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The solving of structured multi-step word problems has been a dominant practice in schools and is seen as a way to develop students' mathematical reasoning abilities. Unfortunately, it is limited in scope and does not provide opportunities for eliciting deeper reasoning as they are neither rich enough nor anchored in authentic data that resemble real-world scenarios. Mathematical modelling activities, on the other hand, feature meaningful real-world situations and data that lead to openness to student solution and student interaction in small group learning. Coupled with the teacher's scaffolding, students are expected to expand and extend their reasoning even more towards solving the modelling task. This paper describes a case study on fostering a group of Primary 5 students' mathematical reasoning during mathematical modelling. The findings reveal that the students displayed a rich repertoire of different forms of mathematical reasoning as they generated their models. The models are sophisticated systems that helped them make decisions.

According to Method 202 proposed by EPA in 2017 and HJ 836-2017 issued by Environmental Protection Department of China, devices of TPM was designed and utilized with which samples of FPM and CPM could be collected simultaneously. FPM, CPM, water soluble ions and elements analysis of CPM in flue gas emitted by three coal-fired power plants named A, B and C were monitored. CFD was used to simulate the diffusion trajectory of PM2.5 formed by CPM emission from fixed sources in stationary weather. The statistical results showed that mass concentrations of TPM emitted by plant A, B and C was 8.63±3.11 mg/m³, 19.05±8.85 mg/m³ and 5.07±1.59 mg/m³, respectively. It was proved that CPM was 90% of TPM and FPM was low mass concentration. Inorganic CPM was dominant in CPM, SO42-, NH4+, Na+ and other water-soluble ions were important components, and the emission of metal elements especially heavy metal should not be neglected. CFD was used to simulate the diffusion trajectory of PM2.5 formed by CPM emission from fixed sources in stationary weather. It was proved that CPM could accumulate below atmospheric boundary layer under meteorological conditions that were not conductive to the diffusion of pollutants, causing PM2.5 accumulation in a short period of time, which was an important factor in the formation of heavy pollutant weather. [ABSTRACT FROM AUTHOR]

The pollution characteristics of multi-size atmospheric particulates in Xinxiang, which was one of the most polluted cities across China, are still unclear even through air quality in Xinxiang has been improved in recent years. PM10, PM2.5, and PM1 samples were synchronously collected from 21 December 2019 to 17 January 2020 to explore pollution levels and reveal sources of PM in Xinxiang. The average mass concentrations of PM10, PM2.5, and PM1 were as high as 155.53 μg m−3, 120.07 μg m−3, and 85.64 μg m−3 during the observation period, respectively. Almost all of the chemical compositions in PM10, PM2.5 and PM1 increased continuously and obviously with the aggravation of the pollution level. Compared with the clean period, the enhancement of sulfate (23–27%) in PM was obvious higher than nitrate (19–22%) during the pollution period, which demonstrated that sulfate was the main contributor to the high concentration of PM in this study. Similar source distributions for PM10, PM2.5, and PM1 were also found, including traffic source, combustion source, secondary aerosols, industrial source, and fugitive dust, by using the positive matrix factorization (PMF) model. Furthermore, the contributions of the combustion source and secondary aerosol were found to be higher in smaller particles (PM2.5 and PM1), while the contribution of fugitive dust was higher in PM10. Moreover, dust and sand were entrained by air masses from the northwest that increased the contribution of dust in PM at the observation site. The potential source contribution function (PSCF) analysis illustrated that regional emission sources in northern and eastern Xinxiang might be important potential contributors to PM pollution in Xinxiang. [ABSTRACT FROM AUTHOR]

The solving of structured multi-step word problems has been a dominant practice in schools and is seen as a way to develop students' mathematical reasoning abilities. Unfortunately, it is limited in scope and does not provide opportunities for eliciting deeper reasoning as they are neither rich enough nor anchored in authentic data that resemble real-world scenarios. Mathematical modelling activities, on the other hand, feature meaningful real-world situations and data that lead to openness to student solution and student interaction in small group learning. Coupled with the teacher's scaffolding, students are expected to expand and extend their reasoning even more towards solving the modelling task. This paper describes a case study on fostering a group of Primary 5 students' mathematical reasoning during mathematical modelling. The findings reveal that the students displayed a rich repertoire of different forms of mathematical reasoning as they generated their models. The models are sophisticated systems that helped them make decisions. [ABSTRACT FROM AUTHOR]

