Megacity Area Research Articles

Морфо- и феноизменчивость Picea pungens Engelm.: анализ пластичности вида в урбосреде Воронежа

In the Central Chernozem region of the Russian Federation, since 2010, the gap between the phenological development of plants and abiotic environmental factors has been increasing. In order to increase the biodiversity of the flora of megacities, the question of selecting an assortment of plant species that are resistant to a complex of natural and anthropogenic changes at the same time remains relevant. One of these species is the prickly spruce (Picea pungens Engelm.). The diameter of the trunk at chest height, the height of the tree, the number of macrostrobes, the length and color of the needles of specimens (N = 50) growing in urban plantations of Voronezh were studied. The length of the needles of the studied trees is identical to the length of the needles of trees in the natural range. In 20-30-year-old trees, blue-coniferous forms predominate, there is a fairly strong positive correlation between the diameter of the trunk and the height of the tree (r = 0.65).The beginning of growth and the end of shoots were recorded, the timing of the laying of wintering buds in prickly spruce trees (Picea pungens Engelm.). The vegetation period of the studied species is comparable with the phenorhythmics of the local (aboriginal) species of European spruce (Picea abies (L.) Karst.). The data indicate a sufficiently high adaptability of the prickly spruce (Picea pungens Engelm.) to the expansion of its potential range. We believe that this species is promising for widespread use in various recreational areas of megacities. In the future, it is necessary to answer the question: how will the phenorhythmics of the studied species affect vegetative reproduction to form the basis of the local phenotype?

The influences of 2D/3D urban morphology on land surface temperature at the block scale in Chinese megacities

Urban heat island (UHI) effects in core areas of megacities pose significant challenges to human health, energy consumption, and air quality. Investigating the relationship between urban morphology indicators and land surface temperature (LST) at the block scale is crucial for targeted urban planning strategies. This study examines the impact of morphology indicators on LST in central Beijing and Shanghai from 2000 to 2020 using the boosted region trees (BTR) model. Results showed: (1) LST increased in both cities in winter and summer, with high-value areas expanding spatially; (2) Comprehensive average impact degree of Beijing and Shanghai in winter and summer, Building density (BD) was the most important factor affecting LST, with 3D building forms being significant; (3) Impact hierarchy on LST: building form > landscape type > land cover type > social development; (4) The relationship between BD, ISA, and LST shifted from negative to positive with increasing values, while SHDI, GS, FAI, AI, and BH relationships with LST turned from positive to negative as values rose. This study highlights addressing UHI effects at the block scale in core urban areas, providing insights for urban planning and sustainable development.

AOD Derivation from SDGSAT-1/GLI Dataset in Mega-City Area

Aerosol optical depth (AOD) is the key parameter for determining the aerosol radiative effects and air quality variation. It is important to quantify nighttime aerosols using satellite-based night light images to understand their diurnal variations. This study selected high-resolution low light images from the Glimmer Imager (GLI) aboard the SDGSAT-1 satellite to examine spatial–temporal changes in night light emitted from the urban surface of Beijing. The radiance observed by SDGSAT-1/GLI was used to discern the AOD changes using the radiance background method (RB) and standard deviation method (SD) based on the characterization of the radiance from artificial light sources. Cloud cleaning processes were conducted to reduce the influence of the cloud cover in the glimmer images of the derived AOD. The results showed that there are good consistencies between the derived AOD results from the remote sensing and nighttime site observations. The radiance background method is better than the standard deviation method for deriving AOD using SDGSAT-1/GLI with the RMSE of its RB (0.0984) being greater than that of the SD (0.7653). The influence of moonlight, atmospheric absorption, and positioning errors on the results is briefly discussed. This paper shows that SDGSAT-1 can obtain relatively reliable night AOD values based on our investigations using the available satellite images taken in winter and spring, and that it has the potential to provide the scientific products of nighttime AOD.

