Introduction

This report provides a summary of the 2015 Air Quality Pollution Inventory (AQPI), covering the years 1990 – 2013. Emission inventories are important in assessing the impact of human activity on atmospheric pollution, and provide policy makers and the public with a valuable understanding of the sources and trends (past and future) of key pollutants. This report is updated annually, providing an overview of the key pollutants contributing to air pollution in the UK, along with information on the sources of pollution and trends in emissions – in particular the progress towards achieving international targets on reducing air pollutant emissions.

Information on the full range of air pollutants is available from the pages of the National Atmospheric Emissions Inventory (NAEI) website.

1.1 Air Quality

When released into the atmosphere air quality pollutants can have a transboundary and/or local impact. Transboundary impacts occur when a pollutant from one area (or country) impacts on another after being transported by weather systems. Examples of transboundary pollutants are acidifying pollutants such as nitrogen oxides (NO_x) and sulphur dioxide (SO₂) as well as ozone (O₃) which is not emitted directly into the atmosphere but may be formed over a large distance by reactions of emitted non-methane volatile organic compounds (NMVOC). Acidifying pollutants can adversely affect buildings, vegetation and aquatic systems, whilst ozone formed in the lower atmosphere (the troposphere) can be damaging to human health, materials, crops and plants. Particulate matter (PM) is formed from chemical reactions in the atmosphere involving NO_x, SO₂ and ammonia (NH₃), as well as being directly emitted from human activities, and is damaging to health.

Atmospheric pollution can also impact on local air quality. Where high concentrations occur, there can be a wide range of negative impacts to human health or ecosystems^[1].

Table 1.1 highlights the key pollutant-source combinations for the five main air quality pollutants as identified in the latest update of the Gothenburg Protocol. The emissions of NO_x, SO₂, and particulate matter (PM_2.5) are all strongly linked to the burning of fuels, which occurs in electricity generation, transport, and industry. These are collectively referred to as fuel combustion sources. NMVOCs are emitted from many sources, including domestic use of products that contain solvents. In comparison, NH₃ emissions are dominated by the agricultural sector. These pollutants are each considered in greater detail in Section 2 of this report.

Table 1.1: Key Pollutant-Source Combinations

(Red = key emission source, Yellow = moderate source, Green = minimal/no emissions)

	NOx	SO2	NMVOC	NH3	PM2.5
Electricity generation	(RED)	(RED)	(GREEN)	(GREEN)	(YELLOW)
Industrial combustion	(YELLOW)	(YELLOW)	(YELLOW)	(GREEN)	(YELLOW)
Residential & commercial	(YELLOW)	(YELLOW)	(YELLOW)	(GREEN)	(RED)
Industrial processes	(GREEN)	(YELLOW)	(YELLOW)	(GREEN)	(YELLOW)
Extraction & distribution of fossil fuels	(GREEN)	(YELLOW)	(YELLOW)	(GREEN)	(GREEN)
Solvents	(GREEN)	(GREEN)	(RED)	(GREEN)	(GREEN)
Road transport	(RED)	(GREEN)	(YELLOW)	(GREEN)	(RED)
Other transport & mobile machinery	(YELLOW)	(YELLOW)	(GREEN)	(GREEN)	(YELLOW)
Agriculture	(GREEN)	(GREEN)	(GREEN)	(RED)	(GREEN)
Waste	(GREEN)	(GREEN)	(YELLOW)	(YELLOW)	(GREEN)

1.2 The UK Inventory

The UK inventory is compiled annually to report emissions totals by pollutant and source sector in a well-defined format. This allows emissions to be easily compared across different countries. National emission estimates for air quality pollutants are submitted to both the European Commission under the National Emissions Ceilings Directive (NECD, 2001/81/EC) and the United Nations Economic Commission for Europe (UN/ECE) under the Convention on Long-Range Transboundary Air Pollution (CLRTAP).

The CLRTAP submissions are available online at the CLRTAP website.

The emissions data are supported by an Informative Inventory Report (IIR), which details the inventory methodology and documents emission factors and other data used in the inventory. All pollutants covered by the UK's air quality pollutant inventory are listed below, and those included in this summary report are indicated by the dotted line.

