Simulation of Wind Circulation and Pollutant Diffusion Over the Pearl River Delta Region

Changes in urban surface areas and population growth have significantly affected the weather and environment. Emissions of nitrogen oxides are increasing in the Pearl River Delta region. Nitrogen compounds emitted by factories and motor vehicles are the major sources of nitric pollution. To study the impacts of urbanization and the relationship between pollutant diffusion and the atmospheric environment, the nonhydrostatic mesoscale forecast model MM5 (v3.73), which was developed by Penn State University and the National Center of Atmospheric Research, and a mass continuity equation for air pollutants, were used in this study. Two experiments were designed. One experiment (BE) applied horizontal grid resolutions of 27, 9, 3, and 1?km in four nested domains. The other experiment adopted new land-use data (in domain 4) directly retrieved from Landsat Thematic Mapper imagery to replace the 1980s data of the United States Geological Survey in BE. A 48-h simulation (from 0000?UTC on 21 October to 0000?UTC on 23 October 2008) was conducted, with the first 12?h being the spin-up time and the remaining 36?h being the effective simulation, so as to capture the diurnal features of the thermally induced winds associated with the land–sea breeze and urban heat island circulations. The different results obtained from the two tests for wind circulation and air pollution dispersion and transportation in the Pearl River Delta region were analyzed. The simulated results show that the both experiments can well simulate land–sea breeze circulation and remarkable land–sea breeze evolution, comparing with observation data. The height of the PBL had a significant diurnal cycle. The structure of the wind field can obviously impact the dispersion of the NO _x in three dimensions. Nitrogen oxides mainly diffused along the dominant wind direction (east or southeast wind), therefore the majority of the pollutants accumulated in the northwest region of the fine domain in both simulation experiments. However, it induced the pollutants concentration in an irregular pattern due to the fine-resolution grid spaces and complicated inland wind field in the northwest area of the inner domain. Moreover, increasing the proportion of urban surface caused sensible heat flux increase, latent heat flux decrease and humility reducing relatively in the region of urban surface characteristics apparently. Urbanization will cause pollution accumulated severely over the urban surface.     

西藏拉萨市热岛效应及其影响因子分析

采用2001年、2004年以及2007年三年的EOS/MODIS遥感信息反演的地面温度以及多年常规气象观测资料,讨论了拉萨市热岛现象及其可能影响因子。结果表明:(1)热岛强度的年、季节变化呈现逐渐增强的趋势,其中,冬季的热岛强度最强,其次是春季,秋季和夏季的热岛效应较弱;高温区基本位于城市中心或者县城所在地及其周围,低温区主要集中在各县的郊区;近年来拉萨地区的城市高温区域逐渐扩大,有些高温中心可能向某些区域偏移;遥感资料所获取的地表温度与平均气温之间存在一定的正相关性。(2)无论是年变化,还是季节变化,热岛强度都与风速呈正相关,与日照时数呈负相关,与蒸发量的相关在夏季和冬季分别呈正相关、负相关的相反状况;地表温度与植被分布具有较好的负相关关系,即在城区存在较高的地表温度分布和较小的NDVI,过渡到郊区具有温度减小、NDVI增加的特征;随着城市化进程的加剧,建筑面积不断扩大,人类活动明显增加,排放至大气的人为热增加,这些因素都可能导致热岛强度的增强。     

基于TM资料对上海区域热环境特征的分析

为了揭示城市热岛(UHI)形成机制,以TM卫星遥感资料为主要数据源,结合地面自动气象站(AWS)实测的气象资料,利用地表能量平衡参数化(SEBAL)的方法估算了净辐射通量和土壤热通量,分析了上海区域热环境特征.结果表明,TM地表温度与AWS实测地表温度具有较好的一致性；不同类型地表其地表温度差异明显,城市道路是城市中重要热量来源,绿地和水体面积的增加能有效地减轻城市热岛强度,同时也表明了卫星遥感资料在城市气候环境研究中的潜在价值.     

