Fabrication of nano-sized Ca(OH)2 with excellent adsorption ability for N2O4

Uniform nano-sized calcium hydroxide (Ca(OH)₂) monocrystal powder was synthesized from calcium oxide in a surfactant solution via a digestion method by decreasing the surface tension of the reaction system to control the growth of crystalline Ca(OH)₂. The Ca(OH)₂ monocrystal powder samples were characterized by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), and Fourier transform-infrared spectroscopy (FT-IR). The NO_x adsorption ability of the samples was evaluated, and the influence of various types and concentrations of surfactants on powder agglomeration and then the specific surface area in the precipitation process were studied. The specific surface area of the samples was found as high as 58 m²/g and 92 m²/g and the particle size, 300–400 nm and 200–300 nm in the presence of 10 wt% PEG600 and 0.086 mL/L SDS at a reaction time of 5 h, respectively. The product has an exceptionally strong adsorption ability for NO_x, which makes it a highly promising adsorbent for emission control and air purification.     

Real-time measurements of PM2.5, PM10–2.5, and BC in an urban street canyon

A continuous dichotomous beta gauge monitor was used to characterize the hourly content of PM_2.5, PM_10–2.5, and Black Carbon (BC) over a 12-month period in an urban street canyon of Hong Kong. Hourly vehicle counts for nine vehicle classes and meteorological data were also recorded. The average weekly cycles of PM_2.5, PM_10–2.5, and BC suggested that all species are related to traffic, with high concentrations on workdays and low concentrations over the weekends. PM_2.5 exhibited two comparable concentrations at 10:00–11:00 (63.4 μg/m³) and 17:00–18:00 (65.0 μg/m³) local time (LT) during workdays, corresponding to the hours when the numbers of diesel-fueled and gasoline-fueled vehicles were at their maximum levels: 3179 and 2907 h⁻¹, respectively. BC is emitted mainly by diesel-fueled vehicles and this showed the highest concentration (31.2 μg/m³) during the midday period (10:00–11:00 LT) on workdays. A poor correlation was found between PM_2.5 concentration and wind speed (R = 0.51, P-value > 0.001). In contrast, the concentration of PM_10–2.5 was found to depend upon wind speed and it increased with obvious statistical significance as wind speed increased (R = 0.98, P-value < 0.0001).     

Flow boiling heat transfer of R134a,R236fa and R245fa in a horizontal 1.030 mm circular channel

This research focuses on acquiring accurate flow boiling heat transfer data and flow pattern visualization for three refrigerants, R134a, R236fa and R245fa in a 1.030 mm channel. We investigate trends in the data, and their possible mechanisms, for mass fluxes from 200 to 1600 kg/m²s, heat fluxes from 2.3 kW/m² to 250 kW/m² at T_sat = 31 °C and ΔT_sub from 2 to 9 K. The local saturated flow boiling heat transfer coefficients display a heat flux and a mass flux dependency but no residual subcooling influence. The changes in heat transfer trends correspond well with flow regime transitions. These were segregated into the isolated bubble (IB) regime, the coalescing bubble (CB) regime, and the annular (A) regime for the three fluids. The importance of nucleate boiling and forced convection in these small channels is still relatively unclear and requires further research.     

A novel method for fast and continuous preparation of superfine titanium dioxide nanoparticles in microfluidic system

Previously we had developed a microfluidic system that can be easily fabricated by bending a stainless-steel tube into large circular loops. In this study, a fast and continuous preparation method for superfine TiO₂ nanoparticles (TiO₂-NPs) was developed for the aforementioned microfluidic system. The proposed method can yield anatase TiO₂ in 3.5 min, in contrast to the traditional hydrothermal reaction method, which requires hours or even days. Different reaction conditions, such as reaction temperature (120–200 °C), urea concentration (20–100 g/L), and tube length (5–20 m) were investigated. X-ray diffraction and Brunauer–Emmett–Teller analysis indicate that the as-prepared TiO₂-NPs have crystalline sizes of 4.1–5.8 nm and specific surface areas of 250.7–330.7 m²/g. Transmission electron microscopy images show that these TiO₂-NPs have an even diameter of approximately 5 nm. Moreover, because of their small crystalline sizes and large specific surface areas, most of these as-prepared TiO₂-NPs exhibit considerably better absorption and photocatalytic performance with methylene blue than commercial P5 TiO₂ does.     

