The fourteenth annual report of the London Air Quality Network (LAQN) provides a strategic overview of air pollution across London during 2006 and 2007 and as such, can act as a stand-alone document for comparison with other cities, as well as part of the ongoing annual air pollution record for London. The report provides a vital resource for anyone interested in air quality, especially those who are working at local and national levels, and for individuals developing policies to help reduce the level of air pollution in the UK.

Air pollution concentrations in London continued to exceed UK Air Quality Strategy Objective (AQS) and EU Limit Values during 2006 and 2007. Progress towards the attainment of these legislated values varies according to pollutant; successes in the control of CO and SO2 concentrations contrast with the less successful control of NO2, PM10 and O3.

Background NO2 concentrations declined until 2002 but have been relatively stable since. Importantly, the annual mean AQS Objective and EU Limit Value of 40 µg m-3 has been attained at background sites in outer London only and this concentration has been consistently exceeded at background sites in inner London and at roadside sites throughout London. Examination of roadside NO2 concentrations on a site by site basis shows a range of changes from little overall change to increases of over 30% at some sites, including Marylebone Road. This increase in roadside NO2 concentrations was caused by a change in the proportion of NO2 directly emitted in vehicle exhausts. During December 2007 London experienced its most severe NO2 episode in ten years. This appears to have been due to both meteorological conditions and changes in NO2 primary emissions. There is clearly a need for additional measures to control concentrations of this pollutant.

Mean PM10 concentrations in London decreased during the late 1990’s but show a steady slow increase since this time at a mean rate of around 0.4% per year. Although the EU Limit Value has been attained at background sites since the late 1990’s the EU Limit Value is regularly breached alongside the busiest parts of London’s trunk road network and close to waste management sites. Throughout north western Europe the PM10 decreases experienced during the 1990s have not continued this century, although considerable efforts have been made to abate emissions of PM10 and PM10 precursor pollutants in London, the UK and throughout Europe. It is unclear why such abatement measures are not yielding a reduction in measured PM10 concentrations. Worryingly there is evidence to suggest that PM10 concentrations arising from London’s emissions have increased.

Measurements of the oxidising potential of airborne particles have been used to determine the toxicity of PM in London. This work has shown toxicity in both the PM10 and PM2.5 fractions and importantly measurements have demonstrated additional toxicity in roadside PM10 when compared with that in background locations. Recent Defra funded research in London has looked at short-term health outcomes and changes in daily mean concentrations of different measurements of particle mass concentration and composition. Measurements of particle mass concentrations eg PM10 and PM2.5 were found to be associated with short-term increases in respiratory health effects while changes in particle number concentrations were associated with cardiovascular effects. Given the localised nature of particle number concentrations and the additional toxicity of roadside PM10, London-wide measures to abate PM10 may be effective in reducing both mass concentration and health effects of PM10 in London. The Greater London Authority and Transport for London funded emissions inventory form a core upon which such abatement scenarios can be assessed. The transport part of this inventory has been recently updated for the 2006 base year