Comparing different light-emitting diodes as light sources for long path differential optical absorption spectroscopy NO2 and SO2 measurements

In this paper,we present a comparison of different light-emitting diodes(LEDs) as the light source for long path differential optical absorption spectroscopy(LP-DOAS) atmospheric trace gas measurements.In our study,we use a fiberoptic design,where high power LEDs used as the light source are coupled into the telescope using a Y shape fiber bundle.Two blue and one ultraviolet(UV) LEDs with different emission wavelength ranges are tested for NO2 and SO2 measurements.The detailed description of the instrumental setup,the NO2 and SO2 retrieval procedure,the error analysis,and the preliminary results from the measurements carried out in Science Island,Hefei,Anhui,China are presented.Our first measurement results show that atmospheric NO2 and SO2 have strong temporal variations in that area and that the measurement accuracy is strongly dependent on the visibility conditions.The measured NO2 and SO2 data are compared to the Ozone Monitoring Instrument(OMI) satellite observations.The results show that the OMI NO2 product underestimates the ground level NO2 by 45%,while the OMI SO2 data are highly influenced by clouds and aerosols,which can lead to large biases in the ground level concentrations.During the experiment,the mixing ratios of the atmospheric NO2 and SO2 vary from 8 ppbv to 36 ppbv and from 3 ppbv to 18 ppbv,respectively.