Unexpectedly Increased Particle Emissions from the Steel Industry Determined by Wet/Semidry/Dry Flue Gas Desulfurization Technologies.

"Ultralow-emission" standards have started to be implemented for steel plants in China. Flue gas desulfurization (FGD) systems integrating desulfurization and dedusting, common end-of-pipe technologies before the stacks, have been a key process for controlling the complexity of sintering flue gas to meet ultralow-emission requirements. This study reports comprehensive analysis of the influence of wet/semidry/dry FGD systems on particulate emissions via a field investigation of five typical sinter plants equipped with various FGD devices. The size distribution and mass concentration of particulate matter (PM) are adjusted to different ranges by these FGD systems. Chemical analysis of the PM compositions shows that 20-95% of the mass of inlet PM is removed by FGD systems, while it is estimated that approximately 17, 63, 59, and 71% of the outlet PMs are newly contributed by desulfurizers and their byproducts for the tested wet limestone, wet ammonia, semidry circulating fluidized bed, and activated coke FGD systems, respectively. The newly contributed compositions of PM2.5 emitted from these FGD systems are dominated by CaSO4, (NH4)2SO4, CaSO4 + CaO, and coke carbon, respectively. These results suggest that the deployment of FGD technology should be comprehensively considered to avoid additional negative impacts from byproducts generated in control devices on the atmosphere.

Commodity plastic burning as a source of inhaled toxic aerosols.

Commodity plastic is ubiquitous in daily life and commonly disposed of via unregulated burning, particularly in developing regions. We report here the much higher emission factors (13.1 ± 7.5 g/kg) and toxicities of inhalable aerosols emitted from the unregulated burning of plastic waste based on field measurements and cellular experiments, including oxidative stress and cytotoxic tests in A549 cells. Plastic foam burning emitted aerosols possesses the highest EFs (34.8 ± 4.5 g/kg) and toxicities, which are 4.2- to 13.4-fold and 1.1- to 2.7-fold higher than those emitted from the burning of other waste types. These quantified toxicities are mainly attributed to aerosols containing carbonaceous matter, especially persistent organic pollutants, including polycyclic aromatic hydrocarbons and dioxins, which originate from incomplete combustion processes. The aerosol emission amounts were estimated from the obtained experimental results. Approximately 70.2 million tons (29%) of plastic waste was burned without regulation worldwide in 2016, leading to 0.92 ± 0.53 million tons of toxic aerosols being released into the air, a majority of which occurred in developing regions. The results indicate improved combustion technology and control strategies are urgently needed in developing regions for discarded plastic -waste to mitigate toxic exposure risks and achieve sustainable development.