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Architectural Mitigating Strategies for Air Pollution in the Built Environment

To cite this article: Ajuluchukwu E. Igwe et al 2022 IOP Conf. Ser.: Earth Environ. Sci. 1054 012046

View the article online for updates and enhancements.

Architectural Mitigating Strategies for Air Pollution in the Built Environment

Ajuluchukwu E. Igwe, Emmanuel C. Ezema, Francis O. Okeke and Cyriacus Okpalike^*

Department of Architecture, University of Nigeria.

*Corresponding author¶s e-mail: [email protected]

Abstract. Air pollution and air pollutants effect on humans and the atmosphere in general, is now an issue of great concern to researchers globally. Consequently, efficient mitigating strategies need to be introduced for the sake of the environment and most importantly human health. To this effect, this study aims to investigate possible ways through which architecture can help curb air pollution and air pollutants in the atmosphere through innovative architectural design strategies and controlled construction practices, with specific guidelines on how to achieve these strategies. The study in the quest to achieve the above aim employed the literature review research design, with particular reference to works of literature that dwelt on innovative and sustainable design strategies within the built environment. Evidence in literature reveals that air pollution is one of the major issues faced by man due to high level of industrialization and lots of other human activities, with a majority of the research dwelling on how pollutants are being generated but just a few studies dealt on how architectural and construction practices contribute to air pollution and the possible ways to reduce the effect of air pollution and air pollutant to the atmosphere through innovative design strategies, which is where this study plays a major role in filling that gap. The research finding from this study ascertained that all stages of building development projects from the inception of the project to its deconstruction release pollutants into the atmosphere. It concludes that the most effective way of controlling air pollution within the built environment is through the use of greenery (bio facade) and adopting a sustainable design system. The study will help inform government environmental agencies, architects, urban planners, builders, and all other stakeholders in the built environment on sustainable ways to tackle air pollution in the urban areas, most especially where there is no luxury of land for the planting of trees and vegetation.

Keywords: Appropriate technology, tropical environment, sustainability, construction, Nigeria

1. Introduction

Humans today are being faced with a lot of challenges that affect their health, productivity and lifestyle.

Amongst these challenges faced by man is environmental pollution which comes in various ways, but the most disturbing of these environmental issues is air pollution. Air pollution has its early reference dating as far back as the middle ages when a ban was placed on the use of coal for heating lime kilns by King

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Edward I because heavy smoke been generated from the kiln [1]. Air is among the five most needed elements that are important for the survival of human; that take an average of 22,000 breathes a day and needs at least 15kg of air per day for subsistence. Air pollution directly affects the air quality not just within an area, but globally. From studies, it is a known fact that the various activities of man especially in industrial areas release a high level of air pollutants to the atmosphere. Air pollution can be simply put as having one or more pollutants in the air, concentrated enough to cause harm to humans. Heidari [2], noted that scholars have been on the issue of air pollution for a while now, intending to detect the major cause of air pollution and its effect on humans and the world at large, but without much emphasis on predicting necessary preventive measures or ways to curb air pollution, especially using our built environment.

Studies in the past two decades show that existing pollutants in the air pose a great threat to human health, and a majority of these pollutants are being generated as a result of man's activity in the construction sector [3]. The world green building council (WGBC) [4], noted that among the issues faced by man, air pollution is ranked as the highest killer within the environment, having over 8million deaths to its record annually, and its occurrence is mostly within developing countries. Over 4.2million of these deaths are linked to exposure to outdoor air pollution, majorly caused by our construction activities. Air pollutants generated within the building sites, quarry sites, sand mines, hardwoods etc. form a large percentage of these ambient air pollutants and the earlier we learn to either reduce the presence of these particles in the atmosphere or curb them entirely, the better we will make our air for humans. Pollutants in the air influence, not just human health but also affect the way we perceive the built environment. Landscape and the environment around our building turn pale, and dusty, taking away the beauty and clarity in the environment using smog as a covering veil [5].

Large cities in developing countries tend to release more pollutants into the atmosphere than those in developed nations, as recorded by the World Health Organization [6]. This is due to the type of activities that takes place in the developing nations, which most of them are still in its raw state, aspiring to give the urban dwellers a better standard of living, using the basic component that influences the health standards and air quality in the environment. Armed with these, planners can easily determine areas that pose a high risk of releasing air pollutants to the environment. Previous studies have been carried out by scientists like John Evelyn, Sir Kenelme, John Graunt, on air pollution with some of them having a keen interest in coal smoke, construction dust and recently traffic-related air pollutants (nitrogen dioxide PM2.5, particles with a 50% cut-off aerodynamic diameter of 2.5 mm and soot), which was identified to be on the increase basically due to the combustion of fossil fuel; these pollutants were linked to the increase in respiratory diseases like asthma, bronchitis and influenza. Also in Kosovo, one of the largest cities in Europe, a study was carried out on energy efficiency and air pollution and how it relates to the country¶s Gross Domestic Product and emission of CO2. Kosovo is one of the places where lignite can be found in large concentrations, so over 95% of its electric power is generated from lignite and at the same time the release the highest CO2 per GDP in economic activities. Ranked as a developing country, Kosovo is acclaimed to be the most polluted country in Europe [5]. Kosovo can be likened to some of the cities in sub Saharan Nigeria like Lagos, Enugu, Anambra and Abuja with high traffic and construction- related air pollutants due to their economic and construction activities.

