Source apportionment of PM<Subscript>2.5</Subscript> in Tangshan,China—Hybrid approaches for primary and secondary species apportionment

The objective of this paper is to propose a hybrid approach for the source apportionment of primary and secondary species of PM_2.5 in the city of Tangshan. The receptor-based PMF (Positive Matrix Factorization) is integrated with the emission inventory (EI) to form the first hybrid method for the source apportionment of the primary species. The hybrid CAMx-PSAT-CP (Comprehensive Air Quality Model with Extensions–Particulate Source Apportionment Technology–Chemical Profile) approach is then proposed and used for the source apportionment of the secondary species. The PM_2.5 sources identified for Tangshan included the soil dust, the metallurgical industry, power plants, coalfired boilers, vehicles, cement production, and other sources. It is indicated that the PM_2.5 pollution is a regional issue. Among all the identified sources, the metallurgy industry was the biggest contribution source to PM_2.5, followed by coal-fired boilers, vehicles and soil dust. The other-source category plays a crucial role for PM_2.5, particularly for the formation of secondary species and aerosols, and these other sources include non-specified sources such as agricultural activities, biomass combustion, residential emissions, etc. The source apportionment results could help the local authorities make sound policies and regulations to better protect the citizens from the local and regional PM_2.5 pollution. The study also highlights the strength of utilizing the proposed hybrid approaches in the identification of PM_2.5 sources. The techniques used in this study show considerable promise for further application to other regions as well as to identify other source categories of PM_2.5.

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Ce-Fe/ZSM-5催化剂NH3选择性催化还原NO性能研究

通过浸渍法将Ce和Fe负载在ZSM-5载体上,制备了1.40%Fe/ZSM-5（数字为金属组分的质量分数,下同）、0.25%Ce/ZSM-5、0.25%Ce-1.40%Fe/ZSM-5和0.50%Ce-1.40%Fe/ZSM-5催化剂。对催化剂进行了表征并研究了其NH₃选择性催化还原（NH₃-SCR）NO的性能。实验结果表明,双金属改性的0.25%Ce-1.40%Fe/ZSM-5催化剂的活性温度窗口范围最广,在350~450 ℃范围内NO转化率超过98%。Ce和Fe以无定型氧化物的形态良好分散在ZSM-5载体表面,没有改变ZSM-5分子筛的微孔结构。0.25%Ce-1.40%Fe/ZSM-5催化剂的有效还原峰面积更大,孤立Fe³⁺和Ce⁴⁺物种含量更多,氧化还原性能显著,催化剂表面具有丰富的中等强度酸性位且酸量较大,有利于 NH₃-SCR 反应的进行。     

Excellent performance of Cu-Mn/Ti-sepiolite catalysts for low-temperature CO oxidation

The Ti-modified sepiolite (Ti-Sep)-supported Mn-Cu mixed oxide (yMn5Cu/Ti-Sep) catalysts were synthesized using the co-precipitation method. The materials were characterized by the X-ray diffraction scanning electron microscope, N₂ adsorption-desorption, H₂-TPR, O₂-TPD, and XPS techniques, and their catalytic activities for CO oxidation were evaluated. It was found that the catalytic activities of yMn5Cu/Ti-Sep were higher than those of 5Cu/Ti-Sep and 30Mn/Ti-Sep, and the Mn/Cu molar ratio had a distinct influence on catalytic activity of the sample. Among the yMn5Cu/Ti- Sep samples, the 30Mn5Cu/Ti-Sep catalyst showed the best activity (which also outperformed the 30Mn5Cu/Sep catalyst), giving the highest reaction rate of 0.875 × 10^–3 mmol·g^–1·s^–1 and the lowest T _50% and T _100% of 56°C and 86°C, respectively. Moreover, the 30Mn5Cu/Ti-Sep possessed the best low-temperature reducibility, the lowest O₂ desorption temperature, and the highest surface Mn³⁺/Mn⁴⁺ atomic ratio. It is concluded that factors, such as the strong interaction between the copper or manganese oxides and the Ti-Sep support, good low-temperature reducibility, and good mobility of chemisorbed oxygen species, were responsible for the excellent catalytic activity of 30Mn5Cu/Ti-Sep.

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A monitoring-modeling approach to SO42 − and NO3− secondary conversion ratio estimation during haze periods in Beijing, China

SO_4~(2-) and NO_3~- are important chemical components of fine particulate matter(PM_(2.5)),especially during haze periods.This study selected two haze episodes in Beijing,China with similar meteorological conditions.A monitoring-modeling approach was developed to estimate the secondary conversion ratios of sulfur and nitrogen based on monitored and simulated concentrations.Measurements showed that in Episode 1(24th–25th October,2014),the concentrations(proportions)of SO_4~(2-) and NO_3~- reached 35.1μg/m~3(14.9%) and 55.0μg/m~3(22.9%),while they reached 14.4μg/m~3(9.3%) and 59.1μg/m~3(38.1%)in Episode 2(26th–27th October,2017).A modeling system was applied to apportion Beijing's SO_4~(2-) and NO_3~- in primary and secondary SO_4~(2-)/NO_3~- emitted from local and regional sources.Thus,secondary conversion contributions considering the local and regional level were defined.The former primarily focused on Beijing atmospheric oxidation ability and the latter mainly considered the existence form of Beijing SO_4~(2-)/NO_3~- under the regional transport impacts.Finally,secondary oxidation ratios were estimated through combining secondary conversion contribution coefficients for simulated and monitored concentrations.At regional level,sulfur oxidation ratios in polluted(clean)days during two sampling periods were0.57–0.72(0.07–0.52)and 0.74–0.80(0.08–0.61),nitrogen oxidation ratios were 0.20–0.29(0.05–0.15)and 0.34–0.38(0.02–0.29),indicating that atmospheric oxidation was enhanced when considering regional transport through 2014–2017.At the local level,sulfur oxidation ratios were 0.66–0.71(0.04–0.48)in haze(clean)days,while nitrogen oxidation ratios were0.16–0.29(0.02–0.16).The atmospheric oxidation ability markedly increased in PM_(2.5)pollution days,but changed only slightly between the two periods.     

