Humidity and PM2.5 composition determine atmospheric light extinction in the arid region of northwest China

Atmospheric visibility can directly reflect the air quality. In this study, we measured water-soluble ions (WSIs), organic and element carbon (OC and EC) in PM_2.5 from September 2017 to August 2018 in Urumqi, NW China. The results show that SO₄^2?, NO₃^? and NH₄⁺ were the major WSIs, together accounting for 7.32%–84.12% of PM_2.5 mass. Total carbon (TC=OC+EC) accounted for 12.12% of PM_2.5 mass on average. And OC/EC > 2 indicated the formation of secondary organic carbon (SOC). The levels of SO₄^2?, NO₃^? and NH₄⁺ in low visibility days were much higher than those in high visibility days. Relative humidity (RH) played a key role in affecting visibility. The extinction coefficient (b_ext) that estimated via Koschmieder formula with visibility was the highest in winter (1441.05 ± 739.95 Mm^?1), and the lowest in summer (128.58 ± 58.00 Mm^?1). The b_ext that estimated via IMPROVE formula with PM_2.5 chemical component was mainly contributed by (NH₄)₂SO₄ and NH₄NO₃. The b_ext values calculated by both approaches presented a good correlation with each other (R² = 0.87). Multiple linear regression (MLR) method was further employed to reconstruct the empirical regression model of visibility as a function of PM_2.5 chemical components, NO₂ and RH. The results of source apportionment by Positive Matrix Factorization (PMF) model showed that residential coal combustion and vehicle emissions were the major sources of b_ext.     

Kinetic and product studies of the reactions of NO3 with a series of unsaturated organic compounds

Rate coefficients for the reaction of NO₃ radicals with 6 unsaturated volatile organic compounds (VOCs) in a 7300 L simulation chamber at ambient temperature and pressure have been determined by the relative rate method. The resulting rate coefficients were determined for isoprene, 2-carene, 3-carene, methyl vinyl ketone (MVK), methacrolein (MACR) and crotonaldehyde (CA), as (6.6 ± 0.8) × 10^?13, (1.8 ± 0.6) × 10^?11, (8.7 ± 0.5) × 10^?12, (1.24 ± 1.04) × 10^?16, (3.3 ± 0.9) × 10^?15 and (5.7 ± 1.2) × 10^?15 cm³/(molecule?sec), respectively. The experiments indicate that NO₃ radical reactions with all the studied unsaturated VOCs proceed through addition to the olefinic bond, however, it indicates that the introduction of a carbonyl group into unsaturated VOCs can deactivate the neighboring olefinic bond towards reaction with the NO₃ radical, which is to be expected since the presence of these electron-withdrawing substituents will reduce the electron density in the π orbitals of the alkenes, and will therefore reduce the rate coefficient of these electrophilic addition reactions. In addition, we investigated the product formation from the reactions of 2-carene and 3-carene with the NO₃ radical. Qualitative identification of an epoxide (C₁₀H₁₆OH⁺), caronaldehyde (C₁₀H₁₆O₂H⁺) and nitrooxy-ketone (C₁₀H₁₆O₄NH⁺) was achieved using a proton transfer reaction time-of-flight mass spectrometer (PTR-TOF-MS) and a reaction mechanism is proposed.     

Effect of intermittent aeration mode on nitrogen concentration in the water column and sediment pore water of aquaculture ponds

Nitrogen in pond sediments is a major water quality concern and can impact the productivity of aquaculture. Dissolved oxygen is an important factor for improving water quality and boosting fish growth in aquaculture ponds, and plays an important role in the conversion of ammonium-nitrogen (NH₄⁺-N) to nitrite-nitrogen (NO₂^?-N) and eventually nitrate-nitrogen (NO₃^?-N). A central goal of the study was to identify the best aeration method and strategy for improving water quality in aquaculture ponds. We conducted an experiment with six tanks, each with a different aeration mode to simulate the behavior of aquaculture ponds. The results show that a 36 hr aeration interval (T_c = 36 hr: 36 hr) and no aeration resulted in high concentrations of NH₄⁺-N in the water column. Using a 12 hr interval time (T_c = 12 hr: 12 hr) resulted in higher NO₂^?-N and NO₃^?-N concentrations than any other aeration mode. Results from an 8 hr interval time (T_c = 8 hr: 8 hr) and 24 hr interval time (T_c = 24 hr: 24 hr) were comparable with those of continuous aeration, and had the benefit of being in use for only half of the time, consequently reducing energy consumption.     

