In this work, the removal of methyl orange (MO) dye by adsorption on silver nanoparticles (AgNPs) coated activated carbon (AC) has been studied. The effect of various process parameters has been investigated by the column adsorption technique. Equilibrium adsorption data of MO were carried out at room temperature. Using AgNPs-coated AC, 72.5 % of MO was removed, whereas only 50.0 % when using AC after reacting for 16 h with an initial MO concentration of 2 mg/L (pH = 7). The equilibrium time is independent of the initial dye concentration and the percentage removal of MO increased with increase in contact time. The adsorption data were analyzed using adsorption isotherm. The characteristic parameters for isotherm and related correlation coefficients were determined from graphs of their linear equations. Kinetic studies showed that the adsorption of MO followed pseudo-second-order kinetics. AgNPs-coated AC is found to be suitable adsorbent for the adsorption of MO. Desorption studies were made to elucidate recovery of the adsorbate and adsorbent for the economic competitiveness of the removal system. The AgNPs-coated AC was successfully recycled for 10 successive adsorption–desorption cycles indicating its high reusability.

PM_2.5 aerosol samples were collected from the Chinese megacity of Nanjing (32.21^∘ N, 118.73^∘ E) during winter and analyzed for a total of 127 compounds from 12 organic compound classes. The most abundant classes of compounds were n-alkanes (mean concentration of 205 ng m⁻³), followed by fatty acids (76.3 ng m⁻³), polycyclic aromatic hydrocarbons (PAHs; 64.3 ng m⁻³), anhydrosugars (56.3 ng m⁻³), fatty alcohols (40.5 ng m⁻³) and phthalate esters (15.2 ng m⁻³), whereas hydroxy-/polyacids (8.33 ng m⁻³), aromatic acids (7.35 ng m⁻³), hopanes (4.19 ng m⁻³), primary sugars and sugar alcohols (4.15 ng m⁻³), lignin and resin products (2.94 ng m⁻³), and steranes (2.46 ng m⁻³) were less abundant. The carbon preference index of n-alkanes (0.83–1.38) indicated that they had a strong fossil fuel combustion origin. Diagnostic concentration ratios of organic tracers suggested that PAHs and hopanes originated mostly from coal burning and traffic emissions, respectively, in the Nanjing urban area. Positive matrix factorization analysis demonstrated that fossil fuel combustion was the major pollution source (28.7 %), followed by emissions from biomass burning (17.1 %), soil dust (14.5 %) and plastic burning (6.83 %) for Nanjing winter aerosols, although the contribution of secondary oxidation products (32.9 %) was the most abundant. Most of the compounds generally showed higher concentrations at nighttime compared with daytime; this was due to the accumulation process associated with inversion layers and the enhancement of emissions from heavy trucks at night. We conclude that fossil fuel combustion largely influences the winter organic aerosols in urban Nanjing. Based on the comparison of this study's results with previous research, we found that pollution levels in organic aerosols have decreased in the urban Nanjing atmosphere over the last decade.

Size-segregated aerosols (nine stages from < 0.43 to > 11.3 µm in diameter) were collected at Cape Hedo, Okinawa, in spring 2008 and analyzed for water-soluble diacids (C₂–C₁₂), ω-oxoacids (ωC₂–ωC₉), pyruvic acid, benzoic acid, and α-dicarbonyls (C₂–C₃) as well as water-soluble organic carbon (WSOC), organic carbon (OC), and major ions (Na⁺, NH₄⁺, K⁺, Mg²⁺, Ca²⁺, Cl⁻, NO₃⁻, SO₄²⁻, and MSA⁻). In all the size-segregated aerosols, oxalic acid (C₂) was found to be the most abundant species, followed by malonic and succinic acids, whereas glyoxylic acid (ωC₂) was the dominant oxoacid and glyoxal (Gly) was more abundant than methylglyoxal. Diacids (C₂–C₅), ωC₂, and Gly as well as WSOC and OC peaked at fine mode (0.65–1.1 µm) whereas azelaic (C₉) and 9-oxononanoic (ωC₉) acids peaked at coarse mode (3.3–4.7 µm). Sulfate and ammonium were enriched in fine mode, whereas sodium and chloride were in coarse mode. Strong correlations of C₂–C₅ diacids, ωC₂ and Gly with sulfate were observed in fine mode (r = 0.86–0.99), indicating a commonality in their secondary formation. Their significant correlations with liquid water content in fine mode (r = 0.82–0.95) further suggest an importance of the aqueous-phase production in Okinawa aerosols. They may also have been directly emitted from biomass burning in fine mode as supported by strong correlations with potassium (r = 0.85–0.96), which is a tracer of biomass burning. Bimodal size distributions of longer-chain diacid (C₉) and oxoacid (ωC₉) with a major peak in the coarse mode suggest that they were emitted from the sea surface microlayers and/or produced by heterogeneous oxidation of biogenic unsaturated fatty acids on sea salt particles.