Inundation risk assessment based on G-DEMATEL-AHP and its application to Zhengzhou flooding disaster

• Proposed G-DEMATEL-AHP method to assess inundation risk. • A new nine-score questionnaire was developed for G-DEMATEL-AHP method. • The five-year average precipitation scenario was set as the benchmark. • Validated by inundation of traffic system during 7.20 storm in Zhengzhou. • G-DEMATEL-AHP can effectively identify the most critical risk areas. This study proposed an integrated approach to investigate the flooding risk in urban areas of mega-cities. The new method integrated the grey decision-making trial and evaluation laboratory (Grey-DEMATEL) into analytical hierarchical process (AHP) (simplified as G-DEMATEL-AHP). The risk distribution was mapped using geographic information system (GIS). A nine-score questionnaire was adopted in Grey-DEMATEL to analyse the inundation risk. Zhengzhou was selected as a case study with different rainfall scenarios, including flooding disaster induced by heavy storm on July 20, 2021 (i.e., “7.20 Storm”) and average rainfall of five years (i.e., “5-Yr Average”). The results showed that the proposed method can assess the flood risk distribution effectively in Zhengzhou. Comparison between the results from different scenarios showed that the impact of the “7.20 Storm” was much stronger than that of the “5-Yr Average” scenario. Moreover, an existing method, fuzzy AHP (FAHP), was also used to assess the same scenario. The results indicated that the G-DEMATEL-AHP method could more effectively identify the most critical risk areas when compared to the FAHP.

Hierarchical Structure of the Central Areas of Megacities Based on the Percolation Theory—The Example of Lujiazui, Shanghai

The study of an urban center’s hierarchical structure is an important subject if one wishes to understand the city. Previous studies on urban hierarchical structure focused mostly on qualitative or quantitative research based on factors such as format, transportation, and economy, and lacked quantitative measurement from the perspective of street networks. This study examined the urban central area of Lujiazui, Shanghai, from the perspective of the percolation of the street network in the urban central area. Then, combined with the actual urban space function, the connotation and fractal nature of the hierarchical structure of the central area of the mega-city were obtained. The resulting nested hierarchies represent a reorganization of these highly agglomerated urban centers that contribute to sustainability. The fractal results were verified by the box counting method. Finally, this study fulfills its main purpose, which is to propose a new method for the study of the hierarchical structure of urban central areas.

Health risk assessment of gaseous elemental mercury (GEM) in Mexico City.

Emissions of gaseous elemental mercury (GEM or Hg0) from different sources in urban areas are important subjects for environmental investigations. In this study, atmospheric Hg measurements were conducted to investigate air pollution in the urban environment by carrying out several mobile surveys in Mexico City. This work presents atmospheric concentrations of GEM in terms of diurnal variation trends and comparisons with criteria for pollutant concentrations such as CO, SO2, NO2, PM2.5, and PM10. The concentration of GEM was measured during the pre-rainy period by using a high-resolution active air sampler, the Lumex RA 915 M mercury analyzer. In comparison with those for other cities worldwide, the GEM concentrations were similar or slightly elevated, and they ranged from 0.20 to 30.23 ng m−3. However, the GEM concentration was significantly lower than those in contaminated areas, such as fluorescent lamp factory locations and gold mining zones. The GEM concentrations recorded in Mexico City did not exceed the WHO atmospheric limit of 200 ng m−3. We performed statistical correlation analysis which suggests equivalent sources between Hg and other atmospheric pollutants, mainly NO2 and SO2, emitted from urban combustion and industrial plants. The atmospheric Hg emissions are basically controlled by sunlight radiation, as well as having a direct relationship with meteorological parameters. The area of the city studied herein is characterized by high traffic density, cement production, and municipal solid waste (MSW) treatment, which constantly release GEM into the atmosphere. In this study, we included the simulation with the HYSPLIT dispersion model from three potential areas of GEM release. Emissions from industrial corridors and volcanic plumes localized outside the urban area contribute to the pollution of Mexico City and mainly affect the northern area during specific periods and climate conditions. Using the USEPA model, we assessed the human health risk resulting from exposure to inhaled GEM among residents of Mexico City. The results of the health risk assessment indicated no significant noncarcinogenic risk (hazard quotient (HQ) < 1) or consequent adverse effects for children and adults living in the sampling area over the study period. GEM emissions inventory data is necessary to improve our knowledge about the Hg contribution and effect in urban megacity areas with the objective to develop public safe policy and implementing the Minamata Convention.Supplementary informationThe online version contains supplementary material available at 10.1007/s10661-022-10107-7.

