Unconventional oil and gas policy: SEA

5 Air

5.1 The overlap between topic areas is recognised within the SEA, and therefore some issues which are associated with some SEA topic areas are addressed under the main topic area to which the effects relate.

• Impacts of GHG emissions on climate change associated with air emissions are addressed under the SEA topic ‘climatic factors’.
• Impacts of GHG emissions on biodiversity are addressed under the SEA topic ‘biodiversity’.

5.2 This SEA topic focuses on the potential impacts of air pollutants on public health and the environment such as impacts on plant health. Other potential impacts of unconventional oil and gas developments on public health will be dealt with in the section ‘Population and Human Health’.

What are the environmental effects of unconventional oil and gas development on air?

5.3 Unconventional shale gas/oil development and CBM development result in the emission of air pollutants from a number of stages of unconventional oil and gas development exploration, appraisal, production and decommissioning. The following sources of air pollution are identified:

• fugitive emissions;
• vented emissions;
• incomplete combustion emissions;
• traffic air pollution;
• leakage from decommissioned wells; and
• emissions associated with land use change (see climatic factors)

5.4 These sources are discussed in greater detail below.

5.5 Fugitive emissions are direct air emissions arising from unintentional leaks in unconventional oil and gas developments^[26]. There are various potential sources of fugitive emissions. These include leaks from valves and pipe joints, compressors, well heads; accidental releases that result from routine wear, tear, and corrosion; or the overpressure of gases or liquids in the system. Methane (CH₄) is the predominant type of greenhouse gas emitted as a fugitive emission. Other noteworthy fugitive emissions include volatile organic compounds (VOCs), carbon dioxide (CO₂), hazardous air pollutants (HAPs), sulphur dioxide (SO₂), and nitrous oxide (N₂O)^[27,28]. Fugitive emissions may also contain hazardous air pollutants (HAPs) which refer to a group of toxic and/or carcinogenic air pollutants. Examples of HAPs include benzene, asbestos, mercury and lead compounds^[29].

5.6 The exact composition of fugitive emissions is variable and depends on the geology of the reservoir. Coal bed methane typically contains a higher proportion of methane than shale gas/oil^[30]. A large proportion of the fugitive emissions have been found to come from a small group of ‘super emitters’. Super emitters have been identified as a key source of greenhouse gas (GHG) emissions, if they are left unchecked for extended periods of time. The emissions can occur during well, development, production and decommissioning. There is recent evidence that 2% of sites on the Barnett shale in Texas, United States, were responsible for half of the methane emissions^[31] from that location.

5.7 Vented emissions are a type of fugitive emissions, and are the result of intentional releases of unburned gases into the atmosphere. These include releases during ‘flowback’, releases for certain maintenance operations and releases for safety reasons to guard against over-pressuring^[32,33]. During venting operations, a number of gases and air pollutants are released. These typically include methane (CH₄), carbon dioxide (CO₂), volatile organic compounds (VOCs) and sulphur compounds^[34].

5.8 Incomplete combustion emissions occur from on-site burning of fossil fuels associated with unconventional oil and gas developments. The emissions come from engines and other equipment used in unconventional oil and gas developments, as well as from any flaring of gas^[35]. Gas flaring is the controlled burning of natural gas. It is used during well production testing as a means to determine the pressure, flow and composition of the gas or oil from the well or as a safety device to minimise explosive conditions^[36,37]. According to a study commissioned by the Department of Energy & Climate Change^[38], incomplete combustion emissions would be mainly carbon dioxide (CO₂). However, incomplete combustion could also result in other emissions such as methane (CH₄), volatile organic compounds (VOCs), nitrogen oxides (NO_x), carbon monoxide (CO), trace amounts of sulphur dioxide (SO₂), particulate matter (PM) and black carbon. Coal and, to a lesser extent, heavy fuel oils contain non-combustible materials such as minerals including calcium, and trace quantities of other metals like selenium, cadmium and so on. Furthermore, polycyclic hydrocarbons (PAHs) are produced when fuel sources such as coal, oil, gas, wood and garbage are burned. PAHs generated from these sources can bind to, or form, small particles in the air^[39].

5.9 The increases in vehicle movements associated with unconventional oil and gas developments is likely to result in an increase in traffic air pollution^[40]. Traffic air pollution is the result of indirect emissions that arise from transporting materials, water supplies and waste to and from the unconventional oil and gas site^[41]. Heavy truck movements for delivery of water which are particularly known to generate nuisance from dust and increased levels of particulate matter, NO_x and exhaust fumes^[42]. However, it is important to note that the exact emissions will depend on the types of vehicle used and their emission standards. Vegetation surrounding the areas with higher vehicle movements can also influence pollution levels through the filtering and removal of particulate matter^[43].

