Urbanization is inevitable and so is the need for energy. During the past two decades, global urban areas have grown exponentially. Cities became major contributors to various pollutions that owe primarily to their population density. Scientists have identified a positive correlation between population density and pollution. Although cities cover only 2% of earth's surface, they are accountable for 75% global resource consumption. Especially, the present 3.5 billion urban population, which is about 50% of total global population with an unsustainable consumption pattern, have contributed to such pollution. Key pollution sources identified are urban production, mobility and transport, infrastructure, population density and urban residential activities. The UN predicts that by 2050, 6 billion people will reside in cities, while developing economies, like those in Asia and Africa are, and will keep experiencing rapid urbanization and population growth. Presently, about 40% of their population are urban, and this number should increase to 62% by 2050. Since this trend will intensify in the imminent decades, urban pollution will keep rising alongside.
There is also a positive correlation between accelerating urbanization and increasing GDP. The type and level of pollution is often correlated with a country’s stage of economic development. At low-income level, households typically rely on solid biomass (as in many African and Asian nations), which exposes them to particulate matters (PM) – often triggering premature death. With industrialization and attainment of higher income levels, use of fossil fuel (especially in power generation and industry) grows. Sulfur dioxide emission alongside other pollutants also increase concurrently. Modern agricultural techniques that involves mechanization, intensification of farming and use of chemical fertilizers and pesticides, also result in higher levels of air pollution. With further income rise, household air pollution may reduce (due to users’ switch to cleaner energy sources), but demand shoots up for more energy-hungry services like appliances, tools and transports. This result in even higher emission of sulfur/nitrogen oxides and other pollutants. Together, global energy consumption contributes to pollution, greenhouse emission and environmental deterioration.
The imminent and inescapable population increase coupled with economic growth and energy demand in developing nations thus have critical implications for the overall environment. Almost all atmospheric emissions of sulfur/nitrogen oxides are energy-related, of which 85% are PMs. Power generation (especially coal industry) and industrial sectors remain the primary sources of sulfur oxides, while oil use in vehicles and power generation remain the primary sources of nitrogen oxides. Consumption of biomass, kerosene and coal in the building and industrial use remain responsible for the bulk of the PM reaching the atmosphere.
The most detrimental urban pollutions emanate from human activities/mobility. In urban areas, the anthropogenic pollution sources, such as factories, industries, transportation etc. are usually worse due to higher occurrence of human activities. Urban pollution is equally affected by global threats such as global warming, and local challenges such as waste management and light/noise pollution. The concept of urban pollution refers to the presence or introduction of harmful substances in cities. There are many such pollutants, and they may occur naturally (from dust, wildfires and volcanoes) or from human activity. They can either be visible or invisible, and could emit odor or could be odorless. A few such types are discussed in the following paragraphs.
Natural water sources such as lakes, rivers, groundwater and oceans often get polluted by building/site runoff from factories, farmlands, chemical spills, raw sewage, industrial waste, and garbage. Liquid pollutants usually originate from liquid waste that may often contain human excreta, industrial waste etc. Factories produce liquid waste from manufacturing, cleaning and chemical mixing. Sewage and human waste from overflowing septic tanks and latrines are typical sources for water pollution. These are typical of less developed nations and especially in particular seasons (e.g. rainy season).
A high concentration of toxic contents in soil pose a high risk for both human health and the ecosystem. A large number of organic and inorganic chemicals and waste from industries or derelict industrial sites, farms, construction sites, automobiles and households contribute to soil pollution.
Waste generation (especially municipal solid waste and pollution caused by it) and its global increase is one of the key concerns for city makers and manages worldwide. Wastes can be of various types, such as food waste, commercial and industrial waste, construction and demolition waste, agricultural waste, hospital waste, and quarrying waste. Disasters also contribute to waste generation. UNEP underscored a clear and direct relationship between the generated solid waste quantity and people’s income level. Especially in developing nations, the necessary instruments and skills to manage different types of waste are scarce. Here uncontrolled waste disposal remain significant contributors to other forms of pollution (water, air etc.).
Pollutants also come in solid form. Plastic bags and products are one of the most commonly produced solid wastes. Industries, businesses and households produce different solid wastes namely paper, plastic, metal, solid chemical, pieces of cloth or food and animal remains.
Noise pollution engenders serious health hazards too, which is often unknown to most. In addition to the immediate impact of noise pollution such as from living beside noisy roads with heavy traffic, there is also disruption of peace, and increased annoyance, headaches, insomnia, hearing loss, neurological disorder and disrupted standard of living in the area subject to pollution.
Cities typically get polluted with signs, advertisements and over-illuminated billboards that cause eyesore and neurological stress of various sorts. Visual pollution can also lower or degrade people’s quality of life, and property values.
Excess heat and/or trapped heat in earth’s atmosphere have already dealt damage to our ecosystem. When earth’s natural thermal cycles are disrupted over a prolonged period, there have been ample evidences of forest fire, melting of polar ice caps, sea level rise and above all, global warming – affecting wind and ocean currents, and intensifying Urban Heat Island effect and flooding in cities. Examples of these are plenty in many of today’s cities.
Among all, air pollution perhaps poses the greatest health risk for the urban population. Urban air is composed of a complex of chemicals and carcinogens, which typically causes acute respiratory diseases, neoplastic or non-neoplastic (e.g. chronic bronchitis) chronic respiratory diseases, cancers and affect other major organs. Transport sector, among others, contributes the most to the deterioration of air quality in cities.