On the Exploitation of Remote Sensing Technologies for the Monitoring of Coastal and River Delta Regions

Remote sensing technologies are extensively applied to prevent, monitor, and forecast hazardous risk conditions in the present-day global climate change era. This paper presents an overview of the current stage of remote sensing approaches employed to study coastal and delta river regions. The advantages and limitations of Earth Observation technology in characterizing the effects of climate variations on coastal environments are also presented. The role of the constellations of satellite sensors for Earth Observation, collecting helpful information on the Earth’s system and its temporal changes, is emphasized. For some key technologies, the principal characteristics of the processing chains adopted to obtain from the collected raw data added-value products are summarized. Emphasis is put on studying various disaster risks that affect coastal and megacity areas, where heterogeneous and interlinked hazard conditions can severely affect the population.

Improvement of the organizational and economic mechanism for ensuring the complexity of the development of residential areas of megacities

Ensuring favorable living conditions of the population and a comfortable urban environment is one of the priority tasks, the solution of which is required in areas of mass residential development. The increasing volume of housing construction causes a proportional increase in the need for social infrastructure facilities. One of the tools for solving this problem can be the improvement of the organizational and economic mechanism of the housing developer's participation in the construction of social infrastructure facilities that ensure the complexity of the development of residential areas of megacities. The criteria for the formation of a list of social infrastructure facilities the construction of which can be assigned to the developer as a social burden, are defined. A list of social infrastructure facilities has been formed, first of all, ensuring the complexity of residential development of megacities, the construction of which can be entrusted to the developer within the framework of social encumbrances. In order to meet the needs for selected social infrastructure facilities: kindergartens, schools and outpatient clinics, the author's methodology for calculating the amount of financial obligations of the developer for the development of social infrastructure facilities has been developed, the results of such calculation are presented. According to the enlarged calculations, the quantitative value of the indicator of the volume of the developer's participation in the construction of the most important social infrastructure facilities affecting the quality of the urban environment will amount to 14311 rubles/sq.m of the total area of apartments. The proposed calculation model can be used as a basis for financial and economic justification of the effectiveness of managerial decision-making in the field of urban planning. As part of the improvement of the organizational and economic mechanism of the developer's participation in the construction of social infrastructure facilities, a proposal has been formulated to create a separate organizational structure – the Social Obligations Fund, which will ensure the accumulation of developers' funds and their fair and efficient distribution in accordance with the order of housing commissioning and within the framework of agreements concluded with developers

Optimization of Landscape Ecological Security Patterns and Planning in Low Hilly Areas —A Case Study of Beigong Town, Fengtai District, Beijing City, China

With the continuous expansion of mega-cities in China, the landscape pattern of the original urban-rural area is broken, resulting in serious fragmentation of landscape patches in the fringe area of the urban center and threatening urban ecological security. Therefore, how to consider the needs for construction and development based on securing ecological security patterns is a key consideration for the fringe areas of megacities. The study takes Beigong Town as the research object and uses the MSPA model analysis method to extract nine ecological source sites that are important for ecological network construction. Then, the study constructs a comprehensive ecological resistance surface based on the MCR minimum cumulative resistance model, generates minimum cost paths to simulate regional potential corridors, and constructs the ecological security pattern in Beigong Town. The study further combines the current situation of land use in Beigong Town to optimize the ecological safety pattern and proposes the planning control systems, which provides the basis for the next planning and construction.

The Impact of COVID-19 Lockdowns on Satellite-Observed Aerosol Optical Thickness over the Surrounding Coastal Oceanic Areas of Megacities in the Coastal Zone

Nearly 40 years of aerosol optical thickness (AOT) climate data record (CDR) derived from NOAA operational satellite Advanced Very High Resolution Radiometer (AVHRR) observation over the global oceans is used to study the AOT changes due to the COVID-19 lockdown over the surrounding coastal oceanic areas of 18 megacities in the coast zone (MCCZ). The AOT difference between the annual mean AOT values of 2020 with COVID-19 lockdown and 2019 without the lockdown along with the 2020 AOT annual anomaly are used to effectively identify the AOT changes that are a result of the lockdown. We found that for most of the 18 MCCZ, the COVID-19 lockdowns implemented to contain the spread of the coronavirus resulted in a decrease between 1% and 30% in AOT due to reduced anthropogenic emissions associated with the lockdowns. However, the AOT long-term trend and other aerosol interannual variations due to favorable or unfavorable meteorological conditions may mask AOT changes due to the lockdown effect in some MCCZ. Different seasonal variations of aerosol amount in 2020 relative to 2019 due to other natural aerosol emission sources not influenced by the lockdown, such as dust storms and natural biomass burning and smoke, may also conceal a limited reduction in the annual mean AOT due to the lockdown in MCCZ with relatively loose lockdown. This study indicates that the use of long-term satellite observation is helpful for studying and monitoring the aerosol changes due to the emission reduction associated with the COVID-19 lockdown in the surrounding coastal oceanic areas of MCCZ, which will benefit the future development of the mitigation strategy for air pollution and emissions in megacities.