Air Quality Pollutants

• particulate matter, PM*
• black smoke, BS
• carbon monoxide, CO
• benzene
• 1,3-butadiene
• polycyclic aromatic hydrocarbons, PAH
• nitrogen oxides, NOx
• sulphur dioxide, SO2
• non-methane volatile organic compounds NMVOC
• ammonia, NH3
• hydrogen chloride, HC1
• hydrogen fluoride, HF

Heavy Metals

• arsenic, As
• beryllium, Be
• cadmium, Cd
• chromium, Cr
• copper, Cu
• lead, Pb
• manganese, Mn
• mercury, Hg
• nickel, Ni
• tin, Sn
• selenium, Se
• vanadium, V
• zinc, Zn

Persistent Organic Compounds (POPs)

• polycyclic aromatic hydrocarbons, PAHs
• dioxins and furans, PCDD/Fs
• polychlorinated biphenyls, PCBs
• pesticides: lindane, hexachlorobenzene (HCB), pentachlorophenol(PCP)
• short-chain chlorinated paraffins, SCCPs
• polychlorinated napthalenes, PCNs
• polybrominated diphenyl ethers, PBDEs

*Particulate matter emissions are given as PM₁₀, PM_2.5, PM_1.0 and PM_0.1 and black carbon (BC).

The methodology for calculating air quality pollutant emissions is consistent with the greenhouse gas inventory methodology.

Emission estimates for historic years are typically calculated by combining an emission factor (for example, tonnes of a pollutant per million tonnes of fuel consumed) with an activity statistic (for example, million tonnes of fuel consumed). Commonly, activity data will consist of official national datasets such as fuel use data from the Department of Energy and Climate Change, population, or GDP.

Emission estimates for future years are called emission projections, and are also produced and reported as part of the inventory process. Emission projections are typically estimated by considering how emissions in the most recent year of the historic emissions inventory are likely to change in the future. For example: Are the existing trends expected to continue? Is there new legislation that will be introduced that will affect the emissions? Will the use of new technology help to reduce emissions? This assessment is done at a detailed level, although there can still be substantial uncertainty associated with estimating data that relate to future years.

1.3 Current Issues and Legislation

Generally, the quality of air in the UK has greatly improved over the last couple of decades. However, air quality is still an important issue at a political level whilst the potential for harm to human health and environmental systems remains. Recently, political and legislative focus has surrounded emissions of PM and its precursors in the atmosphere and the formation of tropospheric ozone (O₃). Both can have severe health impacts to humans, as well as damaging environmental processes e.g. reducing crop yields. In addition, recent evidence suggests that exposure to increased NO₂ concentrations arising from emissions of NO_x, may give rise to human health impacts that are as large (or indeed larger) than those from PM^[2].

In the UK, air quality is managed at both the local and national levels. Part IV of the Environment Act 1995 establishes the system of Local Air Quality Management (LAQM), which requires Local Authorities to carry out regular 'Review and Assessments' of a number of statutory pollutants such as NO₂ and PM in their area and take action to address exceedances of these objectives. At the national level, the Department for the Environment, Food and Rural Affairs is responsible for the national programme of policies and measures that help to ensure that air quality standards are met. Meeting the air quality standards can be achieved in different ways, and controlling emissions is one of several options.

At the international scale, legislation on transboundary pollution requires total annual emissions to meet ceilings under the EU's National Emissions Ceilings Directive (NECD), and to meet emission reduction commitments under the Gothenburg Protocol (UN/ECE legislation).

The 2010 emission ceilings, and new 2020 emission reduction commitments (ERC) under the Gothenburg Protocol are shown in Table 1.3.

Further information on local air quality legislation and both the Gothenburg Protocol and the NECD can be found by exploring the links at the end of this report.

Table 1.3: UK annual emissions and targets 2010 - 2020 (ktonnes)

	NOx	SO2	NH3	NMVOC	PM2.5
2013 emissions	1020	393	271	803	80
2010 Gothenburg Protocol ceiling	1181	625	297	1200	N/A
2020 Gothenburg Protocol ERC[3]	714	291	280	773	67

UK Government has implemented measures to decrease emissions across the key air quality pollutants. Section 2 of this report reviews trends in these pollutants, highlighting the impact of UK Government policies / actions in meeting the necessary agreements and targets. The new 2020 Gothenburg Protocol emission reduction commitments are placed within the context of the historical emissions so that the scale of emission reductions required can be appreciated.