关于确定大气混合层高度的几种方法

本文阐述了大气混合层高度研究在环境保护中的作用，论述了大气混合层高度确定的几种方法，分析了各种方法的特点及应用前景，同时也讨论了目前在我国大气混合层高度研究中提出的一些新方法。     

Distinct potential aerosol masses under different scenarios of transport at a suburban site of Beijing

In order to evaluate the secondary aerosol formation potential at a suburban site of Beijing,in situ perturbation experiments in a potential aerosol mass(PAM) reactor were carried out in the winter of 2014.The variations of secondary aerosol formation as a function of time,OH exposure,and the concentrations of gas phase pollutants and particles were reported in this study.Two periods with distinct secondary aerosol formation potentials,marked as Period Ⅰ and Period Ⅱ,were identified during the observation.In Period Ⅰ,the secondary aerosol formation potential was high,and correlated well to the air pollutants,i.e.,SO_2,NO_2,and CO.The maximal secondary aerosol formation was observed with an aging time equivalent to about 3 days of atmospheric oxidation.In period Ⅱ,the secondary aerosol formation potential was low,with no obvious correlation with the air pollutants.Meanwhile,the aerosol mass decreased,instead of showing a peak,with increasing aging time.Backward trajectory analysis during the two periods confirmed that the air mass in Period Ⅰwas mainly from local sources,while it was attributed mostly to long distance transport in Period Ⅱ.The air lost its reactivity during the long transport and the particles became highly aged,resulting in a low secondary aerosol formation potential.Our experimental results indicated that the in situ measurement of the secondary aerosol formation potential could provide important information for evaluating the contributions of local emission and long distance transport to the aerosol pollution.     

On-board measurements of gaseous pollutant emission characteristics under real driving conditions from light-duty diesel vehicles in Chinese cities

A total of 15 light-duty diesel vehicles(LDDVs) were tested with the goal of understanding the emission factors of real-world vehicles by conducting on-board emission measurements. The emission characteristics of hydrocarbons(HC) and nitrogen oxides(NOx) at different speeds, chemical species profiles and ozone formation potential(OFP) of volatile organic compounds(VOCs) emitted from diesel vehicles with different emission standards were analyzed. The results demonstrated that emission reductions of HC and NOxhad been achieved as the control technology became more rigorous from Stage I to Stage IV. It was also found that the HC and NOxemissions and percentage of O2 dropped with the increase of speed, while the percentage of CO2 increased. The abundance of alkanes was significantly higher in diesel vehicle emissions, approximately accounting for 41.1%–45.2%, followed by aromatics and alkenes. The most abundant species were propene,ethane, n-decane, n-undecane, and n-dodecane. The maximum incremental reactivity(MIR)method was adopted to evaluate the contributions of individual VOCs to OFP. The results indicated that the largest contributors to O3 production were alkenes and aromatics, which accounted for 87.7%–91.5%. Propene, ethene, 1,2,4-trimethylbenzene, 1-butene, and1,2,3-trimethylbenzene were the top five VOC species based on their OFP, and accounted for 54.0%-64.8% of the total OFP. The threshold dilution factor was applied to analyze the possibility of VOC stench pollution. The majority of stench components emitted from vehicle exhaust were aromatics, especially p-diethylbenzene, propylbenzene, m-ethyltoluene, and p-ethyltoluene.     

National emissions inventory and future trends in greenhouse gases and other air pollutants from civil airports in China

Environmental Science and Pollution Research - Civil aviation is an important source of air pollutants, but this field has received insufficient attention in China. Based on the standard emissions...     

A review of the technology and applications of methods for evaluating the transport of air pollutants

A variety of methods based on air quality models, including tracer methods, the brute-force method (BFM), decoupled direct method (DDM), high-order decoupled direct method (HDDM), response surface models (RSMs) and so on forth, have been widely used to study the transport of air pollutants. These methods have good applicability for the transport of air pollutants with simple formation mechanisms. However, differences in research conclusions on secondary pollutants with obvious nonlinear characteristics have been reported. For example, the tracer method is suitable for the study of simplified scenarios, while HDDM and RSMs are more suitable for the study for nonlinear pollutants. Multiple observation techniques, including conventional air pollutant observation, lidar observation, air sounding balloons, vehicle-mounted and ship-borne technology, aerial surveys, and remote sensing observations, have been utilized to investigate air pollutant transport characteristics with time resolution as high as 1 sec. In addition, based on a multi-regional input-output model combined with emission inventories, the transfer of air pollutant emissions can be evaluated and applied to study the air pollutant transport characteristics. Observational technologies have advantages in temporal resolution and accuracy, while modeling technologies are more flexible in spatial resolution and research plan setting. In order to accurately quantify the transport characteristics of pollutants, it is necessary to develop a research method for interactive verification of observation and simulation. Quantitative evaluation of the transport of air pollutants from different angles can provide a scientific basis for regional joint prevention and control.     

铁屑过滤法预处理可生化性差的印染废水

采用铁屑过滤法预处理可化生性差的印染废水,能改善废水的可生化性,降低废水的ＣＯＤ和色度,有利于后续生化处理。