSO4, K2SO4 and NH4NO3 in summer-outdoor. Principal component analysis showed that the main source of PM2.5 in Tangshan suburb were construction dust, wind dust, stationary source and mobile source. However, the ratio for pollution sources were different for indoor and outdoor PM2.5.

Seasonal Variation of Water-soluble Ions in PM2.5 in Xi'an

To explore the seasonal variations and sources of water-soluble ions, PM2.5 samples were collected from 2017 to 2018. Water-soluble ions including SO42-, NO3-, Cl-, F-, Na+, Mg2+, NH4+, K+, and Ca2+ were determined via ion chromatography. Furthermore, the existing form of NH4+, nitrogen oxidation rate (NOR), sulfur oxidation rate (SOR), and [NO3-]/[SO42-] ratio were explored. The results showed that dust, coal combustion, biomass burning, and secondary aerosols were the dominant contributors to water-soluble ions. Ca2+, SO42-, NH4+, and NO3- were the main water-soluble ions in PM2.5 in Xi'an. Correlation analysis results showed that NH4+ could not completely neutralize SO42- in spring; unneutralized SO42- could be mainly combined with K+ and Ca2+. NH4+ mainly existed in the form of ① NH4HSO4 and (NH4)2SO4 in summer; ② NH4HSO4 and NH4NO3 in autumn; and ③ (NH4)2SO4 and NH4NO3 in winter. The yearly mean values of SOR and NOR were 0.35 and 0.16, respectively, indicating a high secondary aerosol transformation rate during the study period. The [NO3-]/[SO42-] ratio showed Xi'an was mainly affected by stationary sources in spring and summer, while the contribution of mobile sources in autumn and winter was greater than stationary sources.

The pollution characteristics and source analysis of water-soluble ions in indoor PM2.5 during the Spring Festival in Jingyue Suburb of Changchun City

The characteristics of water-soluble ions in indoor PM2.5 during the Spring Festival in Changchun City were analyzed by ion chromatography. The results showed that the main water-soluble ionic components in the indoor and non-combustion periods were SO4 2- and Ca2+, and the concentration of Na+, K+, Mg2+, F-, Cl- and NO3 - increased in the fireworks and firecrackers, among which Cl- and NO3 -. The concentration increased significantly compared with the non-combustion period, and peaked with PM2.5 concentration in the first month of the first month and the first month of the first month; the correlation between NH4 + and SO4 2- during the discharge and non-combustion periods was greater than the correlation between NH4 + and NO3 -, NH4 + Sulfate is preferentially combined with SO4 2-, and secondary ions are mainly in the form of (NH4)2SO4 and NH4NO3. Cluster analysis and correlation analysis indicate that the sources of water-soluble ions in indoor PM2.5 during the Spring Festival can be classified into four categories. Biomass combustion source, automobile exhaust gas source, coal-fired emission source and soil dust, among which the main sources of Na+, K+, Mg2+, Cl-, SO4 2- during the discharge period are the fireworks and firecrackers.

Characteristics and sources of WSI in North China Plain: A simultaneous measurement at the summit and foot of Mount Tai

To better understand the characteristics and sources of water soluble ions (WSI) in North China Plain (NCP), fine particles (PM2.5) were simultaneously sampled at the summit (SM) and foot (FT) of Mount Tai during May 12th to June 24th, 2017. Ion chromatography analysis showed that concentration of WSI was lower at SM (22.26 ± 16.53 μg/m3) than that at FT (31.02 ± 21.92 μg/m3). The concentration and proportion of SO42− in total WSI were both lower than the values reported in previous studies. Daytime WSI concentrations were higher than that at nighttime at SM, while the opposite results were obtained at FT, possibly associated with more anthropogenic activities and higher boundary layer height (BLH) during daytimes. A severe pollution event occurred during June 14th – June 16th was documented at both FT and SM. Regional transport and topography-forced vertical transport along the slope of the mountain could explain the higher concentrations of pollutants at SM. The analyses also indicated that NH4+ existed mainly in the form of NH4HSO4 and NH4NO3, but (NH4)2SO4 could also exist, especially when emissions of NH4+ and NH3 were increased during daytime at FT. The results of principal component analysis (PCA) illustrated that secondary aerosols, coal/biomass burnings, sea-salts and crustal/soil dusts were the main sources at SM, and secondary aerosols and crustal/soil dusts contributed most at FT. Backward air-mass trajectories were classified into four clusters, of which air masses with the highest frequency and WSI concentrations were originated from the southwest with secondary ions (SO42-, NO3- and NH4+) as major pollutants.