Human health risk assessment of groundwater nitrate at a two geomorphic units transition zone in northern China

To assess groundwater nitrate contamination and its human health risks, 489 unconfined groundwater samples were collected and analyzed from Zhangjiakou, northern China. The spatial distribution of principle hydrogeochemical results showed that the average concentrations of ions in descend order was HCO₃^?, SO₄^2?, Na⁺, Ca²⁺, Cl^?, NO₃^?, Mg²⁺ and K⁺, among which the NO₃^? concentrations were between 0.25 and 536.73 mg/L with an average of 29.72 mg/L. In total, 167 out of 489 samples (~ 34%) exceeded the recommended concentration of 20 mg/L in Quality Standard for Groundwater of China. The high NO₃^? concentration groundwater mainly located in the northern part and near the boundary of the two geomorphic units. As revealed by statistical analysis, the groundwater chemistry was more significantly affected by anthropogenic sources than by the geogenic sources. Moreover, human health risks of groundwater nitrate through oral and dermal exposure pathways were assessed by model, the results showed that about 60%, 50%, 32% and 26% of the area exceeded the acceptable level (total health index>1) for infants, children, adult males and females, respectively. The health risks for different groups of people varied significantly, ranked: infants> children> adult males>adult females, suggesting that younger people are more susceptible to nitrate contamination, while females are more resistant to nitrate contamination than males. To ensure the drinking water safety in Zhangjiakou and its downstream areas, proper management and treatment of groundwater will be necessary to avoid the health risks associated with nitrate contamination.     

Influence of gaseous and particulate species on neutralization processes of polar aerosol and snow — A case study from Ny-Ålesund

The inter-conversion of nitrogen and sulfur species between the gas and particulate phases and their interaction with alkaline species influences the acidity of the aerosols and surface snow. To better understand these processes, a short field campaign was undertaken in Ny-Ålesund, Svalbard, during 13th April 2012 to 24th April 2012. Air measurements were carried out through a particulate sampler equipped with denuders and filter packs for simultaneous collection of trace gases (HNO₃, NO₂, SO₂ and reactive nitrogen compounds) and aerosols, with daily collection of snow samples. Ionic composition of the samples was analyzed using ion chromatography technique. The results suggested that nitrate-rich aerosols are formed when PAN (peroxy acetyl nitrate) disassociates to form NO₂ and HNO₃ which further hydrolyzes to form pNO₃^? (particulate nitrate). This resulted in a high contribution of pNO₃^? (62%) to the total nitrogen budget over the study area. The acidity of the aerosols and snow evaluated through cation/anion ratio (C/A) indicated alkaline conditions with C/A > 2. The bicarbonates/carbonates of Mg^2 + played an important role in neutralization processes of surface snow while the role of NH₃ was dominant in aerosol neutralization processes. Such neutralization processes can increase the aerosol hygroscopicity causing warming. Chloride depletion in the snow was significant as compared to the aerosols, indicating two important processes, scavenging of coarse sea salt by the snow and gaseous adsorption of SO₂ on the snow surface. However, a more systematic and long term study is required for a better understanding of the neutralization processes and chemical inter-conversions.     

