1. QA flagging of clouds and atmospheric anomalies Fast UV simulation tool - FastRT Ola Engelsen Norwegian Institute for Air Research (NILU)

2. CheckUVSpec Print & Exit Flexstor Data Compute bands Too low? Too high? Snow/ Br.Cl? Clouds? Cloudy throughout? Clear throughout? Cloud H 2 O Aerosol OD ShicRIVM yes no yes no yes no yes no yes no yes no

3. Fastrt UV simulation tool Few milliseconds running time Accuracy comparable to UV measurements Large variety of biological action spectra Ozone Slitfunction Aerosol optical depth Cloud liquid water column Surface albedo / type Broken clouds

6. FastRT error analysis Clear sky: max 4%, mean error 1%, st. dev. 1%. Turbid sky: max 18%, mean 3%, st.dev. 4%. Cloudy: max 35%, mean 8%, st. dev. 9%. CheckUVSpec QA tests: max 1%.

7. Flexstor data extraction Extract following information: Wavelengths Irradiances Slitfunction Ozone column, if available Snow cover info, if available Location Times Compute solar zenith angles Check correctness of input QA-flagging

8. Compute bands Add n irradiances band1 and band2 The spectral location of band 1 and 2 depend on instrument, nominally 330nm and 390nm If slitfunction is available n = 3, otherwise 9 QA-flagging

9. Too low? Flag if band 2 irradiance is lower than simulation for very thick clouds (> 4000 g/m2) QA-flagging

10. Too high? band 2 > thick trapping clouds above snow Thick cloud Snow Sun Clear sky downward total transmittance QA-flagging

11. Snow/Broken Clouds? Snow + broken clouds > band 2 > Clear sky QA-flagging

12. Clouds? Thick clouds < band 2 < cloudless @ 5km visib. QA-flagging

13. Clear throughout? No if: band1 / band2 < simulated (clear band1 / clear band2 ) QA-flagging

14. Cloudy throughout? No if: band1 / band2 > simulated (thick cloud band1 / thick cloud band2 ) QA-flagging

15. Cloud H 2 O? Search for cloud thickness scenario which best fits band 2 QA-flagging

16. Aerosol OD (optical depth)? Search for aerosol optical depth scenario which best fits band 2 QA-flagging

17. ShicRIVM QC/QA of solar spectral UV measurements and standardized spectral data-analysis 6 quality flags: Shift_1 Shift_2 Start_irradiance Spike+local_shape Transmission_2 Scan_variability_2 Code and documentation: ftp.rivm.nl:/outgoing/shicrivm www.rivm.nl/en/millieu/risicos_stoffen/nietioniserende_straling /shic QA-flagging