[The Detection of Atmospheric HONO and NO2 with Fiber Coupling Long-Path Differential Optical Absorption Spectroscopy...

A new type of fiber coupling Long-Path Differential Optical Absorption Spectroscopy System(LP-DOAS) based on schmidt - cassegrain telescope was introduced in detail in this paper and it was applied to the accurate measurement of the actual atmospheric HONO and NO2. This measuring system simplified the structure of traditional LP-DOAS system, combining with the design of optical fiber coupling.It made full use of the telescope primary mirror’s effective area. The effects of the offset, dark current and telescope stray light to the new LP-DOAS system were discussed in this paper; On a clear day, the ratio between telescope stray light and the optical intensities was less than 1%. To verify the accurate of the new LP-DOAS system, the atmospheric NO2 were simultaneously measured with the new LP-DOAS system and traditional LP-DOAS system. The correlation coefficient R2 was up to 0.968. The observation of atmospheric HONO was carried out by using the fiber coupling LP-DOAS in Gucheng, Hebei Province, China, and the detection limit (2σ) of HONO and NO2 was 84.2 and 144.6 ppt , respectively, with 2 490 m path length and the average time resolution of about 30 s. In the whole measurement in Gucheng, the maximum of HONO and NO2 were 3.2 and 37.8 ppb, respectively, and the minimum were both under the detection limits; the ratio of HONO/NO2 at night was calculated.