Urban air pollution monitoring: laser-based procedure for the detection of carbon monoxide gas

Abstract

Urban air quality is of considerable importance in many cities throughout Europe and the USA. In particular, current EU legislation has driven an expansion of monitoring of more pollutants at more sites. At present in the UK, real time readings are now available for benzene, buta-1,3-diene and other volatile organic compounds, airborne fine dust (PM₁₀), CO, O₃, SO₂ and NO_x. Carbon monoxide is produced to varying degrees in all combustion processes but more than 90% is caused by emissions from petrol vehicle exhausts. The World Health Organisation guidelines for exposure to the gas is <10 ppm for 8 h and 85 ppm for periods not exceeding 15 min. All of the pollutants mentioned above are monitored by different detection techniques and it has been the authors’ philosophy to develop instrumentation which can monitor all the different pollutants using a single detector. To this end, a multiphoton laser based procedure, using simple ionization chambers, has been developed to detect the different pollutants with different wavelengths. For CO, a 2 + 1 resonance enhanced multiphoton ionization (REMPI) scheme at 230 nm can be used with detection limits of about 1 ppm.