Step pyrolysis of N-rich industrial biowastes: Regulatory mechanism of NOx precursor formation via exploring decisive reaction pathways

Step pyrolysis of N-rich industrial biowastes was used to explore decisive reaction pathways and regulatory mechanisms of NOx precursor formation. Three typical ones involving medium-density fiberboard waste (MFW), penicillin mycelia waste (PMW) and sewage sludge (SS) were employed to compare the formation characteristics of NOx precursors during one-step and two-step pyrolysis. Results demonstrated that considerable NH3-N pre-dominated NOx precursors for one-step pyrolysis at low temperatures, depending on primary pyrolysis of labile amide-N/inorganic-N in fuels. Meanwhile, NOx precursors differed in the increment of each species yield while resembled in the total yield of 20-45 wt.% among three samples at high temperatures, due to specific prevailing reaction pathways linking with distinctive amide-N types. Subsequently, compared with one-step pyrolysis uniformly (800 degrees C), by manipulating intensities of reaction pathways at different stages (selecting differential intermediate feedstocks), two-step pyrolysis was capable of minimizing NOx precursor-N yield by 36-43% with a greater impact on HCN-N (75-85%) than NH3-N (9-37%), demonstrating its great capacity on regulating the formation of NOx precursors for industrial biowaste pyrolysis. These observations were beneficial to develop effective insights into N-pollution emission control during their thermal reutilization

Sphere-shaped Mn3O4 catalyst with remarkable low-temperature activity for Methyl-Ethyl-Ketone combustion

Mn3O4, FeMnOx, and FeOx catalysts synthesized via a solvothermal method were employed for catalytic oxidation of methyl−ethyl−ketone (MEK) at low temperature. Mn3O4 with sphere-like morphology exhibited the highest activity for MEK oxidation, over which MEK was completely oxidized to CO2 at 200 °C, and this result can be comparable to typical noble metal loaded catalysts. The activation energy of MEK over Mn3O4 (30.8 kJ/mol) was much lower than that of FeMnOx (41.5 kJ/mol) and FeOx (47.8 kJ/mol). The dominant planes, surface manganese species ratio, surface-absorbed oxygen, and redox capability played important roles in the catalytic activities of catalysts, while no significant correlation was found between specific surface area and MEK removal efficiency. Mn3O4 showed the highest activity, accounting for abundant oxygen vacancies, low content of surface Mn4+ and strong reducibility. The oxidation of MEK to CO2 via an intermediate of diacetyl is a reaction pathway on Mn3O4 catalyst. Due to high efficiency and low cost, sphere-shaped Mn3O4 is a promising catalyst for VOCs abatement

Variations of Particle Size Distribution, Black Carbon, and Brown Carbon during a Severe Winter Pollution Event over Xi'an, China

Real-time particulate matter (PM) size distributions, 4-hour time resolution, PM2.5, carbonaceous materials, and their optical properties were measured during a severe pollution event in Xi'an, China High PM2.5 /PM10 ratios were observed on both pollution (0.83) and non-pollution (0.73) days, emphasizing the abundance of fine particles during sampling days. The particle number (PN) first peaked with a wide size range (30-100 nm) before morning rush hours (approximately 01:00-05:00) on pollution and non-pollution days, demonstrating that PN was governed by the accumulation of freshly emitted diesel particles and characterized by distinct aerosol condensation growth. By contrast, the second peak time and size range differed between pollution and non-pollution days because of different formation mechanisms The light-absorbing coefficients of both black carbon (BC, b(abs-880nm,BC)) and brown carbon (BrC, b(abs-370nm, BrC)) were high on pollution days and decreased to approximately half of those values on non-pollution days, indicating that the degree of light absorption is reduced by rain. The diurnal variation in b(abs-880nm, BC) pollution peaked with traffic on January 1 and 2. By contrast, it remained in relatively stable and high ranges (120-160 Mm(-1)) in the second period (January 3-5) without traffic peaks, illustrating that the dominant sources changed even during the same pollution period. High values of both b(abs-370nm, BrC) and b(abs-880nm,) (BC )coincided in the afternoon and evening due to emissions from primary sources, and abundant aqueous secondary organic carbon, respectively. A highly variable mass absorption coefficient of BrC also indicated the variety of fuel combustion sources of primary BrC in Xi'an