Ground level volume mixing ratio of methane in a tropical coastal city

Urban regions are hotspots of greenhouse gas emissions which include CO₂, CH₄, N₂O, etc. Methane is a strong greenhouse gas which is produced from a number of sources including fossil fuel combustion, municipal waste, and sewage processing, etc. Ground level mixing ratio of methane in the tropical coastal city of Thiruvananthapuram in South India, during calm early morning period was measured. Measurements were done during both winter and summer seasons. Concentrations were significantly higher than global average value. Intra-city variation in ground level mixing ratio was also significant. Ground level methane concentration at Thiruvananthapuram urban area showed maximum value of 3.16 ppmV. Under stable atmospheric conditions in early morning, ground level mixing ratio of methane was 2.79 ppmV in winter and 2.54 ppmV during summer. The spatial distribution of methane concentration shows correlation with urban heat island.     

An energy and mortality impact assessment of the urban heat island in the US

Increased summer energy use and increased summer heat related mortality are the two most cited detrimental impacts of the urban heat island (UHI). An assessment of these impacts was made that considered the annual impact of the UHI, not just the summer impact. It was found that in north of the US there was a net decrease in energy use from the UHI, as heating energy reductions were larger than the increase in cooling energy. In the south there was a net energy increase from the UHI. The impact of the UHI on heat related deaths was an estimated increase of 1.1 deaths per million people. The impact of the UHI on cold related deaths was an estimated decrease of 4.0 deaths per million people. These estimates are caveated by the acknowledgement that compounding factors influence mortality. Hypothermia related death rates were three times higher in rural areas than urban areas. This is surprising as the homeless population is usually considered the most at risk, yet they mostly live in urban areas.     

Major inputs and mobility of potentially toxic elements contamination in urban areas

Soil quality in urban areas is affected by anthropogenic activities, posing a risk to human health and ecosystems. Since the pseudo-total concentrations of potentially toxic elements may not reflect their potential risks, the study of element mobility is very important on a risk assessment basis. This study aims at characterising the distribution and major sources of 34 elements in two Portuguese urban areas (Lisbon and Viseu), with different geological characteristics, industrial and urban development processes. Furthermore, the potential availability of As, Co, Cr, Cu, Ni, Pb and Zn was assessed, by measuring the fraction easily mobilised. Lisbon is enriched in elements of geogenic and anthropogenic origin, whereas in the smaller city, the high levels observed are mainly related to a geogenic origin. Background values can be more relevant than the dimension of the city, even when anthropogenic components may be present, and this parameter should be considered when comparing results from different cities. Regarding the potential available fraction, a high variability of results was observed for elements and for sampling sites with an influence of the soil’s general characteristics. Elements showing very high concentrations due to geological reasons presented, in general, a low mobility and it was not dependent on the degree of contamination. For elements with major anthropogenic origin, only Zn was dependent on the pseudo-total content. Yet, the highest available fractions of some elements, both with major geogenic and anthropogenic origin, were observed in specific contaminated samples. Therefore, a site-specific evaluation in urban soils is important due to the high spatial variability and heterogeneity.     

Characterizing ozone pollution in a petrochemical industrial area in Beijing,China: a case study using a chemical reaction model

This study selected a petrochemical industrial complex in Beijing, China, to understand the characteristics of surface ozone (O₃) in this industrial area through the on-site measurement campaign during the July–August of 2010 and 2011, and to reveal the response of local O₃ to its precursors’ emissions through the NCAR-Master Mechanism model (NCAR-MM) simulation. Measurement results showed that the O₃ concentration in this industrial area was significantly higher, with the mean daily average of 124.6 μg/m³ and mean daily maximum of 236.8 μg/m³, which are, respectively, 90.9 and 50.6 % higher than those in Beijing urban area. Moreover, the diurnal O₃ peak generally started up early in 11:00–12:00 and usually remained for 5–6 h, greatly different with the normal diurnal pattern of urban O₃. Then, we used NCAR-MM to simulate the average diurnal variation of photochemical O₃ in sunny days of August 2010 in both industrial and urban areas. A good agreement in O₃ diurnal variation pattern and in O₃ relative level was obtained for both areas. For example of O₃ daily maximum, the calculated value in the industrial area was about 51 % higher than in the urban area, while measured value in the industrial area was approximately 60 % higher than in the urban area. Finally, the sensitivity analysis of photochemical O₃ to its precursors was conducted based on a set of VOCs/NOx emissions cases. Simulation results implied that in the industrial area, the response of O₃ to VOCs was negative and to NOx was positive under the current conditions, with the sensitivity coefficients of ?0.16~?0.43 and +0.04~+0.06, respectively. By contrast, the urban area was within the VOCs-limitation regime, where ozone enhancement in response to increasing VOCs emissions and to decreasing NOx emission. So, we think that the VOCs emissions control for this petrochemical industrial complex will increase the potential risk of local ozone pollution aggravation, but will be helpful to inhibit the ozone formation in Beijing urban area through reducing the VOCs transport from the industrial area to the urban area.     

