4. Biodiversity, air quality and UNDP BANGLADESH / FLICKR human health 1. Introduction million in 2012 (WHO 2014¹). This was equivalent to 1 in every 8 deaths globally, making air pollution Air pollution is a significant problem in cities the most important environmental health risk across the world. It affects human health and worldwide (WHO 2014a). Other diseases affected well-being, ecosystem health, crops, climate, by air pollution include cardiovascular disease, visibility and human-made materials. Health immune disorders, various cancers, and disorders effects related to air pollution include its of the eye, ear, nose and throat such as cataract and impact on the pulmonary, cardiac, vascular and sinusitis. Epidemiological evidence suggests that neurological systems (Section 2). Trees affect air prenatal exposure to certain forms of air pollution quality through a number of means (Section 3) can harm the child, affecting birth outcomes and and can be used to improve air quality (Section infant mortality. Childhood exposure to some 4). However, air pollution also affects tree health pollutants also appears to increase the risk of and plant diversity (Section 5). Bioindicators can developing health problems in later life, affecting be useful for monitoring air quality and indicating the development of lung function and increasing environmental health (Section 6). Understanding the risk for development of chronic obstructive the impacts of vegetation biodiversity on air pulmonary disease (COPD) and asthma. quality and air quality on vegetation biodiversity is essential to sustaining healthy and diverse Several respiratory illnesses caused or otherwise ecosystems, and for improving air quality and affected by air pollution are on the rise. These consequently human health and well-being. include bronchial asthma, which affects between 100 and 150 million people worldwide, with $LUSROOXWLRQDQGLWVHƨHFWVRQ another 65 million affected by some form of human health COPD. Other human health problems from air pollution include: aggravation of respiratory and Air pollution can significantly affect human and cardiovascular disease, decreased lung function, ecosystem health (US EPA 2010). Recent research increased frequency and severity of respiratory indicates that global deaths directly or indirectly symptoms (e.g. difficulty in breathing and attributable to outdoor air pollution reached 7 coughing, increased susceptibility to respiratory ¹ World Health Organization, 2015. Health and the Environment: Addressing the health impact of air pollution. Sixty-eighth World Health Assembly, Agenda item 14.6. A68/A/CONF./2 Rev.1 26 May 2015. http://apps.who.int/gb/ebwha/pdf_files/ WHA68/A68_ACONF2Rev1-en.pdf (last accessed June 2015) Connecting Global Priorities: Biodiversity and Human Health 63 infections), effects on the nervous system (e.g. pollution also affects the earth’s climate by either impacts on learning, memory and behaviour), absorbing or reflecting energy, which can lead to cancer and premature death (e.g. Pope et al. climate warming or cooling, respectively. 2002). People with pre-existing conditions (e.g. heart disease, asthma, emphysema), diabetes, and Indoor air pollution is primarily associated with older adults and children are at greater risk for particulates from combustion of solid fuel (wood, air pollution-related health effects. In the United coal, turf, dung, crop waste, etc.) and oil for heating States (US), approximately 130 000 particulate and cooking, and gases from all fuels (including matter (PM)2.5-related deaths and 4700 ozone natural gas) in buildings with inadequate (O3)-related deaths in 2005 were attributed to air ventilation or smoke removal. The World Health pollution (Fann et al. 2012). Organization (WHO) reports that over 4 million people die prematurely from illness attributable to Air pollution comes from numerous sources. household air pollution from cooking with solid Major causes of gaseous and particulate outdoor fuels. More than 50% of premature deaths among air pollution with a direct impact on public health children under 5 years of age are due to pneumonia include the combustion of fossil fuels associated caused by particulate matter (soot) inhaled from with transport, heating and electricity generation, household air pollution. It is estimated that and industrial processes such as smelting, 3.8 million premature deaths annually from concrete manufacture and oil refining. Other noncommunicable diseases (including stroke, important sources include ecosystem degradation ischaemic heart disease, lung cancer and COPD) (including deforestation and wetland drainage) are attributable to exposure to household air and desertification. pollution (WHO 2014b). Plants provide an important ecosystem service