In a developing and rapidly urbanizing country like Nigeria, with lots of construction and industrial activities going on [7], despite the measures that have been put in place to check the growing incidence of air pollution, some authors have noted that air pollution is still on the increase unabated in the major urban centres [8]. In a bid to find a lasting solution to this challenge of air pollution, researchers have investigated some aspects of air pollution in urban centres. Examples are mitigating strategies for reducing air pollution [8]; influence of vehicular induced turbulence on pollutant dispersion in streets canyon and adjacent urban areas [9]; comparison of predicted vehicular pollution concentration with air

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quality standards for different periods [10]; the increasing awareness and study on influence and how to curb air pollution can help in ensuring sustainable development [11].

A close examination of these studies revealed that they all concentrated on how other human activities influence air pollution outside the built environment, very little research effort has gone into the exploration of air pollution within the built environment, where there is a rapid increase of air pollutants within the system, and lack of land space for vegetation, due to lack of proper planning, need for more housing units for the ever-increasing population of the city dweller. Leaving little or no space for agriculture and planting of vegetation which is the best alternative means to curbing air pollution [12].

From the foregoing, this research sought to explore the use of our building façade and other new ways through which innovative architectural design strategies can help curb air pollution. Architecture and the environmental sciences are known for their ability to proffering solutions to human challenges through nature [13], so this study looked into ways we can curb air pollution and reduce air pollutants in our atmosphere using innovative architectural design strategies. The main strategy discussed in this study is the bio-responsive design, which is a new trend in the built industry; it entails a design that combines architecture, nature and technology. This is currently not popular within Nigeria, but it is already in use in most developed countries. This paper will also serve as an eye-opener to this new and efficient means of controlling air pollution in the built environment.

The study is considered valuable to the ongoing discourse on how to curb the number of pollutants released in the atmosphere, and also on how to improve the public health, environmental quality and life span of urban dwellers globally, by revealing the main source of air pollutants within the built environment and suggesting possible control measures for air pollution using innovative architectural strategies (bio responsive designs). Therefore, the findings of this research are expected to inform architects, builders, and construction managers on how to tackle the growing levels of air pollution in the built environment through innovative architectural design strategies, majorly using greenery and sustainable design systems to effectively curb the effects of air pollution in developing countries.

2. Literature Review

Air pollution occurs when the air is laden with pollutants or particles in high concentration over a long period, long enough to cause harm or unwanted effects on humans, plants, animals and the environment at large [14]. Also, the United States Environmental Protection Agency (EPA) described air pollution as the introduction of harmful substances into the air, which is capable of degenerating human and animal health and the world in general. Furthermore, Babatora [15] defined polluted air as containing harmful compounds in amounts that are detrimental to the wellbeing of humans, plant and animals. [16], noted that there are different types of air pollution, which includes pollution from gases (this comes from the release of gases like ammonia, carbon monoxide, methane etc. into the air). Then there is also another type that is caused by particulates (minute/small particles), which are released into the atmosphere (which can be either organic or inorganic) and then we have the type of air pollution that is caused by biological molecules which can also be called Biomolecules (these are molecules that are found in organisms, that are essential to one or more typical biological process).

From studies, it was discovered that our environment is exposed to air pollutants from both man-made activities and natural occurrences. Air pollution was involved with humans from the very first time fire was created. Natural sources of air pollution can come as a result of various natural occurrences within a particular place, such as volcanic eruptions and forest fire [14], while the human sources emanate from the activities carried out by humans within an environment. These stems from industries, mass transportation and building/construction processes. It is paramount to note that the effects of air pollution irrespective of the source cannot be localized as its effect goes far beyond the point where the pollutant was generated or released into the atmosphere. The studies of [14] highlighted that most air pollutants originate from the

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combustion process of fuel. The first major issue about air pollution discussion was raised before the industrial revolution in the 13th and 14th centuries, then it became worse around the 1760s, in the wake of the industrial revolution when there was a rapid increase in the use of fossil fuel. This singular act intensified the rate of air pollution all over the world. The invention of automobile means of mass transportation that runs on fuel, starting from the advent of locomotive trains that runs on coal, to this present age where we mostly use gasoline-powered cars had a tremendous impact on the number of air pollutants in the atmosphere. As at this moment, air pollution ranks high among the severe environmental issues faced by both man and animals. The Global Burden of Diseases [17] in their recent study estimated that air pollutants (combining both exterior and interior) caused over a 3.1million untimely global deaths annually and 3.2% of the diseases around the world [15].

