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

- A comparison of N2O5 concentrations measured by CRDS and CEAS instruments was carried out in Beijing.
- The excellent agreement demonstrated the two instruments can accurately measure N2O5 on different environment.
- High relative humidity (> 60%) and high concentration of PM2.5 (> 200 μg/m3) cause the discrepancies between two systems.

Dinitrogen pentoxide (N2O5) is one of the basic trace gases which plays a key role in nighttime atmosphere. An intercomparison and validation of different N2O5 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 N2O5 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 R2 = 0.97. In general, the difference between the CRDS and CEAS instruments for N2O5 measurement can be explained by their combined measurement uncertainties. However, high relative humidity (> 60%) and high PM2.5 concentration (> 200 μg/m3) 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 N2O5 with high sensitivity.

Scatter plots for the entire N2O5 dataset from CRDS and CEAS instruments. The red lines illustrate the linear regression. Time series and correlation of N2O5 mixing ratio between CRDS and CEAS instruments from February 29 to March 1, 2016.92