ASSESSMENT OF THE ENVIRONMENTAL SAFETY FACTORS OF PLAY-GROUNDS USING THE RANK CORRELATION METHOD

The process of rapid development in modern cities has led to a significant number of playgrounds being located in confined areas, near roads with heavy vehicle traffic (including tram tracks), next to short-term parking spaces and refuse containers. Particular attention is paid to unauthorised parking which is caused by a lack of designated parking spaces. In addition, in residential areas of modern megacities there is a lot of infill development, which is an additional source of noise and dust. Thus, a significant number of playgrounds are located in areas with excessive anthropogenic load.&#x0D; The materials presented in the article describe the current condition of playgrounds in most big cities of Ukraine. Particular importance is attached to the factors which are connected with vehicle traffic, for example noise pollution, air dustiness and pollutant emissions.&#x0D; At the first stage, a list of factors affecting the environmental safety of children's playgrounds in urbanised areas was compiled and analysed.&#x0D; The next stage involves the development of a questionnaire and the direct assessment of the influencing factors by the experts involved. The article considers the factors that are rarely considered in the study of the impact of individual anthropogenic factors of the environment on public health, however, in modern conditions they cannot be neglected.&#x0D; The final stage consists of data processing and formation of conclusions. Using the method of rank correlation, the main factors of influence on the objects of research are identified.&#x0D; The results of the research stated in the article can be used in further study of the subject and in the development of methods to eliminate the influence of the most significant factors affecting the ecological safety of children's playgrounds.

Peculiarities of formation of recreational land use in the suburban zone of the megapolis

The article highlights the scientific principles of the formation of environmental land use in Ukraine. The components of suburban areas of megacities and the process of their development in modern society are studied. The article reflects the impact of urbanization on land use and the environment. Emphasis is placed on the fact that the development of urbanization is accompanied by the disappearance of valuable natural and recreational complexes, the loss of cultural and historical heritage, increasing social tensions. The study was carried out on the basis of statistical and analytical data of the Ministry of Environmental Protection and Natural Resources of Ukraine, the State Geocadastre of Ukraine, the State Statistics Service of Ukraine, the Ministry of Economy of Ukraine, materials of scientific conferences, seminars, the author's own calculations. The article substantiates the need to create recreational land use in the suburban area of the metropolis. The conceptual apparatus in terms of interpretation of the concepts "recreational areas", "recreational land use", "recreational lands" is studied. An assessment of the peculiarities of the creation, use and maintenance of recreational land use in the suburban area of the metropolis. The procedure of formation of lands of recreational purpose, significance of these territories is revealed. As a result, it is established that the most important problems of recreational land use in Ukraine are ensuring high quality recreation, expanding the diversity of opportunities for recreational lands and resources closely related to them, meeting people's needs to communicate with wildlife and restoring public health. However, the radical transformation of landscapes and the large-scale development of urbanization have led to a decrease in the recreational value of landscapes and thus to the formation of recreational areas on lands unsuitable for other economic uses. All this negatively affects the quality of recreation, the diversity of recreational activities and the ability to remain in the recreational sphere of landscapes that meet the needs of the population in recreation. Key words: recreational land use, suburban area of the metropolis, recreational territories, lands of recreational purpose.

