The Commission of the European Communities has recently published a proposal for a Directive relating to limit values for benzene and carbon monoxide (CO). This is the second Daughter Directive to be brought forward by the European Commission under the Framework Directive on Ambient Air Quality Assessment and Management. The proposed limit value for CO is 10 mgm^-3 (8.59 ppm) as an 8-hour running mean, to be achieved by 1 January 2005.

Road traffic is the dominant source of CO in urban areas in the UK, typically contributing more than 90% of total emissions and concentrations are therefore likely to be highest at the roadside. A method for mapping maximum running 8-hour CO concentrations at the roadside has been developed. This method makes use of emissions estimates from the National Atmospheric Emissions Inventory and monitoring data from roadside monitoring sites within the UK national air quality monitoring networks. Maps of concentrations at the roadside of major urban roads in the UK are presented for both 1998 and 2004 for comparison with the proposed limit value.

Maximum running 8-hour CO concentrations in all background locations in 2004 are predicted to be well within the proposed limit value of 8.59 ppm. Estimated roadside CO concentrations in 2004 are expected to be higher. For typical meteorological conditions, the predictions show that no road links are expected to have concentrations higher than 8.59 ppm by 2004 and only 2 are expected to have concentrations greater than the proposed limit value by 2002. For extreme meteorological conditions, such as the poor dispersion conditions experienced in some UK cities in 1991, the predictions show that one road link is expected to have a concentration higher than 8.59 ppm by 2004 and only 14 are expected to have concentrations greater than the proposed limit value by 2002.

Contents Page         Chapter 1