Synthesis of a Bi2O2CO3/ZnFe2O4 heterojunction with enhanced photocatalytic activity for visible light irradiation-induced NO removal

Although bismuth subcarbonate (Bi2O2CO3), a member of the Aurivillius-phase oxide family, is a promising photocatalyst for the removal of gaseous NO at parts-per-billion level, the large band gap of this material restricts its applications to the UV light region. The above problem can be mitigated by heterojunction fabrication, which not only broadens the light absorbance range, but also inhibits the recombination of photogenerated charge carriers. Herein, we implement this strategy to fabricate a novel Bi2O2CO3/ZnFe2O4 photocatalyst for NO removal under visible light irradiation and authenticate the formation of the above p-n heterojunction using an array of analytical techniques. Notably, the above composite showed activity superior to those of its individual constituents, and the underlying mechanisms of this activity enhancement were probed by density functional theory calculations and photocurrent measurements. Elevated electron/hole separation efficiency caused by the presence of an internal electric field at the Bi2O2CO3/ZnFe2O4 interface was identified as the main reason of the increased photocatalytic activity, with the main active species were determined as center dot O-2(-) and center dot OH by electron spin resonance spectroscopy. Finally, cytotoxicity testing proved the good biocompatibility of Bi2O2CO3/ZnFe2O4. Thus, this work presents deep insights into the preparation and use of a green p-n heterojunction catalyst in various applications

Optical source profiles of brown carbon in size-resolved particulate matter from typical domestic biofuel burning over Guanzhong Plain, China

In this study, both PM2.5 and size-resolved source samples were collected from a "heated kang" and an advanced stove to investigate the optical properties of brown carbon (BrC). The light-absorption coefficient (babs), the absorption Angstrom exponent (AAE), and the mass absorption cross-section (MAC) of both water and methanol-extracted BrC were investigated. The methanol-extracted BrC (BrCmethanol) had higher light absorption than water-extracted BrC (BrCwater). The value of PM2.5 babs of BrCmethanol at 365 nm(b(abs365),methanol) dramatically decreased from 64,669.8Mm(-1) for straw burning in the "heated kang" to 1169.2 Mm(-1) formaize straw briquettes burning in the advanced stove at the same burning rate. The value of PM2.5 MAC for BrCmethanol at 365 nm (MAC(365), methanol) decreased from 1.8 m(2) g(-1) in the "heated kang" to 1.3 m(2) g-1 in the advanced stove. For smoldering burning in the "heated kang", babs365, methanol, MAC365, methanol, and K+ showed a unimodal distribution that peaked at sizes < 0.4 mu m. However, the babs365, methanol and MAC(365), methanol size distributions of the briquette burning in the advanced stove showed a bimodal pattern, with a large peak at sizes < 0.4 mu m and a minor peak in the size range of 4.7-5.8 mu m. The babs365, methanol value for sizes < 0.4 mu m (277.4 Mm(-1)) was only 12.3% compared to those obtained from the "heated kang". The burning rate did not influence the size distribution pattern of either the "heated kang" or the advanced stove. Results from a radiative model show that biomass burning is an important factor for light absorptivity, and the use of an advanced stove can reduce the simple forcing efficiency value by nearly 20% in UV bands compared to the "heated kang". Our results indicate that changing the combustion style from maize straw smoldering to briquette burning in an advanced stove can effectively reduce BrC emissions during heating seasons in rural areas of Guanzhong Plain. (C) 2017 Elsevier B.V. All rights reserved

Characterization and cytotoxicity of PAHs in PM2.5 emitted from residential solid fuel burning in the Guanzhong Plain, China

