Indoor air pollution from the household combustion of coal: Tempo-spatial distribution of gaseous pollutants and semi-quantification of source contribution.

Coal is a widely used solid fuel for cooking and heating activities in rural households, whose incomplete combustion in inefficient household stoves releases a range of gaseous pollutants. To evaluate the impact of coal combustion on indoor air quality, this study comprehensively investigated the indoor air pollution of typical gaseous pollutants, including formaldehyde (HCHO), carbon dioxide (CO2), carbon monoxide (CO), total volatile organic compounds (TVOC), and methane (CH4), during coal combustion process in rural households using online monitoring with high tempo-spatial resolution. The indoor concentrations of gaseous pollutants were considerably elevated during the coal combustion period, with the indoor concentrations being significantly higher than those in courtyard air. The levels of several gaseous pollutants (CO2, CO, TVOC, and CH4) in indoor air were much higher during the flaming phase than the de-volatilization and smoldering phases, while HCHO peaked in the de-volatilization phase. The gaseous pollutant concentrations mostly decreased from the room ceiling to the ground level, while their horizontal distribution was relatively uniform within the room. It was estimated that coal combustion accounted for about 71 %, 92 %, 63 %, 59 %, and 21 % of total exposure to indoor CO2, CO, TVOC, CH4, and HCHO, respectively. Improved stove combined with clean fuel could effectively lower the concentrations of CO2, CO, TVOC, and CH4 in indoor air and reduce the contributions of coal combustion to these gaseous pollutants by about 21-68 %. These findings help better understand the indoor air pollution resulting from residential coal combustion and could guide the development of intervention programs to improve indoor air quality in rural households of northern China.

Catalytic performance and mechanism of bismuth molybdate nanosheets decorated with platinum nanoparticles for formaldehyde decomposition at room temperature.

Catalytic oxidation at room temperature is considered as a promising strategy for removal of formaldehyde (HCHO), a widely occurring indoor air pollutant. A series of Bi2MoO6 nanosheets were prepared via one-step hydrothermal synthesis in this study, followed by decoration with Pt nanoparticles (NPs). The catalyst with Bi2MoO6 support prepared at 180 °C exhibited high and stable activity in catalytic oxidation of HCHO at room temperature. The excellent catalytic performance was attributed to its large specific area and pore volume, high level of surface active oxygen species, high content of metallic Pt NPs, and abundant oxygen vacancies. The good synergy and interaction between Pt and Bi2MoO6 promoted electron transfer, and facilitated the adsorption and oxidation of HCHO. The electronic interaction between Pt NPs and Bi2MoO6 accelerated the activation of oxygen species due to weakening of the surface BiO or MoO bonds adjacent to Pt NPs. Infrared spectra indicated that dioxymethylene and formate species were the main intermediates of HCHO oxidation. Density functional theory calculations showed that the dehydrogenation of HCO2, with an energy barrier of 282.1 kJ/mol, was the rate-determining step in catalytic oxidation process. This study provides new insights on the construction of high-efficiency catalysts for indoor formaldehyde removal.

Impacts of Household Coal Combustion on Indoor Ultrafine Particles-A Preliminary Case Study and Implication on Exposure Reduction.

Ultrafine particles (UFPs) significantly affect human health and climate. UFPs can be produced largely from the incomplete burning of solid fuels in stoves; however, indoor UFPs are less studied compared to outdoor UFPs, especially in coal-combustion homes. In this study, indoor and outdoor UFP concentrations were measured simultaneously by using a portable instrument, and internal and outdoor source contributions to indoor UFPs were estimated using a statistical approach based on highly temporally resolved data. The total concentrations of indoor UFPs in a rural household with the presence of coal burning were as high as 1.64 × 105 (1.32 × 105-2.09 × 105 as interquartile range) #/cm3, which was nearly one order of magnitude higher than that of outdoor UFPs. Indoor UFPs were unimodal, with the greatest abundance of particles in the size range of 31.6-100 nm. The indoor-to-outdoor ratio of UFPs in a rural household was about 6.4 (2.7-16.0), while it was 0.89 (0.88-0.91) in a home without strong internal sources. A dynamic process illustrated that the particle number concentration increased by ~5 times during the coal ignition period. Indoor coal combustion made up to over 80% of indoor UFPs, while in an urban home without coal combustion sources indoors, the outdoor sources may contribute to nearly 90% of indoor UFPs. A high number concentration and a greater number of finer particles in homes with the presence of coal combustion indicated serious health hazards associated with UFP exposure and the necessity for future controls on indoor UFPs.