Controllable hydrothermal synthesis of star-shaped Sr3Fe2(OH)12 assemblies and their thermal decomposition and magnetic properties

Pure phase star-shaped hydrogarnet Sr₃Fe₂(OH)₁₂ assemblies were synthesized by a mild hydrothermal method (210 °C, 12 h), and the effects of the preparation conditions on the phase composition of the product were investigated. It was found that the impurity phases could be decreased or eliminated by increasing the molar ratio of Sr²⁺ to Fe³⁺, and that high temperatures favored the formation of Sr₃Fe₂(OH)₁₂ and reduced the concentration of CO₃^2–-containing byproducts. The thermal decomposition of the star-shaped Sr₃Fe₂(OH)₁₂ assemblies was examined, and the results showed that the dehydration process at higher temperatures is accompanied by the formation of SrFeO_3–δ. Above 655 °C, a solid state reaction between the SrFeO_3–δ and Sr(OH)₂ or SrCO₃ results in the formation of Sr₄Fe₃O_10–δ.The magnetic properties of the as-synthesized Sr₃Fe₂(OH)₁₂ and of samples calcined at different temperatures were assessed. A sample calcined at 575 °C exhibited greatly enhanced ferromagnetic properties, with a remanent magnetization of 1.28 emu/g and a coercivity of 4522.1 Oe at room temperature.     

Chemical characteristics of PM2.5 during dust storms and air pollution events in Chengdu,China

Daily fine particulate (PM_2.5) samples were collected in Chengdu from April 2009 to February 2010 to investigate their chemical profiles during dust storms (DSs) and several types of pollution events, including haze (HDs), biomass burning (BBs), and fireworks displays (FDs). The highest PM_2.5 mass concentrations were found during DSs (283.3 μg/m³), followed by FDs (212.7 μg/m³), HDs (187.3 μg/m³), and BBs (130.1 μg/m³). The concentrations of most elements were elevated during DSs and pollution events, except for BBs. Secondary inorganic ions (NO₃^?, SO₄^2?, and NH₄⁺) were enriched during HDs, while PM_2.5 from BBs showed high K⁺ but low SO₄^2?. FDs caused increases in K⁺ and enrichment in SO₄^2?. Ca²⁺ was abundant in DS samples. Ion-balance calculations indicated that PM_2.5 from HDs and FDs was more acidic than on normal days, but DS and BB particles were alkaline. The highest organic carbon (OC) concentration was 26.1 μg/m³ during FDs, followed by BBs (23.6 μg/m³), HDs (19.6 μg/m³), and DSs (18.8 μg/m³). In contrast, elemental carbon (EC) concentration was more abundant during HDs (10.6 μg/m³) and FDs (9.5 μg/m³) than during BBs (6.2 μg/m³) and DSs (6.0 μg/m³). The highest OC/EC ratios were obtained during BBs, with the lowest during HDs. SO₄^2?/K⁺ and TCA/SO₄^2? ratios proved to be effective indicators for differentiating pollution events. Mass balance showed that organic matter, SO₄^2?, and NO₃^? were the dominant chemical components during pollution events, while soil dust was dominant during DSs.     

Size and shape effects on magnetic properties of Ni nanoparticles

Pure Ni nanoparticles ranging in size from 24 to 200 nm are prepared via thermal decomposition of nickel acetylacetonate in oleylamine. The as-prepared Ni particles change from spherical to dendritic or starlike with increasing precursor concentration. The particles are stable because the organic coating occurs in situ. Magnetic measurement reveals that all the Ni nanoparticles are ferromagnetic and show ferromagnetic–paramagnetic transitions at their Curie points. The saturation magnetization M_s is size-dependent, with a maximum value of 52.01 and 82.31 emu/g at room temperature and 5 K, respectively. The coercivity decreases at first and then increases with increasing particle size, which is attributed to the competition between size effect and shape anisotropy. The Curie temperature T_c is 593, 612, 622, 626 and 627 K for the 24, 50, 96, 165 and 200 nm Ni nanoparticles, respectively. A theoretical model is proposed to explain the size-dependence of Ni nanoparticle Curie temperature.     

