LAQN Pollution Episodes

Pollution Notification released on 18/01/2013

‘Moderate’, ‘high’ and ‘very high’ pollution incident notification for 16th to 17th January 2013

Low wind speeds and cold settled air led to poor pollution dispersion on 16th and 17th January 2013. This caused PM10 to reach ‘very high’, the top level of the Daily Air Quality Index, at two locations in London along with widespread ‘moderate’ PM10, PM2.5 and nitrogen dioxide.

On 16th January, a small number of busy roadside sites measured ‘moderate’ PM10 and PM2.5, including one site in Sussex. One site in the City of London reached ‘high’ PM10. This site measured significantly higher PM10 levels than most other busy roadside sites. We suspect that there could have been an additional local contribution from the resuspension of road salt in this busy enclosed location.

On 17th January ‘moderate’ PM10 and PM2.5 were more widespread with 20 sites measuring ‘moderate’, two sites measuring ‘high’ and two sites measuring ‘very high’ (Merton - Merton Road and City of London - Upper Thames Street).

‘Moderate’ nitrogen dioxide was measured at a number of busy roadside locations on both 16th and 17th January. Road traffic is the main source of nitrogen dioxide. Several sites have recorded multiple exceedences of the nitrogen dioxide hourly mean objective of 200 µg m-3.

A change to snowy conditions has brought about an improvement in air pollution concentrations, though two sites (Westminster - Oxford Street and City of London - Upper Thames Street) have continued to measure ‘moderate’ nitrogen dioxide.