Effect of alkaline earth metal promoter on catalytic activity of MnO2 for the complete oxidation of toluene

Herein, Na⁺ and Ca²⁺ are introduced to MnO₂ through cation-exchange method. The presence of Na⁺ and Ca²⁺ significantly enhance the catalytic activity of MnO₂ in toluene oxidation. Among them, the Ca-MnO₂ catalyst exhibits the best catalytic activity (T₅₀ = 194°C, T₉₀ = 215°C, E_a = 57.2 kJ/mol, reaction rate 8.40 × 10^?10 mol/(sec?m²) at 210°C. T₅₀ and T₉₀: the temperature of 50% and 90% toluene conversion; E_a: apparent activation energy) and possess high tolerance against 2.0 vol.% water vapor. Results reveal that the increased acidic sites of the MnO₂ sample can enhance the adsorption of gaseous toluene, and the mobility of oxygen species and the content of reactive oxygen species in the catalyst are significantly improved due to the formed oxygen vacancy. Thus these two factors result in excellent catalytic performance for toluene oxidation combining with the weak CO₂ adsorption ability.     

Concentration, sources and wet deposition of dissolved nitrogen and organic carbon in the Northern Indo-Gangetic Plain during monsoon

Precipitation represents an important phenomenon for carbon and nitrogen deposition. Here, the concentrations and fluxes of dissolved organic carbon (DOC) and total dissolved nitrogen (TDN) with their potential sources were analyzed in wet precipitation during summer monsoon from the Northern Indo-Gangetic Plain (IGP), important but neglected area. The volume-weighted mean (VWM) concentration of DOC and TDN were 687.04 and 1210.23 µg/L, respectively. Similarly, the VWM concentration of major ions were in a sequence of NH₄⁺ > Ca²⁺ > SO₄^2- > Na⁺ > K⁺ > NO₃^? > Cl^? > Mg²⁺ > F^? > NO₂^?, suggesting NH₄⁺ and Ca²⁺ from agricultural activities and crustal dust played a vital role in precipitation chemistry. Moreover, the wet deposition flux of DOC and TDN were 9.95 and 17.06 kg/(ha?year), respectively. The wet deposition flux of inorganic nitrogen species such as NH₄⁺-N and NO₃^?-N were 14.31 and 0.47 kg/(ha?year), respectively, demonstrating the strong influence of emission sources and precipitation volume. Source attribution from different analysis suggested the influence of biomass burning on DOC and anthropogenic activities (agriculture, animal husbandry) on nitrogenous species. The air-mass back trajectory analysis indicated the influence of air masses originating from the Bay of Bengal, which possibly carried marine and anthropogenic pollutants along with the biomass burning emissions to the sampling site. This study bridges the data gap in the less studied part of the northern IGP region and provides new information for policy makers to deal with pollution control.     

Competing pathways of cresol formation in toluene photooxidation: OH-toluene adducts react with NO2 or with O2?

Methyl-hydroxy-cyclohexadienyl radicals (OTAs) are the key products of the photooxidation of toluene, with implications for the fate of toluene. Hence, we investigated the photooxidation mechanisms and kinetics of three main OTAs (o-OTA, m-OTA, and p-OTA) with NO₂ using quantum chemical calculations as well as the fate of OTAs under the different concentration ratios of NO₂ and O₂. The mechanism results show that the pathway of H-abstraction by NO₂ to anti-HONO (anti-H-abstraction) is more favorable than the syn-H-abstraction pathway, because the strong interaction between OTAs and NO₂ is formed in the transition states of the anti-H-abstraction pathways. The branching ratios of the anti-H-abstraction pathways are more than 99% in the temperature range of 216−298 K. The total rate constant of the OTA-NO₂ reaction is 9.9 × 10⁻¹² cm³/(molecule∙sec) at 298 K, which is contributed about 90% by o-OTA + NO₂, and the main products are o-cresol and anti-HONO. The half-lives of the OTA-NO₂ reaction in some polluted areas of China are 35 times longer than those of the OTA-O₂ reaction. In the atmosphere, the NO₂- and O₂- initiated reactions of OTAs have the same ability to form cresols as [NO₂] is up to 142.1 ppmV, which is impossible to achieve. It implies that under the experimental condition, the [NO₂]/[O₂] should be controlled to be less than 7.8 × 10⁻⁵ to simulate real atmospheric oxidation of toluene. Our results reveal that for the photooxidation of toluene, the yield of cresol is not affected by the concentration of NO₂ under the atmospheric environment.     

