Atmospheric measurements of nitrogen dioxide with a sensitive luminol instrument

A highly sensitive, lightweight, portable instrument has been developed for continuous monitoring of N0₂ in air. It operates by detecting the chemiluminescence produced when N0₂ encounters a surface wetted with a specially formulated solution containing luminol. Unlike other chemiluminescent instruments it measures N0₂ directly and does not require prior conversion of N0₂ to NO. It does not respond to H₂0₂, NO, HNO₃, NH₃, CO, C0₂, S0₂ or organic nitrates. The only interferences encountered to date are from 0₃ and PAN with the response to 0₃ being less than 0.2% of its response to N0₂. The response time of the instrument is less than 1 s and its sensitivity is better than 5 pptv. The instrument shows a negative temperature dependence of about 2% °C^?1 which is compensated electronically. Measurements have been made with the instrument during a number of field missions in polluted urban and relatively clean rural air. The relative influences of photochemistry and transport from local sources has been observed. Simultaneous measurements made with this instrument and the unequivocal tunable diode laser absorption spectroscopy method have shown excellent agreement.