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Abstract. Bruker™ EM27/SUN instruments are mobile commercial solar-viewing near-IR spectrometers. They show promise for expanding the global density of atmospheric column measurements of greenhouse gases and are being marketed for such applications. They have been shown to measure the same variations of atmospheric gases within a day as the high resolution spectrometers of the Total Carbon Column Observing Network (TCCON). However, there is little known about the long-term stability and uncertainty budgets of EM27/SUN measurements. In this study, which includes a comparison of 186 measurement days spanning 11 months, we note that atmospheric variations of Xgas within a single day are well captured by these low-resolution instruments, but over several months, the measurements drift noticeably. We present comparisons between EM27/SUN instruments and the TCCON using GFIT as the retrieval algorithm. In addition, we perform several tests to evaluate the robustness of the performance and determine the largest sources of errors from these spectrometers. We include comparisons of XCO2 and XCH4, and for the first time present comparisons of XCO and XN2O. Specifically we note EM27/SUN biases of 0.03 %, 0.75 %, −0.12 %, and 2.43 % for XCO2, XCH4, XCO, and XN2O respectively with 1σ precisions of 0.08 % and 0.06 % for XCO2 and XCH4 from measurements in Pasadena. We also identify significant error caused by non-linear sensitivity when using an extended spectral range detector used to measure CO and N2O.
Hedelius et al. (Fri,) studied this question.