Concentrations, health risks, and sources of hazardous air pollutants in Seoul-Incheon, a megacity area in Korea

We conducted ambient monitoring of various hazardous air pollutants (HAPs) for 2 years (2013-2015) in two adjacent Korean cities in a megacity area: Seoul and Incheon. Measured HAPs included volatile organic compounds (VOCs), polycyclic aromatic hydrocarbons (PAHs), and heavy metals (HMs). The objectives of this study were to evaluate the spatiotemporal variations of HAPs, to prioritize HAPs based on health risks, to identify sources using a receptor-based model, and to estimate source-specific risks. Overall, the HAP levels in Incheon were higher than those in Seoul. The concentrations of combustion-origin HAPs, such as PAHs and some HMs, were significantly higher during the heating period than during the non-heating period. However, most VOCs exhibited an opposite trend. Benzo[a]pyrene showed the highest cancer risk in both cities, followed by formaldehyde, arsenic, and benzene; trichloroethylene was the only species that exceeded the hazard quotient of 1. Cumulative cancer risks were 2.0 × 10-4 in Seoul and 2.7 × 10-4 in Incheon. Major sources and their contributions to each HAP concentration were estimated by positive matrix factorization modeling. Based on source-specific risk assessments, we suggest that both cities should give high priority to the control of traffic pollution and the supply of cleaner fuels in non-residential sectors. Reducing carbonyl concentrations in Seoul and industrial emissions in Incheon is also necessary. Establishing new ambient standards for benzo[a]pyrene and formaldehyde is worth considering as a long-term measure. This study provides scientific information on the occurrence, health risks, and sources of various HAPs in large urban areas.

The network pattern of underground pedestrian system and its role to urban resilience

In recent years, underground pedestrian system (UPS) has been developed worldwide, especially within central megacity areas, but research on UPS characteristics is still in the qualitative description stage, and quantitative methods are lacking to assess the impact of UPS on resilience. Therefore, it is essential to quantitatively measure UPS resilience and thus be able to make decisions on how UPS can be improved. The authors propose topological analysis of UPS networks based on computational and functional graph representations, which represents a new approach to theoretical discussions and empirical evidence for planning and configuring a UPS, thereby contributing to urban resilience. These representations provide functional views in which nodes represent single underground spaces and links represent underground sideways. Various graph measures are computed for structural analysis, and results provide insights into the required physical properties for planning resilient UPS. Based on validations applied to two typical high-density areas in Nanjing Xinjiekou and Guangzhou Zhujiang New Town, China, the authors examine how different UPS network patterns influence resilience performance, then further discuss the social and economic factors affecting network patterns, and give suggestions.

Urbanization Impacts on Pearl River Delta Extreme Rainfall Sensitivity to Land Cover Change Versus Anthropogenic Heat

AbstractImpacts of urban land cover and anthropogenic heat (AH) on extreme local rainfall over the coastal Pearl River Delta (PRD) megacity region during boreal summer are investigated by conducting numerical experiments using the Weather Research and Forecastingmodel coupled with a single‐layer urban canopy model. To examine the relative importance of land cover change versus the presence of AH, three numerical experiments corresponding to different levels of urbanization in the PRD area were designed: one with cropland covering the whole region, one with urban land cover but zero AH, and one with urban land cover and a strong diurnal maximum of 300 Wm−2 of AH in the model simulations. Results show that the increase of rainfall in the urban area is much more sensitive to the intensity of AH than the mere change of surface properties. Urbanization with intense AH can enhance both the intensity and frequency of extreme rainfall, which can be attributed to higher surface temperature (of about 3.5–4°C), higher convective available potential energy, and lower convective inhibition, thus creating an environment more conducive to strong convection over the urban areas. Moreover, enhanced rainfall is supported by moisture supply from the South China Sea and increased water vapor flux convergence over the PRD city area. The amount of moisture flux converging over the coastal megacity area was found to depend on the direction of prevailing background wind.

Emission Monitoring Mobile Experiment (EMME): an overview and first results of the St. Petersburg megacity campaign 2019