Generally, Smog and Soot are the two known forms of air pollution, where smog (which is also known as ground or base level ozone) is caused by the burning of fuel, soot on the other hand is in form of tiny solid particles and gas that is transported in the air. Soot and smog are generated through similar sources like incinerators, cars, buildings, even factories, one can therefore generalize them to anything that requires fuel to produce energy [18]

2.1. Air pollution in the built environment

The population of the world is rapidly increasing by the hour of the day, this also comes with the need for the provision of the five basic human needs, which shelter belongs to. This gives room for more construction and developmental projects, resulting in the erection of more houses and at some points big structures to accommodate man and also provide for or satisfy his needs. The combination of these many structures is what now leads to urban centres and cities, but we tend to neglect the raw process that leads to these fine developments that we are enjoying today, and its effect on the environment. The World Green Building Council [4] in their recent report noted that over 39% of the carbon emission around the world can be traced back to our buildings or construction related activities. Our cities and buildings, in particular, are responsible for the generation of different kinds of pollutants, they can be categorized into outdoor (pollutants released by human or construction activities outside the house) and indoor air pollution (pollutants released by human or construction activities within or inside the house).

Outdoor Air Pollution: There are many causes or sources of outdoor air pollution, ranging from our transport system (emission from cars, trains, boats etc.) to poor waste management and even poor agricultural practice, but for the sake of this study, we will be looking at how the built environment contributes to air pollution. We will be taking our clue from the ³World Green Building Council´

(WGBC) [4].

(a) Carbon Emission: Carbon footprint is the total greenhouse gas (GHG) emission caused by an individual, organization or project. Greenhouse gases (basically gases that trap heat in the atmosphere and warm the planet) [19], and the carbon-containing gases i.e. Carbon dioxide and methane, can be emitted through the burning of fossil fuels, and various production processes at different levels, construction of buildings, roads and other services [20]. In the construction stage of buildings, the construction sector takes up at least 40% of global energy and 25% of global water, and at the same time, it releases almost 40% of the particles in the atmosphere, of which about 1/3 of it are greenhouse gases (GHG) [21]. The impact of inefficient use of energy in the construction sector slowly degrades the quality of the environment. This implies that the more energy is been wasted, the more the environment is being destroyed in the quest to produce more energy or to replace the wasted one. The more energy we consume in the construction stage of every project, we, directly and indirectly, contribute to the production and release of Co2 into the atmosphere.

(b) Production of Building materials: such as brick, glass etc. according to [4], contributes to a large extent to the number of toxic pollutant in the atmosphere. For instance, approximately over

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1.5billion bricks are produced each year for construction purposes, and these bricks are produced using kilns which are most times not properly managed. It is estimated that brick furnace alone adds to over 20% of the global black carbon in the atmosphere. This also adds to the particles (Pm2.5/

Pm10) which are released from the burning of fuel, either for powering the various production machines or for transporting them from the point of production to where they will be used.

(c) Release of Toxic dust: Dust can be said to be tiny particles of debris which are very small in size, meaning that it can be inhaled and may trigger an immune reaction. It can be managed or sometimes poses a major risk depending on the affected person. Dust-laden particles are always contaminated, serving as ³fomite´ [22]. The building sector due to the nature of its activities is responsible for up to 40% of the total toxic dust in the atmosphere, this can either come from quarry sites, where we get stone and rocks for construction, or the demolition of buildings or parts of buildings, or even the actual construction process too. Almost all the construction phases and processes release dust particles to the atmosphere, to even the finishing and cleaning stage and when the building is already in use.

(d) Hydro Fluorocarbons (HFCs): These are artificial compounds, they are made up of hydrogen and chlorine atoms and they can be said to be the readily available type of organofluorine (meaning an organic compound that contains the carbon-fluorine bond). These gases are normally used in our homes for refrigerators and air conditioners, and they are always at room temperature, also they serve as fire protective solvents and insulating foams [23]. HFCs were chosen to substitute the more effective chlorofluorocarbons (CFCs) because HFCs causes lesser harm to the ozone layer when compared with CFCs, but this does not remove the fact that they still add to the effect of global warming and concentration of greenhouse gases emission to the atmosphere, which is actually on the rise, raising concerns on the waves of forces embedded within them [24].

