Northern Ireland (NI), like the Republic of Ireland (RoI), enjoys relatively clean ambient air, largely because of a low level of industrial activity and a prevailing wind from the west, where there are few adjacent sources for significant air pollution. An exception in NI is the elevated concentration of polycyclic aromatic hydrocarbons (PAHs) in outdoor air. PAHs are organic compounds that contain only carbon and hydrogen, and major sources include road transport and burning of solid fuels in homes. They are carcinogenic. One of the real risks from exposure to PAHs has been documented in a recent study at Columbia University in New York. The study found that when women, none of whom smoked, were exposed to elevated levels of PAHs during pregnancy, they tended to have children with more behaviour problems, including anxiety, depression and attention problems, when the children were six or seven.

PAHs are regulated under the Fourth Air Quality Daughter Directive (2004/107/EC) relating to five pollutants. The legislation relies on one PAH called benzo[a]pyrene (BaP) as a marker substance for PAH chemicals generally because of its elevated toxicity and prevalence in ambient air. (Note 1) For particulate matter of 10 micrometers in diameter (PM10), the EU target value for BaP in ambient air is 1 nanogram per cubic meter (ng/m3) while the UK air quality objective for BaP is 0.25 ng/m3. (Note 2)

In November 2010 the NI Department of the Environment commissioned research to examine the levels and causes of PAH in NI. The report relies on the limited actual sampling in NI for PAHs (three sites) and modeling for estimating the levels of PAHs throughout NI. In February a report on the levels of PAHs was issued.

The Report

 The levels of PAHs in NI have fallen significantly over the past twenty years but they still fail to meet EU target values or UK air quality objectives. Indeed, the levels of PAHs in ambient air in urban areas of NI are comparable to industrial locations (such as steel, coke and aluminium plants) in Great Britain (GB) and are substantially in excess of levels in much larger urban centres, including London and Birmingham. These elevated PAH levels in NI are also higher than levels found at five sites in the Republic of Ireland. The report suggests that a background level can be used from the rural site in County Monaghan with a reading for PAHs at 0.18 ng/m3. In contrast, the measured readings in NI are at 0.745 (Dumurray), 2.460 (Ballymena), and 1.338 ng/m3 (Derry).

 The report concludes that the main source of PAHs in NI is the burning of solid fuels, especially coal, in homes and commercial facilities. While emissions from transport is about the same as in GB and emissions from industry are much less, residential and commercial combustion per capita in NI is four times higher than in GB. Part of this difference is the substantially lower reliance on natural gas in NI, especially outside Belfast.

The levels of BaP emitted vary dramatically dependent on the type of solid fuel burnt, with bituminous coal emitting 5 to 50 times the amount of BaP in solid smokeless fuels and 450 times the amount of BaP in oil. Therefore the type of fuel used and how it is burnt has a dramatic effect on the ambient BaP concentrations.

Clearly one solution is to ban the burning of dirty coal in areas where the PAHs are elevated, as was done in Dublin in the early 1990s and elsewhere, but not everywhere, in the RoI over the past decades. Unfortunately people continue to burn coal in Smokeless Fuel areas in NI, especially with the steady rising cost of oil as an alternative fuel for heating.

What is most disappointing about the study is its assessment of the solutions. Instead of dirty coal the authors suggest that there should be a greater reliance on oil and gas as heating fuels. While these fuels may have a short-term effect on reducing PAHs, they still are fossil fuels that will continue to contribute in a substantial way to the already disturbing climate change impacts from greenhouse gas (GHG) emissions. The report does mention, in passing, the benefits that would accrue from greater energy efficiency, and encourages greater use of existing government programs, but nowhere does it discuss the greater benefits from renewable energy sources as opposed to oil and gas.

Moreover, the study is limited in its cost-benefit assessment. PAHs are subject to EU target values which require only that the pollutant be reduced to the extent possible without requiring any measures with disproportionate costs. To determine the proportionate costs, the study relies only on an assessment of the risks for lung cancer from exposure to PAHs as the “predominant health effect,” concluding that the risks for lung cancer in the areas of elevated PAHs is three extra cancers per lifetime exposure, with estimated economic damages equal to annual cost of £55,617. The authors then estimate that replacing solid fuel heating systems and enforcing smokeless zones would cost £3,184,383 per annum. They conclude that a retrofitting progamme would be too expensive and not justified.

There are two shortcomings with this assessment. First, while the UK air quality objectives rely on lung cancer as the most relevant result from PAH exposure, limiting the risks to such an analysis underestimates the risks form PAHs, as the recent Columbia study demonstrates. Second, the benefits of a retrofitting programme are also underestimated as the analysis does not include the cost savings from reducing GHG emissions and from relying on alternative fuel sources over a long period of time, especially with the projected long-term rise in oil and gas prices.



Note 1. The Columbia University study of the adverse effects of PAHs relied on B[a]P as a representative PAH in its analysis, as well as on other measures.

Note 2. Target value is defined under the EU Directive for air quality as “a level fixed with the aim of avoiding more long-term harmful effects on human health and/or the environment as a whole, to be attained where possible over a given period,” without requiring any measures with disproportionate costs. In contrast, “Limit Value” is defined as “a level fixed on the basis of scientific knowledge, with the aim of avoiding, preventing or reducing harmful effects on human health and/or the environment as a whole, to be attained within a given period and not to be exceeded once attained.”




D M Butterfield and R J C Brown, “Polycyclic Aromatic Hydrocarbons in Northern Ireland,” National Physical Laboratory (February 2012).

Stephen Adams, “Exhaust fumes in pregnancy linked to bad behaviour in kids,” The Independent (Ireland), 22 March 2012. See report, Perera FP, Tang D, Wang S, Vishnevetsky J, Zhang B, Diaz D, et al. 2012. Prenatal Polycyclic Aromatic Hydrocarbon (PAH) Exposure and Child Behavior at age 6-7. Environ Health Perspect :-. [Environmental Health Perspectives (22 March 2012)]

 DIRECTIVE 2004/107/EC OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL of 15 December 2004 relating to arsenic, cadmium, mercury, nickel and polycyclic aromatic hydrocarbons in ambient air.

 UK and EU Air Quality Limits, Department for Environment Food and Rural Affairs (Defra)



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