assessing air quality using usda shadow-band radiometers james slusser usda uv-b monitoring and...
TRANSCRIPT
Assessing Air Quality Using USDA Shadow-band
Radiometers
James SlusserUSDA UV-B Monitoring and Research Program
Natural Resource Ecology LaboratoryColorado State University
Purposes of USDA UVB Monitoring and Research Program
• Furnishes basic information necessary to support research on potential damaging effects of UVB on agriculture, forests, and livestock
• Provides UV climatology data to agricultural and scientific researchers
• Supplies ground truth for satellite retrievals and model development
• Establishes long-term record of UVB to assess trends
USDA UV-B Radiation Monitoring Network
Climatological Sites
Operational
Selected
Incident Solar Radiation (I0) = 1
Stratosphere Ozone Layer
Clouds
fS - Backscattering to space
fA - Absorption in atmosphere
fG - Absorption at ground
fG
fS + fA + fG = 1
Surface Albedo
fS
fA
fG
(absorption <320nm)
(UVB - 290-320 nm)
fS
AerosolsfSAir
PollutionfA
FATE OF SOLAR RADIATION
Clouds
fG
Surface Absorption-Reflection
fS
fA
fG
Ozone Layer(absorption <320nm)
fS
AerosolsfS
AirPollution
fA
Troposphere
Stratosphere
Incident Radiation Incident Radiation
FATE OF SOLAR RADIATION(UVB - 290-320 nm)
Three measures of aerosol and smoke loading:
Aerosol optical depth (AOD) quantifies the attenuation of the direct Solar beam. The AOD is proportional to total column loading of particles of the same size and related to visibility.
Angstrom exponent (alpha) gives the wavelength dependence of the AOD. Large particles (such as cloud drops or ice crystals) are spectrally neutral (alpha close to 0). The very smallest particles , molecules, have an inverse (wavelength) to the fourth dependence (alpha equal to 4). Most aerosols have alpha between 1 and 3.
Single scattering albedo (SSA) is the ratio of scattering to scattering plus absorption. For non absorbing (sulfate and water) particles SSA equals 1.0. Aerosols with black carbon have SSA between 0.7 and 0.9.
Logistics• Basic cost around $12,500• Requires 110 VAC and phone line OR batteries
and memory card• Can be polled in real time as Web site• Calibration is established in situ during clear days• Wind and ancillary instruments can be logged as
well• USDA would be willing to assist with data
analysis on a per cost basis
Conclusions
1. Visible Shadow-band radiometers provide aerosol and cloud information critical to forest fire and air quality studies.
2. Low cost ($12.5K) and automated operation are attractive features.
3. This method provides fine temporal resolution useful for studying smoke and pollution plumes.
4. Ancillary information (e.g. T, RH, wind speed and direction) can be logged simultaneously.
5. USDA would be glad to work with State and Federal agencies on data analysis.