Scottish Transport Statistics No 33 2014 Edition
Chapter 13: Environment and Emissions
- Impact of transport on the environment
- Atmospheric pollutants
- Greenhouse gas emissions by type of transport
- Vehicle emission levels
ENVIRONMENT AND EMISSIONS
1 Introduction
1.1 This chapter provides information about the impact of transport on certain aspects of the environment with a focus on greenhouse gas emissions and air quality. Statistics include atmospheric pollutants and emissions of greenhouse gases by types of transport as well as details of emissions levels of road vehicles. Data from other chapters within Scottish Transport Statistics are referred to in the analysis.
Key points
- Transport accounts for just under a quarter of Scotland's greenhouse gas emissions under the definition set out in the Climate Change Scotland Act.
- Road transport makes up over 70% of transport greenhouse gas emissions.
- There were 1071 Ultra Low Emission Vehicles registered in Scotland at the end of March 2014. Half of these were cars.
- In 2012 transport accounted for 40% of emissions of oxides of nitrogen and 20% of particulate matter (PM10). At the end of 2014 there were 31 active Air Quality Management Areas related to these pollutants.
2 Main Points
Air pollutant emissions
2.1 The main pollutants of current concern in Scotland are:
- Oxides of nitrogen (NOx);
- Particulate matter (PM10 and PM2.5);
- Sulphur dioxide (SO2);
- Non-methane volatile organic compounds (NMVOCs);
- Ground-level ozone (O3); and
- Ammonia (NH3).
2.2 Of these, transport is a significant contributor to emissions of oxides of nitrogen and particulate matter. Transport is also linked to ozone which is a secondary pollutant produced by chemical reactions involving oxides of nitrogen.
2.3 Historically, transport was also a major contributor to emissions of lead and non-methane volatile organic compounds (NMVOCs). The significant decline in lead emissions (98% since 1990) has been mainly driven by the progressive phasing out of leaded petrol. The lead content of petrol was reduced from around 0.34 g/l to 0.143 g/l in 1986. From 1987, sales of unleaded petrol increased, particularly as a result of the increased use of cars fitted with three-way catalysts. Leaded petrol was phased out from general sale at the end of 1999. For NMVOCs, transport sector emissions declined significantly during the 1990s due to the increased use of catalytic converters and fuel switching from petrol to diesel cars. (Chart 13.a)
2.4 Emissions of nitrogen oxides were estimated to be 98kt in 2012 of which transport accounted for 40%. Since 1990, transport emissions have declined by 67%. Transport
emissions have declined due to a number of reasons including the requirement for new petrol cars to be fitted with three-way catalysts since 1989 and, in more recent years, "Euro standards" for new cars have driven a reduction in emissions, although studies show that the diesel Euro 5 cars have not performed as well as expected. Since 2008, there has been a general reduction in the emissions from passenger cars, mainly driven by improvement in catalyst repair rates. (Table 13.a)
2.5 Emissions of PM10 were estimated to be 12kt in 2012, of which transport accounted for 20%. Since 1990, transport emissions have declined by 40%. For particulate matter, the main source of road transport emissions is exhaust gases from diesel engines. Emissions from diesel vehicles have been growing due to the growth in heavy-duty vehicle traffic and the move towards more diesel cars. Since around 1992, however, emissions from diesel vehicles have been decreasing due to the penetration of new vehicles meeting tighter PM10 emission regulations ("Euro standards" for diesel vehicles were first introduced in 1992), while non-exhaust emissions from tyre and brake wear and road abrasion are increasingly more important. (Table 13.a)
Air quality
2.6 Concentrations of air pollutants are sampled at automatic monitoring sites and the information is held in summary form in the Scottish Government database "Scottish Environment Statistics Online" and also in the "Scottish Air Quality Database" on the "Air Quality in Scotland" website (http://www.scottishairquality.co.uk/). The data section of the website provides detailed information on all sites while the publication section of the website includes reports showing trends. Table 13.b in this publication shows concentrations of nitrogen dioxide, ozone and PM10 at a mixture of urban and rural monitoring sites with long time series. Air quality is monitored against standards set as air quality objectives (see Notes and Definitions section).
