Size Distributions Of Water-soluble Ions Research Articles

Distributions of water-soluble ions in size-aggregated aerosols over the Southern Ocean and coastal Antarctica.

To investigate mass size distributions of water-soluble ions in aerosols in the marine boundary layer (MBL) over the Southern Ocean, size-segregated (0.056-18 μm in aerodynamic diameter) aerosols were collected on the 28th Chinese National Antarctic Research Expedition (CHINARE) cruise from November 2011 to March 2012. Major water-soluble inorganic and organic species in aerosols were analyzed by ion chromatography (IC). Results showed that high loadings of aerosol mass were observed over the western sector of the Southern Ocean, attributed to the high mass loadings of Na+ and Cl- in the particles >1.0 μm in diameter and high mass loadings of non-sea-salt (nss) SO42- and methanesulfonate (MSA) in the particles <1.0 μm in diameter. Nss-SO42- and MSA accounted for ∼40% of the total mass in aerosols with particle size <0.56 μm over the eastern sector of the Southern Ocean, while it was elevated to more than 60% over the western sector of the Southern Ocean that could be linked with high marine productivity reflected by high chlorophyll-a occurrence in surface waters in that region. MSA/nss-SO42- ratios showed an increasing trend as latitude increased in the southern hemisphere with a dramatic increase south of 60 °S and the variation of MSA may shape the spatial distribution of the ratios. High MSA concentration and MSA/nss-SO42- ratios were observed in west Antarctica, especially in the supermicron particles. A bimodal mass size distribution of total Ca2+ with a small peak in the 0.18-0.32 μm size range was observed, suggesting different sea spray aerosol (SSA) production mechanisms. Nss-SO42-, MSA was mainly enriched in the particle size range of 0.18 μm to 0.56 μm. The concentrations of formate and oxalate were low and detected only in certain size particles, mainly in the range <0.56-1.8 μm. Further studies should be conducted over the remote Southern Ocean to reveal marine ecosystem-aerosol-climate interactions.

Characteristics of the Size Distribution of Water-soluble Ions During a Heavy Pollution Episode in the Winter in Tianjin

To characterize the size distribution of water-soluble inorganic ions (WSⅡ) during a heavy pollution episode, particle samples were collected by an Andersen cascade sampler in Tianjin in January 2014, and the concentrations of eight WSⅡ (Na+, NH4+, K+, Mg2+, Ca2+, Cl-, NO3-, and SO42-) during a typical haze episode were analyzed by ion chromatography. The sources and formation mechanisms of WSⅡ were analyzed based on their size distributions. The results showed that the daily average concentrations of PM2.5 and PM10 were (138±100) μg·m-3 and (227±142) μg·m-3, respectively, and the average concentration of total WSⅡ concentrations (TWSⅡ) in the coarse and fine particles were (34.07+6.16) μg·m-3 and (104.16+51.76) μg·m-3, respectively. The concentrations of SO42-, NO3-, and NH4+ in the fine particles were much higher than concentrations of the other ions, and there were strong correlations between these three ions. The TWSⅡ on clear days, light pollution days, and heavy pollution days were (41.55±12.41) μg·m-3, (94.46±31.19) μg·m-3, and (147.55±27.76) μg·m-3, respectively. On clear days, SO42- showed a unimodal distribution, peaking at 0.43-0.65 μm; and NO3- showed a trimodal distribution, peaking at 0.43-0.65 μm, 2.1-3.3 μm, and 5.8-9.0 μm. NH4+ had a bimodal distribution, peaking at 0.43-0.65 μm and 4.7-5.8 μm. On heavy pollution days, however, the size distributions of these three secondary inorganic ions switched to a unimodal size distribution, peaking at 0.65-1.1 μm. Unimodal NH4+ mainly coexisted with SO42- and NO3-, and the excess NH4+ was found to be combined with Cl- in the fine particles. In the coarse particles, NH4+ completely coexisted with SO42- and NO3-.

Seasonal variations and size distributions of water-soluble ions of atmospheric particulate matter at Shigatse, Tibetan Plateau.

Size-segregated atmospheric particulate matter (PM) samples were collected from July 2012 to September 2013 at Shigatse, high-altitude (3836 m above sea level) site on the south Tibetan Plateau (TP); objectives were to determine the characteristics and size distribution of water-soluble ions (WSIs). Eight major WSIs (Na(+), K(+), Mg(2+), Ca(2+), NH4(+), Cl(-), SO4(2-), and NO3(-)) were detected by ion chromatography. The total concentrations of WSIs were 6370 ± 1916 ng m(-3) in dry season (October - December, January - April), and 5261 ± 769 ng/m(3) during wet phase (May - September). The contribution of K(+) (130 ng m(-3)), Cl(-) (2035 ng m(-3)), SO4(2-) (1176 ng m(-3)), and NO3(-) (706 ng m(-3))(-)were significantly enhanced in dry season, and that of Na(+) (455 ng m(-3)), Mg(2+)(65.4 ng m(-3)), Ca(2+)(1034 ng m(-3)), and NH4(+) (1948 ng m(-3)) were significantly enhanced during wet phase. Mg(2+) and Ca(2+) were concentrated in the coarse mode, and the other ions concentrated in fine mode and coarse mode during two seasons. The correlation coefficients between K(+) and NH4(+), Cl(-), SO4(2-) and NO3(-) were 0.58 (P < 0.01), 0.40 (P < 0.05), 0.82 (P < 0.01) and 0.69 (P < 0.01), indicating their dominant contribution from biomass burning in dry season. The significant correlation between NH4(+) and HCO3(-) which were calculated by ion balance (r = 0.89, P < 0.01), suggesting the source from nitrogen fertilizers during wet phase.

Seasonal variations and size distributions of water-soluble ions in atmospheric aerosols in Beijing, 2012

The characteristics of water-soluble ions in airborne particulate matter in Beijing were investigated using ion chromatography. The results showed that the total concentrations of ions were 83.7±48.9μg/m3 in spring, 54.0±17.0μg/m3 in summer, 54.1±42.9μg/m3 in autumn, and 88.8±47.7μg/m3 in winter, respectively. Furthermore, out of all the ions, NO3−, SO42− and NH4+ accounted for 81.2% in spring, 78.5% in summer, 74.6% in autumn, and 76.3% in winter. Mg2+ and Ca2+ were mainly associated with coarse particles, with a peak that ranged from 5.8 to 9.0μm. Na+, NH4+ and Cl− had a multi-mode distribution with peaks that ranged from 0.43 to 1.1μm and 4.7 to 9.0μm. K+, NO3−, and SO42− were mainly associated with fine particles, with a peak that ranged from 0.65 to 2.1μm. The concentrations of Na+, K+, Mg2+, Ca2+, NH4+, Cl−, NO3− and SO42− were 2.69, 2.32, 1.01, 4.84, 16.9, 11.8, 42.0, and 44.1μg/m3 in particulate matter (PM) on foggy days, respectively, which were 1.4 to 7.3 times higher than those on clear days. The concentrations of these ions were 2.40, 1.66, 0.92, 4.95, 17.5, 7.00, 32.6, and 34.7μg/m3 in PM on hazy days, respectively, which were 1.2–5.7 times higher than those on clear days.