5 Air Quality
5.1 Environmental Objectives
5.1.1 Scotland's air quality environmental protection objectives are largely derived from the EC Air Quality Directive (2008/50/ EC) and the 4th Air Quality Daughter Directive (2004/107/ EC)  , via the Air Quality Standards (Scotland) Regulations 2010  which transposes these Directives into a Scottish context. There are also domestic objectives as part of the Local Air Quality Management system set under the Environment Act 1995 and associated regulations  . These objectives are largely aimed at reducing air emissions that are potentially harmful to human health and the environment, and together they set out the requirement for monitoring with a particular focus on areas where air pollution is concentrated.
5.2 Environmental Context
5.2.1 As discussed above under 'Population and Human Health', air quality is important for both short and long-term human health. It is also clear that those with pre-existing health issues may be more vulnerable to poor air quality over the long-term  . Air pollution can also cause adverse effects in the wider environment. For example, it can add nutrients to water bodies and soils and contribute to acidification and eutrophication, both of which can impact on plant and animal life. It can also damage the fabric of buildings and monuments, threatening cultural heritage and the historic environment  .
5.2.2 Air quality in Scotland has improved considerably over the last few decades. Between 1990 and 2014 there were decreases of 75% for carbon monoxide, 69% for nitrogen oxides, 65% for non-methane volatile organic compounds , 46% for fine particulate matter ( PM 10) and 90% for sulphur dioxide  . However, there are some towns and cities where air quality has been identified as a concern  , and in Scotland air pollution in estimated to reduce life expectancy by 3-4 months  .
5.2.3 As per section 83(1)  of the Environment Act 1995, where air quality objectives are not being met or are unlikely to be met within the relevant period, Local Authorities are required to designate an Air Quality Management Area (" AQMA"). Within Scotland, 14 of the 32 Local Authorities have currently declared a total of 39 AQMAs. The majority of these are declared in urban areas as a result of nitrogen oxides alone or in combination with PM 10 levels, primarily as a result of traffic emissions. While none of these areas have been declared as a consequence of aviation activities, several AQMAs have been declared along popular traffic routes to and from several airports  .
5.2.4 As set out in the Air Quality Standards (Scotland) Regulations 2010  , Scottish Ministers must ensure that levels of airborne pollutants are maintained below the limit values, and must endeavour to maintain the best ambient air quality compatible with sustainable development.
5.2.5 Emissions attributed to aircraft operations that have local air quality effects are nitrogen oxides, carbon monoxide, unburned hydrocarbons, sulphur dioxide, fine particulate matter ( PM 10 and PM 2.5) and odour  . These arise from a number of sources including the combustion of aviation fuel, vehicles travelling to and from airports, operation of ground service equipment and construction activities associated with infrastructure development  .
5.3 Assessment Findings
5.3.1 The consideration of air quality implications on human health and climate change has been assessed under the respective topics of Population and Human Heath and Climatic Factors.
What are the likely implications of increased passenger and flight numbers on local air quality?
5.3.2 The following paragraphs set out the impacts that arise from aviation activity and how these can impact on air quality. These are considered to be secondary impacts and are based on the assumptions that the implementation of the preferred policy option will lead to increased passenger and flight numbers. However, it is considered that any secondary impacts that arise are outwith the ability of the policy option to influence.
5.3.3 Aircraft engines, support vehicles and equipment, and vehicles accessing the airport are key aviation sources of emissions that affect air quality  . Aircraft engines produce emissions that are similar to those resulting from any oil based fuel consumption and these, like any exhaust emissions, can affect local air quality at ground level. It is the emissions from aircraft below 1,000 feet above the ground (typically 3 kilometres from departure or, for arrivals, around 6 kilometres from touchdown) that are predominantly involved in influencing local air quality  . These emissions disperse with the wind and blend with emissions from other sources such as road transport pollution. Aircraft operations are the most significant source of emissions  .
5.3.4 Ground operations that support flight activity will also be influenced by the estimated growth in the industry, and there is the potential for the increased use of service equipment such as power units and vehicle movements to further contribute to emissions.
