During 2002 the London Air Quality Network continued to expand with additional data from 6 new monitoring sites.

Network annual mean concentrations have been analysed for the period November 1996 to December 2003:

• There was no overall change in annual mean NO2 during 2002. Provisional measurements for 2003 suggest a rise due to photochemistry during the summer. Overall there has been a reduction of approximately 6% in annual mean NO2 concentration during the period November 1996 to November 2003. Annual mean concentrations at typical background sites in outer London have been below the Air Quality Strategy (AQS) Objective since 1998, whereas those at typical roadside and background sites in central London have been consistently above the Objective.
• Overall annual mean NOX concentrations have fallen by 33%.
• The annual mean O3 rose 43% during the period November 1996 to November 2003. During the summer of 2003 the annual mean increased by 20% due to the frequency and magnitude of photochemical episodes at this time.
• The annual mean CO has continued to decline and has reduced by 53%.
• The SO2 annual mean reduced by 66% during the period November 1996 to November 2003. However, provisional measurements suggest a 4% increase during 2003.
• Over the period November 1996 to November 2003, the LAQN annual mean for PM10 decreased by 19% overall. LAQN annual mean PM10 declined steadily to the end of 2000 and then rose at a rate of 3% per year through to spring 2003. The provisional measurements for 2003 show an increase of 23% due a series of pollution episodes.
• The Annual Report contains an analysis of the number of days when mean PM10 exceeded 50 µgm-3. By the end of 2003 many road and kerbside sites in London will exceed the year 2005 AQS Objective. There is also a possibility of the Objective being exceeded at background sites in central and inner London.

Each of the pollutants monitored by the LAQN during 2002 has been compared to the AQS Objectives:

• For the first time in the LAQN’s 10 year history the CO Objective was not exceeded at any site.
• The annual mean Objective for NO2 was exceeded at the majority of kerbside and roadside sites. The Objective was also exceeded at many background sites in inner and west London. The incident based Objective for NO2 was exceeded at the kerbside site Redbridge 2 and the roadside site Kensington & Chelsea 3.
• The O3 Objective was exceeded at 8 sites.
• The PM10 incident based Objective was exceeded at 11 sites and the annual mean Objective for PM10 was exceeded at 3 sites.
• All LAQN sites met the Objectives for SO2.