This study explored unprocessed high-carbon biomass fly ash (BFA) in alkali-activated materials (AAM) with less alkaline Na₂CO₃ as the activator. In this paper, the effects of the Na₂CO₃/Na₂SiO₃ (C/S) ratio and curing temperature (40 °C and 20 °C) on the setting time, structure formation, product synthesis, and physical-mechanical properties of alkali-activated BFA pastes were systematically investigated. Regardless of curing temperature, increasing the C/S ratio increased the density and compressive strength of the sample while a decrease in water absorption. The higher the curing temperature, the faster the structure evolution during the BFA-based alkaline activation synthesis process and the higher the sample’s compressive strength. According to XRD and TG/DTA analyses, the synthesis of gaylussite and C-S-H were observed in the sample with an increasing C/S ratio. The formation of the mentioned minerals contributes to the compressive strength growth of alkali-activated BFA pastes with higher C/S ratios. The findings of this study contribute to the applicability of difficult-to-recycle waste materials such as BFA and the development of sustainable BFA-based AAM.

Significant environmental issues are raised by the phosphogypsum (PG) waste that is being produced. In Lithuania, about 1,500,000 tons of PG waste is generated yearly, and about 300 Mt is generated yearly worldwide. A by-product of burning wood biomass in thermal power plants is biomass fly ash (BFA). By 2035, compared to 2008 levels, industrial biomass incineration for combined heat and power and, as a consequence, BFA, is expected to triple. This study revealed the possibility of using these difficult-to-utilise waste products, such as BFA and PG, in efficient alkali-activated materials (AAM). As the alkaline activator solution (AAS), less alkaline Na₂CO₃ solution and Na₂SiO₃ solution were used. The study compared the physical–mechanical properties of BFA-PG specimens mixed with water and the AAS. After 28 days of curing, the compressive strength of the BFA-PG-based, water-mixed samples increased from 3.02 to 6.38 MPa when the PG content was increased from 0 to 30 wt.%. In contrast, the compressive strength of the BFA-PG-based samples with AAS increased from 8.03 to 16.67 MPa when the PG content was increased from 0 to 30 wt.%. According to XRD analysis, gypsum crystallisation increased when the PG content in the BFA-PG-based samples with water increased. The presence of AAS in the BFA-PG-based samples significantly reduced gypsum crystallisation, but increased the crystallisation of the new phases kottenheimite and sodium aluminium silicate hydrate, which, due to the sodium ions’ participation in the reactions, created denser reaction products and improved the mechanical properties. The outcome of this investigation aids in producing sustainable AAM and applying high volume of hardly usable waste materials, such as BFA and PG.

Coastal and island Aerosol Robotic Network (AERONET) sites are used to determine characteristic aerosol modes over marine environments. They are compared with the assumed modes used in the operational Moderate Resolution Imaging Spectroradiometer (MODIS) ocean aerosol algorithm, and the results show that 1) the standard deviation values of three fine aerosol modes (0.6) and one dustlike aerosol mode (0.8) are much higher than the corresponding statistical AERONET modal values (0.45 and 0.6, respectively). The values of three sea salt aerosol modes (0.6) are somewhat lower than the corresponding statistical AERONET modal value (0.675). 2) The number median radius of the current fine and dustlike aerosol modes cannot span the dynamic range of corresponding aerosol distribution properly. 3) AERONET products show that the standard deviation and the number median radius exhibit an obvious negative correlation, especially for sea salt and dustlike aerosol modes. According to this, a refinement of the current aerosol modes is made. These revised modes are used in a version of the MODIS retrieval over ocean. Compared with the current aerosol modes: 1) more retrieved aerosol optical depths (AODs) from the revised aerosol modes lie within the expected error bars and 2) the linear regression lines of the retrievals from the revised aerosol modes and AERONET are closer to the 1:1 line.