(e) The energy utilized in our homes: This talks about the local cooking stoves, uncontrolled fires, kerosene camp lanterns etc. which are used for either cooking, heating the building or lighting, also the use of generator sets for individual power generation in most homes come into play here. This is mostly seen in the developing or underdeveloped countries, where there is no steady power supply, so virtually every household has to generate their power to meet the demands and needs of their homes. Another fact is that in developing or underdeveloped countries, there is no regulation for the use or burning of gases/fuels and this contributes to a large extent to the amount of CO2 in the atmosphere.

Air Pollution within the indoor environment: These are pollution emanating from within the interior spaces of the building resulting from activities performed inside.

(a) Emission from the burning of fuels: While warming up the internal spaces in our homes and also while cooking, we end up emitting harmful substances into the atmosphere. The WGBC noted that the particulate matter generated from the burning of fuel in our homes have severe health consequences on us as the cause serious ailments like stroke, cold, cardiovascular diseases, and cancer of the lungs.

(b) Biological Contaminants: This particular issue occurs when air infiltrates through the opening on the walls of buildings and the major reason why we have damps in most homes. This aids the growth of moulds and fungi within the walls of building and the result is what we call "Microbial Pollution of Indoor Air". According to the WHO guidelines for indoor air quality [25], Microbial pollution involves hundreds of species of bacteria and fungi that grows indoors when sufficient moisture is made available for them. Studies have shown that this particular issue causes a 40%

increase in Asthma risk when an occupant lives in a home that is contaminated with moulds and fungi. This is the major cause of indoor air pollution according to the studies carried out by the World Green Building Council (WGBC) [4].

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(c) Poor Ventilation: When a living space is not properly ventilated, there tends to be a concentration or moisture pileup, this can activate allergies and encourage the development of moulds and fungi (which is the major cause of microbial pollution).

(d) Furnishing: The type of furnishing and materials we use in decorating or furnishing our indoor spaces determines to an extent how pure the air quality in our indoor spaces will be, some furnishes like chairs, curtains, carpets often release harmful or toxic gases into the atmosphere that affect human health.

(e) Toxic Building Material: Some of the building materials like asbestos, some paints etc. which are used in our day to day construction process are harmful to human health as they release toxic gases and dust to the atmosphere. Dust can be said to be tiny particles of debris, they are so small that they can be inhaled and potentially evoke an immune reaction. Specks of dust can harbour viruses serving as "fomite" and can transfer infection [22]. Also, the activities of those using a particular building material a lot, as activities such as smoking, uncontrolled burning of fuel, and even how the indoor space relates with the outdoor space are all contributing factors to how clean the indoor atmosphere of our homes will be.

The World Green Building Council outlined the specific goal to devise means on how to decrease globally the effect of air pollution especially within the built environment.

For outdoor emission, they outlined:

(a) Operational Emission ± The major purpose of this outline is to find ways to reduce the pollutants that are generated from the building during the daily activities within that particular building (this is talking of the energy use and pollutants generated from the day to day running of a building).

(b) Embodied Emission - The main goal here is to find and endorse strategies that will help lower the carbon and greenhouse gas emissions from building, over the full life cycle of that particular building.

For indoor emission, they outlined:

(a) Materials ± The World Green Building Council, aims to promote the importance of using sustainable, nontoxic and air cleansing materials in our buildings, to curb the introduction of pollutants into the air within our homes and environment in general.

(c) Building Fabrics ± These are the components and materials a building is made of [26]. The WGBC seeks to develop awareness on the importance of building fabrics and construction quality and also to remind us of the role of retrofitting (to furnish with new or modified parts) in buildings, as they help in keeping the building sound and environmentally friendly.

(d) Ventilation ± A well-ventilated space helps in the circulation of air and warmth, thereby reducing the amount of trapped moisture within the building. This helps to prevent the growth of moulds and fungi within the living space thereby preventing microbial air pollution

2.2. Effect of air pollution on human health

According to [6], air pollution in the external environment also known as ambient air quality is among the highest environmental killers in our society. Evidence from the WHO database confirms that in every gathering of 10 people that 9 of them takes in the air that is below the WHO standard, that is, air with a high level of pollutant. These can come in form of smog hovering over the atmosphere, to the smoke within our households. Particles of dust from our various construction, and quarrying sites like silicon dust, and dust from wood are also major causes of severe health risks to humans, leading to sicknesses like asthma, silicosis and other health issues. Also, it is worthy to note that poor indoor air quality reduces the efficiency, cognitive functioning and productivity of humans in general.

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Effect of Air Pollution on the Environment and buildings: The WGBC in their studies, noted that over 40% of the energy-related global carbon emission is generated from the built environment, and it is worthy to note that carbon dioxide has an atmospheric life span of more than hundred years [27], this entails that any carbon dioxide pollutant that is introduced to the atmosphere today will be greatly affecting the atmosphere even in generations to come. The emissions from buildings are not just limited to the construction stage alone, but it includes the whole life cycle of the building, from the construction stage, operation and maintenance stage, till the deconstruction/demolition of that particular building.