Release kinetics of vanadium from vanadium (III, IV and V) oxides: Effect of pH, temperature and oxide dose

Batch experiments were performed to derive the rate laws for the proton-promoted dissolution of the main vanadium (III, IV and V) oxides at pH 3.1–10.0. The release rates of vanadium are closely related to the aqueous pH, and several obvious differences were observed in the release behavior of vanadium from the dissolution of V₂O₅ and vanadium(III, IV) oxides. In the first 2 hr, the release rates of vanadium from V₂O₃ were r = 1.14·([H⁺])^0.269 at pH 3.0–6.0 and r = 0.016·([H⁺])^? 0.048 at pH 6.0–10.0; the release rates from VO₂ were r = 0.362·([H⁺])^0.129 at pH 3.0–6.0 and r = 0.017·([H⁺])^? 0.097 at pH 6.0–10.0; and the release rates from V₂O₅ were r = 0.131·([H⁺])^? 0.104 at pH 3.1–10.0. The release rates of vanadium from the three oxides increased with increasing temperature, and the effect of temperature was different at pH 3.8, pH 6.0 and pH 7.7. The activation energies of vanadium (III, IV and V) oxides (33.4–87.5 kJ/mol) were determined at pH 3.8, pH 6.0 and pH 7.7, showing that the release of vanadium from dissolution of vanadium oxides follows a surface-controlled reaction mechanism. The release rates of vanadium increased with increasing vanadium oxides dose, albeit not proportionally. This study, as part of a broader study of the release behavior of vanadium, can help to elucidate the pollution problem of vanadium and to clarify the fate of vanadium in the environment.     

Characterization of the aerosol chemical composition during the COVID-19 lockdown period in Suzhou in the Yangtze River Delta, China

To control the spread of COVID-19, rigorous restrictions have been implemented in China, resulting in a great reduction in pollutant emissions. In this study, we evaluated the air quality in the Yangtze River Delta during the COVID-19 lockdown period using satellite and ground-based data, including particle matter (PM), trace gases, water-soluble ions (WSIs) and black carbon (BC). We found that the impacts of lockdown policy on air quality cannot be accurately assessed using MODIS aerosol optical depth (AOD) data, whereas the tropospheric nitrogen dioxide (NO₂) vertical column density can well reflect the influences of these restrictions on human activities. Compared to the pre-COVID period, the PM_2.5, PM₁₀, NO₂, carbon monoxide (CO), BC and WSIs during the lockdown in Suzhou were observed to decrease by 37.2%, 38.3%, 64.5%, 26.1%, 53.3% and 58.6%, respectively, while the sulfur dioxide (SO₂) and ozone (O₃) increased by 1.5% and 104.7%. The WSIs ranked in the order of NO₃^? > NH₄⁺ > SO₄^2- > Cl^? > Ca²⁺ > K⁺ > Mg²⁺ > Na⁺ during the lockdown period. By comparisons with the ion concentrations during the pre-COVID period, we found that the ions NO₃^?, NH₄⁺, SO₄^2?, Cl^?, Ca²⁺, K⁺ and Na⁺ decreased by 66.3%, 48.8%, 52.9%, 56.9%, 57.9% and 76.3%, respectively, during the lockdown, in contrast to Mg²⁺, which increased by 30.2%. The lockdown policy was found to have great impacts on the diurnal variations of Cl^?, SO₄^2?, Na⁺ and Ca²⁺.     

