The Impact of Aerosols on Solar Ultraviolet Radiation and Photochemical Smog

Abstract

Photochemical smog, or ground-level ozone, has been the most recalcitrant of air pollution problems, but reductions in emissions of sulfur and hydrocarbons may yield unanticipated benefits in air quality. While sulfate and some organic aerosol particles scatter solar radiation back into space and can cool Earth's surface, they also change the actinic flux of ultraviolet (UV) radiation. Observations and numerical models show that UV-scattering particles in the boundary layer accelerate photochemical reactions and smog production, but UV-absorbing aerosols such as mineral dust and soot inhibit smog production. Results could have major implications for the control of air pollution.

Near-Ultraviolet Absorption Cross Sections of Nitrophenols and Their Potential Influence on Tropospheric Oxidation Capacity

“…Such absorption can indeed be significant: for instance, the same 1 ppbv of nitrophenols would reduce the light transmitted through a 1 km column by about 3% near the absorption maximum of 340 nm. As has been found for particle absorption in aerosols in Mexico City and Los Angeles, [43][44][45] absorption in the near-UV is likely to reduce photochemical production of OH via photolysis of O 3…”

Airborne observations of dust aerosol over the North Atlantic Ocean during ACE 2: Indications for heterogeneous ozone destruction

“…Aerosols are known to impact the Earth's radiation balance because of their ability to scatter and absorb radiation, and thereby they might also influence photochemical processes [Dickerson et al, 1997]. To evaluate the effect of a possible reduction in the photolysis rates, a simulation has been performed in which the photolysis rates are calculated, using the Tropospheric Ultraviolet and Visible (TUV) radiation model [M. adronich, 1993], assuming a mineral aerosol layer between 2 and 6 km altitude with an aerosol optical depth of 0.14 at 500 nm.…”

Airborne analysis of the Los Angeles aerosol

“…Alternatively, vertical aerosol pro"les derived from airborne measurements or vertically resolved models can be used to determine the potential impact of scattering and absorption on photolysis rates. Several investigations of this type have been reported for di!erent regions with varying cloud cover, surface albedo, and solar zenith angle (Demerjian et al, 1980;Ruggaber et al, 1994;Lantz et al, 1996;Castro et al, 1997;Dickerson et al, 1997;Jacobson, 1998;Liao et al, 1999). The extensive aerosol measurements made with the Pelican provide much of the data necessary for such an analysis, thereby reducing uncertainty in the role of the aerosol in atmospheric photochemistry.…”