Large-scale synthesis of hierarchical MnO2 for benzene catalytic oxidation

Hierarchical sea-urchin-shaped manganese oxide microspheres were synthesized via a facile method based on the reaction between KMnO₄ and MnSO₄ in HNO₃ solution at 50 °C. The average diameter of the microspheres is ∼850 nm. The microspheres consist of a core of diameter of ∼800 nm and nanorods of width ∼50 nm. The nanorods exist at the edge of the core. The Brunauer–Emmett–Teller surface area of the sea-urchin-shaped microspheres is 259.4 m²/g. A possible formation mechanism of the hierarchical sea-urchin-shaped microspheres is proposed. The temperature for 90% conversion of benzene (T_90%) on the hierarchical urchin-shaped MnO₂ microspheres is about 218 °C.     

Drag reduction for liquid flow through micro-apertures

Pressure drops in the flow through micro-orifices and capillaries were measured for silicone oils, aqueous solutions of polyethylene glycol (PEG), and surfactant aqueous solutions. The diameter of micro-orifices ranged from 5 μm to 400 μm. The corresponding length/diameter ratio was from 4 to 0.05 and capillary diameters were 105 μm and 450 μm. The following results were obtained: silicone oils of 10^?6 m²/s and 10^?5 m²/s in kinematic viscosity generated a reduction of pressure drop (RPD), that is, drag reduction, similar to the RPD of water and a glycerol/water mixture reported in the previous paper by the present authors. When RPD occurred, the pressure drop (PD) of silicone oils of 10^?6 m²/s and 10^?5 m²/s had nearly the same magnitude. Namely, the difference in viscosity did not influence RPD. A 10³ ppm aqueous solution of PEG20000 provided almost the same PD as that of PEG8000 for the 400 μm to 15 μm orifices, but a greater PD than that of PEG8000 for the 10 μm to 5 μm orifices. A non-ionic surfactant and a cationic surfactant were highly effective in RPD compared with anionic surfactants: the non-ionic and cationic surfactant solutions had PD one order of magnitude lower than that of water under some flow conditions in the concentration range from 1 ppm to 10⁴ ppm, but the anionic surfactant solutions did not generate RPD except in the case of the smallest orifice of 5 μm in diameter. The PD of the non-ionic surfactant solution showed a steep rise at a Reynolds number (Re_t) for 400 μm to 15 μm orifices. The Re_t provides the relationship Re_t = K/D, where D is the orifice diameter, and K is a constant of 2 × 10^?2 m for the 100–20 μm orifices irrespective of liquid concentration. Capillary flow experiment revealed that the PEG, non-ionic and cationic surfactant solutions generated RPD also in a laminar flow through the capillary of 105 μm in diameter, but not in the flow through the capillary of 450 μm in diameter. In order to clarify the cause of RPD, an additional experiment was carried out by changing the orifice material from metal to acrylic resin. The result gave a different appearance of RPD, suggesting that RPD is related to an interfacial phenomenon between the liquid and wall. The large RPDs found in the present experiment are very interesting from both academic and practical viewpoints.     

Synthesis of potassium sodium niobate powders using an EDTA/citrate complexing sol–gel method

Potassium sodium niobate (KNN) powders were synthesized by a modified sol–gel method, using as starting chemicals potassium carbonate, sodium carbonate, and niobium hydroxide, and, as esterification and chelating agents, respectively, ethylene glycol (EG) and ethylene diamine tetraacetic acid (EDTA)/citrate. The effects of citric acid (CA), EG, and EDTA on the stability of the precursor sol were systemically investigated. The powders and gels were characterized by X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, and thermogravimetric analysis-differential scanning calorimetry (TGA-DSC). The results indicated that a stable precursor sol was formed when n(CA):n(Mⁿ⁺) = 3:1, n(EDTA):n(NH₄OH) = 1:3.5, and n(CA):n(EG) = 1:2. The xerogel was calcined at 500–950 °C to prepare the KNN powder. Pure KNN perovskite phase with a cube-like structure was synthesized at 850 °C from the precursor sol for a K/Na molar ratio of 1.2. The formation mechanism of the KNN perovskite phase was also discussed.     

