Wolffe, Mike and Ashworth, Kirsti and Wild, Oliver and Long, Stephen (2023) The Effects of Particulate Matter on Global Crop Yields. PhD thesis, Lancaster University.
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Abstract
Particulate Matter (PM) is understood to harm human health, but little research has assessed its impact on crop yields. Emerging evidence suggests PM may have a sizeable effect on crops. PM reduces yields through indirect and direct mechanisms. In the indirect mechanism, airborne PM intercepts incoming photosynthetically active radiation (PAR) through absorption or scattering. In the direct mechanism, PM deposition on crop surfaces directly blocks PAR transmission. Using the JULES-crop model, this thesis finds PM reduces maize yield by 3.5% on the North China Plains (NCP) via the indirect mechanism. PM deposition is responsible for a further 2.4% maize yield loss in the same area, with rice and wheat crops less affected at 2.0% and 0.3% average yield losses, respectively. India is also particularly affected by PM deposition, with average maize, rice, and wheat losses of 1.2, 0.7, and 0.3%. Specificlocations suffer losses as high as 8%, attributable to a combination of meteorological factors, the black carbon content of bulk PM, and crop-specific factors. Despite these high local impacts, average global cereal crop yield losses to PM deposition circa 1%. The timing of PM perturbations within the crop development cycle also affects yield outcomes. The combined effects of the direct and indirect mechanisms are additive, and most negatively affect crop yields during the early reproductive stage for maize and wheat, and the early vegetative stage for rice. Uncontrolled future PM emissions are found to have particularly substantial effects on crop yields in India, with expected losses of up to 20% on the Indo-Gangetic Plain. The thesis also explores the effects of PM timing in relation to crop development stage, and how this may predict future crop yield losses attributable to PM pollution. Overall, this work highlights the role of airborne PM in limiting PAR availability for photosynthesis, particularly in highly polluted areas of China and India. The effects of PM deposition on cereal crop yields are quantified here for the first time, and are noted as potentially limiting future food supply in India. Identifying the potential impacts of PM highlights the urgency of PM emission reductions for policy makers. The thesis contributes to our understanding of the impacts of PM pollution on food supply, and highlights the need for further experimental studies to better comprehend the scale of threat that this pollution may pose in the future.