Development and deployment of a cavity enhanced UV-LED spectrometer for measurements of atmospheric HONO and NO₂in Hong Kong

An optical analytical instrument based on light emitting diode (LED) incoherent broadband cavity enhanced absorption spectroscopy (LED-IBBCEAS) was developed for simultaneous measurements of HONO and NO2in ambient air. Detection limits (for signal-to-noise ratio, SNR=2) of 0.6ppbv for HONO and 2ppbv for NO2were achieved with an optimum acquisition time of 120s. Field intercomparison campaign at a suburban site of Tung Chung in Hong Kong was carried out. Daytime and nighttime concentrations of HONO and NO2were recorded and compared with data from a long path absorption photometer (LOPAP) and a NOxanalyzer equipped with a blue light converter. The test of such a LED-IBBCEAS setup by the measurement intercomparison with the well established HONO and NO2measurement instruments, for the first time, in a real atmospheric environment, demonstrated the feasibility of the proposed technique for the measurement of environmental HONO and NO2concentrations in a manner that is free of chemical and spectral interference. During the measurement period from 12:32 on May 12th to 12:32 on May 14th, 2012, the quantitative assessments from these techniques showed well agreed data. High temporal correlations of HONO with NOxand CO were observed, and possible formation sources of HONO are discussed. Occasional inconsistencies in the quantitative assessment of HONO were observed during the in-field campaign. The problems encountered by the IBBCEAS technique applied to field observation and the further improvements are discussed.