Characterization Of Water-soluble Inorganic Ions Research Articles

Source apportionment of PM2.5 and sulfate formation during the COVID-19 lockdown in a coastal city of southeast China

Revealing the changes in chemical compositions and sources of PM2.5 is important for understanding aerosol chemistry and emission control strategies. High time-resolved characterization of water-soluble inorganic ions, elements, organic carbon (OC), and elemental carbon (EC) in PM2.5 was conducted in a coastal city of southeast China during the COVID-19 pandemic. The results showed that the average concentration of PM2.5 during the city lockdown (CLD) decreased from 46.2 μg m−3 to 24.4 μg m−3, lower than the same period in 2019 (PM2.5: 37.1 μg m−3). Concentrations of other air pollutants, such as SO2, NO2, PM10, OC, EC, and BC, were also decreased by 27.3%–67.8% during the CLD, whereas O3 increased by 28.1%. Although SO2 decreased from 4.94 μg m−3to 1.59 μg m−3 during the CLD, the concentration of SO42− (6.63 μg m−3) was comparable to that (5.47 μg m−3) during the non-lockdown period, which were attributed to the increase (16.0%) of sulfate oxidation rate (SOR). Ox (O3+NO2) was positively correlated with SO42−, suggesting the impacts of photochemical oxidation. A good correlation (R2 = 0.557) of SO42− and Fe and Mn was found, indicating the transition-metal ion catalyzed oxidation. Based on positive matrix factorization (PMF) analysis, the contribution of secondary formation to PM2.5 increased during the epidemic period, consisting with the increase of secondary organic carbon (SOC), while other primary sources including traffic, dust, and industry significantly decreased by 9%, 8.5%, and 8%, respectively. This study highlighted the comprehensive and nonlinear response of chemical compositions and formation mechanisms of PM2.5 to anthropogenic emissions control under relatively clean conditions.

Highly size-resolved characterization of water-soluble inorganic ions in submicron atmospheric particles

Up to date, few attentions have been given to the special characterization of water-soluble inorganic ions (WSIs) in the submicron atmospheric particles. In this study, to implement a highly size-resolved characterization of WSIs in the submicron atmospheric particles, ten sets of size-segregated submicron atmospheric particles were collected in Hangzhou (China) from November to December 2015, with cut-off diameters of 0.060, 0.108, 0.170, 0.260, 0.400, 0.650, and 1.000 μm. The particulate WSIs, including Cl−, NO3−, SO42−, Na+, NH4+, K+, and Ca2+ were analyzed by ion chromatography, and their mode distributions and potential sources were assessed. It was found that the particulate WSIs constituted a substantial part (40.4~70.9%) in each fraction of submicron particles, of which the secondary inorganic ions (SO42−, NO3−, and NH4+) were the dominant species. The sulfur oxidation rate (SOR) and nitrogen oxidation rate (NOR) were increased when the submicron particles became coarser, indicating the enhanced secondary formation processes of SO42− and NO3− in the coarser submicron particles, thus resulting in the higher fractional contribution of secondary inorganic aerosols in the coarser submicron atmospheric particles. The correlation coefficients between K+ and Cl−, NO3−, and SO42− were 0.9293 (P = 0.002), 0.9702 (P < 0.001), and 0.9723 (P < 0.001), suggesting their dominant contribution from the biomass burning. Furthermore, it was found that PM0.4–1 (aerodynamic diameter of 0.400–1.000 μm) was a substantial part (66.6%) of submicron atmospheric particles. Compared to PM0.4 (aerodynamic diameter ≤ 0.400 μm), the concentration of WSIs in PM0.4–1 was prominently higher, and the secondary formation processes of SO42− and NO3− in PM0.4–1 were significantly enhanced.

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.

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.

Characterization of water-soluble inorganic ions in size-segregated aerosols in coastal city, Xiamen

The samples of water-soluble inorganic ions (WSIs), including anions (F−, Cl−, SO42−, NO3−) and cations (NH4+, K+, Na+, Ca2+, Mg2+) in 8 size-segregated particle matter (PM), were collected using a sampler (with 8 nominal cut-sizes ranged from 0.43 to 9.0μm) from October 2008 to September 2009 at five sites in both polluted and background regions of a coastal city, Xiamen. The results showed that particulate matters in the fine mode (PM2.1, Dp<2.1μm) comprised large part of mass concentrations of aerosols, which accounted for 45.56–51.27%, 40.04–60.81%, 42.02–60.81%, and 40.46–57.07% of the total particulate mass in spring, summer, autumn, and winter, respectively. The water-soluble ionic species in the fine mode at five sampling sites varied from 15.33 to 33.82 (spring), 14.03 to 28.06 (summer), 33.47 to 72.52 (autumn), and 48.39 to 69.75μgm−3 (winter), respectively, which accounted for 57.30±6.51% of the PM2.1 mass concentrations. Secondary pollutants of NH4+, SO42− and NO3− were the dominant contributors of WSIs, which suggested that pollutants from anthropogenic activities, such as SO2, NOx were formed in aerosols by photochemical reactions. The size distributions of Na+, Cl−, SO42− and NO3− were bimodal, peaking at 0.43–0.65μm and 3.3–5.8μm. Although some ions, such as NH4+ presented bimodal distributions, the coarse mode was insignificant compared to the fine mode. Ca2+ and Mg2+ exhibited unimodal distributions at all sampling sites, peaking at 2.1–3.3μm, while K+ having a bimodal distributions with a major peak at 0.43–0.65μm and a minor one at 3.3–4.7μm, were used in most of samples. Seasonal and spatial variations in the size-distribution profiles suggested that meteorological conditions (seasonal patterns) and sampling locations (geographical patterns) were the main factors determining the formation of secondary aerosols and characteristics of size distributions for WSIs.