Will polycentric cities cause more CO2 emissions? A case study of 232 Chinese cities

From 2000 to 2010 China experienced rapid economic development and urbanization. Many cities in economically developed areas have developed from a single-center status to polycentricity. In this study, we used exploratory spatial data analysis (ESDA) to identify the population centers, which identified 232 cities in China as having urban centers. COMP was used to represent urban agglomeration, and POLYD (representing how far is the city's sub-centers to the main center), POLYC (representing the number of a city's centers), and POLYP (representing the population distributed between the main center and the sub-centers) were used to indicate urban polycentricity. Night light data were used to determine the CO₂ emissions from various cities in China. A mixed model was used to study the impact of urban aggregation and polycentric data on the CO₂ emission efficiency in 2000 and 2010. The study found that cities with higher compactness were distributed in coastal areas, and the cities with higher multicentricity were distributed in the Yangtze River Delta and Shandong Province. The more compact the city was, the less conducive it was to improving CO₂ emission efficiency. Polycentric development of the city was conducive to improving the CO₂ emission efficiency, but the number of urban centers had no significant relationship with the CO₂ emission efficiency. Our research showed that the compactness and multicentricity of the city had an impact on the CO₂ emission efficiency and provided some planning suggestions for the low carbon development of the city.     

Ozone pollution characteristics and sensitivity analysis using an observation-based model in Nanjing, Yangtze River Delta Region of China

Ground-level ozone (O₃) has become a critical pollutant impeding air quality improvement in Yangtze River Delta region of China. In this study, we present O₃ pollution characteristics based on one-year online measurements during 2016 at an urban site in Nanjing, Jiangsu Province. Then, the sensitivity of O₃ to its precursors during 2 O₃ pollution episodes in August was analyzed using a box model based on observation (OBM). The relative incremental reactivity (RIR) of hydrocarbons was larger than other precursors, suggesting that hydrocarbons played the dominant role in O₃ formation. The RIR values for NO_X ranged from –0.41%/% to 0.19%/%. The O₃ sensitivity was also analyzed based on relationship of simulated O₃ production rates with reductions of VOC and NO_X derived from scenario analyses. Simulation results illustrate that O₃ formation was between VOCs-limited and transition regime. Xylenes and light alkenes were found to be key species in O₃ formation according to RIR values, and their sources were determined using the Positive Matrix Factorization (PMF) model. Paints and solvent use was the largest contributor to xylenes (54%), while petrochemical industry was the most important source to propene (82%). Discussions on VOCs and NO_X reduction schemes suggest that the 5% O₃ control goal can be achieved by reducing VOCs by 20%. To obtain 10% O₃ control goal, VOCs need to be reduced by 30% with VOCs/NO_X larger than 3:1.     

Chemical characteristics of road dust PM2.5 fraction in oasis cities at the margin of Tarim Basin

In order to understand the compositions characteristics of particulate matter with aerodynamic diameter less than 2.5 μm (PM_2.5) fraction in road dust (RD_2.5) of oasis cities on the edge of Tarim Basin, 30 road dust (RD) samples were collected in Kashi, Cele, and Yutian in the spring, 2018, and RD_2.5 was collected using the resuspension approach. Eight water-soluble ions, 39 trace elements and 8 fractions of carbon-containing species in PM_2.5 were analyzed. Ca²⁺ and Ca were the most abundant ions and elements in RD_2.5 (7.1% and 9.5%). Cl^- in RD_2.5 was affected not only by attributed to saline-alkali soils in oasis cities of the Tarim Basin and dust from Taklimakan Desert but also by human activities. Moreover, the organic carbon/elemental carbon (OC/EC) ratio indicated that carbon components in RD_2.5 in Cele town mainly come from fossil fuel combustion, while those in Yutian and Kashi mainly come from biomass combustion. It is noteworthy that high Ca in RD_2.5 was seriously affected by anthropogenic emissions, and high Na and K contents in RD_2.5 could be derived from soil and desert dust. It was estimated that Cd, Tl, Sn and Cr were emitted from anthropogenic emissions using the enrichment factor. The coefficients of divergence (COD) result indicated that the influence of local emission on road dust emission is greater than that of long-distance transmission. This study is the first time to comprehensively analyze the chemical characteristics of road dust in oasis cities, and the results provides the sources of road dust at the margin of Tarim Basin.     

Investigation to meet China II emission legislation for marine diesel engine with diesel methanol compound combustion technology

In order to reduce the pollutant emission and alleviate the pressure of petroleum resources shortage and greenhouse gas emission at the same time, the use of clean and renewable alternative fuel for marine engines is a promising option. In this study, a marine diesel engine, which was modified to run in diesel methanol compound combustion (DMCC) mode, was investigated. After the diesel injection parameters were calibrated, and combined with a sample after-treatment device DOC (diesel oxidation catalyst), the engine could meet the requirements of China II legislation. The overall MSP (methanol substitute percent) reached 54.1%. The value of each pollutant emission was much lower than that in China II emission legislation, and there was almost no methanol and formaldehyde emissions. When methanol was injected into the inlet manifold, the intake air temperature decreased a lot, as well as the exhaust gas temperature, which were beneficial to increase engine thermal efficiency and improve engine room environment. Compared with the engine running in pure diesel mode, when the engine ran in diesel/methanol dual fuel mode, the combustion phase was advanced, and the combustion duration became shorter. Therefore, the engine thermal efficiency increased, and fuel consumption decreased significantly.     

