Analysis of the Factors Influencing Urban Size on Air Concentrations of Particulate Matter PM_(2.5)and PM_(10)in China

In the construction of resilient cities,regional air pollution prevention plays a pivotal role.Building on the previous research experience,the relationship between air pollution concentration and urban size exhibits a sublinear allometric growth pattern.To identify effective strategies for mitigating particulate matter air pollution,this study quantitatively explored 6 variables influencing urbanization in China’s cities and established an allometry model.Empirical analysis was conducted using data from 293 prefecturelevel cities and 1,827 county-level cities to examine the relationship between annual concentrations of fine particulate matter PM_(2.5) and PM_(10) in the atmosphere.①The findings of this study provided partial validation for the Kuznets curve and demonstrated a reverse‘U’-shaped association between urbanization and levels of PM_(2.5) and PM_(10) pollution.②By partitioning the Hu Huanyong line,this study identified the spatial distribution pattern of PM_(2.5) and PM_(10).In central and western regions,as urban size expands,inhalable particle concentrations tended to increase further;whereas in the southeast region,inhalable particle concentrations gradually decreased and stabilized after a certain threshold of urban scale expansion was reached.Among the factors influencing urban size,green coverage within built-up areas exerted the most significant impact on both PM_(2.5) and PM_(10) concentrations,followed by the extent of built-up areas and the scale of secondary industries.This study presented an effective strategy for reconciling conflicts between urban expansion and air pollution management,while concurrently promoting resilient cities characterized by high levels of modernization and superior quality.

Spatial and Temporal Variability of Farm Size in China in Context of Rapid Urbanization

During the last 30 years,China has witnessed rapid economic growth and dramatic urbanization,with about 1.2 × 107rural people migrating annually into urban areas.Meanwhile,especially since 1995,the rural population has been declining,which is closely linked to land circulation and the increase in farm size in many villages.Increasing scale of farming operations is often regarded as a key to avoiding the abandonment of farmland and to increasing the income of rural farmers.However,until now,there has been little research on the spatial and temporal variability of farm size at the national level in China.Using data from the national agricultural census and rural household surveys,this study examines the characteristics of land use circulation and the consequent changes in the area of farmland per household.The results show that: 1) 12.2% of rural households were involved in land circulation at the national level.The highest amounts of land circulation have occurred in those provinces where the farmland per capita is more than 0.2 ha or less than 0.1 ha;2) over 80% of households operate less than 0.6 ha of farmland;3) the proportion of mid-sized farms(between 0.2 ha and 0.6 ha per household) has decreased while the smallest and the largest farms have increased.This bears some similarity with the phenomenon known as the ′disappearing middle′,referring to the changes in farm size.This study establishes a framework for interpreting the factors affecting the changes in farm size in China,which include two promoting factors(urbanization and agriculture) and four hindering factors(agricultual land system,household registration,stable clan system,and farmland loss).

Distribution of Cu and Pb in particle size fractions of urban soils from different city zones of Nanjing, China

Soil samples from 4 defined city zones of Nanjing were randomly collec ted at 0—5 cm and 5—20 cm intervals and size fractions of soil particles were separated from undisturbed bulk soils by low energy dispersion procedure. The to tal contents of Cu and Pb in the different particle size fractions of the urban soils were analyzed by HNO3-HF-HClO4 digestion and flame atomic absorption spect rophotometer determination. The total content of Cu and Pb in soil particle size fractions varied with their size and with city zones as well. Both the content and variation with the size fractions of Pb was bigger than of Cu supporting our previous finding that there was Pb pollution to different degrees in the urban soils although the two elements were generally enriched in clay-sized fraction. Contaminated Pb tended to be preferentially enriched in the size fraction of 200 0—250 μm and clay-sized fraction. While the size fractions of the soils from n ewly developed and preserved area contained smaller amount of Cu and Pb, the par titioning of them in coarse and fine particle size fractions were insignificant compared to that from inner residence and commercial area. The very high Pb leve l over 150 mg/kg of the fine particle fractions from the soils of the inner city could be a cause of high blood Pb level reported of children from the city as a cute exposure to Pb of fine particles of the urban soil might occur by soil inge stion and inhalation by young children. Thus, much attention should be paid to t he partitioning of toxic metals in fine soil particles of the urban soils and co untermeasures against high health risk of Pb exposure by soil ingestion and dust inhalation should be practiced against the health problem of blood Pb for young children from the cities.