Concentration of people, economic activities and energy demand in cities also made people consider poor air quality as an inevitable urban problem. Researchers found that air pollution poses the fourth greatest overall risk to human health (after high blood pressure, dietary risks and smoking). Globally, 6.5 million premature deaths occur from air pollution yearly. Among major pollutants, fine PM has been identified as the most damaging to human health, while sulfur/nitrogen oxides, and ozone are associated with a range of other diseases. Air pollution poses grave risks to environment, economy and food security too. Pollutants originating from human activity come mainly from energy production and use (combustion of fossil fuels and biomass).
Air pollution can, however, be defined in terms of natural causes (natural fumes, decomposition, and volcanic ash) or anthropogenic causes (resultant of human activities such as industrial emissions). It is a particular condition of air that endangers health, safety and/or wellbeing, interferes with people’s everyday lives, and/or causes damage to people/plant lives or properties. Air pollution is an effect caused by concentrations of solids, liquids or gases in the air that negatively affect people and their environments. Various air pollutants could remain suspended in the atmosphere from minutes to years. It can range between local, national, regional or global, and can take place at both indoors and outdoors. According to WHO, burning biomass fuel in indoors (e.g. for cooking in slums) is five times more dangerous than outdoor air pollution. Women and young children, who typically spend a lot of time home, become particularly vulnerable to the adverse effects of indoor air pollution. Suspended dust in indoors without air change is also detrimental to respiratory health.
Given the rapid rate of urbanization, population density and shift to industrial mode of production in Bangladesh, it is no surprise that a good number of its cities will have the poorest air quality in the world. A recent World Air Quality Report says that Bangladesh has the most polluted air in the world. More than 70% urban roadside environments here are severely polluted and the rest are highly polluted. Among these, Dhaka is the worst, ranking among 2nd to 6th in global air quality index, with a gradually deteriorating situation. In fact, as early as in 1980 Dhaka, lead was found in human bodies – coming from ambient air mainly. A 2012 report titled Air Pollution Reduction Strategy for Bangladesh by GoB’s DoE identifies Motor Vehicles, Brick Kilns, Industries, Biomass Burning, Construction and Vehicular Activities, and Power Sectors being the key air polluting sectors/sources in Bangladesh.
Based on data gathered from 11 air quality monitoring stations in eight urban areas in Bangladesh, concentration of 2.5 microgram PM from 2013 to 2015 was found. These were already five times more than the Bangladesh standard and eight times more than the WHO standard. The health effects of air pollution in Bangladesh have been documented in a few other studies too. A recent DoE study found that among the schoolchildren in Dhaka, respiratory diseases have increased due to elevated PM level in ambient air. DoE believes that the actual impact of fine particles on premature mortality could be even higher.
Large social costs are also associated with air pollution in Bangladesh. In alternative words, large social benefits can be yielded if air pollution is mitigated. According a World Bank report, Bangladesh continued to lose $6.5 billion/year until 2015, which is about 3.4% of the entire GDP. This was due to urban pollution and overall environmental degradation. Of the total economic loss, the ambient air pollution costed about $2.42 billion while household air pollution costed $1.27 billion. Bangladesh saw about 234,000 deaths, including 80,000 in urban areas, due to environmental pollution and related health risks in 2015, making it one of the worst affected nations in the world. This was nearly 28% of all deaths that year, compared to a 16% global average.
Cities consume 75% of the world’s energy and are responsible for 80% of global GHG emission. But rather interestingly, these cities, which are also sources of most pollutions of our present world, offer opportunities to resolve them as well. On this note, the growing concentration of population in cities also means that this high density enables efficiency in terms of economies of scale in all sectors including service provisioning.
Ecosystems are also a proven performer in the fight against pollution. Natural ecosystems often hug cities are found in various forms (naturally or artificially) in most cities. They certainly have the capacity to reduce pollutants in the air, water and soil. Caring for ecosystems (by creating or regenerating) can help neutralize pollutants. Some examples of these environmental measures for cities and in their hinterlands maybe the creation/conservation of wetlands/urban forestry/vegetation belts in and around cities, creation of green walls, roofs and soak-able/permeable surfaces instead of solid pavements, or adoption of productive landscapes. The right policy environment and institutional arrangement toward sustainable and green growth is also necessary for this.
In order to minimize air pollution, DoE previously proposed some interesting sectorial strategies. For transportation, noteworthy strategies were: improved public transport and introduction of non-motorized transport options, sustainable fuel switch and setting strict emission standards for vehicles. For industries, DoE aimed for comprehensive land use plan to determine locations of new industrial sites, clustering high-polluting industries, set technology standards, use alternate/green construction material. For the construction sector, it stressed for better construction practices and transportation, regular road maintenance, landscaping and gardening. As part of soft approaches, it highlighted the need for regulatory and fiscal reform, awareness and motivation, research and development, cooperation and coordination, capacity building and knowledge retention, institutional set up and governance.
In addition to the above, a few more can be suggested from an environmental perspective and having a ‘green’ approach. For transportation, a city-wide ‘green’ pedestrian/bicycling network needs to be created by greening/replacing the hard surfaces. All sorts of building greening should be made mandatory through adequately articulated policies, and some form of ‘compensative greening’ may be enforced for violators. For implementation, NGOs and private sector can be considered. For urban industries, adaptation to clean/net-zero/renewable technologies could be made mandatory. For the building/construction sector, research and development of green (non-cement based) building materials should be funded or subsidized. Green building codes should be mainstreamed and present FAR rules need to be further carried out with necessary modifications/elaborations.
Indeed urbanization, energy needs and pollutions are inevitable. But there is certainly a ‘green’ way out this. Such an approach is sustainable too!
Sheikh Serajul Hakim, Professor, Architecture Discipline, Khulna University