Rural vehicle emission as an important driver for the variations of summertime tropospheric ozone in the Beijing-Tianjin-Hebei region during 2014–2019

Tropospheric ozone (O₃) pollution is increasing in the Beijing-Tianjin-Hebei (BTH) region despite a significant decline in atmospheric fine aerosol particles (PM_2.5) in recent years. However, the intrinsic reason for the elevation of the regional O₃ is still unclear. In this study, we analyzed the spatio-temporal variations of tropospheric O₃ and relevant pollutants (PM_2.5, NO₂, and CO) in the BTH region based on monitoring data from the China Ministry of Ecology and Environment during the period of 2014–2019. The results showed that summertime O₃ concentrations were constant in Beijing (BJ, 0.06 µg/(m³•year)) but increased significantly in Tianjin (TJ, 9.09 µg/(m³•year)) and Hebei (HB, 6.06 µg/(m³•year)). Distinct O₃ trends between Beijing and other cities in BTH could not be attributed to the significant decrease in PM_2.5 (from -5.08 to -6.32 µg/(m³•year)) and CO (from -0.053 to -0.090 mg/(m³•year)) because their decreasing rates were approximately the same in all the cities. The relatively stable O₃ concentrations during the investigating period in BJ may be attributed to a faster decreasing rate of NO₂ (BJ: -2.55 µg/(m³•year); TJ: -1.16 µg/(m³•year); HB: -1.34 µg/(m³•year)), indicating that the continued reduction of NO_x will be an effective mitigation strategy for reducing regional O₃ pollution. Significant positive correlations were found between daily maximum 8 hr average (MDA8) O₃ concentrations and vehicle population and highway freight transportation in HB. Therefore, we speculate that the increase in rural NO_x emissions due to the increase in vehicle emissions in the vast rural areas around HB greatly accelerates regional O₃ formation, accounting for the significant increasing trends of O₃ in HB.     

Brilliant red X-3B uptake by a novel polycyclodextrin-modified magnetic cationic hydrogel: Performance, kinetics and mechanism

A novel polycyclodextrin-modified magnetic cationic hydrogel (PCD-MCH) was developed and its performance, kinetics and mechanism for the removal of reactive brilliant red X-3B (X-3B) were studied. The results showed that the zeta-potential of PCD-MCH was 32.8 to 16.7 mV at pH 3.0–10.5. The maximum X-3B adsorption capacity of PCD-MCH was 2792.3 mg/g. The adsorption kinetics could be well-described by the Weber–Morris model and the homogeneous surface diffusion model (HSDM). Diffusion stages corresponding to surface or film diffusion, intra-particle or wide mesopore diffusion, and narrow mesopore/micropore diffusion occurred at 0–120, 120–480 and 480–1200 min, respectively. The latter two diffusion stages were rate-controlling for X-3B adsorption kinetics. At the initial X-3B concentration of 600 mg/L, the diffusion coefficient (D_s) and external mass transfer coefficient in the liquid phase (k_F) were 3 × 10^?11 cm²/min and 4.68 × 10^?6 cm/min, respectively. X-3B approaching the center of PCD-MCH particles could be observed at 360 min. At the end of the third diffusion stage, the C_p at q/q_e = 0 was 45.20 mg/L, which was close to the homogeneous C_p value of 46 mg/L along the radius of PCD-MCH particles. At pH 3.0–10.0, PCD-MCH showed stable X-3B adsorption capacities. After five regeneration-reuse cycles, the residual adsorption capacity of regenerated PCD-MCH was higher than 892.7 mg/g. The corresponding adsorption mechanism was identified as involving electrostatic interactions, cyclodextrin cavities and hydrogen bonds, of which cyclodextrin cavities showed prominent capture performance towards dye molecules through the formation of inclusion complexes.     