Size structure of urban agglomerations in China:rationality evaluation,patterns, and implications

This paper establishes a diagnostic model for assessing the rationality of size structure of urban agglomerations(UAs) in China. The model is designed to determine from a three-dimensional index including size distribution index(SDI), size compactness index(SCI), and size efficiency index(SEI). The spatio-temporal pattern of size structure involving the studied 19 UAs and its implications are explored. The results indicate that size structure of China's UAs advanced from a low rationality development stage to a moderate rationality development stage in 1995-2015.Among them, the SDI and SEI were reasonably high, and the SCI was relatively low. Spatially, the high rationality UAs were distributed across eastern China, while the low rationality UAs were located in western China. UAs with positive size structure possessed typically a dual-or multicenter urban structure, while UAs with negative size structure usually presented as a single-center structure. The evolutionary trajectories of rationality of size structure of UAs can be summarized as four different stages. Our findings suggest that, in addition to consolidating the status of national-level UAs, the development of regional-level UAs should be promoted. Also, the fostering focus and direction should be oriented toward an UA with dual-or multicenter spatial structure.

基于机器学习的中型城市居民出行方式选择行为研究

为探索中型城市居民出行特征以及不同因素对出行方式选择行为的影响机制,本文以中国某中型城市居民出行数据为例,综合考虑传统离散选择模型和机器学习模型在预测精度和建模合理性上的优劣,以及机器学习模型超参数求解算法的特点和效率,引入变异程序,提出粒子群优化随机森林的中型城市居民出行方式选择预测模型,采用预测准确率、出行方式比例预测绝对误差和期望模拟误差这3项性能指标,量化对比粒子群优化随机森林模型与多种机器学习模型和多项Logit模型统计学上的预测性能差异,利用SHAP(SHapley Additive exPlanation)模型深入分析个人社会经济属性、出行属性及出行方式属性等相关因素与居民出行方式选择之间的非线性关系。结果表明:粒子群优化随机森林模型整体平均预测准确率最高,为0.856,出行方式比例预测平均绝对误差和期望模拟平均误差最低,分别为0.062和0.306,模型间指标差异在统计学检验下显著;距离对不同出行方式选择的影响最显著,步行和私家车出行对距离敏感性更高,不同距离下,两者选择概率变化超过35%;30岁以下群体不同出行方式选择概率差距大于其他年龄段;性别、是否拥有私家车或公交IC卡等因素显著改变公交车和私家车的选择概率。

多源数据视角下黄河流域城市体系的规模等级与网络结构分析

基于宏观统计、微观企业和交通大数据,从规模和网络2个方面及“城市节点-发展轴线-空间格局”3个维度,分析黄河流域城市体系的规模等级和网络结构特征以及二者关系。结果表明:黄河流域城市体系呈现多中心分布特征,规模等级趋于均衡,形成了以兰州-西安-郑州-济南-青岛为主导的发展轴线和“Ψ”型空间格局。规模等级和网络结构成拉平的“S型”曲线关系,可划分为低水平低速耦合、中水平高速耦合和高水平低速耦合3个阶段。

家庭规模收缩对城市经济发展的影响--基于2010-2020年中国城市面板数据的研究

家庭是社会的“细胞”,是人民群众基本生活单位和社会治理的基本单元。第七次全国人口普查结果显示,2020年中国平均家庭户规模首次跌破3,家庭规模小型化已成为当前我国重要的人口特征之一。以我国287个地级及以上城市为研究对象,利用面板固定效应模型、门槛效应模型分析了2010—2020年间家庭规模变动对城市经济发展的影响。全国样本的回归结果显示,家庭规模与以人均GDP表征的城市经济水平存在同向变动关系,但这一关系在不同区域、不同人口增长速度的城市间具有异质性;中介效应结果显示,家庭规模收缩通过抑制城市人口增长和加重城市养老负担两条路径阻碍城市经济发展;门槛效应结果显示,只有当家庭规模收缩到一定程度以后,其对经济发展的作用才逐渐由“促进”转为“抑制”,且随着家庭规模的进一步收缩,这种抑制作用还会进一步增大。

