Effects of aerosols on photosynthesis

Abstract

Air pollution can cause various problems to agriculture through its direct or indirect effects on plants^1,2. The net effects of air pollution on agricultural crop yields are very difficult to estimate quantitatively, and are generally considered secondary to the effects of fertilizers or chemical disease control measures. However, continually increasing air pollution may represent a persistent and largely irreversible threat to agriculture in the future. Here we have examined only one indirect aerosol effect on agricultural plant life—the reduction in photosynthetically active radiation (PAR) reaching the ground in the presence of significant air pollution. This effect can be quantified confidently from results of detailed model calculations of the transfer of solar radiation through the atmosphere with varying levels of air pollution. For the biologically effective wavelength region between 0.35 and 0.72 µm, the reductions in PAR due to increasing tropospheric aerosol loads have been determined for rural and urban pollution scenarios. For example, for the northeastern United States during the summer months, a reduction in PAR of about 20% and 33% was obtained when the visual range due to rural and urbtn aerosols, respectively, was decreased from clear air conditions to 10 km.