The purpose of this report is to review air quality in London during the third quarter of 2001 and to report detailed measurement results for the year ending 30th September 2001.

No new monitoring sites joined the LAQN during the quarter. A PM10 (TEOM) instrument was installed at the Southwark 2 roadside site during August.

Air pollution during the quarter was dominated by 4 photochemical episodes during July and August. An unusual SO2 episode affected Enfield 3 and other north London sites on the 22nd September.

Measurements during the 12 months ending 30th September 2001 have been compared to the Air Quality Strategy (AQS) Objectives:

• The Redbridge 2 kerbside site exceeded the CO objective.
• The annual mean NO2 objective was exceeded at all kerbside and roadside measurement sites except Havering 3. This objective was also exceeded at background and suburban locations in inner and west London.
• The incident based NO2 objective was exceeded at the kerbside sites Marylebone Road, Redbridge 2 and Redbridge 3, and at the roadside sites Brent 2 and Kensington & Chelsea 3.
• Exceedences of the O3 objective were measured in outer London and at sites in the Home Counties.
• The incident based PM10 objective was exceeded at the kerbside sites Marylebone Road and Rebridge 3, and the roadside sites Bexley 4, Enfield 2, Hounslow 3 and Redbridge 4.
• The annual mean PM10 objective was exceeded at Marylebone Road only.