When the atmosphere or outdoor air quality is polluted, passive means of ventilation cannot then be achieved within the internal part of the building, due to the risk of letting in polluted air within the household space, this particular issue will now mean that the house will be ventilated mechanically, leading to further increase in the energy utilized in the running of the house. This directly leads to the burning of more fuel to run the house, thereby polluting the outdoor air quality the more. The use of air conditioning systems in our homes creates a local microclimate warming impact within the atmosphere.

This is because of the release of hot air that is collected from the internal household to the external environment, and this keeps on multiplying over the years, serving as a contributory party to global warming, it is estimated that this microclimate warmth will triple by the year 2050 [4].

In Nigeria, one needs to worry about the air quality level as Nigeria ranks 152 out of 180 countries at the last Environmental Performance Index for air quality, also in the WHO air population database from 2016 till date, the air quality in Nigerian cities reaches PM2.5 concentrations ranging from unhealthy to hazardous levels, with cities like Aba, Onitsha, Kaduna, Lagos and Umuahia having the highest heat, and at such an urgent step needs to be taken [28]. The sources of urban air pollution have been the subject of several scientific inquiries in different countries. For example, [15,10,28,29,30] investigated the different sources of air pollution and have shown that air pollution in urban areas comes from different sources that are mainly related to institutional, industrial and commercial activities. Some authors specifically identified the common sources of air pollution in urban centres to include ± construction activities from quarrying sites, dust from wood, fumes from burning of fuel and other sources, but majorly [29], many authors pointed out the issue of air pollution from all the stages of construction and noted that construction activities are the chief contributors to the level of air pollutants in the urban centres.

In Nigeria, several studies attempted to identify the sources of air pollution within the urban centres, for instance, [10]; noted that urban dwellers in Nigeria are the major contributors to the release of air pollutants to the atmosphere, but the author channelled his thought to the use of automobiles and burning of fuels alone, neglecting the other causal activities to the release of air pollutants. [28] believed that before air pollution can be controlled in Nigeria that there is a need to establish a high-quality management framework which will require the introduction of specific agencies to create awareness amongst the populace to make them understand and also analyse the health risk of air pollution but the author did not point out a specific causal component that directly leads to air pollution. [31], views about the source of air pollution in the country agreed with that of [28], still saying that to curb air pollution in Nigeria, that there is a need for air pollution policy revision, stakeholders' engagement, and policy implementation to mitigate the environmental and health effect of air pollution. [32] also investigated the level of air pollution and its possible impacts with Lagos as a reference point, he reported that the top three sources of P.M2.5 in Lagos are road transport, industrial emission, and generators, with additional pollutants from poor waste management systems. This is similar to the findings of [10]. Further studies from [33], proposed the use of individual components in our buildings to develop a responsive bio façade, but it only dwelt on the use of responsive glass, neglecting other elements in the building façade. On bio façade and sustainable design strategies [8,19,29], discussed extensively on bio facade, noting the challenges of using our building as a harbouring area for vegetation in the urban centres, but they all acknowledged that the advantages outweigh the disadvantages if the proper process is followed. They also

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noted that this process does not cause any harm to the human health, but the major challenge is that this process is still very new, and cost-intensive.

The foregoing review indicates that air pollution has a wide range of hazardous effects on humans including decreased lung functions, aggravated asthma, heart attacks and may even lead to chronic respiratory disease and death. Although the existing studies are very insightful in improving our knowledge on the effects of urban air pollution on humans, plants, and also on the environment. They fail to provide information on how to curb air pollution in urban areas where land is a scarce commodity, leaving us with the building façade as the next alternative means, especially in Nigerian cities with its ever-increasing population. This is the gap the current study attempted to fill in.

3. Research Methodology

Considering that the main purpose of this paper is focused on investigating the possible ways through which architecture can help curb air pollution and air pollutants in the atmosphere through innovative measures, with the fact that the research is interdisciplinary, thus needs a combination of methods as noted by [34]. Therefore, the research design adopted a qualitative research approach and employed review of relevant literature on air pollution and control in the environment. Secondary data for the study were sourced majorly from indexed journals, and they were critically analysed and summarized.

Correspondingly, data from relevant bodies and agencies that regulate the world environment and health issues provided the study with strong backing. After the collection of data, individual studies were stipulated, followed by a comparison between different views, and finally, a summary of the views captured, and what the works of literature did not capture. Analysis were based on thematic content and deductions made on architectural mitigating strategies for air pollution in the built environment.