5.10 Leakage from decommissioned wells is another issue associated with unconventional oil and gas developments. There is a risk that a small proportion of wells may fail. The main cause is cement shrinkage, which often occurs a few years after decommissioning. There also remains a residual risk of failure of well integrity if conventional hydrocarbons in permeable rocks such as sandstones and limestones overlie unconventional oil and gas resources. These relatively soft rock formations may become a potential source of leaks if high formation pressures exist in the reservoir^[44]. There is evidence to suggest that these emissions are low^[45].

5.11 Emissions associated with land use change occur when land is converted from one use to another. Land use changes affect sources of carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O). Emissions of CO₂ and CH₄ are addressed under the Climatic factors SEA topic. Examples of such changes include the clearing of forests or development of land formerly in agricultural use^[46]. Emissions associated with land use change can also result from land remediation during decommissioning^[47].

5.12 The nature, scale, duration and significance of these effects in relation to this SEA topic will be further discussed below.

How do these effects relate to the current pressures and trends?

5.13 Air pollution remains the single largest environmental health hazard in Europe, resulting in a lower quality of life due to illnesses and an estimated 467,000 premature deaths per year^[48].

5.14 The main pollutants of current concern in Scotland are nitrogen oxides (NO_x), particulate matter (PM₁₀ and PM_2.5), sulphur dioxide (SO₂), non-methane volatile organic compounds (NMVOCs), ground level ozone (O₃) and ammonia (NH₃)^[49]. Of these pollutants, nitrogen oxides (NO_x) and particulate matter (PM) are currently of greatest concern, as these are considered to be the most damaging to human health^[50]. Emissions associated with unconventional oil and gas developments contain these pollutants – to lesser or greater extent.

Table 4.1: Air pollutants associated with unconventional oil and gas

Source	Air pollutants
Fugitive emissions	Methane (CH4), carbon dioxide (CO2), volatile organic compounds (VOCs) and sulphur compounds, hazardous air pollutants (HAPs) and nitrous oxide (N2O)
Incomplete combustion emissions	Mainly carbon dioxide (CO2) Other pollutants: methane (CH4), volatile organic compounds (VOCs), non-methane volatile organic compounds (NMVOCs), nitrogen oxides (NOx), carbon monoxide (CO), trace amounts of sulphur dioxide (SO2), sulphur oxides (SOx), particulate matter (PM) and black carbon
Emissions associated with land use change[51]	Carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O) and particulate matter.

NMVOCs and VOCs

5.15 Volatile Organic Compounds (VOCs) are a large group of gases and easily vaporisable liquids that differ widely in their chemical composition but display similar behaviour in the atmosphere. VOCs include both human-made and naturally-occurring chemical compounds. Non-methane volatile organic compounds (NMVOCs) are identical to VOCs, but with methane excluded^[52].

5.16 The largest categories of NMVOC emissions in 2016 were industrial processes and product use (54% of the UK total), followed by extraction and distribution of fossil fuels (16%) and agriculture (14%). By comparison, only 8% of the NMVOC emissions in 2016 arose from transport and other mobile sources. Between 1990 and 2016, UK emissions of NMVOC have decreased by 71%. This reduction is largely due to controls on emissions from road vehicles, which have delivered a 96% reduction in road transport sector emissions since 1990^[53,54].

5.17 NMVOCs are typically emitted during unconventional oil and gas site development activities such as the use of diesel-powered equipment for site construction activities and transport^[55].

5.18 NMVOCs have the potential to adversely impact upon human health. Some NMVOCs damage the ozone layer in the upper atmosphere, thus reducing protection from harmful UV rays^[56]. Other NMVOCs are toxic to humans. For instance, benzene and 1,3 butadiene have shown to be carcinogenic when there is sufficient exposure^[57].

Particulate matter

5.19 Particulate matter (PM) refers to the sum of all solid and liquid particles suspended in the air, many of which are hazardous to health. Major components of PM are sulphate, nitrates, ammonia, sodium chloride, black carbon, mineral dust and water. The release of PM constitutes a health risk as inhaled particles form a complex mixture of hazardous chemical compounds and there is no safe threshold for exposure. Recent evidence shows that PM affects more people than any other air pollutant^[58]. Pollutant particles are measured using a system based on the size of the individual particle; this is measured into micrometres (µ). Commonly, PM are divided into PM₁₀, PM_2.5 and PM_1. The general rule is that the lower the size (µ), the more dangerous the pollutant is because smaller particles can penetrate and lodge more deeply into the lungs. Therefore, PM_2.5 and PM₁ constitute a more serious health concern than PM₁₀^[59].

