A concurrent multi-axis differential optical absorption spectroscopy system for the measurement of nitrogen dioxide and other trace species
Despite improvements in efficiency in many combustion processes including vehicular engines, the level of nitrogen dioxide in the typical urban environment continues to impact a human health and requires regular monitoring. This thesis describes the development of a novel remote-sensing instrument configured for the measurement of nitrogen dioxide and other trace species in an urban environment.;A novel concurrent multi-axis differential optical absorption spectroscopy(CMAX-DOAS) system has been developed in this work based on scattered light spectroscopy. Data from the measurements has a temporal resolution of a minute or less and therefore the capability to spatially resolve different air masses as they traverse the instrument input optics. Such sampling capabilities are unique to a ground-based scattered-light DOAS system and are well suited to analysis of rapidly moving and distinct plumes in an urban environment.;The CMAX-DOAS instrument was built in 2002, and tested and validated during an intercomparison campaign in Norway in 2003. During 2004 concurrent measurements from multiple viewing geometries were made in Leicester (52.6 oN, 1.12o W). Measured slant columns of nitrogen dioxide from the CMAX-DOAS instrument have errors calculated at less than 2% for a single axis, and 4 to 6% for analysis using a reference spectrum from another axis. These measurements agree well with in situ measurements and identify significant boundary layer concentrations (up to 80 microg m--3) of nitrogen dioxide which clearly correlate with anthropogenic activity over diurnal, weekly and annual timescales.;Through concurrent measurement of different air masses, considerable information on individual plumes has been obtained, including estimates of source location, plume size provide on nitrogen dioxide emissions on an urban scale and are necessary to determine the link between urban activity, nitrogen dioxide emissions, air quality and ultimately human health.