CAPS NO2 Monitor

Mobile monitoring is an extremely useful tool for near-source air quality characterization. Nitrogen Dioxide (NO2) is a major atmospheric pollutant which is produced from a variety of anthropogenic sources, notably vehicular emissions. Nitrogen oxides (NOX = Nitric oxide (NO) + NO2) are emitted from motor vehicles in large quantities in urban areas. The Aerodyne Cavity Attenuated Phase Shift (CAPS) monitor is an optical absorption monitor operating at 450 nm where NO2 absorbs light in a highly specific manner. The monitor can measure ppb levels and has a faster than normal response time of < 1 second. The instrument is able to reliably and quantitatively measure both large and small fluctuations in the ambient nitrogen dioxide concentration. Unlike standard chemiluminescence-based monitors, these instruments require no conversion of NO2 to another species and thus are not sensitive to other nitro-containing species. Levels of detection (3σ noise levels) of less than 100 parts per trillion with a 10 second sampling period can readily be attained; a fast response version which offers 1 second time response at reduced levels of detection (1ppb) is also available. These instruments offer completely linear response at concentrations up to several parts-per-million of NO2; this limitation at high concentrations is purely one of optical opacity.