产业转移与城市人口规模——来自“国家承接产业转移示范区”的证据

基于国家级承接产业转移示范区这一外生政策,使用2006—2019年中国288个城市的面板数据,采用多期双重差分模型考察了产业转移承接示范区政策对城市人口规模的影响并进行了机制分析。主要的结论如下:(1)产业转移承接示范区政策使试点城市的人口规模平均增加了5.79%。(2)人口规模的变化引致劳动力资源的再配置,即产业转移承接示范区政策显著增加了试点城市的就业,促进了第三产业的就业。(3)其机制包括产业转移承接示范区政策带来的大量企业进驻、更多的就业机会、地方政府公共品供给水平的提高、吸引人口流入进而扩大城市人口规模。(4)产业转移承接示范区政策效果具有异质性,在经济发展水平高的城市,政策对城市人口规模扩张的促进作用更大。(5)产业转移承接示范区政策通过企业集聚和人口集聚效应改善了区域环境质量。

基于系统GMM门槛模型的我国城市体育场馆营收、科创与经营布局研究

目的:分析中小型城市体育场馆的经营现状。方法:采用文献资料法、中介效应设计、变量选择与测算、数理统计法。结果显示:中小型城市体育场馆在数量、营收、科创投入、经营布局方面存在差异,对经营状况有影响。增加场馆数量、科创投入和城市人口对营收和科创投入有正向影响,但高经营布局可能降低经济绩效。中介效应分析强调了场馆数量、科创投入和经营布局的关键作用。稳健性分析支持模型可信度。门槛效应检验揭示了不同程度的门槛效应。建议:增加场馆数量,加大科创投入,优化经营布局,关注门槛效应,以促进可持续发展。

农村中小金融机构发展对城乡收入差距的影响效应研究

缩小城乡收入差距,实现城乡融合发展的关键在于实现农业农村优先发展。在坚持“金融机构的属性特征和数量分布对资金规模和供给流向具有重要影响”的基础上,文章基于2008—2021年中国省级面板数据实证检验农村中小金融机构发展对城乡收入差距的影响。结果发现,不同于以往大多数关于农村金融发展扩大城乡收入差距的结论,以农村每万人拥有的中小银行网点数衡量的农村中小金融机构发展显著缩小城乡收入差距。该作用在经过一系列内生性及稳健性检验后依然成立。对该作用的机制分析和检验表明,农村中小金融机构通过增加第一产业增加值、提高农业生产率和促进农村中小企业发展三个渠道对城乡收入差距起到缩小作用。这一研究发现深化了金融发展理论,为金融市场体制改革提供了一定理论依据,有利于从全新的角度理解城乡收入差距的影响因素,对经济高质量发展和收入分配状况的改善亦具有重要参考价值。

无人机高光谱在城市水质环境监测应用中反演模型构建的研究

高效的城市水质常态化监测是水环境污染防治的基础所在,无人机载高光谱技术既可以降低传统水质监测方法的人力和时间成本,同时可以推动生态环境智能检测网络的建立。聚焦城市中小河道水质监测的要求,探究无人机高光谱技术中反演模型构建中的关键技术。结果表明,无人机高光谱技术对于城市水质监测具有一定的准确性,具有推广和应用价值。

电动公交车队规模与充电桩配置协同优化

为了保障电动公交系统的车辆能源供给和线路顺畅运营,本文在多线路与多充电站场景下考虑线路行程时间的随机性,建立面向线路层面的电动公交系统车辆与充电桩配置双层优化模型。模型以车辆和充电桩投资成本与乘客候车成本之和的最小化为目标,对各线路车队规模、各充电站充电桩数量及线路与充电站间的充电匹配关系进行优化决策。在下层模型中,为反映随机行程时间下车辆充电过程对线路运营的影响,引入顾客源有限下的多服务台排队模型来刻画固定线路与充电站匹配下的排队充电过程;在上层模型中,考虑充电站与场站容量约束,对电动公交系统的线路与充电站匹配关系进行优化。在求解方面,首先基于排队模型设计算法求解特定线路与充电站匹配下的车队规模及充电桩数量,进而利用CPLEX求解器对线路与充电站匹配关系进行优化。在实验环节,设计不同规模的算例验证本文所提双层模型与算法框架的有效性,计算结果表明,本文所提的双层模型和算法框架可在满足充电站和场站容量限制的前提下尽可能缩减车队成本、充电桩成本与乘客候车成本;相比较两种人工经验方法,本文算法可将总成本分别降低5.65%和4.54%。