Abstract. Global climate change is one of the most important scientific, societal and economic contemporary challenges. Fundamental understanding of the major processes driving climate change is the key problem which is to be solved not only on a global but also on a regional scale. The accuracy of regional climate modelling depends on a number of factors. One of these factors is the adequate and comprehensive information on the anthropogenic impact which is highest in industrial regions and areas with dense population – modern megacities. Megacities are not only “heat islands”, but also significant sources of emissions of various substances into the atmosphere, including greenhouse and reactive gases. In 2019, the mobile experiment EMME (Emission Monitoring Mobile Experiment) was conducted within the St. Petersburg agglomeration (Russia) aiming to estimate the emission intensity of greenhouse (CO2, CH4) and reactive (CO, NOx) gases for St. Petersburg, which is the largest northern megacity. St. Petersburg State University (Russia), Karlsruhe Institute of Technology (Germany) and the University of Bremen (Germany) jointly ran this experiment. The core instruments of the campaign were two portable Bruker EM27/SUN Fourier transform infrared (FTIR) spectrometers which were used for ground-based remote sensing measurements of the total column amount of CO2, CH4 and CO at upwind and downwind locations on opposite sides of the city. The NO2 tropospheric column amount was observed along a circular highway around the city by continuous mobile measurements of scattered solar visible radiation with an OceanOptics HR4000 spectrometer using the differential optical absorption spectroscopy (DOAS) technique. Simultaneously, air samples were collected in air bags for subsequent laboratory analysis. The air samples were taken at the locations of FTIR observations at the ground level and also at altitudes of about 100 m when air bags were lifted by a kite (in case of suitable landscape and favourable wind conditions). The entire campaign consisted of 11 mostly cloudless days of measurements in March–April 2019. Planning of measurements for each day included the determination of optimal location for FTIR spectrometers based on weather forecasts, combined with the numerical modelling of the pollution transport in the megacity area. The real-time corrections of the FTIR operation sites were performed depending on the actual evolution of the megacity NOx plume as detected by the mobile DOAS observations. The estimates of the St. Petersburg emission intensities for the considered greenhouse and reactive gases were obtained by coupling a box model and the results of the EMME observational campaign using the mass balance approach. The CO2 emission flux for St. Petersburg as an area source was estimated to be 89 ± 28 ktkm-2yr-1, which is 2 times higher than the corresponding value in the EDGAR database. The experiment revealed the CH4 emission flux of 135 ± 68 tkm-2yr-1, which is about 1 order of magnitude greater than the value reported by the official inventories of St. Petersburg emissions (∼ 25 tkm-2yr-1 for 2017). At the same time, for the urban territory of St. Petersburg, both the EMME experiment and the official inventories for 2017 give similar results for the CO anthropogenic flux (251 ± 104 tkm-2yr-1 vs. 410 tkm-2yr-1) and for the NOx anthropogenic flux (66 ± 28 tkm-2yr-1 vs. 69 tkm-2yr-1).

Real-time characterization and source apportionment of fine particulate matter in the Delhi megacity area during late winter

National Capital Region (NCR) encompassing New Delhi is one of the most polluted urban metropolitan areas in the world. Real-time chemical characterization of fine particulate matter (PM1 and PM2.5) was carried out using three aerosol mass spectrometers, two aethalometers, and one single particle soot photometer (SP2) at two sites in Delhi (urban) and one site located ~40 km downwind of Delhi, during January–March 2018. The campaign mean PM2.5 (NR-PM2.5 + BC) concentrations at the two urban sites were 153.8 ± 109.4 μg.m−3 and 127.8 ± 83.2 μg.m−3, respectively, whereas PM1 (NR-PM1 + BC) was 72.3 ± 44.0 μg.m−3 at the downwind site. PM2.5 particles were composed mostly of organics (43–44)% followed by chloride (14–17)%, ammonium (9–11)%, nitrate (9%), sulfate (8–10)%, and black carbon (11–16)%, whereas PM1 particles were composed of 47% organics, 13% sulfate as well as ammonium, 11% nitrate as well as chloride, and 5% black carbon. Organic aerosol (OA) source apportionment was done using positive matrix factorization (PMF), solved using an advanced multi-linear engine (ME-2) model. Highly mass-resolved OA mass spectra at one urban and downwind site were factorized into three primary organic aerosol (POA) factors including one traffic-related and two solid-fuel combustion (SFC), and three oxidized OA (OOA) factors. Whereas unit mass resolution OA at the other urban site was factorized into two POA factors related to traffic and SFC, and one OOA factor. OOA constituted a majority of the total OA mass (45–55)% with maximum contribution during afternoon hours ~(70–80)%. Significant differences in the absolute OOA concentration between the two urban sites indicated the influence of local emissions on the oxidized OA formation. Similar PM chemical composition, diurnal and temporal variations at the three sites suggest similar type of sources affecting the particulate pollution in Delhi and adjoining cities, but variability in mass concentration suggest more local influence than regional.