5.20 A study for the European Study of Cohorts for Air Pollution Effects (ESCAPE)^[60] has found that low air concentration of fine particulate matter seem to be associated with mortality. A recent report by Health Protection Scotland (HPS)^[61] estimated that PM_2.5 pollution could have contributed to the deaths of 2094 people aged 25 and over in Scotland in 2010. The areas in Scotland with the highest attributable fraction of total deaths being associated with particulate matter (PM) pollution are: Edinburgh (4.9%), Glasgow City (4.7%), Falkirk (4.3%) and North Lanarkshire (4.3%)^[62].

5.21 Road transport accounts for a considerable share (13%) of particulate matter emissions^[63], and at least 21% of coarse particulate matter (PM₁₀)^[64]. In addition, residential combustion, agriculture and industrial processes each account for over 10% of emissions. In 2015, an estimated 12kt of PM₁₀ was produced^[65]. Since 1992, emissions from diesel vehicles have been decreasing due to the increased uptake of new vehicles meeting tighter PM₁₀ emission regulations^[66]. It is estimated that PM₁₀ emissions have declined by 63% since 1990. Reductions in emissions from energy industries, particularly due to the closure of coal fired stations, have had the most notable impact on this trend^[67].

Ground level ozone

5.22 Unlike stratospheric ozone, which forms naturally in the upper atmosphere, ground-level (or tropospheric) ozone is created through the interactions of man-made (and natural) emissions of volatile organic compounds (VOCs) and nitrogen oxides (NOx). The sun’s direct ultraviolet rays convert VOCs and NOx emissions into ground-level ozone. Many factors impact ground-level ozone development, including temperature, wind speed and direction, time of day, and driving patterns. Due to its dependence on weather conditions, ground-level ozone is typically a summertime pollutant.

5.23 High concentrations of ground level ozone can be harmful to people, particularly to children, the elderly and people of all ages who have lung diseases such as asthma. Ground level ozone can also have harmful effects on sensitive vegetation, ecosystems, animals and crops.

Carbon monoxide

5.24 Carbon monoxide (CO) is a colourless, odourless gas. Carbon monoxide is a product of incomplete combustion emissions associated with unconventional oil and gas developments. Exhaust emissions from transport are another key source of carbon monoxide, particularly in urban areas. Poorly maintained vehicles are known to increase carbon monoxide emissions^[68].

5.25 In large amounts, carbon monoxide (CO) can be harmful as it reduces the amount of oxygen that can be transported in the blood stream critical to organs like the heart and the brain. It is important to note that mortality associated with carbon monoxide poisoning generally occurs in enclosed spaces indoors. Very high levels of carbon monoxide (CO) are not likely to occur outdoors. However, when carbon monoxide levels are elevated outdoors, particularly through exhausts from vehicles, they can be of particular concern for people with some types of heart disease. In addition, they are especially vulnerable to the effects of carbon monoxide (CO) when exercising or when they are under increased stress^[69].

5.26 Therefore, it is judged that elevated carbon monoxide concentrations associated with unconventional oil and gas developments may be a consideration in urban areas characterised by high traffic flows and in locations where there are higher levels of health deprivation– particularly in areas with a relatively high density of people with heart conditions.

Nitrogen oxides (NO_x)

5.27 There are seven nitrogen oxides (NO, NO₂, NO₃, N₂O, N₂O₃, N₂O₄, N₂O₄ and N₂O₅). The most important ones are nitric oxide (NO) and nitrogen dioxide (NO₂), which are together referred to as NO_x. It is estimated that 90% of NO_x comes from natural sources, while the remaining anthropogenic emissions are mainly attributed to combustion processes associated with transport^[70]. Road transport accounts for one-third (33%) of nitrogen oxide (NO_x) emissions^[71].

5.28 Transport movements account for a large share of particulate matter emissions. In 2014, emissions of nitrogen oxides were estimated to be 91kt, of which transport accounted for 41%. Since 1990, transport emissions have declined by 70%. There are a number of reasons why transport emissions have declined; the requirement for new petrol cars to be fitted with three-way catalysts since 1989 and the introduction of ‘Euro standards’ for new cars^[72]. Since 2007, emissions of NO_x have declined notably due to reductions in road transport emissions and the power generation sector^[73].

