Air quality expert group - Fine particulate matter (PM2.5) in ... - Defra

PM2.5 in the UK
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4. In broad terms, the report responds to the following questions:
(a) How well can we understand the PM2.5 environment in the UK in terms of
emissions, modelling and measurement? Where are the key uncertainties in
these and what can be done to address them?
(b) What is the current state of knowledge on PM2.5 in the UK? What does this
tell us about the best way to reduce concentrations, and thus exposure, in
terms of the scale at which controls should operate, the components which
should be addressed and the sectors which may need to be controlled?
(c) What are the key challenges of a legislative target based on change over
time (the exposure reduction target), in particular in terms of the consistency
of assessment, uncertainty in forecasts and the variability of concentrations
due to, for example, meteorology?
1.2 Policy approach
5. The European Union’s (EU’s) Air Quality Directive, the Directive on Ambient
Air Quality and Cleaner Air for Europe (2008/50/EC), transposed into UK law
through the Air Quality Standards Regulations 2010, is one of the key legislative
instruments in place to address air pollution under the European Commission’s
Thematic Strategy on Air Pollution. It was the first EU directive to include
limits on ambient concentrations of PM2.5. In the Directive a new approach for
PM2.5 was introduced in recognition of evidence suggesting that there is no
clear concentration of particulate matter below which health effects do not
occur. This new approach aims to achieve a reduction in the overall exposure
of the population to PM2.5, based on the concept that greater benefits could
be obtained from a general reduction in exposure than by a policy aimed at
reducing concentrations in geographically-limited “hot spots”. Exposure is
assessed through the average concentration measured at urban background
locations across the country.
6. In response to this general reduction approach, the focus of legislation for
PM2.5 is on limiting long-term exposure through the use of annual standards,
coupled to a reduction in PM2.5 background concentration in urban areas across
the UK over the period 2010-2020. Table 1.1 shows various relevant air quality
standards for PM2.5, including the newly-introduced average exposure indicator
(AEI) and exposure reduction target (see also Table 1.2).
7. A number of legislative approaches are being taken to control exposure to PM
in order to achieve the standards in Table 1.1. These include controls on motor
vehicle emissions, controls on industrial sources and controls introduced by local
authorities to address individual hot spots. The National Emission Ceilings (NEC)
Directive (2001/81/EC) underpins the controls at the national level. The Directive
sets national limits on emissions with a date by which they are to be achieved.
In relation to PM, the key controls have been on emissions of nitrogen oxides
(NOx), sulphur dioxide (SO2) and ammonia (NH3), as these are precursors of
secondary inorganic PM (largely ammonium nitrate (NH4NO3) and ammonium
sulphate ((NH4)2SO4)). Emissions of volatile organic compounds (VOCs) are
covered by the NEC Directive as precursors of ozone, rather than as precursors
of secondary organic PM.