Iron oxide nanoparticles were synthesized in a liquid flame spray process from iron(III) nitrate. The choice of chemicals and all other process parameters affects the crystallographic phase composition and the quality of the material. Adjustment of the solvent composition and the gas flow rates was used to control the phase composition of the produced particles. All samples consisted of pure maghemite (γ-Fe 2 O 3 ) or a mixture of maghemite and hematite (α-Fe 2 O 3 ). When using pure alcohols as solvents, the maghemite/hematite phase ratio could be adjusted by changing the equivalence ratio that describes the oxidation conditions in the flame zone. A large residual particle mode formed in the size range of ~20-700 nm along with a dominant very fine particle mode (2-8 nm). Both phases seemed to contain large particles. A partial substitution of methanol with carboxylic acids turned the hematite phase into maghemite completely, even though some of particles were possibly not fully crystallized.Residual particles were still present, but their size and number could be decreased by raising the heat of combustion of the precursor solution. 30 vol-% substitution of methanol with 2-ethylhexanoic acid was adequate to mostly erase the large particles. K E Y W O R D Siron/iron compounds, liquid flame spray, nanoparticles, synthesis

The use of filters to control air quality has been implemented widely in all types of structures. Unfortunately, filters risk becoming platforms for the growth of bacteria, which can then be dispersed further in the air stream. To combat this, antibacterial materials are being incorporated into filter media. In this work, we tested two routes for introducing nanoscale silver into filters containing activated carbon fibers (ACF): first, by adding silver nanofibers directly to the fiber fabrication process and second, by coating a pre-existing filter with silver nanoparticles generated by a liquid flame spray (LFS). The resultant filters were evaluated for methanol adsorption, particle penetration and antibacterial activity. The results show that both methods are suitable for producing antibacterial filters as well as being highly tailorable and scalable for specific needs.

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Fuel-operated auxiliary heaters (AHs) can be notable sources of particle emissions from vehicles. The emissions of AHs are unregulated, and the number of devices is high; therefore, they make considerable contributions to local air quality, and even the global emissions budget. Experiments for studying the emissions were performed in Finland for a total of eight selected vehicles with Original Equipment Manufacturer (OEM) AHs installed, including both diesel- and gasoline-operated heaters. We present the numerical results of particle emissions and compare the particle concentrations in the AH exhaust to values found in the tailpipe exhaust of the same vehicle. Our results show that the emissions from auxiliary heaters are typically several orders of magnitude higher than of a car exhaust when idling. This raises the question of whether the use of heaters is justified based on the goal to reduce total emissions from vehicle use; furthermore, whether fuel-operated heaters should also be applied in electric vehicles for cabin heating. More research will be needed to characterize the emissions more thoroughly to understand the air quality and climate effects from AHs, and to provide further recommendations on the use of these heaters.