2,4,6-Trinitrophenol (TNP) has high explosive risks and biological toxicity, and there has been considerable concern over the determination of TNP. In the present work, fluorescent carbon dots (CDs) stemmed from a green carbon source of pinecone by the facile hydrothermal approach. A novel environment- friendly fluorescent probe was developed to efficiently detect TNP by using the obtained CDs with remarkable fluorescence stability. The fluorescent CDs exhibited obvious excitation dependence with the highest peaks for excitation and emission occurring at 321 and 411 nm, respectively. The fluorescence intensity is significantly reduced by TNP owing to the inner filter effect with the CDs. The probe exhibited good linearity with TNP concentrations in the range of 0.025-20 μg mL -1 , and the limit of detection was as low as 8.5 ng mL -1 . Additionally, the probe proved successful in sensing TNP quantitatively in actual environmental samples with satisfied recoveries of 95.6-99.6%. The developed fluorescent probe offered an environment-friendly, efficient, rapid, and reliable platform for detecting trace TNP in the environmental field.HighlightsNovel carbon dots were synthesised from green precursors of pineal powder.The highly effective quenching process was put down to the inner filter effect.The as-constructed fluorescent probe was successfully utilised for sensing 2,4,6-trinitrophenol in environmental samples.The proposed method was simple, rapid, efficient, economical, and eco-friendly.

To explore high-resolution temporal variation characteristics of atmospheric metal elements concentration and more accurate pollution sources apportionment, online monitoring of metal elements in PM 2.5 with 1-h time resolution was conducted in Beijing from August 22, 2018 to August 21, 2019. Concentration of 18 elements varied between detection limit (ranging from 0.1 to 100 ng/m 3 ) and nearly 25 μg/m 3 . Si, Fe, Ca, K and Al represented major elements and accounted for 93.47% of total concentration during the study period. Compared with previous studies, airborne metal pollution in Beijing has improved significantly which thanks to strict comprehensive control measures under the Clean Air Action Plan since 2013. Almost all elements present higher concentrations on weekdays than weekends, while concentrations of elements associated with dust sources during holidays are higher than those in working days after the morning peak, and there is almost no concentration difference in the evening peak period. Soil and dust, vehicle non-exhaust emissions, biomass, industrial processes and fuel combustion were apportioned as main sources of atmospheric metal pollution, accounting for 63.6%, 18.4%, 16.8%, 1.0% and 0.18%, respectively. Furthermore, main occurrence season of metal pollution is judged by characteristic radar chart of varied metal elements proposed for the first time in this study, for example, fuel combustion type pollution mainly occurs in winter and spring. Results of 72-h backward trajectory analysis of air masses showed that, except for local emissions, atmospheric metal pollution in Beijing is also affected by regional transport from Inner Mongolia, Hebei, the Bohai Sea and Heilongjiang., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Carbonaceous constituents have various adverse impacts on human health, visibility, and climate change. Although comprehensive studies on the characteristics of carbonaceous constituents have been conducted recently, systematic studies covering both the mass characteristics and light-absorption properties of carbonaceous constituents on a regional scale in China are quite limited. In this study, current seasonal measurements of organic carbon (OC) and elemental carbon (EC) in PM 2.5 were investigated during autumn and winter (1-30 October 2017 and December 18, 2017 to January 17, 2018) in six selected cities located at the eastern foot of the Taihang Mountains: Beijing, Baoding, Shijiazhuang, Handan, Xinxiang, and Zhengzhou. Seasonal variations were similar when Beijing was excluded. The lowest concentrations of OC (18.33 ± 9.39 μg/m 3 ) and EC (7.66 ± 5.64 μg/m 3 ) were observed in Xinxiang (autumn) and Beijing (winter), respectively, while the highest concentrations of OC (38.43 ± 62.10 μg/m 3 ) and EC (12.24 ± 24.67 μg/m 3 ) occurred in Baoding during winter mainly due to elevated fuel combustion for space heating. The results of the potential source contribution function (PSCF) analysis suggested that border zones between several provinces in North China should be highlighted in order to strengthen pollution control. Moreover, by separating the optical properties of brown carbon from those of black carbon, we were able to estimate the contributions of brown carbon to the PM 2.5 total light-absorption coefficient. The results show that the brown carbon absorption coefficient (at 405 nm) in winter at six sites accounted for 21.2%, 33.3%, 34.7%, 39.1%, 48.6%, and 23.3% of the PM 2.5 light absorption, which are values that are comparable to the contribution of black carbon in Xinxiang. These results provide a more comprehensive understanding of carbonaceous constituents on a regional scale., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

