Air pollution is one of the primary sources of risk to human health in the world. In this study, seasonal and spatial variations of multiple volatile organic compounds (VOCs) were measured at six sampling sites in Almaty, Kazakhstan. The seasonal and spatial variations of 19 VOCs were evaluated in 2020, including the periods before and after COVID-19 lockdown. The concentrations of 9 out of 19 VOCs had been changed significantly (p < 0.01) during 2020. The maximum concentrations of total VOCs (TVOCs) were observed on 15, 17, and 19 January and ranged from 233 to 420 µg m⁻³. The spatial distribution of TVOCs concentrations in the air during sampling seasons correlated with the elevation and increased from southern to northern part of Almaty, where Combined Heat and Power Plants are located. The sources of air pollution by VOCs were studied by correlations analysis and BTEX ratios. The ranges of toluene to benzene ratio and benzene, toluene, and ethylbenzene demonstrated two primary sources of BTEX in 2020: traffic emissions and biomass/biofuel/coal burning. Most of m-, p-xylenes to ethylbenzene ratios in this study were lower than 3 in all sampling periods, evidencing the presence of aged air masses at studied sampling sites from remote sources.

Calcined and acid-leached kaolin impregnated with Fe(NO₃)₃·9H₂O (6.6 wt. % Fe₂O₃) was developed as an inexpensive bifunctional catalyst for the slow fixed-bed pyrolysis of polypropylene (PP) and low-density polyethylene (LDPE). Experiments were run with catalyst-to-plastic mass ratios of 1:4, 1:2, and 1:1 in a quartz tube reactor heated from 25 to 800 °C. For PP, increasing the Fe/kaolin loading progressively raised non-condensable gas from 26 wt. % to 44 wt. % and drove liquid aromatics from 27.9% to 72.3%, while combined paraffins olefins fell to 2.5% and wax exhibited a 46 → 24 → 36 wt. % trend. In contrast, LDPE at a 1:4 ratio already yielded 56 wt. % oil and only 22 wt. % wax; further catalyst addition mainly enhanced CH₄/CO-rich pyrolysis gas (PyGas) and char without substantially boosting aromatics. Gas analysis confirmed that Fe₂O₃ reduction and kaolin de-hydroxylation generated in situ H₂O, CO, and H₂. Given the catalyst’s low cost, regenerability, and ability to valorize the two most abundant waste polyolefins within the same reactor, the process offers a scalable route to flexible fuel and gas production from mixed plastic streams.

Sewage sludge (SS)-derived materials were investigated as low-cost heterogeneous catalytic materials for polystyrene (PS) pyrolysis, focusing on the effects of thermal treatment, HCl leaching, and Fe impregnation. Sewage sludge ash (SSA), sewage sludge char (SSC), and HCl-leached Fe-impregnated sewage sludge char (Fe-LSSC) were evaluated as in-situ catalytic materials. Catalyst-to-PS ratios of 1:1–1:10 were investigated in a horizontal semi-batch tubular reactor operated in an in-situ catalyst–polymer contact mode at 800 °C. Thermal pyrolysis produced 63.9 wt.% PyOil and 12.6 wt.% PyGas. SSA increased the PyOil yield to 78.0 wt.% at 1:10 and promoted lighter aromatics; at 1:1, light aromatics increased to 66.8 wt.%, BTEX from 5.8 to 24.58 wt.%, and PAHs decreased to 11.8 wt.%. SSC showed a weaker, non-monotonic effect, with PyOil decreasing to 54.4 wt.% and PyChar increasing to 4.7 wt.% at 1:2. Fe-LSSC produced the strongest changes, increasing PyGas to 28.0 wt.% at 1:1 and H₂ to 75.3 vol.% at 1:2. The gasoline-range fraction reached 82.1 wt.% at 1:2, while PAHs decreased to 8.79 wt.% at 1:1. Catalyst reuse altered gas composition, whereas thermal regeneration partially restored catalytic behavior. Overall, SS-derived materials exhibited distinct, loading-dependent catalytic functions, while HCl leaching and Fe impregnation enhanced the conversion of PS pyrolysis vapors toward lighter aromatic and gaseous products.