The changing PM2.5 dynamics of global megacities based on long-term remotely sensed observations

Satellite observations show that the rapid urbanization and emergence of megacities with 10 million or more residents have raised PM2.5 concentrations across the globe during the past few decades. This study examines PM2.5 dynamics for the 33 cities included on the UN list of megacities published in 2018. These megacities were classified into densely (>1500 residents per km2), moderately (300–1500 residents per km2) and sparsely (<300 residents per km2) populated areas to examine the effect of human population density on PM2.5 concentrations in these areas during the period 1998–2016. We found that: (1) the higher population density areas experienced higher PM2.5 concentrations; and (2) the megacities with high PM2.5 concentrations in these areas had higher concentrations than those in the moderately and sparsely populated areas of other megacities as well. The numbers of residents experiencing poor air quality is substantial: approximately 452 and 163 million experienced average annual PM2.5 levels exceeding 10 and 35 μg/m3, respectively in 2016. We also examined PM2.5 trends during the past 18 years and predict that high PM2.5 levels will likely continue in many of these megacities in the future without substantial changes in their economies and/or pollution abatement practices. There will be more megacities in the highest PM2.5 pollution class and the number of megacities in the lowest PM2.5 pollution class will likely not change. Finally, we analyzed how the PM2.5 pollution burden varies geographically and ranked the 33 megacities in terms of PM2.5 pollution in 2016. The most polluted regions are China, India, and South Asia and the least polluted regions are Europe and Japan. None of the 33 megacities currently fall in the WHO’s PM2.5 attainment class (<10 μg/m3) while 9 megacities fall into the PM2.5 non-attainment class (>35 μg/m3). In 2016, the least polluted megacity was New York and most polluted megacity was Delhi whose average annual PM2.5 concentration of 110 μg/m3 is nearly three times the WHO’s non-attainment threshold.

Polycyclic aromatic hydrocarbons in leaves of Cinnamomum camphora along the urban–rural gradient of a megacity: Distribution varies in concentration and potential toxicity

Rapid urbanization and industrialization have precipitated the significant urban-rural gradient involving various aspects of human-related activities especially in megacities. Anthropogenic activities are the main source of polycyclic aromatic hydrocarbon (PAH) contamination, and the rising awareness concerning PAH potential toxicity to human health promotes a further understanding of its spatial distribution pattern in cities. Whether the distribution of PAH concentration and potential toxicity respond to the urban-rural gradient still requires investigation. This study applied a grid sampling method to investigate PAH concentration using Cinnamomum camphora leaves as bioindicators which were obtained from 84 sampling sites in a megacity, Shanghai. The potential toxicity of PAHs in leaves was calculated by toxicity factor equivalent method. Results revealed the patterns of PAH distribution in the city varied in concentration and potential toxicity: the total concentration of PAHs in leaves decreased along the urban–rural gradient, while the potential toxicity peaked at junction areas. The trend of PAH concentration along the distance from urban center corresponded to that of population density. The spatial distribution of potential toxicity did not correspond with the gradient but was influenced by high benzo(a)pyrene concentration originated from the industry districts nearby. Higher potential toxicity of PAHs was observed at the urban-suburban-rural junction areas of megacities, advocating health-risk attention and appropriate plan for land use of these transition areas in cities.

Mitigating air problems and producing renewable energy with solar downdraft tower

Over the past three decades, China, especially in the megacity areas, has suffered from air pollution and heavy haze with its decades-long burst of economic growth and rapidly expanding clout as an industrial giant. The important two elements of air pollutant in China are the fine particles (PM 2.5-PM 10) and non-natural greenhouse gases. To overcome these problems, in this study, we propose a novel inversion solar chimney approach for mitigating the air pollution and haze problems in the megacities of China by using water to scavenge air pollution through spraying water into the atmosphere. For a water drop floating in air or falling through air, the sensible heat of air would transfer to the latent heat of droplets and will cause a decrease in drop size. In a quite short transient time, the droplet evaporates and cools down to air ‘wet-bulb’ temperature. The Direct air capture devices (DAC) are installed at the bottom of the solar downdraft tower to reduce the CO2 in the atmosphere.