The Impacts of Particulate Matter on Crop Yield: Mechanisms, Quantification and Options for Mitigation

Background and aims

Concentrations of particulate matter (PM) regularly exceed levels recommended in the 2021 revision of the World Health Organization (WHO) air quality guidelines (AQGs) in many urban and rural areas of the world, and over 8 million people die prematurely every year from exposure to PM. In addition to affecting people living in rural areas, PM also has an impact on the growth, productivity, yield quantity and quality of crops growing in the same polluted air. Despite long-held knowledge of the potential impacts of natural and anthropogenic PM emissions on crops, summary information is not readily available for crop scientists, modellers, and air quality and climate change strategists. To address this deficit, the Expert Team on Agrometeorological Sciences, which is part of the Standing Committee on Services for Agriculture established by the WMO Commission for Weather, Climate, Hydrological, Marine and Related Environmental Services and Applications (SERCOM), commissioned the drafting of this publication to provide an evidence-based assessment of current knowledge in one, easily accessible document. It is one of two documents that describe the impacts of the two forms of air pollution that are of greatest concern for yield at the global scale; the other document focuses on the impacts of tropospheric ozone pollution on yield. 

Concentrations, sources and hotspots for particulate matter

The term “particulate matter” or “PM” covers a wide range of particles that vary in size, origin and physical and chemical form. Primary PM and precursors of secondary PM are emitted into the atmosphere from both natural sources (for example, volcanoes, soil and rock dust, sea spray, natural vegetation and wildfires) and anthropogenic sources (such as burning of biomass, combustion of fossil fuels, applications of synthetic and animal manure fertilizers, pesticide applications, soil tillage and combine harvesting, exposure of bare soil to wind erosion, animal farming, industrial processes, power generation, and debris from tyre and brake use).

Global hotspots for PM coincide with major crop growing areas, for example, in Central Africa, Pakistan, India, China and South-East Asia. In many of these areas, models predict that annual mean PM2.5 concentrations exceed the most recent WHO AQG levels for health, often by a factor of 5–10 times or more. In order to predict hotspots in agricultural areas, a combination of chemical transport and/or emission source modelling is necessary, using satellite or ground-based measurements. However, almost all ground-based monitoring takes place in urban areas, with very limited regulatory monitoring occurring in rural areas.

Food safety concerns

Where standards for protecting crops from PM exist, they are food safety – rather than yield impact-based, aiming to protect people from eating contaminated crops that may be damaging to their health. The health effects of concern include weakening of the immune system, gastrointestinal cancer, neurological diseases, cardiovascular diseases and retarded mental growth. While there are no standards relating to the concentrations which directly affect crops, there are scientifically based values for PM deposition to agricultural soils (namely, critical loads for heavy metals, set out under the Convention on Long-range Transboundary Air Pollution (LRTAP Convention)).