National Ambient Air Quality Objectives For Particulate Matter - Executive Summary

Environmental Impacts

The primary effects of particulate matter on vegetation are reduced growth and productivity due to interference with photosynthesis and phytotoxic impacts as a result of particle composition. The mechanisms of action are through smothering of the leaf; physical blocking of the stomata; bio-chemical interactions; and/or indirect effects through the soil. Particles make contact with vegetation surfaces in three ways: sedimentation, impaction and deposition. The relative efficiency of these methods will depend upon the plant or soil surface, the micro-climate and ambient (temperature and humidity) conditions. Given the limited amount of information available and specifically the lack of quantitative dose-effect information, it is not possible to define a Reference Level for vegetation and particulate matter.

The deposition of particulate matter on materials can reduce their aesthetic appeal as well as increase their physical and chemical degradation. The primary effects of particulate matter on materials are on the rates of corrosion and erosion, and soiling and discolouration. Particles may act as catalysts for the conversion of SO₂ and NOx to sulphuric acid and nitric acid which accelerate the chemical degradation of susceptible material surfaces on which they are deposited. Most information available is on the effects of particle exposure in combination with SO₂. Given the limited amount of information available and specifically the lack of quantitative dose-effect information, it is not possible to define a Reference Level for materials.