Diurnal Variations and Source Apportionment of Water-soluble Ions in PM2.5During Winter in Nanjing Jiangbei New Area

To gain a better understanding of the day-night variation characteristics of water-soluble ions, PM2.5 samples were continuously collected for two months in the Nanjing Jiangbei New Area during winter. The diurnal variation and sources of water-soluble ions were studied. Results showed that the mass concentration of water-soluble ions ranged from 17.07 μg·m-3 to 168.43 μg·m-3 with a mean value of (59.01±30.75) μg·m-3. The average mass concentration of water-soluble ions in daytime was higher than that in the nighttime. The concentration ratio of NO3- and NH4+ to total ion concentrations was higher at night, while SO42- and Cl- were higher during daytime. SO42-, NO3-, and NH4+ (SNA) were the dominant species of water-soluble ions in PM2.5 in Nanjing. The mass concentration of SNA on polluted days was higher than that on clean days. The ratio of the anion-cation balance (AE/CE) was larger than 1, indicating that the PM2.5 was acidic. There was a significant linear correlation between NH4+ with NO3- and SO42-, indicating that it occurred mainly in the form of NH4NO3 and (NH4)2SO4 in PM2.5. The PMF source apportionment indicated that water-soluble ions of PM2.5 were mainly derived from motor vehicle emissions, fossil fuel combustion, biomass burning, and dust in the Nanjing Jiangbei New Area.

The composition and sources of water soluble ions in PM10 at an urban site in the Indo-Gangetic Plain

Analysis of water soluble ions in PM10 in Pakistan is limited and therefore requires in-depth investigation. In this study composition and sources of ionic profile in PM10 were determined from an urban site of an Asian megacity (Faisalabad) in 2015–2016. The PM10 size fraction sampled on quartz filters was analyzed by ion chromatography for selected inorganic and organic ions. The daily mean PM10 mass concentration was found to be 744 ± 392 μgm−3, exceeding the limits proposed by Pak-EPA (150 μgm−3), US-EPA (150 μgm−3) and WHO (50 μgm−3). The ambient PM10 concentration was found to be highest in winter 2015-16 and autumn 2016, while the lowest in the monsoon 2016. The average total ion concentration was found to be 120 ± 51 μgm−3, which made about 16% of the total PM10 mass. CO32− was the most dominant specie followed by NH4+, Ca2+, K+, NO3−, SO42−, C2O42−, CH3COO−, Na+, Cl− and Mg2+. The ratio analysis of selected ions indicated dominant contribution of biomass burning during autumn and winter and higher impact of fossil fuel burning during spring and summer seasons. Positive Matrix Factorization identified traffic induced soil erosion, biomass burning, fugitive dust from construction activities, secondary aerosol formation processes and fossil fuel emissions from traffic and industry as major sources of particulates.

Characteristics of size distributions and sources of water-soluble ions in Lhasa during monsoon and non-monsoon seasons

To understand the physical and chemical characteristics, particle size distribution and sources of size-separated aerosols in Lhasa, which is located on the Tibetan Plateau (TP), six sizes of aerosol samples were collected in Lhasa in 2014. Ca2+, NH4+, NO3−, SO42− and Cl− were the dominant ions. The ratio of cation equivalents (CE) to anion equivalents (AE) for each particle size segment indicated that the atmospheric aerosols in Lhasa were alkaline. SO42− and NO3− could be neutralized by Ca2+, but could not be neutralized by NH4+, according to the [NH4+]/[NO3− + SO42−] and [Ca2+]/[NO3− + SO42−] ratios. Mobile sources were dominant in PM0.95–1.5, PM1.5–3 and PM3–7.2, while stationary sources were dominant in the other three size fractions according to the [NO3−]/[SO42−] ratios. The particle size distribution of all water-soluble ions during monsoon and non-monsoon periods was characterized by a bimodal distribution due to the different sources and formation mechanisms, and it was revealed that different ions had different sources in different seasons and different particle size segments by combining particle size distribution with correlation analysis. Source analysis of aerosols in Lhasa was performed using the Principal component analysis (PCA) for the first time, which revealed that combustion sources, motor vehicle exhaust, photochemical reaction sources and various types of dust were the main sources of Lhasa aerosols. Furthermore, Lhasa's air quality was also affected by long-distance transmission, expressed as pollutants from South Asia and West Asia, which were transmitted to Lhasa according to backward trajectory analysis.

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.