城市群内中小城市更新策略——以京津冀城市群内徐水区公共空间为例

“城市群”是我国城镇化体系的主体形态和城镇人口的主要空间载体,城市群内的中小城市与核心城市一样肩负着重要的时代使命。以徐水区为例,探讨京津冀城市群内的中小城市如何通过城市更新传承保护城市历史文化、优化城市公共空间、提升城市景观风貌。提出徐水公共空间城市更新技术路线,就城市文化在公共空间表达、街道空间优化、口袋公园营建、门户景观提升等4项景观策略进行详尽阐述,并总结出文化传达的独特性、公共空间提升的节约性、城市景观风貌塑造的特色性、科技赋能的示范性等在京津冀城市群内中小城市实施公共空间更新中可推广的景观策略。

City Size Distribution and Its Spatiotemporal Evolution in China

Based on the National Land Use/Cover Database of China(NLUD-C) in the end of the 1980s(the 1980s,hereafter), 1995, 2000, 2005, and 2010, 665 cities were selected to study the size distribution and its changes of urban lands in China. In this study, the spatiotemporal evolutions of urban land size distribution as well as the influence of administrative-level on these cities were explored by combining urban spatial positions and administrative-levels. Results indicate that: 1) City size distribution using urban lands was more practical and reasonable than using non-agricultural population. 2) In the 1980s, cities with ascending urban land rank were centralized in Eastern China, specially the Changjiang(Yangtze) River Delta, the Zhujiang(Pearl) River Delta, and Beijing-Tianjin-Hebei region. Cities in Central, Western, and Northeast China mainly indicated descending urban land rank. 3) The transfer of national development focus resulted in cities with ascending urban land rank becoming evenly distributed nationwide; however, this trend was slightly centralized around Chengdu, Chongqing, and Wuhan in different periods. 4) During the 1980s to 2010, the proportion of cities with ascending urban land rank in provincial capitals, municipalities, and special administrative regions(high-level cities, hereafter) was consistently higher than those in prefecture- and county-level cities except for 2005–2010. The ranks of the majority of the prefecture- and county-level cities were mainly descending, supported by ascending; the proportion of cities with unchanged rank is small. This study breaks through the bottleneck of traditional research in the area of city size distribution by examining urban land replacing the non-agricultural population. The current study also provides scientific explanation for the healthy and reasonable development of urban land as well as the coordinated development of population urbanization and land urbanization.

城市商业银行在资本新规背景下对小微企业融资的策略研究

在《商业银行资本管理办法》(资本新规)的背景下,城市商业银行的前景充满了挑战与机遇。资本新规提高了商业银行的风险抵御能力,使其在复杂市场环境中运营更为稳健,但同时也对其业务运营效率提出了更高要求。为了更好地支持小微企业的融资与发展,城市商业银行必须调整融资策略,如增加对小微企业的信贷投放、优化审批流程以及提供更加灵活的融资方案。本文通过深入分析小微企业的融资现状和需求特点,以及明确城市商业银行所面临的问题和挑战,提出针对性的策略建议,旨在帮助城市商业银行更好地适应资本新规要求、满足小微企业融资需求、推动实体经济发展,为城市商业银行的发展提供指导和借鉴。