Photodegradation of Hexafluoropropylene Oxide Trimer Acid under UV Irradiation

As a novel alternative to traditional perfluoroalkyl substances (PFASs), including perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS), hexafluoroproplyene oxide trimer acid (HFPO-TA) has been detected worldwide in surface water. Moreover, recent researches have demonstrated that HFPO-TA has stronger bioaccumulation potential and higher hepatotoxicity than PFOA. To treat these contaminants e.g. PFOA and PFOS, some photochemical techniques by adding exogenous substances had been reported. However, there is still no report for the behavior of HFPO-TA itself under direct UV irradiation. The current study investigated the photo-transformation of HFPO-TA under UV irradiation in aqueous solution. After 72 hr photoreaction, 75% degradation ratio and 25% defluorination ratio were achieved under ambient condition. Reducing active species, i.e., hydrated electrons and active hydrogen atoms, generated from water splitting played dominant roles in degradation of HFPO-TA, which was confirmed by different effects of reaction atmospheres and quenching experiments. A possible degradation pathway was proposed based on the products identification and theoretical calculations. In general, HFPO-TA would be transformed into shorter-chain PFASs, including hexafluoropropylene oxide dimer acid (HFPO-DA), perfluoropropionic acid (PFA) and trifluoroacetate (TFA). This research provides basic information for HFPO-TA photodegradation process and is essential to develop novel remediation techniques for HFPO-TA and other alternatives with similar structures.     

Concentrations and chemical compositions of PM10 during hazy and non-hazy days in Beijing

In order to study the concentrations of major components,characteristics and comparison in hazy and non-hazy days of PM_(10) in Beijing,aerosol samples were collected at urban site in Beijing from December 29,2014 to January 22,2015.Heavy metals like Zn,Pb,Mn,Cu,As,V,Cr and Cd were deeply studied considering their toxic effects on human being;nine water-soluble inorganic ions(SO_4~(2-),NO_3~-,NH_4~+,Na~+,K~+,Cl~-,Ca~(2+) and Mg~(2+)) and carbon fractions(OC and EC) were also analyzed.The concentrations of heavy metals were 1.03–1.98 times higher in hazy days than those in non-hazy days,mainly due to biomass burning and coal burning.The trends in total heavy metals concentrations were basically consistent with the trends in PM concentrations except for two obvious periods(12.29–12.30;1.14–1.15);but when air masses accumulated locally or around Beijing,trends in PM concentrations and heavy metals were opposite.The proportion for NO_3~-/SO_4~(2-) indicated that mobile sources such as automobiles were important reasons for haze in Beijing.Correlation between OC and EC during non-hazy days was strong(R~2= 0.95) but it was low(R~2= 0.67) during hazy days,and large variations for OC/EC values occurred in hazy days.The calculated mass concentration of SOC is 2.58 μg/m~3,which only accounted for 10.1% of the OC concentration.When air masses from the far north-west,they decreased PM concentration in Beijing and they were relatively clean;however,those from the near east,south-east and south of the mainland increased PM concentration and they were dirty.     

秸秆还田方式对东北农田土壤NH3挥发和N2O排放的影响

秸秆还田是有效利用资源、增加土壤有机质含量和培肥地力的有效措施,但也会影响土壤NH₃挥发和N₂O的排放.探索不同秸秆还田方式对NH₃挥发和N₂O排放的影响对于减少土壤氮素损失和保护生态环境具有重要意义.采用田间小区试验,利用Los Gatos Research（LGR）超便携NH₃分析仪和密闭式静态箱-气相色谱法探究不同秸秆还田方式下土壤NH₃挥发和N₂O排放的特征,试验设4个处理（覆盖还田,即表面覆盖玉米秸秆,0~20和20~40 cm土壤分层扰动后填回,记为JG0-0;常规还田,即秸秆与0~20 cm土壤混合,20~40 cm土壤扰动后填回,记为JG0-20;深还田,秸秆与20~40 cm土壤混合,0~20 cm土壤挖出后填回,记为JG20-40;对照处理,即无玉米秸秆还田,0~20和20~40 cm土壤分层扰动后填回,记为CK）.结果表明:①相比于CK,不同秸秆还田方式均显著降低了土壤NH₃挥发量,增加了土壤N₂O排放量.与CK相比,JG0-0、JG0-20和JG20-40处理下土壤NH₃累积排放量分别减少了12.38%、9.87%和5.73%;土壤N₂O累积排放量分别增加了30.19%、82.82%和36.53%,其中JG0-0和JG20-40处理之间无显著性差异.②JG20-40处理下玉米产量显著高于其他处理,比CK增加了23.15%,JG0-0处理下玉米产量高于CK和JG0-20处理,但并未达到显著水平.③对于NH₃和N₂O这两种气体的总累积排放量,各处理间均达到显著性差异.与CK相比,JG0-0、JG0-20和JG20-40处理下NH₃和N₂O总累积排放量分别增加了16.67%、52.08%和22.92%.④不同秸秆还田方式下的氮素气态损失率均高于CK,JG0-0、JG0-20和JG20-40处理下氮素气态损失率分别比CK增加了17.50%、52.50%和22.50%.因此,综合考虑土壤NH₃挥发量、N₂O排放量和玉米产量等因素,JG0-0处理优于JG20-40、JG0-20处理.      

Green innovation efficiency across China’s 30 provinces: estimate,comparison, and convergence

Mitigation and Adaptation Strategies for Global Change - Considering government and market failure of environmental regulation to combat increasing GHG (greenhouse gas) emissions, green innovation...