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Zheng, Nina; Chan, Ka Lok; Xie, Pinhua; Qin, Min; Ling, Liuyi; Wu, Fengcheng; Hu, Renzhi (2018): Observations of atmospheric trace gases in China using a compact LED long path DOAS system. In: Atmospheric Pollution Research, Vol. 9, No. 2: pp. 379-387
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In this paper, we present the development and evaluation of a new designed light emitting diodes (LEDs) based optical fiber coupling long-path differential optical absorption spectroscopy (LP-DOAS) instrument for atmospheric SO2, O-3 and NO2 detections. The strongest absorption structures of these trace gases scattered along a wide spectral range which could not be covered by a single LED. Therefore, a new fiber optic coupling telescope was developed to combine multiple LEDs with different spectral emission ranges as broad band light source for atmospheric trace gas detections. Details of the experimental setup, measurement and retrieval procedure, error analysis and the atmospheric measurement results are presented. The new LED LP-DOAS measurement results show perfect agreements with a co-located Xenon Lamp coaxial LP DOAS observations with Pearson correlation coefficient (R) larger than 0.9 for SO2, O-3 and NO2 observations. The estimated background light contributes about 3-10% of the total measurement error during daytime, which is improved by a factor of 3-10 compared to previous study. Diurnal analysis of the measurement results shows a similar diurnal pattern of NO2 and SO2 which implies that they are probably originated from similar emission sources. Satellite observation and backward trajectories analysis indicated local and regional transports of pollutants have significant impacts on the air quality in Hefei. Analysis of the wind speed and wind direction show that elevated NO2 and SO2 levels were related to the emissions of the power plant and factories located at the east and northeast of the measurement site.