Grantee Research Project Results

The UH-Atmospheric Radiation tower facility in Houston has made use a suite of solar instruments to measure total and diffuse solar UV irradiance at multiple wavelengths with a UV multiple filter rotating shadowband radiometers (UV-MFR and MFR). In addition, the direct solar beam irradiance at multiple wavelengths was monitored with a CIMEL sunphotometer and an EPA single pass Brewer spectrometer. The solar UV actinic flux density was measured with an NCAR scanning double actinic flux spectroradiometer (SAFS) during intensive field operations and with a diode array actinic flux spectrograph (Metcon USA) continuously. A Total Sky Imager (YES Inc) and/or a hemispheric field of view Skycam (Metcon USA ) were used to continuously document cloud cover. The data from this suite of instruments was used to calculate aerosol optical depth, aerosol single scattering albedo, overhead ozone column, and 23 different photolysis frequencies. The NCAR TUV radiative transfer model was used to compare the measurements to estimates of the cloud free and background aerosol conditions. The NASA time dependent photochemical box model was used to examine the impact the changes in surface UV on ozone photochemistry, particularly during the intensive monitoring periods.

A 2-year database of surface UV radiation measurements, atmospheric composition, meteorological data, and sky condition has been compiled and has been used to examine the relative importance of aerosols, clouds, and ozone on surface UV levels and ozone photochemistry in Houston . 

2. Work progress:

There were two large data gaps during 2008-09 data sampling period, one in the UV-B monitoring instrumentation and the other in the CIMEL sunphotometer. The UV-B monitoring instrumentation was damaged during Hurricane Ike when 90+ mile per hour winds on the roof of Moody Tower resulted in the building grounding cable becoming unattached and subsequently slammed into UV-B monitoring instrumentation. With the hurricane approaching we removed the Brewer and Cimel instrumentation, but the USDA UV-B monitoring scientists advised us that it would be interesting to try to get data during the hurricane. As a result these instruments went back to Colorado State in Fort Collins to be rebuilt and then were sent to the NOAA Central UV Calibration Facility in Boulder to be re-calibrated with FEL 1000W lamps. The instruments then spent approximately 2 months at the NOAA Table Mountain monitoring station so the angular response of the repaired instruments could be re-evaluated and intercompared to the instruments there.

The UH CIMEL sunphotometer was sent back to NASA GSFC for its’ annual calibration in early May, unfortunately most of the AERONET team was away on an extended field campaign in Africa . We did not get the CIMEL back until mid-June, after they were back and had a chance catchup with the backlog of instruments that needed calibrating. Otherwise, we have been fortunate that the other measurements have proceeded quite well with only minimal data loss. The data analysis of the intensive TexAQS II period has resulted in several papers related to UV photochemistry and aerosols.