Sulphur

5.29 Sulphur oxides (SO_x) may be formed during the combustion of the sulphur contained in either fuel, inorganic and organic compounds. They are corrosive by nature, and have the potential to have adverse effects on public health and the wider environment because of the role they play in creating acid rain. Sulphur dioxide (SO₂) is particularly harmful for public health, as it can affect the respiratory system and cause irritation of the eyes, nose and throat^[74].

5.30 When sulphur dioxide combines with water, it forms sulphuric acid – the main component of acid rain^[75]. In the UK, the predominant source of sulphur dioxide is the combustion of sulphur – containing fossil fuels, principally coal and heavy oils^[76].

5.31 In 2015, emissions of sulphur dioxide were estimated to be 23kt. Emissions have declined by 92% since 1990, due to reductions in energy industries emissions – particularly coal fired power. Road transport emissions have also declined. Restricting sulphur in road fuels, both petrol and diesel, has drastically reduced the emissions of sulphur dioxides from vehicles in Scotland^[77].

5.32 People with pre-existing health conditions (such as heart disease, lung conditions and asthma) may be adversely affected by day-to-day changes in air pollution levels^[78].

5.33 Emissions of these air pollutants are judged to have particularly adverse impacts in urban areas, as most AQMAs are located in the densely populated Midland Valley – the City of Edinburgh, East Dunbartonshire, East Lothian, Falkirk, Fife, Glasgow Midlothian, North Lanarkshire, South Lanarkshire and West Lothian^[79], and the local authorities with AQMA are illustrated on Figure 1, Appendix 1. The number of AQMAs has increased from 26 in 2011 to 38 in 2018. Most AQMAs have been declared due to emissions from traffic^[80]. It is important to note that AQMAs are generally confined to small geographic areas which may limit their strategic importance in relation to future unconventional oil and gas developments.

5.34 In existing literature, it is recognised that a number of gaps remain because the full range of emissions and air pollutants from drilling, well completion and other activities remains unknown^[81]

What current regulatory processes control these effects?

5.35 There is regulation in place to protect air quality in Scotland. SEPA currently regulates over 500 major industrial sites that have the potential to cause air pollution through the Pollution and Prevention and Control (PPC) (Scotland) Regulations 2012^[82]. In this context, SEPA sets limits for certain pollutants emitted^[83].

5.36 In Scotland, releases of VOCs, NO_x, SO₂, particulate matter and carbon monoxide (amongst other polluting substances) are controlled under the Pollution and Prevention and Control (PPC) (Scotland) Regulations 2012^[84]; and the National Air Quality Strategy^[85], which provides a framework for improving air quality, in which VOCs (1,3 butadiene and benzene) are one of the main air pollutants targeted for reduction^[86]. The World Health Organisation (WHO) have guidelines for ambient VOCs, but these are recommendations and therefore not mandatory.

5.37 In 2016, Scotland became the first country in Europe to adopt the WHO recommended limit for PM_2.5. However, a small proportion of Scotland is still characterised by air pollution levels above the limits contained in Scotland’s air quality regulations^[87].

5.38 Any unplanned release of fluids (liquid or gas) from an oil or gas well must be reported to HSE under Schedule 2, Part 1, Section 20 of the Reporting of Injuries, Diseases and Dangerous Occurrences Regulations 2013^[88]. The Management of Extractive Waste (Scotland) Regulations 2010^[89] requires that extractive waste will be managed without using processes or methods which could adversely impact upon local air quality and harm the wider environment.

5.39 Furthermore, the Town and Country Planning (Environmental Impact Assessment) (Scotland) Regulations 2017^[90] relate to the assessment of the impact of certain public and private projects on the environment through the planning system.^[91] This would require consideration of impacts on local air quality where unconventional oil and gas developments are of a size and scale to require EIA.

5.40 Baseline monitoring and post-decommissioning monitoring are critical in the assessment of the long-term risk of leakage from wells, because leaks typically start within several years following well abandonment. For this reason, monitoring for leakage from decommissioned unconventional oil and gas wells is required by SEPA to allow environmental authorisations to be surrendered. Where leaks are identified, the unconventional oil and gas operator should take remedial action based on a risk assessment – all in accordance with the steps that SEPA consider necessary^[92].