Evolution of planetary boundary layer under different weather conditions,and its impact on aerosol concentrations

A field experiment was conducted in Tianjin, China from September 9–30, 2010, focused on the evolution of Planetary Boundary Layer (PBL) and its impact on surface air pollutants. The experiment used three remote sensing instruments, wind profile radar (WPR), microwave radiometer (MWR) and micro-pulse lidar (MPL), to detect the vertical profiles of winds, temperature, and aerosol backscattering coefficient and to measure the vertical profiles of surface pollutants (aerosol, CO, SO₂, NO_x), and also collected sonic anemometers data from a 255-m meteorological tower. Based on these measurements, the evolution of the PBL was estimated. The averaged PBL height was about 1000–1300 m during noon/afternoon-time, and 200–300 m during night-time. The PBL height and the aerosol concentrations were anti-correlated during clear and haze conditions. The averaged maximum PBL heights were 1.08 and 1.70 km while the averaged aerosol concentrations were 52 and 17 μg/m³ under haze and clear sky conditions, respectively. The influence of aerosols and clouds on solar radiation was observed based on sonic anemometers data collected from the 255-m meteorological tower. The heat flux was found significantly decreased by haze (heavy pollution) or cloud, which tended to depress the development of PBL, while the repressed structure of PBL further weakened the diffusion of pollutants, leading to heavy pollution. This possible positive feedback cycle (more aerosols → lower PBL height → more aerosols) would induce an acceleration process for heavy ground pollution in megacities.     

Fabrication of magnetic nanosized γ-FeNi-coated ceramic core–shell microspheres by heterogeneous precipitation and thermal reduction

Precursors with NiCO₃·2Ni(OH)₂·2H₂O- and Fe₂O₃·nH₂O-coated alumina, graphite and cenosphere were synthesized by precipitation using ferrous sulfate, nickel sulfate, ammonium bicarbonate, alumina, graphite and cenosphere as the main starting materials. Magnetic γ-FeNi-coated alumina, graphite and cenosphere core–shell structural microspheres were subsequently prepared by thermal reduction of the as-prepared precursors at 600 °C for 2 h. Precipitation parameters, e.g. concentration of ceramic micropowders (10 g/L), sulfate solution (0.2 mol/L), rate of adding reactants (3 mL/min) and pH value were optimized by a trial-and-error method. Powders of the precursors and the resulting coating of γ-FeNi with grain size below 40 nm on alumina, graphite and cenosphere microspheres were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The magnetic properties of the nanosize γ-FeNi-coated alumina, graphite and cenosphere microspheres were measured by vibrating sample magnetometer (VSM). The results show that the core–shell structural γ-FeNi-coated ceramic microspheres exhibited higher coercivity than pure γ-FeNi powders, indicating that these materials can be used for high-performance functional materials and devices.     

An evaluation of mass,number concentration,chemical composition and types of particles in a cafeteria before and after the passage of an antismoking law

This study assessed air quality indicators before and after enactment of the Spanish anti-smoking law. Mass and number concentrations and the chemical composition of particles were evaluated. Microscopy analyses were also conducted. Real time concentrations of PM₁₀, PM_2.5, PM₁ and ultrafine particles were measured under ventilated and non-ventilated conditions and PM₁₀ samples were collected for detailed inorganic and organic chemical characterization. Before enactment of the law in 2010, tobacco smoke produced significant indoor ambient particulate matter pollution, with elevated particulate matter mass concentrations (PM₁₀ and PM₁ concentrations of 122–220 and 48–85 μg/m³, respectively) and ultrafine particle numbers (75,000 and 48,000 cm^–3 under ventilated and non-ventilated conditions, respectively). Typical tobacco smoke tracers including iso- and anteiso-alkanes and elements including La and Ce from the ignition of lighters were abundant. Additionally, several toxic substances derived from tobacco smoke, including Cd (3.1 ng/m³) and benzo[a]pyrene (1.0 ng/m³) were present at concentrations approximately 10 times greater than those measured after enactment of the anti-smoking law. The anti-smoking law significantly reduced exposure to potentially toxic compounds by approximately 90%. This law is expected to have a positive health impact, particularly for people who spend considerable time in affected environments, such as employees.     

Synthesis of layered cathode materials Li[CoxNiyMn1−x−y]O2 from layered double hydroxide precursors

Cathode materials Li[Co_xNi_yMn_1?x?y]O₂ for lithium secondary batteries have been prepared by a new route using layered double hydroxides (LDHs) as a precursor. The resulting layered phase with the α-NaFeO₂ structure crystallizes in the rhombohedral system, with space group R-3m having an interlayer spacing close to 0.47 nm. X-ray photoelectron spectroscopy (XPS) was used to measure the oxidation states of Co, Ni and Mn. The effects of varying the Co/Ni/Mn ratio on both the structure and electrochemical properties of Li[Co_xNi_yMn_1?x?y]O₂ have been investigated by X-ray diffraction and electrochemical tests. The products demonstrated a rather stable cycling behavior, with a reversible capacity of 118 mAh/g for the layered material with Co/Ni/Mn = 1/1/1.     

