Influence of aerosol dry deposition on photosynthetically active radiationavailable to plants: A case study in the Yangtze delta region of China

In this paper, a new mechanism is proposed by which aerosols decrease the a mount of photosynthetically active radiation (PAR) available to plants for photosynthesis. The mechanism involves the scattering and absorption of PAR by water insoluble aerosol particles (WIA) which deposit on leaves and are not washed off by precipitation. A simple model is developed that predicts the change in the transmittance of PAR, T-PAR, for plant leaves due to WIA dry deposition as a function of aerosol chemical, physical, and optical pr operties. Model estimates for the agricultural Yangtze delta region of Chin a indicate that over a 2-month period during a growing season, dry depositi on of WIA may account for a similar to 35% reduction in PAR available for p lant photosynthesis. Although, the estimate is sensitive to several factors that are uncertain including aerosol dry deposition velocity, leaf area in dex, and removal rate of particles by precipitation. Results suggest that i mpacts on crop yields due to aerosol dry deposition could be considerable i n this region and suggest a previously neglected economic incentive for Chi na to miti-ate air pollution. Additionally, WIA dry deposition may influenc e carbon uptake by plants in other locations that experience regional haze.