4. Results and Discussions

Deductions from studies have shown that there are many ways through which pollutants are absorbed from the atmosphere. According to [35], all these methods fall into either abiotic (uses of physical or chemical means) or Biotic means (use of natural means). The idea of architectural based facades for controlling air pollution is critical and very crucial at this point in time the menace is almost unavoidable within the built environment.

Architecture in its unique nature can easily adopt the biotic approach as it can through design harbour the natural components needed for the absorption of air pollutants from the environment which are vegetation. [19], noted that this new concept even though it absorbs pollutants in a rather slow way, also at the same time helps keep the environment cool, and helps regulate the thermal comfort of the internal space. Research have proposed, some biotic ways to help in the absorption of air pollutants from the atmosphere, which will be discussed in the subsequent section. Though some of these processes are yet to be fully accepted and integrated into the design process, most developed countries have tried out a few of them especially in Asia, and they proved effective but cost-intensive and requires special skill to implement

4.1. Ways to control air pollution

Architecture can help in curtailing or reducing the amount of energy used in a building and it can also help improve the quality of air within and outside our buildings. We will be looking at some of the ways Architecture can help improve the air quality in our building such as through the planting of trees, the use of bio-based facades, cyclone collectors, and other strategies that will be discussed in this study. Using nature as a means to resolve human issues has been proven to be working [36] and this environmental issue can be addressed using architecture. Human and environmental survival has always been dependent

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on the preservation of the environment and also balance within the environment. The architectural mitigating strategies for air pollution in the built environment include;

(a) Vegetation and plants ± It is an established fact that the world forest absorbs a third (1/3) of the world global emission yearly. Therefore, vegetation and plants are the most effective tools easily available for humans to handle air pollution. It affects localized air pollutant depositions with the additional benefit of getting rid of particulate pollutants within the immediate atmosphere as also supported by the findings of [37]. Trees absorb pollutants and gasses in the atmosphere through their leaves, the stomata and pores of these trees help efficiently in the filtering of these chemicals and particles out of the environment. Trees help to reduce the effect of greenhouse gases by reducing heat levels, reducing ground-level ozone and give back oxygen to the environment. The fact is that in most urban centres, they hardly find or have space for planting of trees, this is due to the quest to make maximum profit from the available land space. Therefore, the study also considers how our building façade can help in the fight against air pollution. We will be looking at how we can use different façade types including "Watery based facades", "algae-based facades", "green and alive based facades" to help filter the air around our buildings.

(b) Using water in the building's façade ± The idea behind the use of water layers on the building façade was borrowed from the concept of rainfall. Rainfall serves as a natural air purifier, whenever it rains, the raindrops traps the pollutants in the atmosphere and at the same time pollutant gasses will be absorbed into the rainwater which will now come down as rain droplets [38]. For this study, two ideas on how we can employ water in our building facades to control air pollution will be analysed:

Spraying of water on the building facade and water-based curtain. (i) Spraying of water on the facade has been tried in some countries like India, and it proved to be effective. The simple process in this idea is to sprinkle water on the façade of the building at intervals using mechanized sprinklers, the water droplets will easily trap the air pollutants around the building and send them down. The aim of this technique is just to trap the dust-laden particles using rain droplets which is similar to what natural rainfall does. Also, other chemicals can be added to water spraying for other purposes [39].

(ii) Watery based curtain facades; This is a simple alternative to spraying water on the building façade. Here a layer of water is formed as a second wall or fake wall at the front of the main building envelope (see figure 1). The water traps pollutants as it flows, and the good thing about this technique is that the water is recycled and used again, forming a continuous cycle. This is already being implemented in some cities, as seen at the Hydro place building in Manitoba with green building certification from LEED Canada.

Figure 1. A representation of watery wall details [2].

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(c) Algae façade - In contemporary architecture and urban buildings, the popularity of glass spaces is still high because of their aesthetic value. However environmental effects of using glass facades bring up a lot of concerns due to the amount of heat it transfers into the building and undesired hot weather increase [29]. Algae live systems is proposed as a sustainable alternative that can synthesize a bioreactor alga in a glass façade. Algae façade can provide light transmission and as a porter wall, it can replace current glass systems with proper thermal and structural function. Algae façade is designed for improving air quality in the environment by producing oxygen and absorbing CO2 through algae's photosynthesis [19]. The bioreactor system is placed between two acrylic papers and algae are growing in a rich liquid full of nutrients. This container is designed in a way that it can present good energy and structural function. Through this facade, there is a possibility for observing daily light and ventilation, see details below.