5.3.5 The preferred policy option could also influence road traffic levels as a result of an increase in passengers, workers and supplier journeys. As discussed previously, there is also the potential for a modal shift to arise which could have implications for air quality. For example, through longer road surface journeys being undertaken, thereby contributing to increased GHG emissions. Whilst this remains a relevant consideration, this SEA cannot predict to an acceptable level the impact on overall emissions should a modal shift arise.
5.3.6 The SEA of the NPF3 considered the proposed Strategic Airport Enhancements and noted that mixed effects on air quality could be expected  . The assessment reported that there was potential for negative effects to arise as a result of increased levels of traffic to and from airports, in addition to increased flights. However, it was also considered that there could be benefits to air quality through increased public transport connectivity.
5.3.7 These secondary impacts will also be further influenced by the extent to which passenger numbers increase. For example, when considering the illustrative scenarios of adopting a differential approach to how the tax reduction is applied. There is the potential that applying a zero tax rate amount to only short-haul flights as a means of delivering the preferred policy option could lead to a higher number of additional passengers, compared to reducing the tax charged on both short and long-haul flights by an equal proportion. Conversely, applying a zero tax rate amount to only long-haul flights could lead to a lower number of additional passengers compared with reducing both short and long-haul flights proportionally equally. As discussed previously, this is due to factors such as passenger demand on long-haul flights being the most price inelastic ( i.e. least price sensitive) and there being fewer long-haul flights.
5.3.8 Under the reasonable alternative, it is considered that there would be no direct impact on passenger and flight numbers as this would approach would lead to no reduction in the overall tax burden of ADT. As such, there would be no additional pressure on local air quality beyond that currently experienced.
What wider context and potential mitigation measures should be taken into account?
5.3.9 Internationally, work is being undertaken by ICAO on initiatives to improve air quality, as well as developing measures to reduce the impact of aircraft emissions on local air quality  . These measures focus on the effect of aircraft engine emissions below 3,000 feet and emissions from airport sources such as airport traffic, ground service equipment and de-icing operations. ICAO also state that technological innovations in aviation will continue to lead the way towards effective and efficient measures to support their environmental goals of limiting or reducing the impact of air craft emissions on local air quality  .
5.3.10 At a local level, many airports and airlines have made changes to their operations to help improve air quality through improvements to aircraft and engine design, operational procedures and fuels  . The " UK Aviation and Air Quality Report"  also sets out a range of initiatives to reduce emission in and around UK airports such as the introduction of cleaner or zero emission aircraft handling equipment and airport vehicles to replace diesel versions.
5.3.11 NPF3 is one of a number of plans and strategies that set out objectives for greater connectivity. This vision is set out in "a successful, sustainable place" which considered a range of topics, including the role of green networks and linking development with public transport networks, aimed at promoting active and sustainable travel options.
5.3.12 A number of airports also produce surface access strategies which set out alternative travel options to and from the airport for passengers, workers and suppliers  . Measures promoted include the investment in new or improved infrastructure to enhance traffic flow and ease congestion, encouraging staff car sharing schemes and actively discouraging the number of car journeys to and from the airport.
What is the likely significance of the predicted impacts?
5.3.13 There are a number of factors that make assessing the impacts on air quality difficult. Firstly, when assessing the atmospheric emissions that arise from aviation activity there are variables that affect individual airports differently. For example, operational procedures and mitigation measures applied at a local level will be specific to individual airports.
5.3.14 Additionally, any potential effect that may arise with regard to road traffic movement is a complex issue. There are a number of factors that outwith the aviation sector that can influence modal shift. The estimated increase of passenger numbers predicted in the 2017 research  sits within the wider context of growth within a range of sectors which all have the potential to individually influence local air quality.
5.3.15 Although there are many factors that influence air quality, it is considered likely that the predicted increase in passenger and flight numbers could contribute to pressures experienced at a local level. Any pressure placed on local air quality through aviation activity is likely to be influenced by the degree of the predicted increase in passenger numbers.
5.3.16 The significance of the secondary impacts to air quality identified as likely to occur from the policy will be dependent on factors such as the location. For example, there is the potential that problems experienced in areas designated as AQMAs may be further exacerbated through increased pressure from any activity that contributes to air pollution. The secondary impacts identified may be long-term in nature as a result of operational activity, in addition to short-term impacts that may arise from any construction works undertaken.
Box 5.1 Air Quality: Summary of impacts and key points