Nitrogen dioxide (NO2)
2.7 For some of the selected monitoring sites, nitrogen dioxide concentrations show a downward trend. In 2013, 7 of the 15 sites selected had the lowest concentrations over the period 2003-2013. In 2010, concentrations at ten of the selected sites were higher than in the previous year and all subsequent years. In 2013, 70 sites in Scotland recorded nitrogen dioxide concentrations with a data capture rate of over 75%, of which 59 were roadside or kerbside locations. Of these 70 sites, 14 had concentrations in excess of the air quality strategy objective of 40 mg/m3 as an annual mean. All 14 sites were located at the roadside or kerbside. (Table 13.b)
Ozone (O3)
2.8 Though transport emissions contribute to ozone formation, levels of ozone are generally higher in rural areas due to the long-range transportation of primary pollutants from urban source. In addition, ozone reacts with nitric oxide, which is more abundant in urban areas due to traffic emissions; therefore ozone levels are usually lower in urban areas. While at the selected monitoring sites there is some indication of a downward trend in the number of occurrences of maximum daily concentrations exceeding 100 mg/m3, there is no trend in average annual concentrations. In 2013, of the 8 sites in Scotland recording ozone with a data capture rate of over 75%, 3 sites had more than 10 occurrences of maximum daily concentrations exceeding 100 mg/m3. (Table 13.b)
Particulate matter (PM10)
2.9 PM10 concentrations show a general downward trend at the selected sites. In 2013, of the 59 sites in Scotland recording PM10 with a data capture rate over 75%, 15 (all kerbside or roadside) had concentrations greater than the air quality objective of 18 mg/m3 as an annual mean. Two of these sites also exceeded the air quality objective set as 7 occurrences of a daily mean above 50 mg/m3. (Table 13.b)
Air Quality Management Areas
2.10 Whenever it appears that one or more of the air quality objectives is unlikely to be met by the required date, the local authority concerned must declare an Air Quality Management Area (AQMA) covering the area of concern. The authority must then prepare and implement an action plan outlining how it intends to tackle the issues identified. Table 13.c summarises active AQMAs and the pollutants of concern. At the end of 2014 there were 32 active AQMAs, all but one of which related to either NO2 or PM10.
Greenhouse gases
2.11 In 2012, Transport (including international aviation and shipping) accounted for 12.9 million tonnes of carbon dioxide equivalent (MtCO2e). This represents 24.4% of net greenhouse gas emissions allocated to Scotland in the Greenhouse Gas Inventories, down from 24.9% in 2011. Total net emissions from all sources rose by 0.8% between 2011 and 2012. Within Transport's emissions, Road Transportation accounted for approximately 72 % of the transport total, (Passenger Cars contribute 40% alone). Heavy Goods Vehicles and Light Goods Vehicles were the other significant contributors to Road Transportations emissions (24% and 15% respectively of road transport emissions). International Aviation and Shipping contributed roughly 18% and Domestic Aviation (including military aviation and aircraft support vehicles) 5% of transport's total emissions. Railways contributed less than 2%. As these are estimates, using methodology designed to produce internationally-comparable estimates, apparent year-to-year fluctuations could be due in part to limitations in the underlying data. See Section 4.2 for details. (Table 13.2)
2.12 Chart 13.1 shows emissions over time by mode. Estimated car emissions have fallen by 15 per cent from a 2002 peak and by 11 per cent since 2008. Traffic levels have remained relatively stable over the last few years so the reduction in emissions will be largely due to the introduction of lower emission vehicles as well as other factors such as more fuel efficient driving. More detail on car emissions is set out from paragraph 2.7 of this chapter while more details on traffic volumes by mode can be found in chapter 5 of STS. Details of personal modal choice can be found in chapter 11.
2.13 The Greenhouse Gas Inventories report the emissions of the six gases that are listed under the Kyoto Protocol I. In the case of transport, the quantities of gases involved are relatively small except for carbon dioxide, which accounts for about 99% of all its emissions of greenhouse gases. (Table 13.3).