Figure 2. Algae façade¶s components. Figure 3. Operation mechanism of algae façade [2]

(d) Green Facades - Plants to a great extent help improve the quality of air in our environment. The UN Environment Program (UNEP) noted that greenery can serve as a possible solution to achieving sustainability in our cities. Even though we are aware that planting trees in populated cities is not always an easy task due to lack of space [40]. Green facades can be an appropriate alternative and provide the necessary green spaces earlier mentioned to achieve sustainability in urban spaces. Green facades can serve as a good means to creating an environment free of pollution. These green walls can filter toxic gases and particles that are suspended in the air and a lot of other pollutants in the atmosphere through the leaves of plants. Leaves can absorb particles of dust and even filter toxic gasses in the environment. The idea of living architecture is the concept of infusing plants on the building surface, this helps improve the quality of life and air within our environment and also helps to control the effect of rainwater on our buildings [41]. Although Green Facades can be achieved using two common techniques namely, Root in the soil and Root in the vase or box. Root in the soil:

Here, plants go on the wall naturally without using supportive structures. In these types of green walls, it usually takes a long time for the plant to cover the whole surface of the wall [29]. Root in the vase or box: In this type, plants grow from vases of medium size. An irrigation system is always needed for this group since the root of the plants are not directly in the ground soil. Some of these plants can also be used indoors to improve the quality of air within the interior spaces, plants like English Ivy ³Hedera helix´, Bamboo palm ³Chamaedorea seifrzii´, Chinese Evergreen ³Aglaonema modestum´, Rubber Tree ³Ficus elastic´ and a whole lot of other plants has proved effective in purifying the indoor air quality.

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Figure 4. Root in the soil green facade [41]. Figure 5. Root in the vase or box green façade [29].

(e) Premade living walls: This system is made up of premade panels or Integrated fabric which are attached to a frame or structural wall. The walls made by this system can support a variety of plants.

Boxes and geotextile sacks are used in this type. These boxes are attached to a buffer and sometimes can be attached to a wall structure [29].

Figure 6. Premade living walls [29].

(f) Cyclone collectors - These are devices that remove solid particles from an effluent stream [42].

Small cyclones devices are often installed to control pollutions from mobile sources, they can achieve efficiency of up to 90% when filtering particles larger than 20micrometers. Though this is not up to the stringent air quality standards. Cyclone collectors mostly serve as initial cleansers before the more efficient air filtering process or equipment are applied. Contaminated or dust-laden air gets into the system through an air inlet and with the aid of helical baffle, they are diverted, using centrifugal force the heavy dust is moved to the inner parts of the wall and are dropped to the base of the unit, the clean air will now be released to the atmosphere through the inner cylinder [42].

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Figure 7. A representation of how a cyclone collector works [42].

(g) Wet Scrubbers - These are air pollution control devices that remove particulate matter or gases from the industrial exhaust, it is used in industries, the scrubber filters air from an industry with the aid of a liquid, especially water [43]. Scrubbers use two techniques that remove pollutants from an industrial gas system. The 1st technique entails getting the particles wet by introducing a liquid into the system, then the 2nd technique, which is very important when using wet scrubbers is trapping the particles that are wet on a collecting surface, then from there, it is eventually removed entirely from the system. A bed or any flat surface can serve as the collecting interface.

Figure 8. A representation of how a wet scrubber functions [43].

(h) Fabric-filter baghouse - This can be described as one of the most efficient devices for removing particles from the atmosphere using assembled fabric bags. This has the ability of filtering particles as small as 1micrometer, but it impedes the flow of airflow, due to the nature of the fabrics [14]. A normal baghouse is made up of narrow filter bags, which are about 25cm (10 inches) in diameter, mostly placed to be facing down within a big compartment. Then fans are used as a means to blow

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the dust-laden air up through the base of the compartment, then, particles in the air will be trapped in the filter bag placed inside the compartment, whereas the clean air will now move through the fabric, exiting via the upper part of the baghouse. Note that some of the sections within the filter bags can be used separately as one baghouse [14].

Figure 9. A representation of how a fabric-filter baghouse functions [14].

(i) Adequate and routine building maintenance - Proper building maintenance is one of the most effective ways of curbing Microbial air pollution, as this ensures that the worn-out parts of the are changed as when due. Maintenance also ensures that some of the toxic embodied materials are changed early to reduce their effect on the building occupants.

4.2 Merits and results of having bio facades in our buildings The merits of having bio facades in our buildings are as follows;

a. Production of needed energy in the building using Biomass; biomass is a sustainable means of energy that can be used to generate other forms of energy needed in the building and it does not affect global warming.

b. Optical function; Aside from controlling air pollution, bio facades help to also reduce glare from the sun by absorbing the sun rays and heat from the sun.

c. Thermal performance; vegetation is known for its ability to absorb sun rays and also give shade to the walls of our building, thereby keeping the interior spaces cool.

d. Acoustic performance; microalgae can refract sound through their physical structure, which helps absorb noise from the environment. Though as at this moment no study has been done to measure the level of sound absorption by algae.

e. Aesthetics of the façade; the introduction of bio components to the surfaces of our buildings heightens the beauty of the building, Genin noted that bio façade walls can create inviting and pleasing scenes of our buildings that can help lure people to a building [44].

