Intercomparison of in situ CRDS and CEAS for measurements of atmospheric N2O5 in Beijing, China

Abstract Dinitrogen pentoxide (N 2 O 5 ) is one of the basic trace gases which plays a key role in nighttime atmosphere. An intercomparison and validation of different N 2 O 5 measurement methods is important for determining the true accuracy of these methods. Cavity ring down spectroscopy (CRDS) and cavity enhanced absorption spectrometer (CEAS) were used to measure N 2 O 5 at the campus of the University of Chinese Academy of Sciences (UCAS) from February 21, 2016 to March 4, 2016. The detection limits were 1.6 ppt (1σ) at 30 s intervals for the CEAS instrument and 3.9 ppt (1σ) at 10 s time resolution for the CRDS instrument respectively. In this study, a comparison of the 1 min observations from the two instruments was presented. The two data sets showed a good agreement within their uncertainties, with an absolute shift of 15.6 ppt, slope of 0.94 and a correlation coefficient R 2  = 0.97. In general, the difference between the CRDS and CEAS instruments for N 2 O 5 measurement can be explained by their combined measurement uncertainties. However, high relative humidity (> 60%) and high PM2.5 concentration (> 200 μg/m 3 ) may contribute to the discrepancies. The excellent agreement between the measurement by the CRDS and CEAS instruments demonstrates the capability of the two instruments for accurately measuring N 2 O 5 with high sensitivity.