Enhanced adsorption of arsenate by spinel zinc ferrite nano particles: Effect of zinc content and site occupation

In this work, zinc ferrite spinel with different zinc contents (Zn_xFe_3-xO₄) was synthesized by a hydrothermal method and used for removing As(V) in aqueous solution. X-ray diffraction (XRD) results indicated that in the crystal structure of Zn_xFe_3-xO₄, the zinc atoms tended to occupy the octahedral sites for x?<?0.6 and diffused into the tetrahedral sites gradually with x?>?0.6. The size of Zn_xFe_3-xO₄ crystallites increased with the increasing zinc content. Batch adsorption experiments showed that the adsorption isotherms could be well described by the Langmuir model, while the adsorption kinetics followed the pseudo-second-order kinetic model. Zinc ferrite exhibited the highest adsorption capacity towards As(V) when x?=?0.6. Study of the mechanism indicated that doping with zinc increased the number of surface hydroxyl groups on ferrite spinel, and thus enhanced the adsorption capacity when x?=?0.6. This work revealed the effects of doping site and content of metal atoms on the adsorption ability of ferrite spinel towards As(V).     

Measurement of heterogeneous uptake of NO2 on inorganic particles, sea water and urban grime

Heterogeneous reactions of NO₂ on different surfaces play an important role in atmospheric NO_x removal and HONO formation, having profound impacts on photochemistry in polluted urban areas. Previous studies have suggested that the NO₂ uptake on the ground or aerosol surfaces could be a dominant source for elevated HONO during the daytime. However, the uptake behavior of NO₂ varies with different surfaces, and different uptake coefficients were used or derived in different studies. To obtain a more holistic picture of heterogeneous NO₂ uptake on different surfaces, a series of laboratory experiments using different flow tube reactors was conducted, and the NO₂ uptake coefficients (γ) were determined on inorganic particles, sea water and urban grime. The results showed that heterogeneous reactions on those surfaces were generally weak in dark conditions, with the measured γ varied from <10^?8 to 3.2 × 10^?7 under different humidity. A photo-enhanced uptake of NO₂ on urban grime was observed, with the obvious formation of HONO and NO from the heterogeneous reaction. The photo-enhanced γ was measured to be 1.9 × 10^?6 at 5% relative humidity (RH) and 5.8 × 10^?6 at 70% RH on urban grime, showing a positive RH dependence for both NO₂ uptake and HONO formation. The results demonstrate an important role of urban grime in the daytime NO₂-to-HONO conversion, and could be helpful to explain the unknown daytime HONO source in the polluted urban area.     

Measurement of HONO flux using the aerodynamic gradient method over an agricultural field in the Huaihe River Basin, China

To investigate nitrous acid (HONO) levels and potential HONO sources above crop rotation fields. The HONO fluxes were measured by the aerodynamic gradient (AG) method from 14 December 2019 to 2 January 2020 over an agricultural field in the Huaihe River Basin. The ambient HONO levels were measured at two different heights (0.15 and 1.5 m), showing a typical diurnal cycle with low daytime levels and high nighttime levels. The upward HONO fluxes were mostly observed during the day, whereas deposition dominated at night. The diurnal variation of HONO flux followed solar radiation, with a noontime maximum of 0.2 nmol/(m²∙sec). The average upward HONO flux of 0.06 ± 0.17 nmol/(m²∙sec) indicated that the agricultural field was a net source for atmospheric HONO. The higher HONO/NO₂ ratio and NO₂–to–HONO conversion rate close to the surface suggested that nocturnal HONO was formed and released near the ground. The unknown HONO source was derived from the daytime HONO budget analysis, with an average strength of 0.31 ppbV/hr at noontime. The surface HONO flux, which was highly correlated with the photolysis frequency J(NO₂) (R² = 0.925) and the product of J(NO₂) × NO₂ (R² = 0.840), accounted for ∼23% of unknown daytime HONO source. The significant correlation between HONO fluxes and J(NO₂) suggests a light-driven HONO formation mechanism responsible for the surface HONO flux during daytime.     