基于Landsat 7的武汉市热岛效应研究

城市化使得城市数量和规模不断增加,城市作为人类对自然环境改造最为剧烈的部分,具有独特的区域环境,其中城市内部温度显著高于周边郊区的热岛效应是一个突出的城市环境问题,受到了普遍关注和研究。武汉市是长江中游特大城市,城市热岛效应明显,但对其研究很少。利用Landsat TM6波段数据,生成武汉市城市亮温场,分析了武汉市热场的分布、大小,利用亮温场均值、方差和相对温度评价城市热岛强度,并对城市热场的范围及强度变化与城市发展规模及方向进行了分析,取得了较好的效果。     

Spatial patterns of nitrate,chloride, sulfate,and fluoride concentrations in the Woodbine Aquifer of north-central Texas

A geographic information system was used to map and analyze nitrate, chloride, sulfate, and fluoride concentrations in 110 wells tapping the Woodbine Aquifer. The study area, covering ninecounties in north-central Texas, includes large percentages of both urban and agricultural land uses. Land use maps were compared with solute concentration data, and statistics were applied to detect associations between solutes, well depth, andland use. Anthropogenic sources such as fertilizer applications and natural sources such as gypsum, lignite, and clay deposits controlled nitrate, chloride, and sulfate concentrations, each inversely correlated with well depth. However, only one nitrate observation – from a shallow well in the aquifer's outcrop zone – surpassed the maximum contaminant level (MCL) of 44.3 mg L^-1. By comparison, nearly half of the sulfate and several of the chloride observations surpassed the MCL of 250 mg L^-1for each of those ions. Volcanic ash deposits influenced fluorideconcentrations, which directly correlated with well depth. There were no statistically significant associations between solute concentrations and land use. Low recharge rates and confining layers have mitigated anthropogenic impacts on solute levels in the aquifer.     

Temporal and spatial characteristics of the urban heat island during rapid urbanization in Shanghai, China

Based on meteorological data from 1978 to 2007, we investigated the annual, seasonal, and fixed hourly variations of Shanghai urban heat island (UHI) in urban and suburban areas and spatial distribution of UHI. The results demonstrated a remarkable interannual increase of UHI intensity in Shanghai. The UHI was the strongest in autumn and the weakest in summer, as a consequence of the prevailing weather conditions. Similar to previous studies of other cities, the UHI in Shanghai was stronger in the nighttime than in the daytime. The SW–NE cross section followed the general cross section of the typical UHI described by Oke (1987) who defines its characteristic parts as “cliff”, “plateau”, and “peak”. Analysis of the association of UHI and urbanization indicated that the UHI increased with the expansion of population and rapid increase of gross domestic product. The continuous increase of power consumption and area of paved road and decrease of area of cropland caused the growth of UHI intensity. Green land had a positive effect on mitigation of heat island based on an inversed U-shaped curve with UHI intensity.     

Monitoring the changes in impervious surface ratio and urban heat island intensity between 1987 and 2011 in Szeged,Hungary

Landsat time series data make it possible to continuously map and examine urban land cover changes and effects on urban environments. The objectives of this study are (1) to map and analyse an impervious surface and its changes within a census district and (2) to monitor the effects of increasing impervious surface ratios on population and environment. We used satellite images from 1987, 2003 and 2011 to map the impervious surface ratio in the census district of Szeged, Hungary through normalized spectral mixture analysis. Significant increases were detected from 1987 to 2011 in industrial areas (5.7–9.1%) and inner residential areas (2.5–4.8%), whereas decreases were observed in the city centre and housing estates due to vegetation growth. Urban heat island (UHI) values were derived from the impervious surface fraction map to analyse the impact of urban land cover changes. In 2011, the average value in the industrial area was 1.76 °C, whereas that in the inner residential area was 1.35–1.69 °C. In the city centre zones and housing estates, values ranging from 1.4 to 1.5 °C and from 1.29 to 1.5 °C, respectively, were observed. Our study reveals that long-term land cover changes can be derived at the district level from Landsat images and that their effects can be identified and analysed, providing important information for city planners and policy makers.     