Stoichiometry of water-soluble ions in PM2.5: Application in source apportionment for a typical industrial city in semi-arid region, Northwest China

Water-soluble ions (WSIs) are major components of PM2.5 and it is valuable for understanding physical and chemical characteristics, sources, behaviors and formation mechanism of WSIs. Baotou is a traditionally industrial city in semi-arid region and frequently subjected to dust storms from March to May. In recent years, air pollution has been listed as one of the most important environmental problems in Baotou. To investigate the seasonal variations and sources of WSIs in PM2.5, the WSIs including SO42−, NO3−, Cl−, F−, NH4+, K+, Na+, Ca2+ and Mg2+ were monitored at six urban sites in Baotou. The results showed that high concentrations of Ca2+ and Na+ were found responding to dust storm events, while high concentrations of SO42−, NO3−, NH4+, K+ and Cl− were observed during haze days. The correlations analysis indicated that excess sulfuric and nitric acid was likely neutralized by carbonate minerals such as calcite, aragonite and dolomite in normal days and cations were fully neutralized during all the sampling periods, while cations were excessive in dust storm days. The concentrations of [NH4+ + SO42− + NO3−], [Na+ + Ca2+ + Mg2+] and [Cl− + K+ + F−] indicated the northwest and southeast region of Baotou presented comparatively high contributions of secondary aerosol and crustal dust, respectively, which were mainly related to the industrial distribution and urbanization process. The cluster analysis, ternary diagram and principal component analysis have a good agreement in source apportionment, where crustal dust sources, secondary aerosol source and the mixture of coal combustion, biomass burning and industrial pollution sources were the main sources of WSIs in PM2.5. The seasonal pattern of sulfur oxidation ratio (SOR) was September > April > November > January, while the nitrogen oxidation ratio (NOR) April > January > November > September in Baotou. This work evaluated the seasonal variation, distribution and source of WSIs on the basis of its stoichiometry in PM2.5, which help to explore the potential sources of these inorganic aerosols and provide scientific suggestion for air quality improvement in Baotou.

Concentrations and Size Distributions of Water-soluble Inorganic Ions in Aerosol Particles in Taiyuan, Shanxi

Size-resolved filter samples were collected in Taiyuan every other week from June 2012 to May 2014. The mass concentrations of water-soluble ions (Na+, NH4+, K+, Mg2+, Ca2+, F-, Cl-, NO3- and SO42-) were measured by ion chromatography. The results showed that the total concentrations of measured water-soluble ions were (15.39±9.91), (21.10±15.49) and (36.34±18.51) μg·m-3 in PM1.1, PM2.1 and PM9, respectively. In PM1.1 and PM2.1, secondary water-soluble ions (SO42-, NO3- and NH4+) comprised 87.59% and 86.30% of all water-soluble ions, respectively, while in PM9, SO42- and Ca2+ comprised 32.78% and 28.54% of all water-soluble ions, respectively. SO42- and NH4+ had higher concentrations in winter and summer, and lower in spring and autumn. NO3-, K+and Cl- presented similar seasonal variation with a descending order of winter >autumn >spring >summer, and Ca2+ and Mg2+ followed the sequence of spring >winter >autumn >summer. SO42- and NH4+ showed a unimodal size distribution and the peak in the fine mode shifted from 0.43-0.65 μm in spring and autumn to 0.65-1.1 μm in summer. NO3- showed a bimodal size distribution. NO3- and NH4+ were dominated by the fine mode peaking at 0.43-2.1 μm in winter, and NO3- was dominated by the coarse mode peaking at 4.7-5.8 μm in summer. K+, Na+and Cl- also showed a bimodal size distribution with the fine mode at 0.43-1.1 μm and the coarse mode at 4.7-5.8 μm. Ca2+, Mg2+ and F- were unimodal with the peak in the coarse mode of 4.7-5.8 μm. On heavily polluted days, the mass concentrations of secondary water-soluble ions and Cl- accumulated, and secondary water-soluble ions were unimodal with the peak in the fine mode of 1.1-2.1 μm. However, on clear days, secondary water-soluble ions showed a bimodal size distribution with the fine mode at 0.43-0.65 μm and the coarse mode at 4.7-5.8 μm. The peak of secondary water-soluble ions in the fine mode shifted. PCA analysis showed that the sources of water-soluble ions were dominated by the secondary formation, coal combustion, industrial emission, biomass burning, and soil particles or falling dust.

