DOAS Technique; Emission Measurements in Urban and Industrial Regions

Object of this study is to describe the versatility of the Differential Optical Absorption Spectroscopy (DOAS), a remote sensing measurement system through experimental survey of the levels of primary and secondary pollutants. This analytical technique is based on the UV and Vis light absorption (from 240 nm to 450 nm) of species with fine vibrational structures like SO2, NO2, ozone, nitrous acid, formaldehyde, benzene and toluene; the Lambert-Beer’s law regulates the relationship between the absorbed light intensity and the concentration of each species. The DOAS system is constituted by the following components: a light source, a receiver, a spectrophotometer equipped with an optical fiber and a computer for the system management (data elaboration and data storage). The light source is a Xenon lamp. A transmitter sends the light to the receiver that transmits the beam through the optical fiber to the analyzer. The absorption spectra of each monitored chemical species are acquired at their relative typical wavelength ranges; subsequently, the interferences are eliminated by comparison with the reference spectra. Measurements of NO2, O3, SO2, nitrous acid, formaldehyde, benzene and toluene are extensively discussed, after intensive measurement campaigns in different seasonal periods by means of two DOAS systems installed at ground level and on the roof of the ISPESL Mobile Laboratory, respectively. The daily trends of pollutant concentrations have been interpreted using the measurements of the concentrations of natural radioactivity (radon and its short-lived decay products) as tracer of the dynamic properties of the atmospheric boundary layer.