2.14 Comparisons with the UK are shown in Table 13.4. Scotland's emissions account for 8.1% of UK transport emissions. Looking at individual transport sectors, road and rail each account for 8.6% of the UK total. Domestic aviation (17.0%), Bus (12.4%) and maritime (11.4%) - the latter due to allocation of oil traffic – account for a significantly greater than proportionate share by mode. (Table 13.4)
2.15 Estimates of carbon dioxide emissions per passenger-km for different modes of transport are available only for GB/UK as a whole. The lowest emitting modes of transport per passenger-km are national coaches and national rail - 29 and 47 grams of CO2 respectively. Air travel tends to be the highest emitter per passenger-kilometre, particularly domestic flights, which account for 155 grams of CO2 per passenger kilometre. The basis of the estimates is described in section 4.3 (Table 13.5).
Car emissions
2.16 Newly registered cars are becoming more efficient in terms of carbon dioxide emissions. Figure 13.3 shows the trend in average CO2 emissions for newly registered cars in Scotland. Average CO2 emissions in Scotland for new car registrations has fallen by 24 per cent over the last ten years and by 3.6 per cent in the last year. (Table 13.6)
2.17 This pattern is shown in more detail in figure 13.4. If vehicles with unknown emissions are excluded (i.e. recalculating the percentages with unknowns removed from the total), the proportion of newly registered cars with emissions of 140g/km or lower has increased from 16 per cent in 2002 to 77 per cent in 2013. Cars with emissions of over 200g/km have decreased from 18 per cent of new cars to under 2 per cent. These changes are at least in part the result of changes to vehicle excise duty bandings made by the UK Government in recent years. (Table 13.6)
Ultra low emission vehicles (ULEV)
2.18 The numbers of ultra-low emission vehicles registered in Scotland has trebled between 2011 Q4 and 2014 Q3. The biggest increase has been in Plug-in-Grant Eligible cars which now account for more than half of all ULEV vehicles and around 90 per cent of newly registered ULEVs in 2014. (Table 13.7 & 13.8)
Registrations by type of vehicle
2.19 The overwhelming majority (99.5 per cent) of vehicles licensed for use on the roads in Scotland are powered by either petrol or diesel. Historically petrol powered vehicles have outsold diesel but in 2011 diesel overtook petrol for the first time. The 2013 data shows that diesel vehicles just outsold petrol ones 120 thousand to 119 thousand, although petrol cars continue to outsell diesel. Further, while 26 per cent of newly registered diesel vehicles were body types other than cars only 5 per cent of petrol vehicles were not cars. (Table 1.1 & 13.9 &13.10)
2.20 Overall there is a gradual move to alternative fuel sources with 1 per cent of new registrations in 2013 being powered by means other than petrol or diesel alone. Last year 0.8% of new cars are either hybrid electric or electric. (Table 13.9)
Source: National Atmoshpheric Emissions Inventory - Not National Statistics
- From the Air Quality Pollutant Inventories for England, Scotland, Wales and Northern Ireland: 1990 - 2012.
Emissions are available annually only with effect from 1998. All the figures in this table are updated annually to reflect changes to the methodology used. - The Road Transport emissions database uses emission factors (g/km) for different types of vehicles, which depend on the fuel type (petrol or diesel) and are influenced by the drive cycle or average speeds on the different types of roads; traffic activity for each DA region, including distance and average speed travelled by each type of vehicle on each type of road; DA-specific fleet data on petrol/diesel car mix, car engine size and fleet composition (including age).
The sum of emissions across all parts of the UK equates to the total for the UK inventory where that total is normalised using fuel sales data of petrol and DERV. - Only take-off and landing emissions are reported.
- Includes emissions from coastal shipping, shipping betweeen Scotland and the Overseas Territories, fishing vessels, marine engines, personal watercraft, inland goods-carrying vehicles, motorboats and sail boats with auxiliary engines.
- Includes military aviation and naval vessels, aircraft support vehicles and railways stationary combustion.