Design and performance of a novel direct Z-scheme NiGa2O4/CeO2 nanocomposite with enhanced sonocatalytic activity.

A novel direct Z-scheme NiGa2O4/CeO2 nanocomposite was designed and prepared via simple sol-hydrothermal and calcination methods, and its sonocatalytic activity was tested by studying the degradation of a model antimicrobial agent, malachite green (MG), under ultrasonic irradiation. Near complete (96.2%) degradation of MG (at 10 mg/L) could be achieved by the NiGa2O4/CeO2 nanocomposite (at 1.0 g/L) after ultrasonic irradiation (40 kHz, 300 W) for 60 min at 25 °C. Under the same conditions, only 51.2 and 72.0% of the MG degraded in the presence of NiGa2O4 and CeO2 (at 1.0 g/L), respectively. These results demonstrate that the direct Z-scheme NiGa2O4/CeO2 nanocomposite has excellent sonocatalytic activity, which is attributed to the matching band-gaps between NiGa2O4 and CeO2. The sonocatalytic activity of NiGa2O4/CeO2 nanocomposite decreased by 17% after four cycles of reuse, which is indicative of relatively good reusability. Scavenging experiments revealed that sonocatalytic degradation of MG results from the combined action of hydroxyl radicals (OH) and holes (h+), with the latter having a greater contribution. The pathways and mechanism of MG degradation were proposed based on the degradation intermediates detected. The results demonstrate that the prepared direct Z-scheme NiGa2O4/CeO2 nanocomposite worked as designed and exhibited high and stable sonocatalytic activity during MG degradation, and could thus serve as a promising candidate in sonocatalytic treatment of other organic pollutants in wastewaters. The findings also provide new insights on the mechanism of sonocatalytic degradation and the design of efficient Z-scheme sonocatalysts.

Facile synthesis of flower-like CoFe2O4 particles for efficient sorption of aromatic organoarsenicals from aqueous solution.

HYPOTHESIS: Aromatic organoarsenicals are heavily used as poultry feed additives, and the application of manure containing these compounds could release toxic inorganic arsenic into the environment. Bimetal ferrites are recognized as promising sorbents in removal of organoarsenicals with formation of FeOAs complexes, and their high saturation magnetization also allows easy sorbent separation. EXPERIMENTS: Herein, a flower-like CoFe2O4 sorbent was synthesized through an environmental-friendly process. FINDINGS: The flower-like CoFe2O4 particles have abundant mesopores and a large specific surface area of 48.4 m2/g. At an equilibrium concentration of 80 µmol/L, the sorption capacities towards p-arsanilic acid (p-ASA), roxarsone (ROX), 4-hydroxyphenylarsonic acid (4-HPAA), 2-aminophenylarsonic acid (2-APAA), phenylarsonic acid (PAA), and 2-nitrophenylarsonic acid (2-NPAA) were 38.1, 45.7, 38.7, 39.3, 33.0, and 32.8 mg/g, respectively. Langmuir model and pseudo-second-order kinetics could well fit the sorption isotherms and rates. The sorption performance was better under acidic conditions due to enhanced electrostatic attraction. Humic acid (HA) and PO43- inhibited the sorption through competing for sorption sites, while Fe3+ promoted sorption due to formation of additional FeOAs complexes on sorbent surface. The experimental observations, spectroscopic insights, and density functional theory (DFT) calculations consistently indicate that the sorption of aromatic organoarsenicals on the flower-like CoFe2O4 particles occurs mainly through formation of inner-sphere complexes. The flower-like CoFe2O4 could be regenerated and reused over multiple cycles. The high sorption capacities, together with its magnetic property, make the flower-like CoFe2O4 an attractive sorbent for removing aromatic organoarsenicals from wastewater.