@article{barnard_saxena_wenny_deluisi_2003, title={Daily surface UV exposure and its relationship to surface pollutant measurements}, volume={53}, ISSN={["1047-3289"]}, DOI={10.1080/10473289.2003.10466134}, abstractNote={Abstract For the past 30 years, the stratospheric ozone layer has decreased in the Northern Hemisphere. The main effect of this ozone decrease was an expected increase in the UV radiation at the Earth’s surface, but there has been no clear evidence of an increasing urban trend in surface UV. This study shows that specific air pollutants can reduce the increased surface levels of UV radiation and offers an explanation for why the expected surface UV increases have not been observed, especially in urban regions. A U.S. Environmental Protection Agency (EPA) UV monitoring site at the University of California at Riverside combined with air pollution data from a site operated by the California Air Resources Board in Rubidoux, CA, provided the basis of this study. The 1997 South Coast Ozone Study (SCOS-97) provided three key ingredients: black carbon, PM10 concentrations, and collocated radiometric measurements. The Total Ozone Mapping Spectrometer (TOMS) satellite data were used to provide the stratospheric ozone levels that were included in the statistical model. All of these input parameters would be used to test this study’s hypothesis: the expected increase of surface UV radiation, caused by decreases in stratospheric ozone, can be masked by increases in anthropogenic emissions. The values for the pollutants were 7:00 a.m.-5:00 p.m. averages of the instrument’s values taken during summer 1997. A statistical linear regression model was employed using the stratospheric ozone, black carbon, PM10 , and surface ozone concentrations, and the sin (Θ) and cos (Θ). The angle Θ is defined by Θ = 2π (Julian date/365). This model obtained a coefficient of determination of 0.94 with an uncertainty level (p value) of less than 0.3% for all of the variables in the model except ground-level ozone. The final model, regressed against a data set from a remote, western North Carolina site, resulted in a coefficient of determination of 0.92. The model shows that black carbon can reduce the Diffey-weighted UV levels that reach the surface by as much as 35%, depending on the season.}, number={2}, journal={JOURNAL OF THE AIR & WASTE MANAGEMENT ASSOCIATION}, author={Barnard, WF and Saxena, VK and Wenny, BN and DeLuisi, JJ}, year={2003}, month={Feb}, pages={237–245} }
 @article{wenny_schafer_deluisi_saxena_barnard_petropavlovskikh_vergamini_1998, title={A study of regional aerosol radiative properties and effects on ultraviolet-B radiation}, volume={103}, ISSN={["2169-897X"]}, DOI={10.1029/98JD01481}, abstractNote={A field experiment was conducted in western North Carolina to investigate the relationship between aerosol optical properties and atmospheric transmission. Two research measurement sites in close horizontal proximity but at different altitudes were established to measure the transmission of UV radiation through a slab of atmosphere. An identical set of radiation sensing instruments, including a broadband UV‐B radiometer, a direct Sun pyrheliometer, a shadowband radiometer, and a spectral photometer, was placed at both sites, a mountaintop site (Mount Gibbes 35.78°N, 82.29°W, 2004 m elevation) and a valley site (Black Mountain, North Carolina 35.66°N, 82.38°N, 951 m elevation). Aerosol size distribution sampling equipment was located at the valley site. Broadband solar pseudo‐optical depth and aerosol optical depths at 415 nm, 500 nm, and 673 nm were measured for the lowest 1‐km layer of the troposphere. The measurements exhibited variations based on an air mass source region as determined by back trajectory analysis. Broadband UV‐B transmission through the layer also displayed variations relating to air mass source region. Spectral UV transmission revealed a dependence upon wavelength, with decreased transmission in the UV‐B region (300–320 nm) versus UV‐A region (320–363.5 nm). UV‐B transmission was found to be negatively correlated with aerosol optical depth. Empirical relations were developed to allow prediction of solar noon UV‐B transmission if aerosol optical depth at two visible wavelengths (415 and 500 nm) is known. A new method was developed for determining aerosol optical properties from the radiation and aerosol size distribution measurements. The aerosol albedo of single scatter was found to range from 0.75 to 0.93 and the asymmetry factor ranged from 0.63 to 0.76 at 312 nm, which is close to the peak response of human skin to UV radiation.}, number={D14}, journal={JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES}, author={Wenny, BN and Schafer, JS and DeLuisi, JJ and Saxena, VK and Barnard, WF and Petropavlovskikh, IV and Vergamini, AJ}, year={1998}, month={Jul}, pages={17083–17097} }