Source: Scottish Government - Not National Statistics
- The sites chosen are a mixture of urban and rural site types with long time series
- Annual mean concentration of atmospheric nitrogen dioxide.
- Annual mean ground level ozone concentration.
- Annual mean atmospheric PM10 concentration.
(a) those to which transport is understood to contribute significantly - see text.
Source: Scottish Air Quality website - Not National Statistics
Source: Carbon Account for Transport (see sources section for more details) - Not National Statistics
- From the Greenhouse Gas Inventories for England, Scotland, Wales and Northern Ireland: 1990 - 2011. Emissions are available annually only with effect from 1998. All the figures in this table have been updated to reflect changes to the methodology used. They are therefore not comparable with those previously published.
- The method used to estimate carbon dioxide (CO2) emissions from road transport is based on vehicle kilometre travelled data constrained so that the sum of emissions across all parts of the UK equates to the total for the UK inventory where that total is derived from fuel sales data of petrol and DERV within the UK as specified in the reporting guidelines of the Intergovernmental Panel on Climate Change. Further detail can be found in Section 3.3 of the report and in Annex 2.
- Includes emissions from fishing vessels, marine engines, personal watercraft, inland goods-carrying vehicles, motorboats and sail boats with auxiliary engines.
- Net emissions take account of removals of carbon dioxide due to carbon sinks.
- Includes LPG and road vehicle engines.
- A split between International aviation and international shipping can be found in the Carbon Accout for Transport
Source: Scottish Government - Not National Statistics
- The footnotes to Table 5.12 also apply to this table, including revision of the figures; though note that emisions of methane and nitrous oxide from road transport are estimated using vehicle kilometre data in both of the calculation methods, and the total emissions of these GHGs from the two methods are identical. There are no emissions of other greenhouse gases by Transport in the Inventory.
- The figures for greenhouse gas emissions are expressed in terms of their Global Warming Potential in tonnes of carbon dioxide equivalent. To convert from tonnes of carbon dioxide equivalent to tonnes of other gases multiply by the following factors: methane - 1/21, nitrous oxide - 1/310.
Source: Carbon Account for Transport (see sources section for more details) - Not National Statistics
- Cars includes all LPG emissions and road vehicle engines (the 'passenger cars' and 'other' category in Table 13.2)
Source: DEFRA - Not National Statistics
- Source: http://www.ukconversionfactorscarbonsmart.co.uk/ All figures are estimated using data for GB/UK as a whole so do not specifically relate to Scotland.
- All Car figures assume an average car occupancy rate of 1.53 passengers based on the Scottish Household Survey Travel Diary: 2011
- The long haul estimate is based on a flight length from the Guidelines of of 6482 km, short haul 1108km and domestic 463km.
- In keeping with evidence from the IPCC, a 9% upflift factor has been applied to allow for sub-optimal routing and stacking at airports during periods of heavy congestion
Source: DVLA//DVADfT - GB figures published as DfT table VEH0256
- The Department for Transport uses the term 'ultra-low emission vehicles' to refer to vehicles with significantly lower levels of tailpipe emissions than conventional vehicles. In practice, the term currently refers to electric, plug-in hybrid and hydrogen fuel-cell vehicles. For the purposes of this indicator, vehicles with fully electric powertrains, and cars with tail-pipe emissions below 75 g/km g/km of CO2 have been included at this stage.
Source: DVLA//DVADfT - Published as DfT table VEH0170
Notes & definitions (https://www.gov.uk/transport-statistics-notes-and-guidance-vehicle-licensing)
- The Department for Transport uses the term 'ultra-low emission vehicles' to refer to vehicles with significantly lower levels of tailpipe emissions than conventional vehicles. In practice, the currently refers to electric, plug-in hybrid and hydrogen fuel-cell vehicles. For the purposes of indicator, vehicles with fully electric powertrains, and cars with tail-pipe emissions below 75 g/km g/km of CO2 have been included at this stage.
Source: DVLA//DVADfT - Published as DfT table VEH0130
Notes & definitions (https://www.gov.uk/transport-statistics-notes-and-guidance-vehicle-licensing)
~ denotes fewer than 50.