5.41 A study by the Committee on Climate Change^[93] concludes that there are gaps in the current regulatory framework in Scotland for greenhouse gases from unconventional oil and gas developments. The current framework lacks clarity over the responsibilities and roles of the various actors and that there are gaps in relation to emissions to the atmosphere, particularly fugitive methane emissions. Following from this, the report states that the regulatory framework should be enhanced to ensure that regulation covers all emissions of both CO₂ and methane, which requires strict limiting of these emissions and entails long-term monitoring.

What stages of unconventional oil and gas development result in these effects, and what is the nature of these effects?

Fugitive emissions

Business as usual – shale oil and gas extraction

5.42 Emissions associated with unconventional oil and gas development primarily come from the well development and production stages. There is little information available on emissions associated with the exploration stage. Most studies either ignore this phase or assume that the emissions are negligible. Therefore, it should not be assumed that emissions from exploration will be low, especially for any extended well tests^[94].

5.43 It is important to note that there is mixed evidence about the level of fugitive emissions potentially arising from unconventional oil and gas developments. In the United States, the level of fugitive emissions from shale gas operations has been estimated to range from 0.42-7.9% of total gas production. Other recent airborne measurements of methane fluxes in Pennsylvania indicated that seven well pads accounted for 4-30% of the flux in a 2800 km² area. However, these recent levels cannot be assumed to represent the Scottish situation due to contrasts in geology and source material. Therefore, there is uncertainty as to the extent to which results from US case studies could apply in Scotland^[95].

5.44 The potential impacts of vented emissions could occur with immediate effect during the exploration, appraisal and production stage. These stages together could occur over a period of approximately 20 years. The effects of vented emissions are anticipated to be temporary, due to the fact that these disturbances are caused by the venting of gases on site (when necessary). The scale of the effects is uncertain, depending on the size of the unconventional oil and gas pad and the sensitivity of the receiving environment.

5.45 Fugitive emissions could occur with immediate effect during the exploration, appraisal, production and decommissioning stage. These stages together could occur over a period of approximately 30 years for an individual development.

5.46 The potential impacts of super-emitter sites could occur with immediate effect during the exploration, appraisal, production and decommissioning stage. These stages together could occur over a period of approximately 30 years for an individual development. The scale of these effects is uncertain, however the impact of the effects on health could be permanent for those affected. As mentioned previously, there is recent evidence that 2% of sites on the Barnett shale in Texas, United States, are responsible for half of the methane emissions from this location^[96]. However, these recent levels cannot be assumed to represent the Scottish situation due to contrasts in geology and source material^[97]. Therefore, there is uncertainty as to the extent to which results from US case studies could apply in Scotland.

5.47 In addition, further work is required to understand the characteristics that cause individual sites to be a ‘super-emitter’^[98]. Therefore, there is uncertainty as to the extent to which ‘super-emitters’ could occur in Scotland, and therefore the risk of these events occurring.

5.48 Leakage from decommissioned wells can occur from the decommissioning stage. Evidence shows that leakages are most likely to happen within a few years of well abandonment and decommissioning, and that cement shrinkage is the main cause of leakage^[99]. Should leakage from decommissioned wells occur, it is judged that the duration of these effects would be temporary – provided that monitoring results in appropriate remediation measures. However, the nature of the effects in terms of emission of greenhouse gases and climate change are effectively permanent. The probability, risk and scale of this effect is uncertain, as it depends on the construction of the well and/or the approach to monitoring and remediating leaks.

5.49 In addition, the plugs intended to prevent further fluid migration can deteriorate, releasing methane that has built up in the well. There is recent evidence to suggest that these methane emissions from decommissioned wells are low^[100,101].

5.50 The current regulatory framework identifies potential areas of uncertainty in relation to fugitive emissions, and the potential impacts on air quality associated with this uncertainty. The level of unconventional oil and gas development under the high KPMG scenario increases the number of wells from which these potential impacts may occur. It also potentially increases the density of pad and well development, with cumulative effects on local air quality. These effects are likely to be lower for the central and low KPMG scenarios. Taking the known issues with air quality in the Central Belt into account, the overall impacts on air quality are therefore judged to be significant negative but uncertain.

Business as usual – CBM

5.51 In the case of CBM exploration, cores have typically low fugitive emissions – particularly in the initial development stages. The reason for this is that dewatering processes associated with CBM operations have not started at this stage, supressing potential gas flows. Pilot CBM wells are often not associated with collection and processing infrastructure and so initial gas flows may be vented or flared^[102].