The emission factors (EFs) of polycyclic aromatic hydrocarbons (PAHs) in PM2.5 were measured from commonly used stoves and fuels in the rural Guanzhong Plain, China. The toxicity of the PM2.5 also was measured using in vitro cellular tests. EFs of PAHs varied from 0.18 mg kg(-1) (maize straw charcoal burning in a clean stove) to 83.3 mg kg(-1) (maize straw burning in Heated Kang). The two largest influencing factors on PAH EFs were air supply and volatile matter proportion in fuel. Improvements in these two factors could decrease not only EFs of PAHs but also the proportion of 3-ring to 5-ring PAHs. Exposure to PM2.5 extracts caused a concentration-dependent decline in cell viability but an increase in reactive oxygen species (ROS), tumor necrosis factor alpha (TNF-alpha) and interleukin 6 (IL-6). PM2.5 emitted from maize burning in Heated Kang showed the highest cytotoxicity, and EFs of ROS and inflammatory factors were the highest as well. In comparison, maize straw charcoal burning in a clean stove showed the lowest cytotoxicity, which indicated a clean stove and fuel treatment were both efficient methods for reducing cytotoxicity of primary PM2.5. The production of these bioreactive factors were highly correlated with 3-ring and 4-ring PAHs. Specifically, pyrene, anthracene and benzo(a)anthracene had the highest correlations with ROS production (R = 0.85, 0.81 and 0.80, respectively). This study shows that all tested stoves emitted PM2.5 that was cytotoxic to human cells; thus, there may be no safe levels of exposure to PM2,5 emissions from cooking and heating stoves using solid fuels. The study may also provide a new approach for evaluating the cytotoxicity of primary emitted PM2.5 from solid fuel burning as well as other PM2.5 sources. (C) 2018 Elsevier Ltd. All rights reserved

Impact of primary and secondary air supply intensity in stove on emissions of size-segregated particulate matter and carbonaceous aerosols from apple tree wood burning

In order to assess emission factors (EF) more accurately from household biomass burning, a series of laboratory controlled apple tree wood burning tests were conducted to measure the EFs of size-segregated particulate matter (PM) and carbonaceous aerosols. The controlled burning experiments were conducted with designed primary air (PA) and secondary air (SA) supply intensity. An optimum value of 7 m(3).h(-1) was found for SA, resulting the highest modified combustion efficiency (92.4 +/- 2.5%) as well as the lowest EFs of PM2.5 (0.13 +/- 0.01 g.MJ(-1)), OC (0.04 +/- 0.03 g.MJ(-1)) and EC (0.03 +/- 0.01 g.MJ(-1)). SA values of 7 and 10 m(3).h(-1) resulted the lowest EFs for all the different PM sizes. In a test with PA of 6 m(3.)h(-1) and SA of 7 m(3).h(-1), very low EFs were observed for 0C1 (8.2%), 0C2 (11.2%) and especially OP (Pyrolyzed OC) (0%, not detected), indicating nearly complete combustion under this air supply condition. Besides SA, higher PA was proved to have positive effects on PM and carbonaceous fraction emission reduction. For example, with a fixed SA of 1.5 m(3).h(-1), EFs of PM2.5 decreased from 0.64 to 0.27 g.MJ(-1) when PA increased from 6 to 15 m(3).h(-1) (P < 0.05). Similar reductions were also observed in EFs of OC, EC and size segregated PM

Enhanced light absorption due to the mixing state of black carbon in fresh biomass burning emissions

lack of information on the radiative effects of refractory black carbon (rBC) emitted from biomass burning is a significant gap in our understanding of climate change. A custom-made combustion chamber was used to simulate the open burning of crop residues and investigate the impacts of rBC size and mixing state on the particles' optical properties. Average rBC mass median diameters ranged from 141 to 162 nm for the rBC produced from different types of crop residues. The number fraction of thickly-coated rBC varied from 53 to 64%, suggesting that a majority of the freshly emitted rBC were internally mixed. By comparing the result of observed mass absorption cross-section to that calculated with Mie theory, large light absorption enhancement factors (1.7-1.9) were found for coated particles relative to uncoated cores. These effects were strongly positively correlated with the percentage of coated particles but independent of rBC core size. We suggest that rBC from open biomass burning may have strong impact on air pollution and radiative forcing immediately after their production