4.3. Analysing the differences between bio-based façade surfaces in attaining satisfactory environmental conditions Nigerian cities

In the previous section of this study, we discussed how bio facades and other means can be used to curb the amount and effect of pollutants in the environment, especially in urban centres. For optimal performance, we will examine the strength and weaknesses of some of them.

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i. Water-based Façade: This creates a sub-climate for the immediate environment, by reducing the temperature of the surrounding environment. But on the other hand, it cannot be used in all climates, consumes energy and water especially in regions with low rainfall.

ii. Algae Façade: it can regulate the temperature of the internal space thereby keeping the internal space comfortable. Reduced energy consumption, but on the other hand lack of knowledge about algae facades and lack of technology is a key component affecting this particular system.

iii. Green Façade: Works perfect in reducing heat island, reduces the cost of energy required to cool the building, and increases the plant coverage in urban centres. But on the other hand, it cannot be implemented in all climates because of high water consumption and building cost. Also, it is not easy to maintain.

It is proper to note that the overall benefits of these façade types are not overlooked, but what is important is a close analysis comparing their attributes to ascertain the level of possibility in applying these design strategies to our buildings. This analysis was done considering the weather conditions, the economic value, architecture and structures of the environment. It should also be noted that there is currently a lack of sufficient experience in this aspect of Architecture, especially in the context of the Algae façade. However, water façade and green façade (green living wall facade) can be used interchangeably especially in the southern part of Nigeria, where there is a relatively enough supply of water and conducive weather that can accommodate the growth of plants on special surfaces

5. Conclusion and Recommendations

The study investigated possible ways through which architecture can help curb air pollution and air pollutants in the atmosphere through innovative architectural design strategies and controlled construction practices, and how it can be implemented in our urban centres. The study specifically through the review of relevant works of literature provide a better understanding of how bio façade walls operate in the course of controlling air pollution, and how it also affects the other aspects of human life. The lack of quantitative or empirical data on the performance of the systems introduced in the discussions is an issue raised by this study, which should be considered in further research.

But from the review of relevant literature, sourced from highly indexed journals, it was found that the built environment is a major contributor to the level of pollutants in the environment, noting that our building, from construction to deconstruction generates pollutants which are released to the atmosphere.

The study also noted that the effects of these pollutants from our buildings and construction practices are on the increase because more construction and developmental projects are being undertaken daily, without any meaningful solution from the built industry to help control the level of pollution generated within resulting to an increase in health complications among urban dwellers.

The findings of this research have key implications for building design and construction as well as the planning of our urban city centres, which needs to be elaborated. First is that every building development in urban centres should as a matter of requirement be given a stipulated percentage of greenery to be provided in the development, with the option of having the conventional planting of trees, or using the building walls as a means to provide greenery. To this effect the should be educative and interactive forums, where stakeholders in the building industry will be enlightened on the need and usefulness of bio responsive designs and how to inculcate some of these simple steps in our designs. Steps as having water fountains around building, creating green roofs and gardens in balconies, which are simple and cost-effective. This will ensure that the environment within our buildings is less polluted. In order to achieve a sustainable design and reduce the amount of energy utilized in the built industry, bio facades are the best alternative because it helps regulate the immediate temperature of the environment, improve indoor thermal comfort for building occupants while using little or no energy and at the same time curtailing air pollution. Furthermore, with the epileptic power supply currently being experienced in

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Nigeria, bio facades can ultimately turn building walls into mini power plants, even though this study is still at infancy, and is not yet cost-effective. It is however noted that integration of bio facades into architectural buildings ensures a sustainable source of energy, which can be utilized in housing units, and it will also directly contribute to a clean, healthy and sustainable environment. Creating values in our system.

Finally, bio façades can complement to a great extent the current quest to curb the air pollution problems we are facing today, especially in urban centres. In line with the idea of [29,45], on green facades, Bio-inspired designs are sustainable and efficient options, which can serve as a reliable means of reducing the running energy, and cost consumption of our buildings, at the same time creating a pleasing aesthetics and improving the climatic condition of the environment. Bio façade ideas and strategies are gradually evolving, and stakeholders in the built industry around the world are now adopting them into their designs. However, in Nigeria today our city developers are yet to explore the potentials of bio facades and it has not yet formed an accepted standard of construction in our building sector. Hence, more research is needed to enhance the quality of architecture in the aspect of protecting the environment and taking advantage of its capabilities in creating sustainable architecture especially by exploring the idea of bio facades.

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