A new ambient air quality directive, due to come into force in May 2008, consolidates existing EU legislation and includes new controls over very fine particulate matter (PM 2.5), where the World Health Organisation (WHO) advises that there is no safe level of exposure. The main elements are a 'backstop' limit value, to be met everywhere by 2015, and an 'exposure concentration obligation' to be met across urban background locations (as an average), also by 2015. The directive must be transposed into UK law within two years of it coming into force.
Estimates of future air pollution emissions from transport include assumptions modelling the increase in diesel car market share, with an assumption that this will stabilise at 42 per cent. in 2010. These estimates are used for assessing new vehicle emissions standards and the revised National Air Quality Strategy, published in 2007. Diesel cars currently emit significantly higher levels of both particulate matter and oxides of nitrogen than petrol cars. However, the recently agreed Euro 5 and 6 emissions standards will reduce particulate emissions from new diesel cars to comparable levels to petrol cars by 2011 and substantially reduce the difference between petrol and diesel NOx emissions by 2015.