The contribution of small leaks in a baghouse filter to dust emission in the PM2.5 range—A system approach

The contribution of leakage in a baghouse filter (defined as a short circuit between the upstream and downstream sides of the filter) to the emission of fine particles is quantified in comparison to other dust emission sources, and the influence of key operating variables on overall system response is analyzed. The study was conducted on a well-maintained pilot-scale filter unit (9 bags of 500 g/m² calendered polyester needle felt; total surface area 4.2 m²) operated in Δp-controlled mode over a range of pulsing intensities, with two types of test dust (one free-flowing and the other cohesive) at inlet concentrations of 10 and 30 g/m³. Leaks included single holes between 0.5 and 4 mm diameter, intentionally placed in either the plenum plate or one of the filter bags, as well as seamlines from bag confectioning. Emissions were separated by source into a transient contribution due to dust penetration through the filter bags after each cleaning pulse, and a continuous contribution from leaks. This separation was based on a novel method of data processing that relies on time-resolved concentration measurements with a specially calibrated optical particle counter. Tiny leaks on the order of 1 mm generated the same emission level as all the bags combined, and dominated continuous emissions. The equivalent leak cross section (leakage = media emission) was about 1 ppm of the total installed filter surface, independent of upstream dust concentration. Leakage through open seamlines amounted to 75% of media emissions in case of free-flowing test dust. Leakage was restricted to aerodynamic diameters less than ∼5 μm (roughly the PM_2.5 mass fraction). For comparison, time-averaged mass penetration through conventional needle-felt media ranged from about 10⁻⁵ to 10⁻⁶, depending on cohesiveness of the particle material and pulse cleaning intensity, giving emission levels between about 0.02 and 0.2 mg/m³ at the reference concentration of 10 g/m².     

Mass and isotopic concentrations of water-insoluble refractory carbon in total suspended particulates at Mt. Waliguan Observatory (China)

Mass concentration and isotopic values δ¹³C and ¹⁴C are presented for the water-insoluble refractory carbon (WIRC) component of total suspended particulates (TSP), collected weekly during 2003, as well as from October 2005 to May 2006 at the WMO-GAW Mt. Waliguan (WLG) site. The overall average WIRC mass concentration was (1183 ± 120) ng/m³ (n = 79), while seasonal averages were 2081 ± 1707 (spring), 454 ± 205 (summer), 650 ± 411 (autumn), and 1019 ± 703 (winter) ng/m³. Seasonal variations in WIRC mass concentrations were consistent with black carbon measurements from an aethalometer, although WIRC concentrations were typically higher, especially in winter and spring. The δ¹³C PDB value (−25.3 ± 0.8)‰ determined for WIRC suggests that its sources are C₃ biomass or fossil fuel combustion. No seasonal change in δ¹³C PDB was evident. The average percent Modern Carbon (pMC) for ¹⁴C in WIRC for winter and spring was (67.2 ± 7.7)% (n = 29). Lower pMC values were associated with air masses transported from the area east of WLG, while higher pMC values were associated with air masses from the Tibetan Plateau, southwest of WLG. Elevated pMC values with abnormally high mass concentrations of TSP and WIRC were measured during a dust storm event.     

Magnetic and electrochemical behavior of rhombohedral α-Fe2O3 nanoparticles with (1 0 4) dominant facets

Uniform rhombohedral α-Fe₂O₃ nanoparticles, ～60 nm in size, were synthesized via a triphenylphosphine-assisted hydrothermal method. Scanning electron micrograph (SEM) and transmission electron micrograph (TEM) analyses showed that the as-synthesized rhombohedral nanoparticles were enclosed by six (1 0 4) planes. The concentration of triphenylphosphine played an important role in morphological evolution of the α-Fe₂O₃ nanoparticles. The as-prepared rhombohedral nanoparticles possessed remanent magnetization M_r of 2.6 × 10^?3 emu/g and coercivity H_C of 2.05 Oe, both lower than those of other α-Fe₂O₃ particles with similar size, indicating their potential applications as superparamagnetic precursor materials. Furthermore, these rhombohedral α-Fe₂O₃ nanoparticles exhibited good sensor capability toward H₂O₂ with a linear response in the concentration range of 2–20 mM.     