城市化进程对城市热岛效应因子的对比分析

采用1990～2004年乌鲁木齐市和其郊区的温度差值作为衡量其城市热岛效应的标准,以乌鲁木齐市城市化七项指标作为城市热岛效应的形成因子.通过多元回归模型分析了各热岛效应因子对城市热岛的影响.文章主要结论包括乌鲁木齐市各热岛效应因子时城市热岛的影响是不同的,居民生活条件的改善和公共基础设施的改善减轻了热岛效应的影响,热岛效应也符合环境库兹涅茨曲线规律.     

Characteristic Air Temperature Distributions Observed in Summer and Winter in Urban Area in Japan

The air temperature distributions in August (summer) and December (winter) were measured in an approximately 15 × 15-km urban area in Hyogo Prefecture, Japan, in order to study the spatial distribution of the air temperature and to propose effective measures against the heat island phenomenon. The air temperature was measured mainly by using thermometer shelters installed in an elementary school and a junior high school. The characteristic air temperature distribution depended on the season. The air temperature was higher inland than in the coastal region in August but was higher in the coastal region in December. The air temperature index indicated that the area where higher air temperatures would most likely appear was 5 to 10 km inland from the coast in August and around the coast in December. The seasonal air temperature distribution was presumably due to the strength of solar radiation and anthropogenic exhaust heat.     

Determining the impact of urban components on land surface temperature of Istanbul by using remote sensing indices

For the past 60 years, Istanbul has been experiencing an accelerated urban expansion. This urban expansion is leading to the replacement of natural surfaces by various artificial materials. This situation has a critical impact on the environment due to the alteration of heat energy balance. In this study, the effect upon the urban heat island (UHI) of Istanbul was analyzed using 2009 dated Landsat 5 Thematic Mapper (TM) data. An Index Based Built-up Index (IBI) was used to derive artificial surfaces in the study area. To produce the IBI index, Soil-Adjusted Vegetation Index, Normalized Difference Built-up Index, and Modified Normalized Difference Water Index were calculated. Land surface temperature (LST) distribution was derived from Landsat 5 TM images using a mono-window algorithm. In addition, 24 transects were selected, and different regression models were applied to explore the correlation between LST and IBI index. The results show that artificial surfaces have a positive exponential relationship with LST rather than a simple linear one. An ecological evaluation index of the region was calculated to explore the impact of both the vegetated land and the artificial surfaces on the UHI. Therefore, the quantitative relationship of urban components (artificial surfaces, vegetation, and water) and LST was examined using multivariate statistical analysis, and the correlation coefficient was obtained as 0.829. This suggested that the areas with a high rate of urbanization will accelerate the rise of LST and UHI in Istanbul.     

酒泉市城南热岛成因分析

根据遥感资料分析了酒泉市城市热岛的成因。指出建筑空间、污染物、水体都是影响城市热岛的主要因素。     

Simulation and optimization of pedestrian evacuation in high-density urban areas for effectiveness improvement

Rapid urbanization has made many cities in China enter an era that increment and stock develop in parallel. Urban central area presents the characteristics of complex spatial structure and high functional complexity, resulting in the huge disaster risks and severe security issues of evacuation. This paper proposes a method of improving emergency evacuation effectiveness under the restriction of limited available land resources in high-density areas, which is combined with urban renewal planning, aiming at optimizing the layout of shelters and evacuation passageway by cyclic evacuation simulation, evaluation and optimization with Anylogic software and facility location tool based on ArcGIS. Taking the renewal planning of Jintang Road Area in Tianjin, a typical high-density urban area, as a case study. The results showed that: 1) The evacuation space system of Jintang Road Area exists potential danger that severe congestion occurred in the simulation process and the congested section spread outward with three shelters as the center. Which lasted for several hours. The rate of successful asylum in 5 min and 30 min was 13% and 34%; 2) The matching degree between spatial layout of emergency shelters and population distribution is low, which is reflected in the utilization rate of shelter: the rate of shelter No.1 is as high as 826%, while that of No 4 and No 5 is 48% and 11%, and also causes unreasonable distribution of people flow in evacuation passages during the evacuation process; 3) The research method of integrating simulation, facility location and renewal planning is an effective way to improve the effectiveness of pedestrian evacuation in high-density urban areas. After the improvement, the four indexes have been effectively improved.     