Characterization and physicochemical aspects of novel cellulose-based layered double hydroxide nanocomposite for removal of antimony and fluoride from aqueous solution

A series of novel adsorbents composed of cellulose (CL) with Ca/Al layered double hydroxide (CC_xA; where x represent the Ca/Al molar ratio) were prepared for the adsorption of antimony (Sb(V)) and fluoride (F^?) ions from aqueous solutions. The CC_xA was characterized by Fourier-transform infrared spectroscopy (FTIR), Brunauer–Emmett–Teller (BET), elemental analysis (CHNS/O), thermogravimetric analysis (TGA-DTA), zeta potential, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX) analysis. The effects of varying parameters such as dose, pH, contact time, temperature and initial concentration on the adsorption process were investigated. According to the obtained results, the adsorption processes were described by a pseudo-second-order kinetic model. Langmuir adsorption isotherm model provided the best fit for the experimental data and was used to describe isotherm constants. The maximum adsorption capacity was found to be 77.2 and 63.1 mg/g for Sb(V) and F^?, respectively by CC₃A (experimental conditions: pH 5.5, time 60 min, dose 15 mg/10 mL, temperature 298 K). The CC₃A nanocomposite was able to reduce the Sb(V) and F^? ions concentration in synthetic solution to lower than 6 μg/L and 1.5 mg/L, respectively, which are maximum contaminant levels of these elements in drinking water according to WHO guidelines.     

Interference from HONO in the measurement of ambient air NO2 via photolytic conversion and quantification of NO

The reference method to quantify mixing ratios of the criteria air pollutant nitrogen dioxide (NO₂) is NO-O₃ chemiluminescence (CL), in which mixing ratios of nitric oxide (NO) are measured by sampling ambient air directly, and mixing ratios of NO_x (= sum of NO and NO₂) are measured by converting NO₂ to NO using, for example, heated molybdenum catalyst or, more selectively, photolytic conversion (P-CL). In this work, the nitrous acid (HONO) interference in the measurement of NO₂ by P-CL was investigated. Results with two photolytic NO₂ converters are presented. The first used radiation centered at 395 nm, a wavelength region commonly utilized in P-CL. The second used light at 415 nm, where the overlap with the HONO absorption spectrum and hence its photolysis rate are less. Mixing ratios of NO₂, NO_x and HONO entering and exiting the converters were quantified by Thermal Dissociation Cavity Ring-down Spectroscopy (TD-CRDS). Both converters exhibited high NO₂ conversion efficiency (CF_NO2; > 90%) and partial conversion of HONO. Plots of CF against flow rate were consistent with photolysis frequencies of 4.2 s^-1 and 2.9 s^-1 for NO₂ and 0.25 s^-1 and 0.10 s^?1 for HONO at 395 nm and 415 nm, respectively. CF_HONO was larger than predicted from the overlap of the emission and HONO absorption spectra. The results imply that measurements of NO₂ by P-CL marginally but systematically overestimate true NO₂ concentrations, and that this interference should be considered in environments with high HONO:NO₂ ratios such as the marine boundary layer or in biomass burning plumes.     

Peroxymonosulfate decomposition by homogeneous and heterogeneous Co: Kinetics and application for the degradation of acetaminophen

Peroxymonosulfate (PMS) decomposition, hydroxyl radical (^?OH) generation, and acetaminophen (ACT) degradation by the Co/PMS system using homogeneous (dissolved cobalt) and heterogeneous (suspended Co₃O₄) cobalt were assessed. For the homogeneous process, >99% PMS decomposition was observed and 10 mmol/L of ^?OH generation was produced using 5 mmol/L of PMS and different dissolved cobalt concentrations after 30 min. A dissolved cobalt concentration of 0.2 mmol/L was used to achieve >99% ACT degradation using the homogeneous process. For the heterogeneous process, 60% PMS decomposition and negligible ^?OH generation were observed for 5 mmol/L of the initial PMS concentration using 0.1 and 0.2 g/L of Co₃O₄. Degradation of ACT greater than 80% was achieved for all experimental runs using 5 mmol/L of the initial PMS concentration independently of the initial Co₃O₄ load used. For the heterogeneous process, the best experimental conditions for ACT degradation were found to be 3 mmol/L of PMS and 0.2 g/L of Co₃O₄, for which >99% ACT degradation was achieved after 10 min. Because negligible ^?OH was produced by the Co₃O₄/PMS process, a second-order kinetic model was proposed for sulfur-based free radical production to allow fair comparison between homogeneous and heterogeneous processes. Using the kinetic data and the reaction by-products identified, a mechanistic pathway for ACT degradation is suggested.     

