Grantee Research Project Results
1998 Progress Report: Surface Levels of Ultraviolet-B Radiation Under Variable Conditions of Tropospheric Air Quality And Cloudiness
EPA Grant Number: R825248Title: Surface Levels of Ultraviolet-B Radiation Under Variable Conditions of Tropospheric Air Quality And Cloudiness
Investigators: Saxena, Vinod K. , Frederick, John
Institution: North Carolina State University , University of Chicago
EPA Project Officer: Hahn, Intaek
Project Period: October 1, 1996 through September 30, 1999
Project Period Covered by this Report: October 1, 1997 through September 30, 1998
Project Amount: $374,702
RFA: Exploratory Research - Air Chemistry & Physics (1996) RFA Text | Recipients Lists
Research Category: Air Quality and Air Toxics , Air , Safer Chemicals
Objective:
Surface levels of UV-B radiation determine the safe duration of human exposure to direct solar radiation-the basis for estimating the UV-B Index. The former are affected by tropospheric air quality and the cloud coverage conditions of the locality. The overall objective of the project is to provide a pilot database for interpreting the measurements of surface UV-B radiation under variable conditions of tropospheric air quality and cloud cover. Results will help determine how successfully a downward trend in stratospheric ozone can be detected by monitoring the surface UV-B irradiance from a network of ground-based stations in the United States. The database will also help refine the forecast of the UV-B Index.
Progress Summary:
During the second year of the study, the analysis of the data focused on: (1) the spectral transmission of UV-B radiation through a cloudy atmosphere, and (2) further characterization of the aerosol physico-chemical properties of the contrasting air mass types overlying the research sites. The analysis entailed utilization of both the actual field measurement data and numerical modeling techniques.
Specific products obtained from the collected data sets are: (1) application of radiative transfer model techniques predicts a spectral dependence of UV transmission through a cloudy atmosphere with an added dependence on the amount of aerosols present; (2) spectral UV-B measurements using the Brewer spectrophotometer display evidence of the spectral dependence of UV transmission as predicted by the modeling; (3) the aerosol optical depth and diffuse-to-direct solar irradiance ratio shows a dependence on air mass type; (4) realistic values of the ground albedo, single scattering albedo, asymmetry parameter, and imaginary component of the refractive index were retrieved for a number of cases using a new method involving the combination of measurements and modeling; (5) aerosol physico-chemical properties derived from measurements during an intensive field campaign in November 1997 reveal dependencies on air mass type; (6) background black carbon mass concentrations for different air mass types were measured in order to assess the imaginary component of the refractive index; (7) the detection of the Mexican forest fire smoke plume in May 1998 through black carbon and light scattering measurements add further evidence that the mountain research site is uniquely suitable for detecting the long-range transport of pollutants; and (8) an intercomparison of ozone column measurements obtained from three independent sources, a Brewer, a hand-held Microtops II Ozone Monitor, and the TOMS satellite, showed good agreement, thus opening the possibility of deploying Microtops II for obtaining comprehensive measurements in various locales with cost-effectiveness.
Future Activities:
The field campaign has resulted in a large body of data, the analysis of which is under way. The ongoing nature of the field campaign will further enlarge and add to this database. The analysis of this large data set will be carried out through the combined efforts of North Carolina State University, the University of Chicago, and NOAA-SRRB. Some anticipated future work includes: (1) deriving aerosol optical depth in the UV from the UVMFR instrument; (2) retrieving aerosol optical properties in the UV using spectrally resolved Brewer measurements; (3) implementing intercomparison of TOMS, Brewer and Microtops ozone column measurements; (4) testing the sensitivity of the UV Index determination using additional information on aerosols not currently included in the UV Index calculations; 5) analyzing the long-term database for seasonal trends; (6) applying the search-graph method to the TSIN aerosol spectral extinction data; and (7) incorporating aerosol physico-chemical measurements into radiative transfer model calculations.
Journal Articles:
No journal articles submitted with this report: View all 32 publications for this projectSupplemental Keywords:
atmosphere, stratospheric ozone, UV-B radiation, solar radiation, modeling, southeast United States., RFA, Scientific Discipline, Air, Environmental Chemistry, climate change, tropospheric ozone, Atmospheric Sciences, urban air, environmental monitoring, ambient ozone data, boundry layer processes, climate variations, ozone, weather factors, aerosol/ cloud interactions, air pollution models, air quality data, aerosol sampling, atmospheric monitoring, ambient aerosol particles, UV-B radiation, climate variabilityRelevant Websites:
http://www4.ncsu.edu/unity/users/s/saxena/public/cloud.html Exit
Progress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.