To investigate the up-to-date migration and emission characteristics of NH 3 /NH 4 + in coal-fired power plants (CFPPs) after implementing ultralow emission retrofitting, typical air pollution control devices (APCDs) in CFPPs, including flue gas denitrification, dust collectors, combined wet flue gas desulfurization (WFGD), and wet precipitators are involved in field measurements. The results show that most of the excessive injected and/or unreacted ammonia from the flue gas denitrification system, whether selective catalytic reduction (SCR) or selective noncatalytic reduction (SNCR), is converted into particle-bound NH 4 + (>91%), and the rest (less than 9%) is carried by flue gas in the form of gaseous NH 3 , with a concentration value of 0.15-0.54 mg/(N m 3 ) at the denitrification outlet. When passing through dust collectors, particle-bound NH 4 + concentration decreases substantially along with the removal of particle matter. In WFGD, the dissolution and volatilization effects affect the gaseous ammonia concentration, which decreases when using limestone slurry and a 20% solution of ammonia as a desulfurization agent, while liquid ammonia solution with a high concentration (99.8%) may cause the flue gas NH 3 concentration to increase considerably by 13 times. Particle-bound NH 4 + concentration is mainly influenced by the relative strength of desulfurization slurry scouring and flue gas carrying effects and increases 2.84-116 times through ammonia-based WFGD. Furthermore, emission factors of NH 3 for combinations of APCDs are discussed.

In order to probe the seasonal variation, formation mechanisms as well as geographical origins of fine particles and its chemical components in two cities (Zhengzhou, ZZ and Xinxiang, XX) in Central Plains Urban Agglomeration, daily PM 2.5 aerosol samples were collected for four consecutive seasons during 2017-2018. The annual average concentrations of PM 2.5 (particulate matter with an aerodynamic diameter smaller than 2.5 μm) were calculated at 70.5 ± 50.8 and 69.0 ± 46.3 μg m -3 at ZZ and XX, respectively. Daily ambient PM 2.5 concentrations ranged from 18.2 to 303.0 μg m -3 , among which >81% of the total sampling days exceeded the National Ambient Air Quality Standard of China (NAAQS, 35 μg m -3 as an annual average). Additionally, concentrations of PM 2.5 and its major chemical components were seasonally dependent, usually with the highest mass concentration in winter. Compared with previous studies, higher NO 3 - /SO 4 2- were observed in this study depicted that air pollution caused by motor vehicle exhaust cannot be ignored. OC concentration was higher at ZZ than XX during sampling campaign likely partially caused by larger number of motor vehicles, chemical pesticide and solvent used in ZZ. Both homogeneous and heterogeneous reactions played an important role in the formation of nitrate, while heterogeneous reactions dominated the formation of sulfate. We also found a faster increase in nitrate than in sulfate during the evolution of haze. The characteristics of long-range transportation of PM 2.5 and its major chemical components and gaseous precursors were observed at both sites through back trajectories and WPSCF analysis, suggesting the complexity of air pollution and the multi-influence among cities., (Copyright © 2018 Elsevier B.V. All rights reserved.)

PM 2.5 and its major chemical compositions were sampled and analyzed in January, April, July and October of 2014 at Beijing (BJ), Tianjin (TJ), Langfang (LF) and Baoding (BD) in order to probe the temporal and spatial characteristics as well as source apportionment of PM 2.5 in the Beijing-Tianjin-Hebei (BTH) region. The results showed that PM 2.5 pollution was severe in the BTH region. The average annual concentrations of PM 2.5 at four sampling sites were in the range of 126-180 μg/m 3 , with more than 95% of sampling days exceeding 35 μg/m 3 , the limit ceiling of average annual concentration of PM 2.5 regulated in the Chinese National Ambient Air Quality Standards (GB3095-2012). Additionally, concentrations of PM 2.5 and its major chemical species were seasonally dependent and demonstrated spatially similar variation characteristics in the BTH region. Concentration of toxic heavy metals, such as As, Cd, Cr, Cu, Mn, Ni, Pb, Sb, Se, and Zn, were higher in winter and autumn. Secondary inorganic ions (SO 4 2- , NO 3 - , and NH 4 + ) were the three-major water-soluble inorganic ions (WSIIs) of PM 2.5 and their mass ratios to PM 2.5 were higher in summer and autumn. The organic carbon (OC) and elemental carbon (EC) concentrations were lower in spring and summer than in autumn and winter. Five factors were selected in Positive Matrix Factorization (PMF) model analysis, and the results showed that PM 2.5 pollution was dominated by vehicle emissions in Beijing, combustion emissions including coal burning and biomass combustion in Langfang and Baoding, and soil and construction dust emissions in Tianjin, respectively. The air mass that were derived from the south and southeast local areas around BTH regions reflected the features of short-distant and small-scale air transport. Shandong, Henan, and Hebei were identified the major potential sources-areas of secondary aerosol emissions to PM 2.5 ., (Copyright © 2017 Elsevier Ltd. All rights reserved.)