5.52 As noted for shale oil and gas vented emissions, there is some uncertainty around the potential scale and regulatory control of these emissions. The duration of the impacts of the effects from the release of emissions would be effectively permanent for the health of those affected. However, the lower risk of fugitive emissions from CBM, and the smaller potential scale of effects from the two CBM pads is significantly lower than that for the KPMG scenarios for shale oil and gas and therefore minor negative but uncertain effects are identified.

Pilot project

5.53 The PPC regulations are designed to control emissions to the environment from certain specified activities. SEPA note that the activities carried out at the initial exploration stage, such as drilling and core sampling, may not fall within the current PPC Regulations. However, it is likely that a PPC permit will be required at a later stage, such as refining of natural gas, and this must be in place before specific PPC activities commence. The scope of a pilot project is not defined, but is assumed to be subject to regulatory control through PPC regulations. Before a pilot project commences, the application of PPC and other regulatory regimes such as the Management of Extractive Waste (Scotland) 2010 Regulations may need reviewed, as highlighted in the HPS report. (2016)^[103]. The development of a pilot project is assumed to involve the development of a single pad and an unknown number of wells, and the duration of the pilot project is unknown. The location of a pilot within the semi-urban or urban fringe location may have greater impacts on air quality than for a rural pilot, due to the assumed current levels of poorer air quality in these areas. However, the scale and extent of emissions on local air quality from a single pilot is judged to be negligible.

Preferred policy position

5.54 The preferred policy position means that adverse impacts on air quality associated with fugitive emissions from shale oil and gas production (greatest for the KPMG high production scenario, and less for the central and low scenarios), CBM production and, to a lesser extent, a pilot development, would be avoided.

5.55 The timeframe for the avoidance of these effects is effectively permanent. This is considered to be a significant positive effect.

Construction and site traffic emissions

Business as usual – shale oil and gas extraction

5.56 Ricardo Energy and Environment^[104] found that the range of unconventional oil and gas development scenarios considered could give rise to between 210 and 1,670 traffic movements per week on average across the country as a whole, with a further 99 movements associated with the coal bed methane scenario^[105]. The study concluded that additional traffic movements associated with unconventional oil and gas developments are unlikely to be significant at a regional or national scale, in view of the much greater number of traffic movements resulting from other activities. However, the potential for localised impacts would depend on the nature, scale and location of the proposed development. For instance, the proximity to a sensitive area, such as an Air Quality Management Area (AQMA) or near to sensitive receptors (e.g. schools, hospitals, residential properties etc.), would increase the scale of, and potential for, significant localised impacts.

5.57 The potential impacts caused by air pollution from traffic would occur with immediate effect during the exploration, appraisal and production stage. These stages combined could occur over a period of approximately 20 years. The rate of vehicle movements fluctuates throughout the life of each well, with the full extent of these effects peaking during the production phase^[106]. For instance, it is estimated that the construction of each well pad would require between 7,000-11,000 truck visits^[107].

5.58 Under the KPMG high scenario, the level of development has the greatest number of pads and wells, and therefore generates the highest level of traffic movements. This has the potential for cumulative effects on air quality for local communities where traffic from multiple pads uses the same routes. The location of pads under the central and low scenario could also result in this effect. The location of the pads is unknown, but if they are located within close proximity to sensitive receptors this could increase the local significance of effects. Reflecting the evidence base for air quality impacts from traffic, and the potential for locally significant effects, the impacts from unconventional oil and gas development for shale oil and gas are judged to be significant negative but uncertain depending on local circumstances.

Business as usual – CBM

5.59 CBM is characterised by a significantly reduced need for imported water, which is likely to require fewer traffic movements. As a result, CBM operations are expected to generate fewer traffic movements per pad than for shale oil and gas, with lower impacts on air quality from traffic emissions. As noted in the above section on shale oil and gas extraction, the conclusion of Ricardo Energy and Environment are that additional traffic movements associated with unconventional oil and gas developments are unlikely to be significant at a regional or national scale. The location of the CBM pads is unknown, but if they are located within close proximity to sensitive receptors this could increase the local significance of effects. The impacts from the development of two CBM pads and associated wells are judged to be minor negative but uncertain.

Pilot project

5.60 The development of a pilot project is assumed to involve the development of a single pad and an unknown number of wells, although it is assumed that the overall scale of development would be less than for a pad at full production. If a pilot was located within the semi-urban location, it may have greater impacts on air quality than a rural or urban fringe pilot, due to the assumed proximity to areas of poorer air quality. This would increase the likelihood of cumulative effects on local air quality. Therefore, the scale and extent of emissions on local air quality from traffic associated with a single pilot is judged to be minor negative but uncertain.