An approach to analyzing the intensity of the daytime surface urban heat island effect at a local scale

A landscape index LI is proposed to evaluate the intensity of the daytime surface urban heat island (SUHI) effect at a local scale. Three aspects of this landscape index are crucial: the source landscape, the sink landscape, and the contribution of source and sink landscapes to the intensity of the SUHI. Source and sink landscape types are identified using the thermo-band of Landsat 7 with a spatial resolution of 60 m, along with appropriate threshold values for the Normalized Difference Vegetation Index, Modified Normalized Difference Water Index, and Normalized Difference Built-up Index. The landscape index was defined as the ratio of the contributions of the source and sink landscapes to the intensity of the SUHI. The intensity of the daytime SUHI is assessed with the help of the landscape index. Our analysis indicates the landscape index can be used to evaluate and compare the intensity of the daytime SUHI for different areas.     

Diatoms as indicators in the Environmental Monitoring and Assessment Program-Surface Waters (EMAP-SW)

As a part of the U.S. Environmental Protection Agency's Environmental Monitoring and Assessment Program-Surface Waters (EMAP-SW), sedimentary diatom assemblages were studied from 66 lakes in the northeastern U.S.A. to evaluate the applicability of diatoms for this nation-wide monitoring program. Sediment cores were collected from the study lakes and diatoms were analyzed from the top (present-day) and bottom (pre-industrial) sediment samples. Canonical correspondence analysis (CCA) was used to examine which environmental variables correlate most closely with the distributions of diatom taxa in the top (surface) samples. Forward selection and Monte Carlo permutation tests showed that diatom species distributions were significantly related to total lakewater phosphorus (TP), pH, chloride, Secchi depth, and lake size and maximum depth. We developed weighted-averaging calibration and regression models for inferring TP (r ²=0.62), chloride (r ²=0.61), pH (r ²=0.86), and Secchi depth (r ²=0.62). An index of overall lake disturbance was also developed. Our diatom data indicate that marked changes have occurred in the study lakes since pre-industrial times as a result of anthropogenic activity.     

Evaluating the urban climate of a typically tropical city of northeastern Brazil

This study attempted to assess a bioclimate index and the occurrence of an urban heat island in the city of Campina Grande, northeastern Brazil, using data taken from mobile measurements and Automatic Weather Stations (AWS). The climate data were obtained during two representative months, one for the dry season (November 2005) and one for the rainy season (June 2006) at seven points in an urban area. Ten-minute air temperatures recorded by an AWS installed in urban areas were compared to those from a similar station located in a suburban area to assess the urban heat island (UHI). The data were collected using a 23X data logger (Campbell Scientific, Inc.) programmed for collecting data every second. The thermal discomfort level was analyzed by Thom’s discomfort index (DI), and an analysis of variance was applied for assessing if there was any statistically significant difference at the 1% and 5% significance level of thermal comfort among points. Mann–Kendall statistical test was used for identifying possibly significant trends in a time series for air temperature, relative humidity, and class A pan evaporation for the city of Campina Grande. The present study found UHI intensities of 1.48°C and ??0.7°C for the months taken as representative of the dry and rainy seasons, respectively. Summer in the city has partially comfortable conditions while the winter is fully comfortable. There are significant changes in DI hourly values between seasons. Only during the rainy season did all points of the city have a comfortable condition until 8:19 h, at which time they become partially comfortable for the rest of the day. Results indicated that there was a 1.5°C increase in air temperature and a 7.2% reduction in relative humidity throughout the analyzed time series. The DI also showed a statistically significant increasing trend (Mann–Kendall test, p?<?0.01) for the dry and rainy seasons and annual period of approximately 1°C in the last 41 years in the city of Campina Grande.