Water Soluble Ionic Species in Atmospheric Aerosols: Concentrations and Sources at Agra in the Indo-Gangetic Plain (IGP)

This study presents a comprehensive set of 2 years of data (January 2009–December 2010) on the chemical composition of ambient aerosols collected at a university campus in Agra, which lies on the Indo-Gangetic Plain (IGP). The average concentration of total suspended particles (TSP) was 213.2 ± 91.4 μg/m 3 . The most abundant ions in TSP were Ca 2+ , NO3 – and SO4 2– , which contributed about 3.2%, 3.1% and 2.7%, respectively. TSP and most of the ions, such as F – , Cl – , NO3 – , SO4 2– , NH4 + and K + , had the highest mass concentrations in winter, while higher mass concentrations of Ca 2+ and Mg 2+ were found in summer. Higher ionic concentrations during the winter season may be attributed to a combined effect of biomass burning and meteorological conditions (low temperature, wind speed and mixing height). The [NO3 – ]/[SO4 2– ] ratio at the present sampling site was 1.1 ± 0.4, which indicates that there were equal contributions from both stationary sources and vehicles. In winter, high [NO3 – ]/[SO4 2– ] ratios (1.7 ± 0.4) could be due to the extensive use of fuelwood and cowdung cakes to combat the cold. The acidity in aerosols is neutralized by the alkaline species, as indicated by the correlation between NO3 – and SO4 2– and sum of (Ca 2+ , Mg 2+ and NH4 + ). Ca 2+ is the major acid neutralizing cation in the aerosols, followed by Mg 2+ and NH4 + . The crustal source contribution was observed based on the ratios of various ions with respect to Ca in soil and aerosol. On the basis of backward trajectories and the associated concentrations of the ions, the aerosol samples were classified into sectors in relation to their origin to determine the related sources. The major sources of water soluble ions identified at Agra are biomass combustion and local soil.

Characterization of PM 2.5, PM 2.5–10 and PM > 10 in ambient air, Yokohama, Japan

This study elucidated the characteristics of ambient PM 2.5, PM 2.5–10 and PM > 10 with water soluble ions, i.e., Cl −, NO 3 −, SO 4 2−, Na +, NH 4 +, K +, Mg 2+ and Ca 2+ and carbonaceous aerosol, i.e., EC and OC in above size fractions from the samples collected for the period of 2007–2008. The total numbers of PM 2.5, PM 2.5–10 and PM > 10 samples collected with MCI sampler were 91, 87 and 79, respectively. The ambient particulate samples were collected twice in a week for a period of 24 h at the roof of a three-storied building in Yokohama National University. The annual arithmetic mean concentrations of PM 2.5, PM 2.5–10 and PM > 10 were 20.6, 9.6 and 5.1 µg m − 3 , respectively. The results of the daily PM 2.5 concentrations indicated that 67% of the daily PM 2.5 exceeded USEPA National Ambient Air Quality Standards (NAAQS) (15 µg m − 3 ) while 95% in respect of WHO ambient air quality guidelines (10 µg m − 3 ). The concentrations of water soluble ions in PM 2.5, PM 2.5–10 and PM > 10 accounted for 40%, 31% and 19%, respectively. The estimation of non-sea-salt particles implies that the major sources of water soluble ions in PM 2.5 are anthropogenic. On the other hand, a large proportion of sea salt particles contributes to PM 2.5–10 and PM > 10 . Spearman correlation indicated that the concentrations of OC and EC in PM 2.5 can originate from similar type of sources. However, the concentration of OC and EC in PM 2.5–10 and PM > 10 can have multiple sources. In addition, some atmospheric reactions were also characterized in this study.

Evaluation of the Characteristics of Acid Precipitation in Taipei, Taiwan Using Cluster Analysis

This work investigated the characteristics of acid precipitation collected in Taipei, Taiwan during 1991–1995 by performing cluster analysis. The extent to which meteorological conditions influence precipitation chemistry was also elucidated. Three potential sources of water-soluble ions in rainwater were identified: seasalt aerosols (Na+, Cl- and Mg2+), anthropogenic pollutants (H+ and NO3-), and mixing sources associated with sulfate (nss-SO42-, NH4+ and Ca2+). As the northeast flow prevailed during the northeast monsoon season, the concentrations of seasalt and sulfate ions in rainwater were significantly high. During that season, a typically high ratio of nss-SO42-/NO3- was also observed, indicating that Taipei might receive foreign pollutants via a long-range transport. In contrast, when the Pacific high dominated the region, nitrate concentration in rainwater was significantly elevated. Also during that period, the ratio of nss-SO42-/NO3- was substantially lower, indicating the prominence of acidic substances contributed by local sources.