Daily surface ultraviolet exposure and its relationship to surface pollutant measurements

For the last 30 years the stratospheric ozone layer has been on a slow decline in the Northern Hemisphere. The main effect of this ozone decrease was an expected increase in the ultraviolet (UV) radiation at the Earth's surface, but there has been no clear evidence of an increasing 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.; An EPA UV monitoring site at the University of California at Riverside, CA, combined with a SLAMS site operated by the California Air Resources Board in Rubidoux, CA provided the basis of this study. The 1997 South Coast Ozone Study provided three key ingredients, black carbon, PM-10 concentrations, and collocated radiometric measurements. The NASA's 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 the hypothesis: Has the expected increase of surface UV radiation, caused by decreases in stratospheric ozone, been masked out by increases in anthropogenic emissions? ; The values for the pollutants were 7am–5pm averages of the instrument's values taken during the summer of 1997. A statistical linear regression model was employed using the stratospheric ozone, black carbon, PM-10, and ground-based 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-based ozone.; The final model, regressed against a data set from a remote, western North Carolina site, resulted in having a coefficient of determination of 0.92. The model shows that black carbon can reduce the DUV levels that reach the surface by as much as 35 percent, depending on the season.