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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union

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doi:10.5194/amt-2016-367
© Author(s) 2016. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
16 Dec 2016
Review status
This discussion paper is under review for the journal Atmospheric Measurement Techniques (AMT).
Aerosol optical depth determination in the UV using a four-channel precision filter radiometer
Thomas Carlund1,a, Natalia Kouremeti1, Stelios Kazadzis1, and Julian Gröbner1 1Physikalisch-Meteorologisches Observatorium Davos/World Radiation Center (PMOD/WRC), Dorfstrasse 33, 7260 Davos Dorf, Switzerland
afrom 1 April 2017 at: Swedish Meteorological and Hydrological Institute, 60176 Norrköping, Sweden
Abstract. The determination of aerosol properties, especially the aerosol optical depth (AOD) in the UV wavelength region is of great importance to understand the climatological variability of UV radiation. However, operational retrievals of AOD at the biological most harmful wavelengths in the UVB are currently only made at very few places. This paper reports on the UVPFR sunphotometer, a stable and robust instrument that can be used for AOD retrievals at four UV wavelengths. Instrument characteristics and results of Langley calibrations at a high altitude site were presented. It was shown that due to the relatively wide spectral response functions of the UVPFR, the calibration constants (V0) from Langley plot calibrations underestimate the true extra-terrestrial signals. Accordingly, correction factors were introduced. In addition, the instrument spectral response functions also result in an apparent airmass dependent decrease in ozone optical depth used in the AOD determinations. An adjusted formula for the calculation of AOD, with a correction term dependent on total column ozone amount and ozone air mass, was therefore developed. Langley calibrations performed 13–14 months apart resulted in sensitivity changes of ≤ 1.1 %, indicating good instrument stability. Comparison with a standard PFR, measuring AOD at 368–862 nm wavelengths with high accuracy, showed consistent results. Also very good agreement was achieved comparing the UVPFR with AOD at UVB wavelengths derived with a Brewer spectrophotometer, which was calibrated against the UVPFR at an earlier date. Mainly due to non-instrumental uncertainties connected with ozone optical depth, the total uncertainty of AOD in the UVB are higher than the ones reported from UVA and visible AOD measuring instruments. However, the precision can be high between instruments using harmonized algorithms for ozone and Rayleigh optical depth as well as for air mass terms. For several months of comparison measurements with the UVPFR and a Brewer the root mean squared AOD differences were < 0.01 at all the 306–320 nm Brewer wavelengths.

Citation: Carlund, T., Kouremeti, N., Kazadzis, S., and Gröbner, J.: Aerosol optical depth determination in the UV using a four-channel precision filter radiometer, Atmos. Meas. Tech. Discuss., doi:10.5194/amt-2016-367, in review, 2016.
Thomas Carlund et al.
Thomas Carlund et al.
Thomas Carlund et al.

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Short summary
Aerosols play an important role in atmospheric processes. Aerosol optical depth is the most common measure of columnar aerosol load. We present a sunphotometer called UVPFR that is able to measure aerosol optical depth in the ultraviolet range, including the calibration, characterization and validation of the instrument/measurements. The instrument will serve as a reference on the intercalibration of Brewer spectrophotometers that are also able to measure aerosol optical depth in the UV region.
Aerosols play an important role in atmospheric processes. Aerosol optical depth is the most...
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