Some pollutants, both gaseous and particulate, are through the regulation of air quality. Although directly emitted into the atmosphere and include the effects of plants on air quality are generally sulfur dioxide (SO2), nitrogen oxides (NOx), positive, they can also to some degree be negative carbon monoxide (CO), particulate matter (PM) (as discussed in section 3 below). Likewise, air and volatile organic compounds (VOC). Other quality can have both positive and negative pollutants are not directly emitted; rather, they are impacts on plant populations. These various formed through chemical reactions. For example, impacts are partially dependent upon the diversity ground-level O3 is often formed when emissions of the plant species, vegetation assemblages and of NOx and VOCs react in the presence of sunlight. size classes. This chapter explores the role of Some particles are also formed from other directly biodiversity in regulating air quality in positive emitted pollutants. and negative terms, including a discussion of current knowledge gaps and recommendations. 3. Impacts of vegetation on air Air pollution also affects the environment. Ozone quality and other pollutants can damage plants and trees, There are three main ways in which plants affect and pollution can lead to acid rain. Acid rain can local air pollution levels: via effects on local harm vegetation by damaging tree leaves and microclimate and energy use, removal of air stressing trees through changing the chemical pollution, and emission of chemicals. Each of and physical composition of the soil. Particles these are described below. in the atmosphere can also reduce visibility. The typical visual range in the eastern US parks is (ƨHFWVRISODQWVRQORFDO 15–25 miles, approximately one third of what it would be without human-induced air pollution. microclimate and energy use In western USA, the visual range has decreased Increased air temperature can lead to increased from 140 miles to 35–90 miles (US EPA 2014). Air energy demand (and related emissions) in the 64 Connecting Global Priorities: Biodiversity and Human Health summer (e.g. to cool buildings), increased air winter-time heating energy demand by tending pollution and heat-related illness. Vegetation, to reduce cold air infiltration into buildings. On particularly trees, alters microclimates and the negative side, reductions in wind speed can cools the air through evaporation from tree reduce the dispersion of pollutants, which will transpiration, blocking winds and shading various tend to increase local pollutant concentrations. In surfaces. Local environmental influences on air addition, with lower wind speeds, the height of the temperature include the amount of tree cover, atmosphere within which the pollution mixes can amount of impervious surfaces in the area, time be reduced. This reduction in the “mixing height” of day, thermal stability, antecedent moisture tends to increase pollutant concentrations, as the condition and topography (Heisler et al. 2007). same amount of pollution is now mixed within a Vegetated areas can cool the surroundings by smaller volume of air. several degrees Celsius, with higher tree and shrub cover resulting in cooler air temperatures (Chang 2) Removal of air pollutants et al. 2007). Trees can also have a significant impact on wind speed, with measured reductions Trees remove gaseous air pollution primarily by in wind speed in high-canopy residential areas uptake through the leaves, though some gases (77% tree cover) of the order of 65–75% (Heisler are removed by the plant surface. For O3, SO2 1990). and NO2, most of the pollution is removed via leaf stomata.³ Healthy trees in cities can remove 2Temperature reduction and changes in wind significant amounts of air pollution. The amount speed in urban areas can have significant effects of pollution removed is directly related to the on air pollution. Lower air temperatures can lead amount of air pollution in the atmosphere (if to lower emission of pollutants, as pollutant there is no air pollution, the trees will remove no emissions are often related to air temperatures air pollution). Areas with a high proportion of (e.g. evaporation of VOCs). In addition, reduced vegetation cover will remove more pollution and urban air temperatures and shading of buildings have the potential to effect greater reductions in can reduce the amount of energy used to cool air pollution concentrations in and around these buildings in the summer time, as buildings are areas. However, pollution concentration can be cooler and air conditioning is used less. However, increased under certain conditions (see Section 4). shading of buildings in winter can lead to increased Pollution removal rates by vegetation differ among building energy use (e.g. Heisler