2022年世界城市轨道交通运营统计与分析综述

参考国际上较为通用的统计标准,将城市轨道交通分为地铁、轻轨和有轨电车三大类,对世界城轨交通运营现状进行统计。分析表明:截至2022年底,全球有78个国家和地区的545座城市开通了城市轨道交通系统,总里程超过41 386.12 km,其中地铁、轻轨、有轨电车分别占48.9%、9.8%和41.3%。截至2022年12月31日,中国(含港澳台)累计有61座城市开通运营轨道交通,运营里程达10 857.17 km,其中中国内地运营里程10 291.96 km。2021年,全球46个国家的157座城市地铁累计运送乘客498.66亿人次,平均负荷强度0.74万人次/(d·km),其中中国(含港澳台)地铁年客流量为256.86亿人次。我国城市轨道交通持续稳步发展,线网规模和客流规模继续稳居全球第一。对中国内地市域(郊)铁路线路进行统计,开通运营里程为2 954.67 km,在建里程为2 826.91 km。市域(郊)铁路将为都市圈、城市群发展提供有力支持,为实现“双碳”愿景做出积极贡献,为交通强国建设奠定基础。

城市人口规模、就业密度与生产性空气污染排放——双重倒“U”型关系的解析与检验

随着中国城镇化快速推进,城市生产活动的活跃引致空气污染排放的加剧,明晰城市人口规模和就业密度对生产性空气污染排放的影响效应意义深远。该研究通过构建理论模型开展数值模拟,发现城市人口规模、就业密度与城市生产性空气污染排放之间均满足倒“U”型关系,且规模与密度均对倒“U”型门槛值存在调节效应。基于此,利用2010—2018年中国274个地级以上城市的面板数据进行实证检验,估计结果表明:①城市人口规模、就业密度对生产性空气污染排放的影响均符合稳健的倒“U”型特征,2018年生产性空气污染排放由升转降的规模门槛值和密度门槛值分别为105万人和3469人/km2。②目前,中国部分城市的人口规模与就业密度已超过门槛值,步入生产性空气污染排放的“双下行”通道,这些城市人口增加延长了非生产时间,对有效劳动供给造成的损失超过劳动力时间禀赋的增加,从而使得生产受限减少了生产性空气污染排放;同时,城市高就业密度有利于创新扩散和知识外溢,对生产性空气污染排放产生的减排作用强于高就业密度带来的生产激励效应对空气污染排放的增排作用,这些作用的综合结果使得生产性空气污染排放趋于下降。③城市人口规模扩张有助于降低密度门槛值,城市就业密度的提升也有助于降低规模门槛值。人口规模的扩张能够为知识外溢等提供有利条件,促使密度门槛前移;而就业密度的提升则会产生一定的拥挤效应,使得非生产时间更快增长,生产扩张提前受限,促使规模门槛前移。以上结论对推进新型城镇化与高质量发展具有启示意义。

金融集聚、创新创业活跃度与城市经济韧性

基于2004—2020年中国264个城市的面板数据,采用面板计量模型与中介效应模型考察金融集聚对城市经济韧性的影响及作用机制。研究结果表明:金融集聚对城市经济韧性提升具有显著驱动效应,且在运用替换变量指标、倾向得分匹配—双重差分法验证后,该结论依然稳健。中介机制检验结果表明:创新创业活跃度存在明显U形中介效应,即当金融集聚程度较低时,可能会由于金融支持不足抑制创新创业活跃度提升,从而降低城市经济韧性;随着金融集聚程度不断加深,创新创业活跃度显著提升,有助于提高城市经济韧性。异质性分析显示:在经济韧性强劲城市、经济韧性优良城市、经济韧性一般城市、中规模城市、中城市流强度、低城市流强度样本中,创新创业活跃度在金融集聚驱动城市经济韧性中的U形中介效应更为显著。为此,应培育金融创新源动力、优化创新创业生态圈和着力打造梯度韧性城市,以增强城市经济韧性并驱动经济高质量发展。

长三角城市群最优人口规模及其空间格局优化

长三角城市群的人口发展及空间格局关系到长三角区域一体化和高质量发展,关系到国家整体城市群发展战略的实现。本文通过构建城市最优人口规模理论模型,利用2009—2020年数据,使用系统广义矩估计(GMM)方法计算长三角城市群首位城市——上海市的最优人口规模,并结合城市体系位序—规模法则中的齐普夫标准分布指数,测算了基于城市群人口空间格局优化目标的长三角城市群的其余城市人口规模。通过计算发现,长三角城市群超大城市人口规模过大,特大城市人口规模不足,大城市人口分布相对合理,中小城市人口规模过小。最后,本文依据上述发现得出了针对不同城市发展与人口调控的政策启示。