Preferred policy position

5.61 The preferred policy position means that adverse impacts on air quality associated with emissions from traffic movements (greatest for the KPMG high production scenario, and less for the central and low scenarios), CBM production and, to a lesser extent, a pilot development, would be avoided.

5.62 This is considered to be a significant positive effect.

Cumulative, secondary and synergistic effects

Business as usual – shale oil and gas and CBM

5.63 The combined effect of air pollution from fugitive emissions and from transport is likely to be greatest under the KPMG high production scenario for shale oil and gas extraction which has the highest number of pads and greatest number of wells developed per pad.

5.64 The larger number of pads and wells increases the likely extent of adverse effects on air quality. It also increases the likelihood of development taking place within close proximity to an area with existing air quality issues, with potential greater significance of effect. However there is uncertainty over the location of pads under all three of the development scenarios. Conversely, positive synergy could also result from the high development scenario for shale oil and gas extraction which could facilitate sharing of pipelines, reducing overall impacts from individual pipeline construction or traffic impacts. The contribution of fugitive emissions in combination with transport emissions is however judged to be significant negative but uncertain for all three KPMG scenarios. The cumulative effects of CBM are based on lower levels of traffic pollution and the smaller scale of CBM development, however reflecting the potential for cumulative effects from fugitive emissions and transport to affect sensitive receptors, these effects are judged to be minor negative but uncertain.

Pilot project

5.65 An individual pilot project would result in cumulative effects from fugitive emissions and transport. This effect would be greater in combination with existing pressures on air quality from a site in close proximity to an AQMA. However the cumulative effects from a single pilot are judged to be minor negative uncertain.

Preferred policy position

5.66 The preferred policy position means that cumulative adverse impacts on air quality associated with fugitive and transport emissions from shale oil and gas production (greatest for the KPMG high production scenario, and less for the central and low scenarios), CBM production and, to a lesser extent, a pilot development, would be avoided.

The timeframe for the avoidance of these additional effects is approximately the next 40 years, although pressures from transport are focused within the exploration, appraisal and production stages of development. The avoidance of these effects is judged to be permanent within the context of the SEA. The scale of avoidance of effects reflects the geographic area identified as prospective for shale oil and gas, across the Central Belt of Scotland.

5.67 In summary, although the air quality of the Central Belt of Scotland will continue to face existing pressures, the preferred policy position means that additional pressures on air quality which could directly result from unconventional oil and gas development in Scotland would be avoided. This is considered to be a minor positive effect.

Scope for further mitigation

5.68 The assessment results are based on the application of existing regulatory controls. The evidence base includes information on a number of processes which could be implemented to reduce the scale of impact from fugitive and transport emissions. These could reduce the overall potential scale of effect from unconventional oil and gas development, and therefore the associated scale of effect avoided as a consequence of the preferred policy position.

5.69 The applicability and practicality of many of these additional measures would be determined at a site specific level so it is not possible to draw firm conclusions as to the extent to which they would mitigate predicted effects successfully.

5.70 Currently, there are technologies for limiting and monitoring fugitive methane emissions following shale gas extraction and CBM. Case studies from the US have demonstrated that these measures can be costly, lowering economic profitability. As a result, uptakes of measures for limiting emissions have been relatively low in the US due to the high costs of emission prevention and mitigation. Therefore, developments in the US unconventional oil and gas industry are currently focussed on reducing the cost of sensors and other related technologies^[108]. However, it is recognised that the regulatory situation relating to emission limitations is different in Scotland. Potential areas of additional mitigation include:

• Vented emissions – gases that are being vented could be burnt rather than dispersed into the atmosphere. Combustion would partially reduce the environmental impacts, because the process serves to incinerate many of the volatile organic compounds (VOCs) and hazardous air pollutants (HAPs) that would otherwise be released directly into the atmosphere. It should be noted that the combustion process would still result in adverse environmental impacts so there is a limit to extent to which associated impacts could be reduced.
• Super emitters – A large proportion of the fugitive gas which is emitted has been found to come from a small group of ‘super emitters’. Although a complete avoidance of super-emitters may be unachievable, with suitable operational control and maintenance procedures these high emitters could largely be eliminated. The International Climate Fund (ICF) suggests that annual inspections and repair would reduce emissions by 40%, quarterly inspections by 60% and monthly inspections by 80%. If the super emitters could be brought in line with the average, then total supply chain emissions would be reduced by 65%-87%^[109]. Although the potential reduction in greenhouse gases achieved through mitigation measures is likely to be considerable, there is likely to be limited scope for further mitigation because super emitters comprise a relatively small proportion of unconventional oil and gas wells^[110]. Further work is required to understand the characteristics that cause individual sites to be a ‘super-emitter’^[111].
• Leakage from decommissioned wells: Ensuring well integrity is highly dependent upon the application of best practice standards for well design and construction. The risk of gas leakage (including methane) from abandoned unconventional oil and gas wells is expected to be very low if constructed and abandoned to comply with international standards and industry best practice. To further reduce potential impacts, monitoring technology can be used so that remedial measures can be taken at an early stage. Examples include fibre optic sensing techniques including Fibre Bragg gratings (FBGs), Distributed Temperature Sensing (DTS) and Distributed Acoustic Sensing (DAS). Recent evidence suggests that fibre optic sensing technology has existed for decades, but most techniques are not yet mature for commercial deployment in the unconventional oil and gas industry. DAS has matured most rapidly, as is currently deployed on a commercial basis for selected geophysical and flow applications following a recent trial^[112].

5.71 There are a number of ways to reduce the air quality impacts of increased vehicle movements associated with unconventional oil and gas developments. Firstly, transport capacity can be optimally deployed using supply chain management systems and ICT resources. These measures have the potential to reduce the impacts on local air quality associated with vehicle movements. Secondly, emissions can be reduced or avoided through the use of pipelines or the re-use of wastewater^[113].

Table 5.1: Summary of impacts on Air

Environmental impact	Alternative	Potential scale of development	Timescale when effect may occur	Duration of effect	Predicted effect taking account of existing regulation	Key areas of uncertainty
Fugitive emissions to air	Business as usual – shale oil and gas extraction	Major	Short to long term	Temporary	A significant negative effect is identified reflecting the potential scale of emissions, the scale of development and the known issues with air quality in the Central Belt.	There is mixed evidence about the potential level of fugitive emissions and regulatory control of these emissions.
	Business as usual – coal bed methane	Minor	Short to long term	Temporary	A minor negative effect is identified reflecting that CBM typically have low fugitive emissions, and the more limited scale of development.	There is uncertainty around the potential scale of fugitive emissions for CBM and regulatory control of these emissions.
	Pilot project	Minor	Short to long term	Temporary	A negligible effect is identified reflecting the scale and extent of emissions on local air quality from a single pilot.	There is mixed evidence about the potential level of fugitive emissions and regulatory control of these emissions. The location of a pilot is uncertain, and therefore the sensitivity of the location and potential impact is uncertain.
	Preferred Policy Position	None	Short to long term	Permanent	A significant positive effect is identified reflecting the avoidance of significant negative effects.
Construction and site traffic emissions	Business as usual – shale oil and gas extraction	Major	Short to long term	Temporary	A significant negative effect is identified reflecting the potential scale of air quality impacts from traffic, and the potential for locally significant effects.	The potential for localised impacts would depend on the nature, scale and location of the proposed development including the proximity to sensitive receptors/areas.
	Business as usual – coal bed methane	Minor	Short to long term	Temporary	A minor negative effect is identified reflecting that CBM results in fewer traffic movements than shale oil and gas extraction and has a lower level of potential overall development.
	Pilot project	Minor	Short to long term	Temporary	A minor negative effect is identified reflecting the potential scale and extent of emissions on local air quality from traffic associated with a single pilot.
	Preferred Policy Position	None	Short to long term	Permanent	A significant positive effect is identified reflecting the avoidance of significant negative effects.
Cumulative	Business as usual – shale oil and gas extraction	Major	Short to long term	Temporary	A significant negative effect is identified from the combined effect of air pollution from fugitive emissions and from transport. This is likely to be greatest under the KPMG high production scenario for shale oil and gas extraction	The potential location of pads in proximity to sensitive receptors/areas is an area of uncertainty under all development scenarios.
	Business as usual – coal bed methane	Minor	Short to long term	Temporary	A minor negative effect is identified reflecting the potential for cumulative effects impacting on sensitive receptors.
	Pilot project	Minor	Short to long term	Temporary	A minor negative effect is identified reflecting the potential for cumulative effects impacting on sensitive receptors.
	Preferred Policy Position	None	Short to long term	Permanent	A significant positive effect is identified reflecting the avoidance of significant negative effects.