The purpose of this report is to review air quality in London during the 1st quarter of 2004 and to report detailed measurement results for the year ended 31st March 2004.

During the quarter 2 new monitoring sites joined the London Air Quality Network (LAQN); Brent 5 and Lambeth 4.

The series of PM10 incidents during the 1st quarter of 2003 were not repeated during the 1st quarter of 2004. The first widespread ‘moderate’ O3 of the year was measured at the end of March for only the 3rd time in the 11 year history of the LAQN.

Measurements during the year ended 31st March 2004 have been compared to the Air Quality Strategy Objectives. Assessments of measurements for the 12 month period are dominated by pollution incidents during 2003:

• The CO Objective was met at all CO monitoring sites.
• The annual mean NO2 Objective was exceeded at all road and kerbside sites in London.
• The annual mean NO2 Objective was also exceeded at background sites in inner and west London.
• Incident based PM10 Objective was exceeded at kerbside and roadside TEOM sites in inner London and at several such sites in outer London. All background and suburban TEOM sites met the incident based Objective. All BAM monitoring sites exceeded the Objective.
• The annual mean Objective of 40 µgm-3 for PM10 was exceeded at the roadside TEOM site Bexley 4 and at the kerbside TEOM site Marylebone Road. The annual mean Objective was also exceeded at all kerbside and roadside BAM sites.
• All sites met the Objective for SO2.