Catalytic oxidation of benzene over Ce–Mn oxides synthesized by flame spray pyrolysis

Flame spray pyrolysis (FSP) was utilized to synthesize Ce–Mn oxides in one step for catalytic oxidation of benzene. Cerium acetate and manganese acetate were used as precursors. The materials synthesized were characterized using X-ray diffraction (XRD), N₂ adsorption, X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), Raman spectroscopy, and H₂-temperature programmed reduction (H₂-TPR) and their benzene catalytic oxidation behavior was evaluated. Mn ions were evidenced in multiple chemical states. Crystalline Ce–Mn oxides consist of particles with size <40 nm and specific surface areas (SSA) of 20–50 m²/g. Raman spectrums and H₂-TPR results indicated the interaction between cerium and manganese oxides. Flame-made 12.5%-Ce–Mn oxide exhibited excellent catalytic activity at relatively low temperatures (T₉₅ about 260 °C) compared to other Ce–Mn oxides with different cerium-to-manganese ratios. Redox mechanism and strong interaction conform to structure analysis that Ce–Mn strong interaction formed during the high temperature flame process and the results were used to explain catalytic oxidation of benzene.     

Controlled synthesis of Ce(OH)CO3 flowers by a hydrothermal method and their thermal conversion to CeO2 flowers

Highly uniform Ce(OH)CO₃ flowers were successfully prepared in large quantities using a facile hydrothermal approach from the reaction of Ce(NH₄)(NO₃)₄ with CO(NH₂)₂ at 160 °C in a water–N₂H₄ complex. The influences of the N₂H₄ content and temperature on flower formation were discussed. CeO₂ flowers were prepared by thermal conversion of Ce(OH)CO₃ flowers at 500 °C in air. Both Ce(OH)CO₃ and CeO₂ flowers were characterized by X-ray powder diffraction (XRD), and scanning electron microscopy (SEM). The UV–vis adsorption spectrum of the CeO₂ flowers showed that the band gap energy (E_g) is 2.66 eV, which is lower than that of bulk ceria.     

Emission of organic carbon,elemental carbon and water-soluble ions from crop straw burning under flaming and smoldering conditions

Emissions from major agricultural residues were measured using a self-designed combustion system. Emission factors (EFs) of organic carbon (OC), elemental carbon (EC), and water-soluble ions (WSIs) (K⁺, NH₄⁺, Na⁺, Mg²⁺, Ca²⁺, Cl⁻, NO₃⁻, SO₄^2–) in smoke from wheat and rice straw were measured under flaming and smoldering conditions. The OC₁/TC (total carbon) was highest (45.8% flaming, 57.7% smoldering) among carbon fractions. The mean EFs for OC (EF_OC) and EC (EF_EC) were 9.2 ± 3.9 and 2.2 ± 0.7 g/kg for wheat straw and 6.4 ± 1.9 and 1.1 ± 0.3 g/kg for rice straw under flaming conditions, while they were 40.8 ± 5.6 and 5.8 ± 1.0 g/kg and 37.6 ± 6.3 and 5.0 ± 1.4 g/kg under smoldering conditions, respectively. Higher EC ratios were observed in particulate matter (PM) mass under flaming conditions. The OC and EC for the two combustion patterns were significantly correlated (p < 0.01, R = 0.95 for wheat straw; p < 0.01, R = 0.97 for rice straw), and a higher positive correlation between OC₃ and EC was observed under both combustion conditions. WSIs emitted from flaming smoke were dominated by Cl⁻ and K⁺, which contributed 3.4% and 2.4% of the PM mass for rice straw and 2.2% and 1.0% for wheat straw, respectively. The EFs of Cl⁻ and K⁺ were 0.73 ± 0.16 and 0.51 ± 0.14 g/kg for wheat straw and 0.25 ± 0.15 and 0.12 ± 0.05 g/kg for rice straw under flaming conditions, while they were 0.42 ± 0.28 and 0.12 ± 0.06 g/kg and 0.30 ± 0.27 and 0.05 ± 0.03 g/kg under smoldering conditions, respectively. Na⁺, Mg²⁺, and NH₄⁺ were vital components in PM, comprising from 0.8% (smoldering) to 3.1% (flaming) of the mass. Strong correlations of Cl⁻ with K⁺, NH₄⁺, and Na⁺ ions were observed in rice straw and the calculated diagnostic ratios of OC/EC, K⁺/Na⁺ and Cl⁻/Na⁺ could be useful to distinguishing crop straw burning from other sources of atmospheric pollution.