Brewer instruments are sensitive to temperature. The temperature dependence is mainly due to the transmission properties of the nickel sulfate filter, which is used as part of the order-blocking filter combination for UV operation and is necessary to reduce stray light in the spectrometer. The temperature dependence is linear; however, it increases non-linearly with increasing wavelength (Kerr, 2002). Temperature of the instrument near the nickel sulfate filter is measured, so the response can be determined and corrections can be made. Sensitivity to temperature is measured both under controlled cold chamber conditions as well as field operational conditions. Typical temperature sensitivities range from about -0.5%/°C to +0.1%/°C and vary from instrument to instrument. Temperature response corrections have been routinely made to ozone measurements prior to submission and analysis of data records. Temperature response has also been measured and applied to spectral UV data (Weatherhead et al., 2001; Siani et al., 2003; Garane et al., 2006). Uncertainty of the temperature corrections is about ± 0.05%/ °C. The double monochromator Mark EI version of the Brewer instrument has significantly less stray light, and the nickel sulfate filter is not required for order blocking. Temperature response of the Mark EI is therefore less of a problem.
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