Physiological and biochemical responses of Microcystis aeruginosa to phosphine (PH3) under elevated CO2

Phosphine (PH₃) is an important factor driving the outbreak of cyanobacterial blooms that produce toxic microcystin threating human health. To clarify the physiological and biochemical responses of cyanobacteria to PH₃ under elevated CO₂ concentration, Microcystis aeruginosa was used in the coupling treatment of 1000 ppmv CO₂ and PH₃ at different concentrations respectively. The chlorophyll a (Chl-a), carotenoid, net photosynthetic rate and total protein of M. aeruginosa exhibited evidently increasing tendency under the coupling treatment of 1000 ppmv CO₂ and PH₃ at different concentrations (7.51 × 10^?3, 2.48 × 10^?2, 7.51 × 10^?2 mg/L). The coupling treatments resulted in the higher concentrations of Chl-a and carotenoid of M. aeruginosa, compared to those in the control and the treatment with CO₂ alone, and their enhancement increased with the increase in PH₃ concentrations. The total antioxidant capacity (T-AOC) in the coupling treatment with CO₂ and PH₃ of 2.48 × 10^?2 mg/L and 7.51 × 10^?3 mg/L showed increasing tendency, compared to the treatment with PH₃ alone. Additionally, the coupling treatment with 1000 ppmv CO₂ and PH₃ also altered the pH and DO level in the culture medium. In this regard, the coupling treatment with CO₂ and PH₃ at an appropriate concentration can enhance the resistance of M. aeruginosa to PH₃ toxicity and is beneficial to the reproduction of M. aeruginosa, presumably resulting in potential for the outbreak of cyanobacteria bloom. Given the concern about global warming and the increase in atmospheric CO₂ level, our research laid a foundation for the scientific understanding of the correlation between PH₃ and cyanobacteria blooms.     

Mechanochemical synthesis of MAPbBr3/carbon sphere composites for boosting carrier-involved superoxide species

Lead halide perovskites MAPbX₃ (MA = CH₃NH₃ or Cs; X = I, Br, Cl) are well considered to be potential candidates for photocatalytic reaction due to its excellent photoelectrical properties, but they still suffer from the low charge separation efficiency and slow catalytic reaction dynamics. To tackle the drawbacks, herein, MAPbBr₃/carbon sphere (CS) composite photocatalysts using glucose as the carbon source were elaborately designed and fabricated via a dry mechanochemical grinding process. The interfacial interaction Pb-O-C chemical bonds were constructed between MAPbBr₃ and the carbon sphere surface containing organic functional groups. By optimizing the content of CSs, the enhanced photocatalytic degradation kinetic rate of Malachite Green (MG) pollutants (92% within 20 min) for MAPbBr₃/CS_x (x = 17 wt.%) is about 3.6-fold of that for pristine MAPbBr₃, which is attributed to the corporative adsorption and enhanced carrier transportation and separation of MAPbBr₃/CS_x. Furthermore, the possible degradation mechanism was proposed on basis of the electrochemical, mass spectrometry and optical characterization results. Owing to the robust interfacial interaction, effective electron extraction rate (k_et = 4.6 × 10⁷ sec^?1) from MAPbBr₃ to CS can be established, which driven oxygen activation where superoxide radicals (?O₂^?) played an important role in MG degradation. It is expected that mechanochemistry strategy may provide a new route to design efficient lead halide perovskite-carbon or metal oxide or sulfide composite photocatalysts.